B Nettier

L Dobremez

P Lamarque

C Eveilleau

F Quétier

F Véron

S Lavorel

How would Farmers in the French Alps Adapt their Systems to Different Drought and Socio-economic Context Scenarios?

Keywords: drought, livestock farming system, adaptation, scenario

The French Alps are considered as an area that is particularly vulnerable to climate change. Several droughts have already occurred since 2003. In order to assess the ability of farming systems to adapt to future drought events, we developed prospective scenarios combining different climatic and socio-economic contexts. Four scenarios were defined based on (i) prospective studies conducted at national and international levels, and (ii) a participatory approach with various stakeholders to transcribe these scenarios at a local level. Farmers and shepherds in the Vercors and Oisans massifs were surveyed in order to understand how they had reacted to previous droughts, and how they would plan to react to our scenarios. Results show first that the farmers would strive to continue their activity in each scenario, taking advantage of the flexibility of their farming systems, as in previous years. However, in the most pessimistic climatic scenario, they would also decrease the size of their herds. Depending on the socioeconomic hypothesis, they would adopt farm structural changes (farm processing activities, direct selling, etc.), or look for part-time non-agricultural jobs. Three types of strategies were identified, depending on the farmers' objectives and adjustments. Finally, public policies to accompany these changes are considered.

Introduction

Reports of the Intergovernmental Panel on Climate Change (IPCC) identify mountain ecosystems as highly vulnerable to global climate changes. Climate change scenarios not only highlight the continued warming observed in the Alps, but also an increase in climatic extremes, in particular drought phenomena in areas subject to Mediterranean influences. Alpine ecosystems are considered especially sensitive to these changes, which are likely to lead to losses in biodiversity and landscape modifications [START_REF] Thuiller | Climate change threats to plant diversity in Europe[END_REF].

The SECALP research project (2009)(2010)(2011), which brought together agricultural scientists, foresters and ecologists, aimed to analyse the ability of Alpine farming and forestry stakeholders to adapt to increasing droughts. In this paper, we propose to characterise the way livestock farmers have adapted to the droughts to which they have been subject over the last ten years and identify the solutions they have implemented to counter these events [START_REF] Nettier | Attitudes des éleveurs et sensibilité des systèmes d'élevage face aux sécheresses dans les Alpes françaises[END_REF]. We shall then describe the prospective phase of our research: based on scenarios combining both an increase in droughts and socio-economic contextual changes, we shall analyse farmers' reactions and the adaptive behaviour they would implement. Finally, we shall discuss the scope of the lessons learnt from our field studies and describe possible policies to support farmers in their efforts to adapt.

Material and Methods

The research work was carried out on the two 'Zone Atelier Alpes' sites, one in the Vercors (a regional natural park covering 85 municipalities), and the other in the Oisans (Villar d'Arène municipality) where the economy is based on agriculture and tourism. Both sites are located on critical climatic limits and are subject to oceanic and Mediterranean influences. Over the last two decades, the predominance of the Mediterranean influence has increased: for example, the Vercors pre-Alpine massif is now experiencing a significant increase in drought events [START_REF] Bigot | Contraintes climatiques dans les Préalpes françaises : évolution récente et conséquences potentielles futures[END_REF].

Farm surveys following droughts

To characterise the methods employed to adapt to the droughts experienced since 2003 (year of an exceptional summer drought and heat wave in France), we conducted farms surveys using semi-directive interviews. We identified the way the forage system worked [START_REF] Fleury | Forage management in dairy farms: a methodological approach[END_REF] together with (i) changes operated within this system, (ii) how consistency between the forage system and the livestock system [START_REF] Dedieu | Système d'élevage, un concept pour raisonner les transformations de l'élevage[END_REF] was maintained, and (iii) changes to all farm household activities. For the Villar d'Arène site, we decided to make the research work by interviewing every farm (9 livestock farmers and one transhumant shepherd), who used the municipality's farming areas, in order to take into account possible interactions between farms. On the Vercors massif, it was impossible to apply the same exhaustive approach. Classified as Natura 2000 sites and of great heritage value, the Alpine pastures in this area are considered important for their biodiversity. We therefore decided to take a sample of the various Alpine pastures (according to type of summer grazing animal and shepherding mode) and of the farms using these pastures during the summer period (farms located on the Vercors plateau or in the foothills and transhumant herds from the south of France). In all, 27 farms and 18 alpine pastures generally kept by shepherds were included in the survey.

