João Manuel Cabral
email: jcabral@fc.ul.pt

Fernando Marques

Paula Figueiredo

Luís Matias

Active surface faulting or landsliding in the Lower Tagus Valley (Portugal)? A solved controversy concerning the Vila Chã de Ourique site

Keywords: surface faulting, landsliding, paleoseismicity, Lower Tagus Valley, mainland Portugal

come   L'archive ouverte pluridisciplinaire

Introduction

The study area is located in central-western Portuguese mainland (W Iberia), in the Lower Tagus Valley (LTV). The LTV corresponds to the lower reach of the Tagus River, forming a conspicuous NE-SW morphological lineament, and comprises the densely populated and highly developed area of Lisbon (Figure 1). Earthquakes that caused severe damage and many casualties have affected this region, making seismic hazard evaluation a major regional issue.

According to some authors (Fonseca et al. 2000a(Fonseca et al. ,b, 2001;;[START_REF] Vilanova | Sismicidade e perigosidade sísmica do Vale Inferior do Tejo[END_REF][START_REF] Vilanova | Seismic hazard impact of the Lower Tagus Valley Fault Zone (SW Iberia)[END_REF], paleoseismic evidence was found at a site on the right margin of the Tagus river 60 km N of Lisbon, at Vila Chã de Ourique (VCO) (Figure 1), where four trenches were excavated. According to these authors, trenching at the VCO site revealed an active thrust fault, which was considered a source of the regional historical seismicity, evidencing the surface rupture of a large earthquake that severely affected the LTV region in 1531.

However, a reconnaissance trip to the VCO trenches showed us that the active surface faulting interpretation of Fonseca and collaborators (op. cit.) might be wrong, requiring further studies at the site. Our complementary research comprised field observations, including a reappraisal of the trench outcrops previously excavated by Fonseca and collaborators, borehole drilling, sample collection, and seismic reflection acquisition, as well as laboratory characterization and shear strength testing of the collected samples.

Based on our observations, we have proposed an alternative interpretation which considered that the structures exposed in the VCO trenches probably were of gravitational and not of tectonic origin [START_REF] Cabral | Paleoseismological studies in Portugal: Holocene thrusting or landslide activity?[END_REF][START_REF] Cabral | Paleoseismicity evidence in the Lower Tagus Valley (Lisbon Region)? An example of misinterpretation of geological data. 3ª Assembleia Luso-Espanhola de Geodesia e Geofísica[END_REF][START_REF] Cabral | New data on the active surface faulting vs. landsliding controversy concerning the Vila Chã de Ourique site (Lower Tagus Valley)[END_REF]. This controversy has been recently referenced by McCalpin and Carver (2009, p. 366) as "a recent European example (that) illustrates the ambiguity (between landslide toe thrusts and true thrust faults), and the result on seismic hazard assessment". The authors conclude that "… at this time the ambiguity remains whether the fault exposed in the Portuguese trench is tectonic and seismogenic, or nontectonic and nonseismogenic".

The present work intends to resolve this issue based upon a refinement of previously performed slope stability analysis, newly acquired seismic data and new observations at the VCO site. Actually, a new seismic reflection profile was acquired transversely to the expected prolonging of the structures encountered in the trenches, employing higher natural frequency geophones (28 Hz instead of the previous 10 Hz) for tentatively improving the quality of the seismic section. Also, detailed observations were performed at new outcrops that were exposed at the VCO site as a result of works for building a railway underground passage, which crosscut the structures exposed at the trenches allowing a view further in depth.

As discussed below, the seismic data and the new outcrops, where an eastwards steeply dipping slip surface was exposed, preclude the thrust fault interpretation of the slip surfaces identified in the trench walls, proposed by Fonseca and collaborators, and strongly support a landslide model for all the observed structures.

Regional geological setting and seismicity

The LTV is located mostly in the Lower Tagus Cenozoic Basin (LTCB), a NE-SW elongated tectonic depression filled with Cenozoic sediments. This basin evolved since the Eocene as a transpressive foredeep related to the tectonic inversion of the former, extensional Mesozoic Lusitanian Basin (LB), located to west, mainly under the action of a NW-SE Miocene compression (Figure 2) (Ribeiro et al. 1990;[START_REF] Cabral | Neotectónica em Portugal Continental[END_REF][START_REF] Cabral | New data on the active surface faulting vs. landsliding controversy concerning the Vila Chã de Ourique site (Lower Tagus Valley)[END_REF][START_REF] Carvalho | Sísmica de alta resolução aplicada à prospecção, geotecnia e risco sísmico[END_REF].

The LTCB comprises up to about 2000 m of Tertiary (Paleogene to Pliocene) sediments, and also a thick (up to 70 m) Upper Pleistocene to Holocene alluvial cover due to Wurmian drainage incision followed by aggradation.

Entrenchment of the fluvial network and the presence of Quaternary terraces provide evidence of reversal of the regional subsidence to uplifting since the Early Pleistocene [START_REF] Cabral | Neotectónica em Portugal Continental[END_REF].

The Cenozoic evolution of the LTCB was controlled by the NNE-SSW main structural trend of the LB. Tectonic inversion of former normal faults generated ESE verging reverse faults, as those that limit the LTCB on the NW side, placing Mesozoic rocks of the LB, to the NW, over Cenozoic sediments of the LTCB, to the SE. A major example is the Vila Franca de Xira fault [START_REF] Cabral | New data on the active surface faulting vs. landsliding controversy concerning the Vila Chã de Ourique site (Lower Tagus Valley)[END_REF][START_REF] Carvalho | Geophysical Methods Applied to Fault Characterization and Earthquake Potential Assessment in the Lower Tagus Valley, Portugal[END_REF][START_REF] Carvalho | Geophysical characterization of the Ota-Vila Franca de Xira-Lisbon-Sesimbra fault zone, Portugal[END_REF] (Figure 2). Surface geology, seismic reflection and potential field data (gravimetric and geomagnetic) point to further complexity, evidencing structural lows and highs that are delimited by WNW-ESE to NW-SE faults, transverse to the LTV trend, in addition to the NNE-SSW "longitudinal" faults [START_REF] Cabral | Neotectónica em Portugal Continental[END_REF][START_REF] Rasmussen | Aspects of the structural evolution of the Lusitanian Basin in Portugal and the shelf and slope area offshore Portugal[END_REF][START_REF] Cabral | New data on the active surface faulting vs. landsliding controversy concerning the Vila Chã de Ourique site (Lower Tagus Valley)[END_REF][START_REF] Carvalho | Sísmica de alta resolução aplicada à prospecção, geotecnia e risco sísmico[END_REF][START_REF] Carvalho | Geophysical Methods Applied to Fault Characterization and Earthquake Potential Assessment in the Lower Tagus Valley, Portugal[END_REF][START_REF] Carvalho | Geophysical characterization of the Ota-Vila Franca de Xira-Lisbon-Sesimbra fault zone, Portugal[END_REF]. This indicates the presence of a segmented fault system, with NNE stepped fault segments evidencing Neogene vertical offsets (mostly high angle reverse) in the framework of overall left-lateral transpression, which are linked by WNW faults also accommodating significant vertical offsets.

According to data from borehole breakouts and earthquake focal mechanisms, the maximum horizontal compressive stress presently trends NW-SE to WNW-ESE [START_REF] Ribeiro | Tectonic stress pattern in Portugal mainland and the adjacent Atlantic region (West Iberia)[END_REF][START_REF] Borges | Seismotectonics of Portugal and its adjacent Atlantic area[END_REF].

Regional seismicity comprises relatively distant events, as the 1755 earthquake, one of the largest historical events ever described (estimated M W 8.5), which was generated in the broad deformation zone of the Eurasia-Africa plate boundary (Grácia et al. 2003;Terrinha et al. 2003;[START_REF] Zitellini | The tectonic source of the 1755 Lisbon earthquake and tsunami[END_REF][START_REF] Zitellini | The 1755 Lisbon earthquake and Tsunami: localization and investigation of the tectonic source[END_REF]Zitellini et al. , 2004)). The study region also experiences a significant local seismicity, attested by the occurrence of moderate to large historical earthquakes, as in 1344, 1531 and 1909, with estimated magnitudes ranging from 6 to 7 (Martins and Mendes Victor 2001;[START_REF] Mezcua | Catalogo General de Isossistas de la Peninsula Iberica[END_REF][START_REF] Moreira | Seismotectonics of Portugal and its adjacent area in the Atlantic[END_REF][START_REF] Moreira | Historical seismicity and seismotectonics of the area situated between the Iberian Peninsula, Morocco, Selvagens and Azores Islands[END_REF][START_REF] Oliveira | A Sismicidade Histórica e a Revisão do Catálogo Sísmico[END_REF]) (Figure 3a,b).

The 1344 event in particular, but also the earthquake in 1531, are poorly located due to the scarcity of historical descriptions, being positioned in the LTV based upon the destruction that they produced in the Lisbon area. The 1531 event caused severe damage and many casualties in the town of Lisbon, reaching an intensity of IX MM [START_REF] Moreira | Sismicidade histórica de Portugal Continental[END_REF][START_REF] Mezcua | Catalogo General de Isossistas de la Peninsula Iberica[END_REF][START_REF] Oliveira | A Sismicidade Histórica e a Revisão do Catálogo Sísmico[END_REF][START_REF] Henriques | Sismicidade de Portugal. O Sismo de 26 de Janeiro de 1531[END_REF][START_REF] Justo | The 1531 Lisbon earthquake[END_REF] (Figure 3a).

The April 23 rd 1909 earthquake was definitely located NE of Lisbon, near Benavente, where it was felt with a maximum intensity of IX (MM) (Figure 3b), causing several fatalities. It reached M W =6 [START_REF] Teves-Costa | Source parameters of old earthquakes: semi-automatic digitization of analog records and seismic moment assessment[END_REF], and a focal mechanism solution has been calculated by [START_REF] Stich | Moment tensor inversion with single-component historical seismograms: The 1909 Benavente (Portugal) and Lambesc (France) earthquakes[END_REF] indicating reverse faulting with nodal planes trending ENE-WSW. Concerning the instrumental seismicity, the earthquake activity in the study area has been relatively low and diffuse as shown in Figure 3c. The earthquake dataset for the period considered (1960 to 2007) is nearly complete for M2, with only 14 M≥4 earthquakes (M=4.5 maximum) occurring in that period.

The regional seismicity clearly evidences the presence of active seismogenic faults, and detailed research has been conducted for characterizing the regional seismotectonics. Studies from several authors show the importance of the local seismic sources to the seismic hazard of the LTV area (e.g. [START_REF] Peláez | Deaggregation in magnitude, distance, and azimuth in the South and West of the Iberia Peninsula[END_REF][START_REF] Vilanova | Lisbon 1755: A Case of Triggered Onshore Rupture?[END_REF][START_REF] Vilanova | Seismic hazard impact of the Lower Tagus Valley Fault Zone (SW Iberia)[END_REF][START_REF] Cabral | New data on the active surface faulting vs. landsliding controversy concerning the Vila Chã de Ourique site (Lower Tagus Valley)[END_REF][START_REF] Cabral | The Azambuja fault: An active structure located in an intraplate basin with significant seismicity (Lower Tagus Valley, Portugal)[END_REF][START_REF] Carvalho | Geophysical Methods Applied to Fault Characterization and Earthquake Potential Assessment in the Lower Tagus Valley, Portugal[END_REF][START_REF] Carvalho | Geophysical characterization of the Ota-Vila Franca de Xira-Lisbon-Sesimbra fault zone, Portugal[END_REF], although they are still deficiently known due to the low strain rates and the thick Tertiary and Quaternary sedimentary cover that conceals most of the active faults, rooted in the Mesozoic and Paleozoic basement rocks located underneath.

The low instrumental seismicity, the poor earthquake location and the depth at which the earthquakes are generated in the study region also prevent a reliable relationship between the earthquakes and the faults recognized at the ground surface or in the uppermost 2-3 km of the crust, where they cut through the Mesozoic and Cenozoic rocks of the Lusitanian and Lower Tagus basins, respectively. The geometry of the Tertiary sedimentary basin may also play an important role on local energy enhancement and site-effects, masking the relationship between the historical events location based on seismic intensity studies and the earthquake sources.

Geomorphologic, stratigraphic and structural setting of the VCO site

The landscape in the study region shows wide and levelled interfluves evidencing the presence of a rather uniform plateau incised by the drainage network, which correlates with an erosion surface of probable Lower Quaternary age that occurs along most of the Lower Tagus sedimentary basin [START_REF] Martins | Planaltos do Nordeste da Bacia Terciária do Tejo (Portugal)[END_REF][START_REF] Martins | Geomorphological correlation of the tectonically displaced Tejo River terraces (Gavião-Chamusca area, central Portugal) supported by luminescence dating[END_REF][START_REF] Cabral | The Azambuja fault: An active structure located in an intraplate basin with significant seismicity (Lower Tagus Valley, Portugal)[END_REF]) (Figure 4). This erosion surface relates to the first incision of the regional drainage network on a former, Piazencian, alluvial plain, and so it may register tectonic deformation accumulated since the Lower Pleistocene.

In the VCO area, this plateau is at an elevation of 60-70 m, which is 30 to 40 m lower than its common height of approximately 100 m. The lower elevation of the erosion surface and a gentle tilt towards the south reveal deformation related to a major active structure located to the west -the Azambuja fault, which presents a conspicuous NNE-SSW trending scarp that gets progressively higher southwards [START_REF] Cabral | The Azambuja fault: An active structure located in an intraplate basin with significant seismicity (Lower Tagus Valley, Portugal)[END_REF]) (Figure 4).

A striking geomorphic feature of the VCO area is the prominent, though sinuous and discontinuous steep slope that extends for approximately 25 km along the right bank of the Tagus river valley, from Azambuja, at the south, to Santarém, at the north (Figures 4 and5). This slope was interpreted as a fault scarp by Fonseca and collaborators (Fonseca et al. 2000a(Fonseca et al. ,b, 2001;;[START_REF] Vilanova | Sismicidade e perigosidade sísmica do Vale Inferior do Tejo[END_REF][START_REF] Vilanova | Seismic hazard impact of the Lower Tagus Valley Fault Zone (SW Iberia)[END_REF]) and it was thus a major incentive for field prospecting. Trenching was then performed by these authors based on the observation of anomalous structures at the toe of the riverbank slope at the VCO site, where an active thrust fault was allegedly exposed.

Besides the fault scarp evidence for active faulting, this tectonic activity should also be expressed on the regional landscape by localized uplifting.

However, the general trend of the regional plateau described above, which is the older geomorphic reference recognizable in the area, does not reveal any restricted rising related to an active thrust fault at the VCO area. Actually, the plateau is locally lower than its typical regional elevation, and slightly tilted southwards, as it is positioned in the downthrown block of the Azambuja fault, referred above.

As a result, the NE-SW to NNE-SSW slope bordering the Tagus valley in the study area gradually decreases height from approximately 70 m, at the NE, to approximately 20 m at the SW (near Azambuja), reflecting the southward tilting of the erosion surface located at the top.

The presence of a major active thrust fault near the VCO site should also produce fault-related deformation on the local sediments, such as tilting, folding and/or fracturing by subsidiary faults. However, the geological structure at VCO and surrounding area is simple and regular: Miocene sands, clays, marls and some intercalated limestone beds, of Vallesian (Tortonian) age, rest sub-horizontally, with Pliocene sands lying unconformably on the top, partially truncated by the regional erosion plateau. At the base of the steep slopes generated by river incision, they contact with clayey sediments of the alluvial plain of the Tagus River and of some tributaries. The Neogene sedimentary units are slightly tilted, accompanying the morphological gradient towards the south, and do not show any evidence of significant local tectonic deformation.

Accordingly, we interpret the prominent slope that margins the Tagus River alluvial plain in the study area as non-tectonic, but due to the drainage entrenchment of around 100 m since Lower Quaternary [START_REF] Cabral | Neotectónica em Portugal Continental[END_REF][START_REF] Martins | Planaltos do Nordeste da Bacia Terciária do Tejo (Portugal)[END_REF][START_REF] Martins | Geomorphological correlation of the tectonically displaced Tejo River terraces (Gavião-Chamusca area, central Portugal) supported by luminescence dating[END_REF], corresponding mainly to a cliff carved by basal fluvial erosion. Landslide activity is also an important evolutionary process of this slope, very well documented in several locations along its strike, especially near Santarém city (e.g. [START_REF] Oliveira | Carta Geológica de Portugal, Escala 1:500.000, Instituto Geológico e Mineiro, Lisboa Oliveira R[END_REF][START_REF] Coelho | Historia de las laderas de Santarém (Portugal). Problemas de estabilización de laderas alcantiladas coronadas por un estrato rocoso. V Simposio Nacional sobre Taludes y Laderas Inestables[END_REF], 9km NE of the VCO site.

The dominant action of erosion is supported by the rather sinuous trend of the slope and by the distinct profiles that it shows along strike, being steepest at the northern sector, in the vicinity of the VCO site (Figure 4). Map view suggests that the stronger dip of the slope in this sector is probably due to slope retreat by lateral fluvial erosion at the concave margin of a sinuosity of the Tagus river channel, under conditions of deeper incision related to a Wurmian glacio-eustatic sea level low stand.

Actually, data from boreholes drilled for various purposes (underground water exploitation, geotechnical prospecting, and scientific exploration) in the Tagus alluvial plain show that the Late Pleistocene to Holocene alluvial cover of the Tagus River is very thick, reaching a depth of down to approximately -70 m in the downstream sector of the valley, near Lisbon. This is due to a time of deeper incision of the Tagus River related to a lower base-level (-120 m) during the last glacial maximum ( 20,000 yrs ago), followed by aggradation in response to climate change and rapid base-level rise, which occurred until  7,000 yrs ago, when sea level stabilized [START_REF] Vis | Late Pleistocene and Holocene palaeogeography of the Lower Tagus Valley (Portugal): effects of relative sea level, valley morphology and sediment supply[END_REF].

The thickness of this alluvial cover progressively reduces upstream, though it still exceeds 32 m approximately 1.5 km east of the VCO site, as evidenced in a borehole drilled in the area (core VAL, end depth of 32.20 m; Vis 2009). Four samples collected at different depths in this core were dated (Vis, op. cit.). The deepest one (27.48-27.53 m) was radiocarbon dated at 10,190-9,740 cal. BP, giving an average aggradation rate of 2.7-2.8 mm/yr roughly in the Holocene.

In a borehole drilled in the alluvial plain near the base of the slope at VCO (borehole 0501.042, Benfica do Ribatejo section; [START_REF] Vis | Fluvial and marine sedimentation at a passive continental margin. The late Quaternary Tagus depositional system[END_REF], the Quaternary sediments exceed 9.10 m (reached depth). A sample collected from a depth of 2.45 m in this borehole was dated at 2720-2360 cal BP (Vis, op. cit.), giving an average aggradation rate of 0.88-1.01 mm/yr. In another borehole located approximately 500 m further east (borehole 0501.041, Vis 2009), the Tagus alluvial sediments exceed 13.90 m (reached depth), and a sample collected from a depth of 11.65 m was dated at 6510-6300 cal BP, giving an average aggradation rate of 1.77-1.83 mm/yr. A rather similar average sedimentation rate of 2.2 mm/yr was estimated for the last 3.4 ka, based upon a 7.4 m core drilled in the alluvial plain 2 km ESE of the VCO site [START_REF] Ramos | Late Holocene evolution of the Lower Tagus alluvial plain and heavy metals content: preliminary results[END_REF]. This geomorphologic evolution is consistent with the trend of the longitudinal profiles of some tributary streams in the VCO area, which show knick points produced by downstream entrenchment in response to the above referred processes of recent fast entrenchment of the Tagus River in relation to a lower Wurmian sea level, and also to the coeval bank-slope retreat. This interpretation is supported by the slope of the longitudinal profiles of the creeks, evidencing downstream steepening related to a lower base level, followed by gradient reduction due to the recent aggradation near their mouth (Figure 6)

The Holocene aggradational effect is clearly expressed in the lower stretch of the tributaries by enlarged alluvial plains and low longitudinal dips. In these downstream stretches, the valley slopes show profiles that can be related to the Wurmian period of deeper incision, and the steeper longitudinal profiles located immediately upstream also correlate with the same lower base level, strongly supporting the erosional interpretation of the convex stream profiles (Figure 6).

The VCO trenching site

The VCO trenching site is located at the toe of the above referred NE-SW The gravitational instability is promoted by the slope profile, the presence of a low shear strength Miocene clayey and silty unit at its middle and lower section, overlaying and concealing coarse sands of high permeability where seasonal high pore water pressures are generated, with water head frequently above ground level at the lower part of the slope.

We performed detailed observations at the trenches that Fonseca and collaborators excavated at the VCO site, near the base of the presumed fault scarp.

As they state (Fonseca et al. 2000a(Fonseca et al. ,b, 2001;;[START_REF] Vilanova | Sismicidade e perigosidade sísmica do Vale Inferior do Tejo[END_REF][START_REF] Vilanova | Seismic hazard impact of the Lower Tagus Valley Fault Zone (SW Iberia)[END_REF]) several striated slip surfaces outcropped at the trench walls, generally dipping towards the Northwest and designing an imbricate geometry. Some of them presented very low dips and even reversed their plunge. The slip surfaces, particularly those cut on the Miocene clayey and silty unit, presented abundant north-south striations, pointing directly to the nearest steep slope segment, which designs a free face cut on the harder Miocene marls immediately north of the trench site, supporting a gravitational origin (Figure 7).

To assess the possibility of occurrence of landslides which could explain the features observed in the trenches, slope stability analysis were performed using: 1) accurate topography survey of the slope using a total station (Figure 7), completed by a detailed survey carried out for the 2006 engineering works; 2) assessment of the geometry and position of internal shear planes by purpose made boreholes with continuous sampling and field observations; 3) soil properties measured in laboratory testing for index and direct shear strength. 4) limit equilibrium methods for circular and fully specified failures;

A preliminary slope stability analysis was performed using the Bishop simplified method [START_REF] Bishop | The use of the slip circle in the stability analysis of slopes[END_REF], with soil properties obtained in laboratory direct shear tests and the geometry of the slope assessed by a detailed topographical survey carried out with a total station. Considering several circular failure surfaces, the results indicated that the landslide hypothesis was highly plausible and could explain the features surveyed at the VCO trenches, namely the northwest dipping striated slip surfaces which are typical features of the down slope end of a circular or near circular failure surface [START_REF] Cabral | Paleoseismological studies in Portugal: Holocene thrusting or landslide activity?[END_REF].

In order to confirm the proposed landslide model, a vertical boring with continuous recovery, 14.6 cm in diameter, was drilled 20 m to the north of the trenches, reaching a depth of 18.37 m. A lithological log was constructed and samples were collected for laboratory testing. Several striated surfaces were intersected by the boring, crossing massive clay between the depths of 0.90 m and 2.10 m. Most of the observed striae were approximately rectilinear with a 90º pitch (Figures 7 and8). Slip sense criteria in several of the striated surfaces indicated downthrowing of the hanging wall, which is compatible with gravitational sliding. Two other boreholes were drilled with a hand-auger, one located midway between the previously drilled boring and the trenches, and the other at the lowest point of the trenches floor (Figure 7). The local lithologies were crossed at the expected depths, attending to the previously obtain log, and there wasn't any evidence of fault offset [START_REF] Cabral | Paleoseismicity evidence in the Lower Tagus Valley (Lisbon Region)? An example of misinterpretation of geological data. 3ª Assembleia Luso-Espanhola de Geodesia e Geofísica[END_REF][START_REF] Cabral | New data on the active surface faulting vs. landsliding controversy concerning the Vila Chã de Ourique site (Lower Tagus Valley)[END_REF].

The sedimentary sequence crossed by the continuous recovery boring, the small depth at which it intersected the slip surfaces in the Miocene clayey sediments, and the geometry shown by recent slides on the same slope, suggested however that the gravitational sliding interpreted at the trench was shallower and flatter than previously proposed by [START_REF] Cabral | Paleoseismological studies in Portugal: Holocene thrusting or landslide activity?[END_REF]. The geometry of the structures exposed at the outcrops that were opened during the 2006 engineering works at the VCO site confirmed this analysis, and revealed another steep, deeper rooted, slip surface that we also interpret as of gravitational origin.

Interpretation of the new outcrops at the VCO site

As mentioned above, after the previous research was concluded [START_REF] Cabral | Paleoseismicity evidence in the Lower Tagus Valley (Lisbon Region)? An example of misinterpretation of geological data. 3ª Assembleia Luso-Espanhola de Geodesia e Geofísica[END_REF](Cabral et al. , 2003) ) new outcrops were uncovered at the VCO site, as a result of the works for building a railway underground passage. These outcrops crosscut the structures that were exposed at the trenches opened by Fonseca and collaborators, allowing a view at further depth and permitting a reappraisal of the previous data and proposed models.

The new outcrops showed a major, southeastwards steeply dipping, slip surface, which puts clayey colluvium in the hanging wall, to the SE, in mechanical contact with whitish Miocene sands in the foot wall, to the NW (Figure 9). In detail, this structure presents a relatively complex geometry, showing rather curved and branched, polished and striated slickensides where they penetrate the clayey material. Upwards, this major slip surface progressive reduces dip, merging into another low dip slip surface which apparently accommodates later movements and seals the underlying structure.

The exposed geometry precludes the thrust faulting interpretation of the slip surfaces identified in the trench walls, one of which corresponds to the uppermost slip surface uncovered in the new outcrop (Figure 9), and supports a gravitational slip model for all the observed structures, triggered by high pore water pressure (Figure 10).

The evolutionary stages of the proposed landsliding model are depicted in (2002) and [START_REF] Vis | Fluvial and marine sedimentation at a passive continental margin. The late Quaternary Tagus depositional system[END_REF]. At that time, the toe of the slope merged into a narrow erosion pediment which was approximately 7-8 m below the present alluvial plain (Figure 11a-c), as suggested by the depth to the base of the Recent alluvial infill in borehole II (Fonseca et al, personal communication) (Figures 10 and11e).

Slip postdates the paleosol that is buried within the colluvial wedge (Ps, at the top of colluvium 1 in Figure 9), as it is tilted towards the slip surface, evidencing a listric geometry. This paleosol outcropped in the trenches opened by Fonseca and collaborators, where two samples were radiocarbon dated, giving an average age of 2,700 yrs BC [START_REF] Fonseca | Paleoseismological studies near Lisbon: Holocene thrusting or landslide activity? -Reply[END_REF][START_REF] Vilanova | Seismic hazard impact of the Lower Tagus Valley Fault Zone (SW Iberia)[END_REF]), corresponding to 4,650 yrs BP.

Considering an average sedimentation rate of about 1.8 mm/yr for the alluvial sediments in the last ca. 6.4 ka, inferred from data from borehole 0501.041, located approximately 500 m east of the VCO site (see discussion above), we may deduce a thickness of alluvial aggradation of roughly 8.4 m since the development of the reference soil horizon, which is coherent with the proposed model.

Laboratory testing and slope stability analysis

Laboratory testing of samples of the clay and silts unit indicate that it is mainly composed by high plasticity overconsolidated clays with small carbonate content which corresponds to small nodules of weak and porous limestone (Table 1). The direct shear tests were performed with intact samples, with 0.01 mm/min shear velocity, which coupled with the increased permeability of the soil caused by the presence of the limestone nodules, correspond to near drained shear conditions. For each sample a first test was made for peak strength measurement, followed by a residual test in the same direction of the peak test.

The results obtained indicate peak shear strength parameters c=13kPa, =19º (10 tests) and residual strength c=5kPa, =11.5º (10 tests) (Figure 12), which can be taken as a close estimate of shear strength drained parameters. The positive cohesion intercept for residual tests may have been caused by the presence of the small limestone nodules, which tend to increase the shear plane roughness and in consequence, to produce slightly increased strength values especially for the test performed at lower normal stress.

The slope stability analysis carried out for the shear planes depicted in Figures 10 and 11e were made using GeoSlope SLOPE/W v.5 software considering circular and fully specified failure surfaces, with the piezometric line slightly above ground, which is a condition likely to occur during heavy or prolonged rainfall, and using [START_REF] Bishop | The use of the slip circle in the stability analysis of slopes[END_REF], [START_REF] Jambu | Application of composite slip surface for stability analysis[END_REF] and [START_REF] Morgenstern | The analysis of the stability of general slip surfaces[END_REF] limit equilibrium methods (Figure 13). Considering the long term conditions that prevail in these slope failures, residual strength parameters were used.

The results obtained for different failure conditions that cover all the groups of shear planes identified in the VCO trenches, indicate safety factors lower than 1 in heavy or prolonged rainfall periods, and thus landslide triggering is certain in these conditions. This is further supported by the recurrent slope instability events that affected the railway line at VCO: as referred above, the slope sections located northwards were object of various heavy engineering stabilization works, but in spite of these, their intermediate portions, located approximately one hundred metres to NNE, started to move in the 2000/2001 winter, and subsequently the slope drainage system was completely destroyed with heavy deformation of the slope profile in the 2005/2006 winter.

Seismic reflection data

In order to confront the models of faulting vs. landsliding, four highresolution seismic reflection profiles (VCO1-4) were first performed at the trenching site, two of them perpendicularly, and the other two parallel to the slope (and presumed fault?) trend, with lengths ranging between 25 and 70 m (Cabral et al. 2003[START_REF] Simão | Aplicações de Sísmica de Reflexão e Refracção na Geotecnia[END_REF]) (Figure 14). A hammer was used as energy source, and the P wave arrivals were registered by 10 Hz, vertical component, geophones. A 24 channels Seistronix RAS-24 Remote Acquisition System was employed for signal transferring and processing.

The quality of the obtained seismic sections was generally poor, possibly due to bad coupling of the geophones, the low level of maximum frequencies provided by the used energy source, and also the low natural frequency of the geophones that were employed (10 Hz). Particularly in what concerns profile VCO2 and the key line VCO3 (acquired perpendicularly to the studied slope, aligned along one of the trenches and passing at the drilled well location), the resolution was low and there was lack of coherence of reflectors along most of the sections. Yet, profiles VCO1 and VCO4 showed enough coherence to support a reliable geological interpretation [START_REF] Cabral | New data on the active surface faulting vs. landsliding controversy concerning the Vila Chã de Ourique site (Lower Tagus Valley)[END_REF][START_REF] Simão | Aplicações de Sísmica de Reflexão e Refracção na Geotecnia[END_REF].

Line VCO1 was acquired at the alluvial plain east of the Tagus riverbank and parallel to the slope, so that it does not provide direct information concerning the structures under study. But seismic section VCO4 was obtained at the alluvial plain of the small tributary creek located south of the trenches site, crossing the foreseeable prolonging of the tectonic structure proposed by Fonseca et al. (2000b).

In this section, an uppermost almost continuous reflection horizon can be recognized, which is interpreted as the base of the Holocene alluvial infilling, evidencing the absence of surface, or near-surface faulting, for the resolution of the seismic data (estimated at approximately 3 m) (Figure 15). The base of this sedimentary cover is located at a two-way travel time (twt) of about 20 ms, corresponding to a depth of approximately 7 m taking a seismic wave velocity of 700 m/s [START_REF] Simão | Aplicações de Sísmica de Reflexão e Refracção na Geotecnia[END_REF]. Some other reflection horizons are recognizable below, most probably corresponding to the bedding of the Miocene sediments. Below 100 ms twt coherence is poor for allowing a reliable interpretation.

To get further information and improve reliability, another high resolution seismic reflection profile was acquired later (VCO-AB, Figure 15), approximately coincident with the former VCO4 section, using this time higher frequency (28 Hz) geophones. The same energy source, geophone layout (1.5 m separation) and acquisition system were used but we obtained a new seismic section with improved resolution on the top 100 ms TWT. As in the previous section, an upper set of almost continuous reflection horizons is recognized on profile VCO-AB (Figure 16). A sharp, continuous horizon is evident at a depth of approximately 20 ms (twt), which we again interpret as Holocene alluvial infilling. Similarly to the VCO4 section, this reflection horizon identified on the new seismic profile at a depth of ca. 7 m (for a seismic wave velocity of 700 m/s), and interpreted as the base of the Recent alluvial sediments, doesn't show any evidence of fault displacement, for the resolution of the seismic data, now estimated as approximately 2 m.

Conclusions

The results of the studies that we have performed at the VCO site, which comprised field reconnaissance, a reappraisal of the trench outcrops previously excavated by Fonseca and collaborators (Fonseca et al. 2000a(Fonseca et al. ,b, 2001;;[START_REF] Vilanova | Sismicidade e perigosidade sísmica do Vale Inferior do Tejo[END_REF][START_REF] Vilanova | Seismic hazard impact of the Lower Tagus Valley Fault Zone (SW Iberia)[END_REF]) and the interpretation of new outcrops meanwhile uncovered at the site, borehole drilling, soil mechanics laboratory testing, slope stability analysis, and seismic reflection acquisition, point to the alternative interpretation that the outcropping structures are gravitational and not of tectonic origin.

The new outcrops that were exposed at the VCO site crosscutting the structures that outcropped at the trenches enabled a view further in depth and increased the knowledge about the local stratigraphy. These new outcrops, where an eastwards steeply dipping slip surface was exposed, together with the refined slope stability analysis, and newly acquired high resolution seismic reflection data, all preclude the thrust fault interpretation of the slip surfaces identified in the trench walls and support a gravitational slip model for all the observed structures.

The gravitational slip was mainly caused by the presence of low shear strength clays and triggered by high pore water pressure, coupled with slope toe river erosion giving rise to a steep profile. We do not discard the possibility that the studied landslide was activated by an earthquake, though, as explained in the text, the slope is unstable enough to slide without the action of earthquake shaking. The gravitational slides must have occurred prior to development of the present sedimentation level of the Tagus alluvial plain, which was attained in the last few thousand years as indicated by borehole data and estimations of sedimentation rates.

The fact that we interpret the structures identified in the VCO site as non tectonic does not rule out the presence of an active tectonic structure in the area.

Actually, there probably is a major NNE-SSW trending active fault to the East of the VCO site, belonging to the Lower Tagus Valley fault system, which is concealed beneath the late Pleistocene to Holocene alluvial fill of the Tagus River.

The presence of this active fault is suggested by morphotectonic and hydrogeological data [START_REF] Cabral | Neotectónica em Portugal Continental[END_REF][START_REF] Mendonça | Identificação de falhas na Bacia Cenozóica do Tejo através de técnicas de investigação hidrogeológica[END_REF]Martins et al. 2009) and is still to be confirmed.

  steep slope, at the right bank of the Tagus river, where it is intersected by a tributary valley that creates a wedge-shaped cliff pointing southwards. By the toe of this slope passes the most important railway line in Portugal. Intense instability affects a 300 m long slope section located NNE of the VCO site (including fissuring, slide scars, steep down-dip profile, ongoing landsliding), and the need to insure safe operation of the railway line induced the construction of engineering slope stabilization works which include drainage, toe retaining walls and extensive surface modelling. These stabilization works suffered considerable deformations during the 2000/2001 winter and severe damage by excessive slope deformation during the 2005/2006 winter, which caused subsequent extensive repair works of the slope and the railway line platform.

Figure 11 .

 11 Figure 11. As schematically shown, the first gravitational slide on the lower, steep surface activated the contact between the former lower slope profile and an overlaying colluvial wedge (Figure 11c, event 6), and must have occurred prior to the development of the present sedimentation level of the Tagus alluvial plain, which was attained in the last few thousand years as indicated by estimations of aggradation rates performed above, based upon borehole data from Ramos et al.

Fig 1 Fig 2 Fig 4 Fig 6 Fig 7 Fig 9 Fig 14 Fig 15

 1246791415 Fig 1 Geographic setting of the study region (framed area). Portuguese mainland relief from 200 m grid digital terrain model; VCO, Vila Chã de Ourique

Table 1

 1 ) Index properties of samples of the clays and silts unit (from 0.5 to 5.9m depth in the borehole located on the slope, Figures7 and 8)

	Slide clay 1	5.4	25.4 64.2 7.8	2.6	55	18	10	37	20.209
	Top clay 2	6.8	-	-	-	-	53	21	11	32	19.816
	Lower clay 3 7.9	-	-	-	-	57	23	10	34	18.149

table

  Click here to download table: Table1_Cabral_et_al_VCO_JOSE.doc

Acknowledgments

Financial support for this work was provided by Fundação para a Ciência e a Tecnologia in the scope of projects Seismic Hazard Evaluation of the Lower Tagus Valley (POCTI/CTA/11178/1998 -SHELT), Seismotectonics GIS Database for Mainland Portugal (POCI/CTE-GIN/58250/2004 and Paleoseismological Study of Active Faults in Mainland Portugal (PTDC/CTE-GIN/66283/2006

). We thank Nuno Simão for his help in the acquisition and processing of the seismic profiles. We are grateful to Prof. K. Reicherter and an anonymous reviewer for their careful reviews and comments that significantly improved the manuscript.


Risk calculation and precautionary uncertainty: two configurations within crime assessment

INTRODUCTION

This paper draws upon international literature on risk and uncertainty and on pilot interviews with security personnel and other managers in the private sector and with law enforcement personnel in Belgium regarding the vulnerability of economic sectors to crime. 1The aim of the paper is to draw attention to two configurations of thinking in crime assessing amongst security managers economic sectors and law enforcement agencies.

The literature on risk and uncertainty literature spans the disciplines ( [START_REF]Uncertainty and risk: Multidisciplinary perspectives[END_REF] p. 288), from the natural sciences to social sciences and law, 2 and some of the ideas have entered popular discourse. 3 Following O'Malley ( [START_REF] O'malley | Risk, Uncertainty and Government[END_REF] pp. [START_REF] Haggerty | From Risk to Precaution: The Rationalities of Personal Crime Prevention[END_REF][START_REF] Kambhu | Part3: Systemic risk in ecology and engineering[END_REF] -who considers risk and uncertainty 'as distinguishable ways of imagining and governing the future' and analyses them in terms of 'configurations or assemblages' -we observe two such configurations concerning public sector and private sector thinking about crime in economic sectors in Belgium. Each of these has specific strengths, weaknesses and (we argue) purposes. We call these 'risk calculation' and 'precautionary uncertainty' and, in the second part of this paper, we link them to certain developments and thinking in law. 4 On the one hand, one finds an established, technocratic and expert-based form of risk calculation for purposes of risk management, generating quantitative estimates of the probabilities and impacts of everyday (routine) crime events. Risk calculation specialists seek to make estimates of probabilities, using various conceptual models, known past cases and available historical data. Risk calculations are shared between senior managers in the private sector, policy makers, police and the public -all of whom are advised to support countermeasures, seeking to interpose barriers between perpetrators and their targets/victims, using techniques of guardianship, disruption and/or prosecution. In short, risk calculation specialists produce knowledge having implications for the thinking and conduct of others. For example, public policing agencies, the specialised security industry [START_REF] Williams | Reflections on the private versus public policing of economic crime[END_REF][START_REF] Zinn | Social theories of risk and uncertainty: an introduction[END_REF] and security units inside large firms 'responsibilise' [START_REF] Garland | The culture of control: crime and social order in contemporary society[END_REF] firms, their managers and staff, in the sense of giving them forms of risk knowledge and risk solutions.

Whilst there may be nothing anti-democratic in the process of specialist risk calculation, it is not intrinsically democratic either: citizens should do what policy-makers tell them, and policy-makers are suitably informed by risk specialists. Citizens would be disadvantaged in querying specialists' assessments, since the models and language may be unfamiliar, the data bewildering and/or non-available (for reasons of confidentiality and security), and citizens are positioned as customers for, not co-authors of, such assessments.

By contrast with such technocratic assessments, we argue, one finds (especially since 2001) the rise of an ambiguous and contested politics of precaution concerning crime risks. This concerns not the most likely, rather the worse imaginable events -inspired by the precautionary 'turn' after the attacks of 9/11. Abandoning as futile the attempt to attach probabilities to rare but very high-impact events, this configuration focuses on the potential instability of targets, systems and victims, including those yet to be exploited by criminals (as far as is known). It aims at identifying the vulnerabilities that would lead to the most devastating consequences. It spans business continuity planning in the face of potential disruptions from a variety of sources including (for example) extortion by criminals, major frauds by managers or traders, industrial espionage and infrastructure misuse by business partners. Such disruptions may involve shut-downs, severe reputational damage, even bankruptcy (see eg. WorldCom, Enron etc.). Private sector interviewees of larger companies in Belgium report that such considerations have led to the introduction of back-up and replacement systems capable of supporting firms' normal activities, in the event of major disruptions caused by crime. This precautionary approach potentially widens the responsibility for knowledge-production, from specialists (whose risk calculation techniques cannot quantify systemic uncertainties), to all those who have to live with consequences, since it is they who must decide how far precautionary measures may be justified. The democratisation implied is, if not a poisoned chalice, at least a bitter drink, as citizens get drawn into debates on what restrictions may be merited on liberty and privacy, what administrative actions may be taken against suspected persons and what changes may be made to legal standards of proof.

Caution is needed when considering the historical emergence of the two perspectives. The present authors wish to make clear that they are not saying that the more recently emerging precautionary uncertainty configuration have displaced or replaced risk calculation. It is more a case of both approaches being both widely being operationalised alongside each other, in policing and intelligence agencies, in private sector enterprises, etc., depending on the context. To give some brief examples from our respondents, very serious (and potentially difficult to reverse) consequences may arise from terrorism, or from the corruption of systemically-important markets or institutions, or from penetration of governments by top-level crime groups -meriting a precautionary approach. At the same time, however, there may be a continuing shower of thousands of lower-level offences, which by their number, persistence and uneven focus seriously effect some local communities and businesses -meriting everyday risk calculation and management [START_REF] Tilley | Organized crime and local businesses[END_REF]. Risk calculation is about 'known quantities' (historically-observed event frequencies, quantifiable data on loses, creating a sense of manageability). Precautionary uncertainty is about 'unknown quantities' (new categories of or single events, qualitative analysis and crisis management).

The authors acknowledge that risk calculation and precautionary uncertainty are not the only perspectives that can be used in this discussion against the preliminary results of the held interviews. It is for example possible to argue that exceeding the limits of calculative and instrumental rationality does not necessarily imply a shift into uncertainty deliberations. Some techniques or methods allow to work with uncertainties within a risk and rational perspective. Scenario-playing [author ref later to insert] or enactment 5 allow players to create new forms of knowledge and practices that allow rational reflections about uncertainties that can be employed in the private sector (in larger companies and in security consultancies) in order to conceptualise and fine-tune risks and uncertainties. Best [START_REF] Best | Ambiguity, uncertainty, and risk: rethinking indeterminacy[END_REF] argues that risk and uncertainty are not just two sides of a coin, but part of a more mixed, sometimes overlapping or ambiguous continuum. O'Malley [START_REF] O'malley | Risk, Uncertainty and Government[END_REF] denies such a view and considers risk as one specific way to manage uncertainty by calculative techniques.

In short, there are a variety and diversity of ways and techniques for deploying thinking and action in terms of risk and uncertainty. How, then, can they be positioned in relation to each other? There are practical difficulties in running the two perspectives alongside each other concerning crime, since evidently they differ considerably in terms of assumptions, content and outputs. 6 In what circumstances could decisive arguments be marshalled, by a law enforcement agency or a large private company or a security consultancy, in favour of having conducted a risk calculation -or by contrast in favour of an precautionary uncertainty analysis or other techniques? These are questions that security analysts and their customers, including citizens, may be called upon to answer. They are also among the questions raised by contemporary work on (crime) risk and uncertainty [START_REF] Haggerty | From Risk to Precaution: The Rationalities of Personal Crime Prevention[END_REF][START_REF] O'malley | Risk, Uncertainty and Government[END_REF]. Recent work by Elizabeth Fisher [START_REF] Fisher | Risk regulation and administrative constitutionalism[END_REF] and others on the justiciability of risk assessments -meaning the legal determination of their fitness for specific policy purposes -could be a way of exploring their optimal applications and their limitations.

Fisher constructs two 'ideal types': a rational-instrumental approach assessment of specific and relatively bounded risks (like our risk calculation), and a deliberative-constitutive approach to systemic and less bounded uncertainties and 'tipping points' (like our precautionary uncertainty). Fisher examines justiciability of risk and uncertainty assessments: the extent to which, as a result of judicial review, administrative decisions based on such assessments may upheld or struck down by the courts. What is stake here is the fitness-for-purpose of assessments, as established by legal action: justiciability is the equivalent in legal terms to the managerialist notion of fitness-for-purpose. This approach looks as much at the policy making process as it does at the sources of risk and uncertainty; and also it concerns itself with robustness of process/procedure in the face of possible legal challenges. Given the increasingly litigious environment -including the use of judicial review at national level and the increasing involvement of the European Court of Justice in matters of criminal law [START_REF] Mitsilegas | EU Criminal Law[END_REF] -it would seem important as well as interesting for crime risk calculations in EU member states to be legally robust (or, to put it the other way around, it could be dangerous for assessments to be legally vulnerable). Nor can it be ruled out that a civil action could be brought by a legal person considering himself to have been harmed by a shortfall in security assessments (for example, by alleged inattention to certain crime risks or terrorist risks on the part of an enforcement ministry, state agency or private sector risk calculation contractor).

The structure of the paper is therefore as follows. First, the nature of, and some issues in, risk calculation are reviewed. Second, the same is done for the analysis of precautionary uncertainty. Finally, the relationship between both is analysed and linked to the fitness-forpurpose/justiciability discourse. From that a meta-narrative is proposed in relation to which risk calculation and precautionary uncertainty can be discussed. Throughout, we seek to bring in examples from pilot interviews with security personnel and other players in the private sectors in Belgium carried out in late 2008 and early 2009 and other examples from the literature.

RISK CALCULATION: ASSESSING ROUTINE RISKS AS A TECHNOCRATIC PRODUCTION

Practitioner and academic discourses on crime risks may be located within the broader context of new (reflexive, late, post-) modern 'risk society', in which risks such as criminality and the mastery of these risks have taken a major role [START_REF] Beck | The risk society: Towards a new modernity[END_REF][START_REF] Garland | The culture of control: crime and social order in contemporary society[END_REF][START_REF] O'malley | Risk, Uncertainty and Government[END_REF]. According to Zinn ([49] p. 4) there are at least three different, although connected ways for the use of the term 'risk': (i) a defensive state of mind in which risk may refer to unwanted events, the word being used, with some interchangeability, alongside terms such as hazard, loss, damage or threat (although there may be significant distinctions between such categories, or between specialists' preference for use of some terms and dislike of others); (ii) a calculative frame of mind in which risk may indicate a concern with both costs and benefits and the balance between them, and (iii) a positive frame of mind in which the idea of risk appetite is represented, which refers to a willingness to take extreme risks in order to maximise returns (some criminals have greater risk appetite than others, and police also may differ in this respect (see e.g. [START_REF] Dorn | Drugs importation and the bifurcation of risk. Capitalization, cut outs and organized crime[END_REF]). From a crime-control perspective, type (i) risks, forms of risk that are to be avoided, in particular the risk of criminal victimisation, are of special interest. The demand for control and management of these risks caused the spread of risk analyses [START_REF] Walklate | Risk and criminal victimization. A modernist dilemma[END_REF].

According to this way of thinking, risk is defined as a function of the probability of various risk events and the costs of their impacts. Strategic risk calculations of crime attempt to project this configuration into the future, through relying on past available data such as criminal statistics. In the private sector, security departments build the expertise on which higher company management rely on for decision making. Their knowledge is inter alia based on crime incident statistics. Police strategic risk analysis and assessments are regularly focussed on the risk of offending, rather than on the risk of victimisation, whereas it is the opposite for the private sector.

Risk calculation and situational crime prevention

O'Malley & Hutchinson ( [START_REF] O'malley | Reinventing Prevention. Why did 'crime prevention' develop so late?[END_REF] pp. 374-375), identify a threefold trend in crime prevention and control since the mid-1990s: "[...] first toward statistical and actuarial preventative technologies; second, toward the networked extension of the government of crime beyond police and the state [...]; third, toward to a focus on 'designing out' crime and on situational opportunity reduction rather than previous preventative models focussed on deterrence, correction and the social and psychological causes of crime". Several of our interviewees, mainly from the transport business, confirmed the influence of such measures. Methods include incident statistics, interrogated by techniques such as crime scripting. Incidents are first 'mapped' in order to highlight hotspots of probable criminal victimisation, making possible a focussing of resources (this is called 'situational prevention'). Crime scripting goes further than this, by identifying the necessary steps of the perpetrators' modus operandi, for example with respect to vehicle or cargo theft. All identified risk-points are then confronted with a prevention measure, such as locks, alarms or GPS systems for trucks, trailers and/or the transported goods themselves (tracing devices). This is done within specific companies but may then be shared with other businesses, through organisations such as TAPA (Transported Asset Protection Association) [START_REF]Transported Asset Protection Association[END_REF] and its Incident Information Service (IIS) and with law enforcement agencies. Based on the measured probabilities for victimisation, new counter measures or prevention measures are applied, in an attempt to forestall future incidents. Concerning cargo theft, the Cargo Theft Report of Europol [START_REF]Cargo Theft Report[END_REF] demonstrates how risk calculation is handled in practice. The IIS of TAPA is promoted as a potential tool in combating cargo theft ([17] p. 22). Geographical Information System (GIS) is another instrument for identifying and mapping crime hotspots that law enforcement and environmental criminologists are using, contributing to crime pattern theory [START_REF]Environmental Criminology[END_REF][START_REF] Ratcliffe | Crime mapping and the training needs of law enforcement[END_REF][START_REF] Ratcliffe | The hotspot Matrix: A framework for the spatio-temporal targeting of crime reduction[END_REF].

One well known model is routine activity theory [START_REF] Cohen | Social Change and Crime Rate Trends: A Routine Activity Approach[END_REF]. In their original formulation, Cohen & Felson [START_REF] Cohen | Social Change and Crime Rate Trends: A Routine Activity Approach[END_REF] explained crime as the product of the convergence of three minimal elements in time and space: (i) motivated offenders, (ii) suitable targets, and (ii) the absence of capable guardians. The capable guardian "serves by simple presence to prevent crime" ( [START_REF] Felson | Those Who Discourage Crime[END_REF] p. 53). Situational crime prevention [START_REF] Clarke | Situational Crime Prevention: successful case studies[END_REF] focuses on concrete steps that can be taken to reduce crime opportunities. 7 Attempts have been made to expand this approach to organised crime [START_REF]Situational Prevention of Organised Crimes[END_REF]. For our interviewees in the Belgian transport and hotel, restaurant, café business, it seems beyond debate that surveillance (guardianship) by situational prevention measures, like cameras, alarm systems or guards, are useful, indeed indispensable tools for decreasing the probability of crime (at least for certain crime types). Law enforcement respondents also consider these measures as useful in prevention and also for investigation and detection of perpetrators. To give a mundane example, one security manager from a multinational transport company reported that a high incidence of casual thieves cutting the covering of lorry trailers with a knife to steal the load, leading the company to change to a hard protective cover, in order to avoid this modus operandi in the future.

The point for our analysis is this is a frequency-based analysis. Likewise, concerning targets, 'crime proofing' of products is seen by some as a way of decreasing the probability of theft. The acronym CRAVED -Concealable, Removable, Available, Valuable, Enjoyable, Disposablewas developed to forecast the probability of theft, based on those six risk factors [START_REF] Clarke | Hot products: Understanding, anticipating and reducing demand for stolen goods[END_REF] and to offer prevention measures [START_REF] Ekblom | Designing products against crime[END_REF]. Since the means of crime (transport) can also be a target of crime (trucks), anti-theft locks to prevent theft of the whole trucks are now routine, as observed by one of our interviewees at a transport company. Furthermore, small and highly valuable goods are accorded special measures, such as documentation, seal procedures, tracking [37] and bar codes) and also may be camouflaged: small, highly valuable goods may be transported inside big and unwieldy boxes, without external identification of the goods. Since some customers ask for these 'extra' measures, although not all companies are willing to supply them, since they are not organisationally and/or financially capable. Another development of crime proofing is 'legislative crime proofing', which aims to detect crime opportunities inadvertently created by legislation. 8These examples show that probability-based risk calculation is widespread in the private sector and in law enforcement, forming the basis for crime assessment and prevention.

Criticisms and limitations

Criticisms of such risk calculation and management can be classified as technical or as social. Technical criticisms involve propositions that models are poorly designed or have not been implemented well [START_REF] Van Duyne | The indications of the EU organised crime policy making[END_REF]. The risks dealt with are always 'known' risks. Data is derived from the past and is extrapolated to the future. Decision makers rely on these models and for some it might be helpful -especially when the law of large numbers applies 9 -but for others not. Crime events that have never occurred before in a company or in an economic sector can cause more harm, as one is completely unprepared. This challenges risk calculation based on probability and focuses attention on 'improbable' events that could cause unknown consequences. Donald Rumsfeld, US Secretary for Defence from 2001 to 2006, famously (notoriously for some) distinguished between "known unknowns" (risks that are known to exist but whose timing or magnitude is not predictable) and "unknown unknowns" (risks that are not imagined until the moment they impact) [START_REF] Longstaff | Security, resilience and communication in unpredictable environments such as terrorism, natural disasters and complex technology[END_REF]. If only statistical probabilities are used for risk analysis, statistically improbable events, the so-called Black Swans [START_REF] Taleb | The Black Swan: The Impact of the highly Improbable[END_REF], stay out of the radar and are not prepared for. Decision makers (whether individuals or organizations) seem to have several blind spots when confronted with dangers in their environments. 10 On the other hand, this blindness may have some advantages, since all actions have unanticipated consequences. Decisions based just on risk calculation that is based on past probabilities can open other crime risks, making an enterprise more vulnerable than before taking the prevention measure. Furthermore, if crime risks are represented by a few indicators, then in relation to more complex crime risks -where the time and space of the criminal act is not fixed, as routine activity theory demands -then it is difficult to find prevention measures. Where does the crime risk occur? Do statistics of past cases covered by the police have any value with regard to situational prevention measures regarding the future? Counting numbers of cases of cargo theft on Belgian highway parking places, and reacting by installing camera surveillance on the 'hot parking spaces' close to the Dutch boarder, reduced theft rates there (not taking into account a possible displacement of the perpetrators). Because the availability of highway parking spaces is limited, they can be observed (at some cost), making risk calculation there possible. However, is not the case in many other crime contexts, undermining risk assessments (for example, threat assessments on the basis of criminal statistics, where national crime rates do not say much about crime risks, particularly in particular localities [START_REF] Haggerty | From Risk to Precaution: The Rationalities of Personal Crime Prevention[END_REF]. These are just some of the technical criticisms of risk calculation Some authors advance social criticisms of this form of assessment. Displacement of crime [START_REF] Repetto | Crime prevention and the displacement phenomenon[END_REF], from protected to unprotected areas, would mean that those not able to follow the prevention advice would be easy targets for the criminal. This would hit the financially weaker companies or persons in society [START_REF] O'malley | Risk, Uncertainty and Government[END_REF]. Our own preliminary research is consistent with this. Consider for example the decision mentioned above, to change the usually used 9 "*E]ven if individual events happen in a random way, when enough of these events are put together in a reasonably stable environment one can make predictions that have a reasonable chance of being accurate. So, for example, one cannot predict whether an individual coin toss will turn up heads or tails, but many coin tosses will follow a fixed probability ratio (an even chance)" [START_REF] Longstaff | Security, resilience and communication in unpredictable environments such as terrorism, natural disasters and complex technology[END_REF]. 10 For a critique of the efforts of local governments, see for instance Wolensky & Wolensky [START_REF] Wolensky | Local governments problem with disaster management: a literature review and structural analysis[END_REF].

trailers' cover to a hard protective cover to avoid cargo theft by cutting the cover with a knife: another respondent from a smaller company reported that many middle seized or smaller companies do not have the financial capacity to update their lorries with these sort of measures. On the wider social canvass, Power argued that a society preoccupied with "the management of everything" [START_REF] Power | The risk management of everything: rethinking the politics of uncertainty[END_REF] is a dysfunctional society. Consider also the Foucauldian proposition that risk mentality is deployed as a strategy of governance, meaning that citizens follow leaders who point to possible risks and promise firm action against them [START_REF] Garland | The culture of control: crime and social order in contemporary society[END_REF]. Precaution invites one to anticipate what one does not yet know, to take into account doubtful hypotheses and simple suspicions" ( [START_REF] Ewald | The Return of Descartes' Malicious Demon: An Outline of a Philosophy of Precaution[END_REF], see also Haggerty op cit).

Thus, whilst probability-based crime risk calculation may seem like 'common sense' to its practitioners, it is open to technical and social criticisms.

DELIBERATING EXCEPTIONAL UNCERTAINTIES

The starting point of this mentality is that attempts to quantify probability may be inherently misleading or not possible -hence precautionary approaches. These have arisen in many fields, including environmental protection (from the 1990s), terrorism (especially from 2001) and financial market security (from 2008). In this configuration, quantification of probability of crime risks is replaced by the avoidance or minimisation of harms, not relying on expertise because it is in doubt or not available but deploying "informal knowledge and techniques [in order] to achieve security"([29] p. 23).

This approach prioritises the highest-impact events, however they may be caused: for example what could follow if an aeroplane falls onto a chemical works, or if hundreds of thousands of mortgages are mis-sold, or if criminality taints or derails a nationally important procurement contract? The two main elements are (i) a willingness to expend considerable resources in order to try to prevent (insofar as is possible) the occurrence of events that would have the greatest impacts and, (ii) an acceptance that, despite all such efforts, some such events may occur, hence it is important to have sufficient resilience (back-up systems, redundancy, self-healing systems, ability to rapidly replace damaged capacity, etc.) in order to enable recovery. Alongside disaster recovery plans and business contingency plans, an important precautionary tool is redundancy (duplication of systems), especially in the logistic business. Interviewees from major transport companies reported that, instead of creating only a few big hubs through which to transport good, or depots in which to store them, it is considered safer to make several smaller hubs in different geographic locations. In case of an incident, the tasks of one unusable hub can be taken over by others.

Criticisms of precautionary uncertainty and similar approaches are diverse, including that they go beyond available data and become ideological [START_REF] Sunstein | Beyond the precautionary principle[END_REF]; that they have become discredited as a result of a realisation that high-handed action may be entered into as a precaution against threats that are subsequently found not to exist [START_REF] Sunstein | Beyond the precautionary principle[END_REF]; that they justify a never-ending stream of emergency actions and controls that become permanent. Nevertheless, there remains strong interest in precautionary uncertainty, for reasons of recent history.

From calculable crime risk to precaution: a short history

Concerning crime we can say that, prior to 2001, strategic criminal assessment focussed on what we may call 'common criminals', meaning that they were conceptualised as acting for financial gain, and in some cases power, whether that be at a local level, regionally or across global markets. Following 2001, strategic analyses of crime became influenced by antiterrorism policies, in some instances leading to so-called 'organised crime' being elevated from being a serious crime category, to being considered by some commentators to form, if not a bridge between criminality and terrorism, at least a facilitating factor. Anti-terrorist policies thus reinforced the tendency to pose some 'organised crime' phenomena as having potentially systemic consequences (penetration of the licit economy and/or of political elites, collapse of the state's monopoly of violence, breakdown of social order, etc. (see e.g. [START_REF]Organised Crime and Corruption in Georgia[END_REF]).

In parallel, and arising from the 1990s onwards and from neo-liberal tendencies in the market economy and political life, risk calculation took a far broader form: it became a standard management tool [START_REF] O'malley | Risk, Uncertainty and Government[END_REF]. Initially, managerial risk calculation took the same broad strategy as in the security field, as it sought to identify specific risks and to calculate their probabilities and impacts, then trying to build up from these specific estimations to a notion of overall risk [START_REF]EU Organised Crime Threat Assessment[END_REF]. However, the 'bottom up', aggregating style of calculation of crime risk has been brought into question by the New York attacks of 2001, also by the financial crisis of 2007 onwards, which is seen as being conjoined with various criminal phenomena, such as Ponzi frauds, insider trading and conflicts of interest [author ref later to insert]. Increasingly, systemic vulnerabilities are seen as requiring a more holistic approach, looking not at individual risks but at connections between them [START_REF]Emerging Systemic Risks in the 21st Century: An Agenda for Action[END_REF][START_REF] Renn | Systemic risks: a new challenge for risk management[END_REF].

Identification of uncertainties that might have far-reaching effects cannot be accomplished by specialists alone, since they don't have a wide enough view (per definition, they are specialists). Such issues require inputs from the widest possible set of perspectives [START_REF] Beck | The risk society: Towards a new modernity[END_REF]. As interdisciplinary work published by the New York Federal Reserve outs it: "To identify systemic risks, one has to look at everything. Since no one can really capture all of the relevant perspectives, systemic risks must be assessed through consultations with multiple players, which ultimately converge on a picture of the most important risks" ( [START_REF] Kambhu | Part3: Systemic risk in ecology and engineering[END_REF] p. 36).

Thus, anti-terrorist and financial market developments and policies introduced, alongside the assessment of discrete risks, an enhanced awareness of the uncertainties attaching to systemic turning points, and a certain humility amongst security assessment specialists. This has led to an enrichment of the interdisciplinary debate, as scholars from different disciplines -natural science, environmental studies, disaster-management, business, markets -are brought together to explore what if any general statements might be arrived at, concerning uncertainty. According to some recent analyses from studies of resilience in natural and man-made environments and in financial markets, attempts to lowering specific risks by linking together support mechanisms might have the effect of increasing systemic risks, whilst attempts to lowering systemic risks by reducing interlinkages might deepen the risks to specific elements. For example: "When a system is too homogeneous, it cannot adapt. Modularity -the degree to which a system can be decoupled into discrete components -also influences robustness. A basic principle in the management of forest fires and epidemics is that if systems are all connected, a perturbation will encounter nothing to stop it from spreading. But when a system is compartmentalized (when firebreaks exist or high-risk parts of a population are vaccinated against an epidemic), then the spread may be contained. Modularity can thus be an important part of robustness if it ensures that an affected component will be isolated from destabilizing feedbacks. However, modularity often involves a trade-off between local and systemic risk [uncertainty]. Because the compartmentalized elements of a system will be less able to withstand some shocks, modularity tends to increase the risk that individual elements will be critically damaged" ([24] p. 28). The possibility that 'best practice' in security policies -based on too close an attachment to probability sampling -might be envisaged as a form of 'herding' and a deepening of shared vulnerabilities may be a bitter pill to swallow for those advocating and enforcing greater cooperation and convergence in security planning [author ref later to insert]. This leads to the question, to be addressed at the end of this paper, what basis could be adopted for judging (literally) the reasonableness of reliance upon risk calculation and on systemic uncertainty?

Reducing impacts in conditions of uncertainty: difficulties and criticisms

The key characteristic here is a willingness to 'think the unthinkable', in the sense of identifying what could be the worse things that might happen, in terms of their impacts, whilst disregarding any preconceptions about their likelihood. This Cassandra-like style of assessment is not, therefore, about events that seem likely to happen -rather, it is about events that would have the greatest negative consequences. One security manager gave us the following example: "We are sitting with a bunch of people around the table ... to think about the totally unexpected ... for example, within our company we follow of policy of screening our employees, under the slogan: all old criminals out of our house! And now we start thinking we had to employ only criminals, what would be the consequence?" 11Such a 'blue sky (could turn black)' thinking is not easy to maintain in an operational setting, since it does not easily fit with the 'action' frame or frame of thinking about existing, known risks and the need to manage them. Furthermore, a precautionary uncertainty approach, focusing on events that would have the biggest impacts (should they ever occur) would seem to draw attention away from events that may entail much lesser impacts -even quite trivial impacts -yet which are actually known to be occurring every day. Therefore one potential criticism of such an approach would be that it is socially irresponsible and economically wasteful, since it can result in insufficient attention being paid to known risks and their accompanying hurts which, in aggregate, are no doubt considerable. For example the international literature suggests that locally-focussed crime against businesses and, in some districts, households, may be both 'organised' (meeting national and/or EU criteria for 'organised crime') and considerably burdensome for those affected [START_REF] Tilley | Organized crime and local businesses[END_REF]. If these known and constantly ongoing hurts were to be neglected in favour of allocating police resources to possible yet shadowy or non-existent 'Mr Bigs', then questions may arise about priorities and use of resources. 12Another potential criticism of precautionary uncertainty -which emerges both from antiterrorist policies and, more recently, from financial market precautionary policies post-2008 -is that the precautionary interventions taken to forestall possible future, uncertain but bigimpact events may carry with them their own risks [START_REF] Sunstein | Beyond the precautionary principle[END_REF]. This is now a familiar theme in relation to the interventions into Afghanistan and Iraq, which definitely triggered unexpected difficulties and which may on balance, have magnified political dissatisfactions and hence threats. However, such large interventions are difficult to evaluate, because of the lack of a 'control group' -what would have happened if the intervention had not been made? That aside, large interventions made in order to forestall possible disasters may be very costly in economic terms, even to the point of being unaffordable, an evaluation that some commentators have made not only in relation to anti-terrorist policies bit also to current approaches to the financial market crisis [START_REF] Dizard | Who can afford the next national recovery plan? Financial Times from[END_REF]. There may be similar, but unknown, risks in relation some of the precautionary tactics that enforcement agencies adopt. For example, disruption is sometimes directed towards objectives such as weakening crime groups that are difficult to bring to court -for example undercover agents may try to sow mistrust between criminal groups/networks, thus discouraging them from cooperating together -yet it can be difficult to know all the consequences, side-effects and unintended consequences, when acting against targets that are only partially in sight.

A provisional conclusion might be, either that precautionary action should be conducted only in exceptional situations (criteria for which need to be clearly delineated); or that the precautionary approach should extent its logic from identification of possible but uncertain) threats, to encompass also all the possible (but uncertain) consequences of taking actions against those threats. If any of the imaginable consequences appear to unacceptable, then that would be reason for reconsideration of the proposed action. To be credible, such checks and balances would need to be intrinsic aspects of the model, not afterthoughts.

In this way, an precautionary uncertainty configuration might come more closely to approach the more conventional risk calculation approach, insofar as risk management involves analysis not only of the problems but also a cost-benefit analysis of alternative interventions. None of this undercuts the case for analysis in conditions of uncertainty, rather is makes it more complex. And it begins to raise the question of which approach, risk or uncertainty (or some mix of the two) may be suitable in particular circumstances.

JUSTICIABILITY: ADJUDICATING FITNESS FOR PURPOSE

Here we examine some issues of concern to security policy-makers and managers, whether in the public sector or the private sector, who are in a position of deciding in what circumstances to apply probability-based risk assessments, and/or precautionary uncertainty assessments. When is each of these most appropriate or, more worryingly, when is one or the other inappropriate? On what basis, could it be decided in principle to rely on one or the other; or possibly to employ both but in respect of different issues?

We give two answers, one 'commonsensical' and pragmatic (and consistent with our interviews with security manages and others in Belgium), the other based in law.

From the commonsensical and pragmatic point of view, the following views have been expressed to us. If the concern is something like low-level pilfering of goods by staff or customers, that could be calculated by routine risk calculations. By contrast, centralised IT communication and control systems seem to call out for a 'worst case scenario' approach, involving wide-ranging 'what if?' discussions. However, there may also be circumstances which, at the start, it is difficult to define issues exclusively in terms of either routine risks or exceptional vulnerability: the two forms of thinking will co-exist as techniques of 'knowing'. Inputs from lawyers at the risk/uncertainty intersection come from the perspective of the justiciability of policy assessments, meaning the legal determination of their fitness for specific policy purposes. This claims to be an authoritative way of exploring the optimal applications of, and limitations to, the risk calculation and precautionary uncertainty configurations. It is from this perspective that we now consider the two 'ideal types' of forms of procedure in the assessment of risk/uncertainty as proposed by Elizabeth Fisher [START_REF] Fisher | Risk regulation and administrative constitutionalism[END_REF][START_REF] Fisher | Models, regulation and legal cultures: A transatlantic perspective[END_REF]: the rational-instrumental (our risk calculation) and the deliberative-constitutive (our precautionary uncertainty).

The present authors point to parallels between, on the one hand, a degree of correspondence between probability-based crime risk calculation and Fisher's rationalinstrumental category. On the other hand, there is also some correspondence, we suggest, between precautionary assessments of uncertainty, and her deliberative-constitutive category. These links are indicated in Figure 1 Fisher suggests that her 'rational-instrumental' approach (our risk calculation: objectivist, 'scientific' and technocratic) will continue to co-exist with her 'deliberative-constitutive' approach (our precautionary uncertainty), rather than merging. She opines that: "the most legitimate state of affairs is the simultaneous operation of both paradigms. This is what is occurring in many contexts and, while, resulting in risk evaluation being a rather messy practice, it guarantees the most acceptable balance between enabling and restraining public administration" [START_REF] Fisher | Risk regulation and administrative constitutionalism[END_REF]. Refining this view, we argue that depending on the context they might sit alongside each other whilst remaining distinct modes of thought, merge or be complemented by other paradigms.

Fisher's rational-instrumental approach relies upon (and assumes the possibility of) a sound scientific basis for risk calculation. Risks are taken as knowable in principle, and information about them being assessable, reasonably robust and free of too much latitude in terms of alterative interpretations. The models are taken to represent social and natural realities and, when populated with data, cause and effect relations can be clearly and confidently identified.

By contrast, Fisher's deliberative-constitutive approach maintains that scientific methods can neither grasp nor decide the phenomena in question, because these are complex, uncertain and socially-politically ambiguous. This does not mean that technical modelling of the issues cannot be done, it means that models and data are inadequate as a substitute for judgement, especially since some of the apparent finding of modelling ('outputs') may be strongly influence by model assumptions ('inputs'). At best, models act as a contribution to reasoning, the latter having a primarily normative basis [START_REF] Fisher | Risk regulation and administrative constitutionalism[END_REF][START_REF] Fisher | Models, regulation and legal cultures: A transatlantic perspective[END_REF].

This objectivist/subjectivist, science/norms, technocratic/democratic split is deeply rooted in western cultures and in their social sciences, including in criminology and security studies. However, consensus does not exist on where and how to draw the line between these tendencies.

Some commentators would argue for the exclusion of models of systemic uncertainty, on the grounds that the models and data are insufficient to support robust findings [START_REF] Kopp | A methodology to measure the impact of organised crime activities at the EU level, Examining the feasibility of the methodology: a pilot study on international fraud[END_REF]. On those grounds, one might (at least in principle) arrive at quite a neat conclusion, in which further public and private investment should be made in the continuing development of risk calculations, whilst uncertainty modelling should be abandoned.

By contrast, from the more overtly normative position implied in Fisher's deliberative/constitutive approach, the supposed precision of technical risk calculations should be viewed with some scepticism. Indeed the acknowledged lack of a firm science base for discussions of systemic and precautionary matters could be all the more reason to advance those discussions in an exploratory and open manner in the public policy arena. In short, 'scientific' risk calculation assessments and 'political' precautionary uncertainty approaches are matters of contention.

The answer, according to Fisher, to be found through the legal system. Legal challenges have been mounted to a variety of policy decisions, on the basis that they relied on unsound science, or took on a precautionary basis that was unmerited. Thus, courts (especially but by no means exclusively in the US) and various commissions of enquiry have been drawn into a critical exploration of the fitness for purpose of such approaches, in principle and in terms of their execution in practice. As a sympathetic Belgian commentator puts it, the aim of Fisher's work is "recasting the terms of the debate [on risk and uncertainty] and, more specifically, rehabilitating the role of law and centrality of public administration" [START_REF] Meuwese | Book review: Risk Regulation and Administrative Constitutionalism by Elisabeth Fisher[END_REF]. Indeed, this work clearly signals its objective as overcoming a perceived sidelining of legal analysis in relation to risk and uncertainty, which has been dominated by concepts from economics, psychology and policing. Fisher asserts that "the legal dimension is a significant one and the body of law in this area is a complex, dynamic and constantly shaping understandings" [START_REF] Fisher | Risk regulation and administrative constitutionalism[END_REF]. We agree, and we argue for greater attention in risk/uncertainties to the legal dimension.

DISCUSSION: RISK/UNCERTAINTY DICHOTOMY OR CONTINUUM?

The social science, security studies and legal literatures suggest that security issues may be constructed or modelled either in terms of repetitive relations between elements (known, cause and effect relations) or in terms of unpredictability of relations. This difference may be represented in terms of the two configurations, as we have in this paper, or as a continuum, as some others have suggested: "At one end of this continuum are systems in which all the variables are predictable (A always follows B). Then there are systems that have low uncertainty (A almost always follows B) and medium uncertainty (we can calculate the probability that A will follow B). At the far end of this continuum are high uncertainty or stochastic systems (in which we cannot even predict a probability that A will follow B). In systems where uncertainty is relatively low it is easier to plan for any possible dangers, while in highly uncertain systems security becomes more problematic" ([26] p. 9).

So, categories or a continuum? There can be no settlement of this question except by appeal to criteria, which might be theoretical, practical or (more frankly) political. The concepts and techniques chosen for representing security (and other) issues depend also on cultural background, language, history (see [START_REF] Zinn | Social theories of risk and uncertainty: an introduction[END_REF]) and, for some academics, on past intellectual investments or commitments. Risk calculation and precautionary uncertainty are therefore likely to remaining matters of healthy debate concerning crime assessments, as is the question of whether they are best seen as being categorically distinct approaches, as a continuum or even as a homogenous blur.

Our reasons for preferring a categorical approach rest upon the following criteria and value judgements: conceptual sharpness; openness to public debate; and justiciability. Valuing conceptual sharpness, in our view, favours the categorist road: Occam's Razor might be thought to favour a blurring or a continuum, however much then is lost in terms of differences in risk/uncertainty narratives, methodologies and fitness-for-purpose. A criterion of openness to public debate strongly favours distinct perspectives on crime risk probability and on precautionary uncertainty: their analytical styles have very different policy implications, which should not be inadvertently 'bought' as the technical output of a methodology, but should be appreciated at the onset of the analysis (what kind of policy are actors trying to construct, when they model security problems?). Lastly, justiciability is an important issue in all societies of law: courts provide another valuable forum for challenge and debate, and so the contributions to legal theory provided by Fisher (above) must be valued and linked to other aspects of scholarship.

CONCLUSION

Risk calculation and precautionary uncertainty are two configurations that characterise the Zeitgeist in public and private sector thinking about crime and insecurity. Placing the social sciences and legal scholarship alongside each, risk calculation is seen to correspond to Elizabeth Fishers' legally-based 'rational-instrumental' approach, whilst precautionary uncertainty corresponds to her 'deliberative-constitutive' approach. The justiciability of risk and uncertainty assessments provides a framework for exploring the optimal applications and limitations of both configurations. This legal determination of their fitness for specific policy purposes provides a way to disentangle the discussion of risk calculation and precautionary uncertainty. We have argued here that the two forms of knowledge differ considerably in terms of assumptions -Gaussian continuities versus sudden breaks), types of content (quantitative versus qualitative), policy uses and participation (technocratic expertise versus wider stakeholder deliberation -and so should be regarded as distinct

  below.Figure 1. Two configurations, drawing upon, social sciences, security studies and law

	Ideal types	PROBABILITY RISK CALCULATION	PRECAUTIONARY UNCERTAINTY
	Main contents of	'RISK', where probabilities are knowable,	'UNCERTAINTY', where 'tipping points' are
	model	possibly quantifiable	unknowable
	Types of problems	ASSESSABLE, routine, known, predictable	CATASTROPHIC potential events
	addressed	problems
	Conceptual starting	PROBABILITY, calculated from past	POTENTIAL INSTABILITY of targets or
	point	frequencies, of the co-presence of	systems, meaning that, if hit, they might fall
		perpetrators, targets and insufficient
		guardianship
	Who describes the	EXPERTS, specialists, technocrats	ALL STAKEHOLDERS: policy-makers, citizens,
	problems		experts
	What is the	Intelligence 'PRODUCT', which aims to be	Emphasis on 'PROCESS', which must be
	deliverable	correct (the model represents reality)	widely 'owned' (the model is a tool for
			thinking)
	What society is	One in which technocratic experts lead,	One in which civil society and the private
	thereby reproduced	policy makers and civil society follow	sector face difficult decisions about
			precaution
	Corresponding to	Rational-instrumental	Deliberative-constitutive
	Fisher's legal
	categories

During the second half of

and the first half of

2009, 8 pilot interviews were held: 5 with personnel in the transport sector (including import-export) and 3 in the hotel, restaurant and café business (horeca). We also studied 9 files of the police concerning these sectors and discussed issues with several agents of different police and customs services' sections. The interviews were carried out under the auspices of the federal office for Belgian Science Policy in the program 'Society and Future'.[START_REF]Uncertainty and risk: Multidisciplinary perspectives[END_REF] For the social sciences Zinn[START_REF] Zinn | Social theories of risk and uncertainty: an introduction[END_REF] made efforts to map the different conceptualisations of risk and uncertainty generated by various positions. A more multidisciplinary research project on risk and uncertainty was launched by the University of Kent (Peter Taylor-Gooby and Jens Zinn) linking conceptual and methodological analysis from psychology, economics and sociology. See http://www.kent.ac.uk/scarr/index.htm.[START_REF] Beck | The risk society: Towards a new modernity[END_REF] Exemplarily for the enormous amount of contributions the notion "risk" shows circa 3.060.000 hints on www.GoogleScholar.be and "uncertainty" circa 2.220.000 (accessed on 20 May 2010), ISI Web of Science showed 73.243 articles dealing with the topic "risk" and 62.231 articles dealing with "uncertainty" among all subject areas. (accessed on 20. May 2010).[START_REF] Best | Ambiguity, uncertainty, and risk: rethinking indeterminacy[END_REF] These notions are chosen deliberately. 'Risk calculation' refers to what law enforcement and private sector interviewees refer to while talking about the described way of assessment. Other scholars employ other notions describing a similar mechanism dedicated to other contexts than crime. See eg. Weir[START_REF] Weir | Recent developments in the government of pregnancy[END_REF] who uses 'clinical risk' in the context of medical diagnosis of pregnancy or Collier[START_REF] Collier | Enacting Catastrophe: Preparedness, Insurance, Budgetary Rationalization[END_REF] who refers to 'archival-statistical' in the context of insurance. The aim is not to find 'the' generalised notion of description of what is happening but rather keep it close to the context under research. 'Precautionary uncertainty' is taken over from O'Malley ([START_REF] O'malley | Risk, Uncertainty and Government[END_REF] p. 23) who label this set-up with regard to the precautionary logic behind it. This logic was observed during the interviews as well.

Collier [11] introduces 'enactment based knowledge produced by 'acting out' uncertain future threats in order to understand their impact.' as another configuration of assessment with regard to catastrophe insurance.

Haggerty [23] observed that much crime prevention is precautionary in nature as there are not always probability assessments building the basis of decision but rather uncertainty. Concerning crime assessments the purpose and the way of measurement should be outlined clearly to avoid misleading communications and interpretations of the results towards other stakeholders and the public.

Clarke & Eck [9] identified 25 techniques of crime opportunity reducing measures.

Research on legislation proving on European Union level is inter alia carried out by Vander Beken & Balcaen[START_REF] Vander Beken | Crime Opportunities Provided by Legislation in Market Sectors: Mobile Phones, Waste Disposal, Banking, Pharmaceuticals[END_REF], Dorn & Levi[START_REF] Dorn | From Delphi to Brussels, The Policy Context: Crime Prophecy, Proofing, Assessment[END_REF]. See also:[START_REF] Albrecht | Crime Risk Assessment, Legislation, and the Prevention of Serious Crime -Comparative Perspectives[END_REF].

Translated from Dutch to English by the authors.

If on the other hand all analytic attention and operational resources are targeted upon the bestknown and more easily manageable risks, then uncertain but potentially gravely harmful possibilities may be neglected: it seems therefore that some way of balancing known risk and unknowable uncertainties may be needed.

configurations, not as a continuum. However, whether or not in practice risk calculation and precautionary uncertainty eventually merge, in crime assessments and in other fields of application, or remain distinct, remains an area for empirical research in the coming years.