Prospective scenarios

To develop our prospective approach (de Jouvenel, 2002), we opted for 4 scenarios coupling two different climatic contexts and two different socio-economic contexts. This coupling was notably the result of the lessons learnt from the surveys performed in the first stage of our research. These pointed to drought events as being only one of the factors influencing the decisions of farmers, who were also found to consider the socio-economic context. The difficulty entailed in developing these scenarios lay mostly in the choice of contrasting but plausible conditions and the way to apply these locally so that they included characteristics specific to the field of study and hence were meaningful for the farmers. We therefore co-built these scenarios with a group of local experts. These scenarios were applied locally through discussions between the SECALP project group of researchers and the group of experts.

The "intermittent" climate context was based on an increase in spring and summer drought periods alternating between wetter years to reflect the recent situation in some sectors of the Alps. The "shock" climate context was based on four consecutive years of springtime drought. With the help of the ecologists involved in the SECALP project and agricultural experts, the climatic contexts were translated into consequences for the areas studied, particularly seasonal production losses in a drought year (table 1). Moreover, using the observations relating to the recent droughts and experimental drought simulations, the ecology researchers demonstrated that the Alpine vegetation was highly resilient [START_REF] Lavorel | Adaptation des territoires alpins à la recrudescence des sécheresses dans un contexte de changement global (SECALP)[END_REF]: these results were included in the "intermittent" context. Two socio-economic contexts were chosen from national and international prospective studies: Millenium Ecosystem Assessment (MEA) [START_REF] Carpenter | Ecosystems and Human Wellbeing: Scenarios[END_REF], Les Nouvelles Ruralités (NR) [START_REF] Mora | Les nouvelles ruralités à l'horizon[END_REF][START_REF] Agrimonde® | Agricultures et alimentations du monde en 2050 : scénarios et défis pour un développement durable[END_REF]. The first one, called "global" socio-economic context, was based on continued globalisation in a free economy and a process of urban concentration (cf. MEA 'Global orchestration' scenario, Agrimonde G0 and NR Scenario 1); the second one -"territorial" context -was inspired by the emergence of the "territorial fact" (cf. MEA 'Adapting mosaic' and NR Scenario 4). In the "global" socio-economic context, the areas and their stakeholders were confronted with continued globalisation and urban concentration with agriculture being supported only for its role as a producer of global environmental services (e.g. carbon storage). In the "territorial" context, citizens showed a growing interest in their geographic area and its activities while mountain farming was supported so that it continued to act as a producer of quality food in line with strict environmental requirements (table 2). The two climatic contexts and the two socio-economic contexts were combined in pairs to form the four scenarios. The four scenarios were then transcribed into storylines before being submitted to the group of experts for validation.

Climate context

Intermittent

Socio-economic context

Return to the farms

To help the interviewees understand and appropriate the various aspects of the scenarios, illustrative documents were prepared in addition to storylines: drawings (showing landscape changes), graphs showing changes to fodder productivity according to different types of vegetation, changes to aid in line with the CAP reform (pillars 1 and 2), and changes to farming product prices. We interviewed all of the farmers from Villar d'Arène and 8 farmers from the Vercors. These farmers were selected for their receptiveness during the previous phase and so that the sample would reflect the diversity of situations. In all, 17 interviews were performed with livestock farmers. As the shepherds work on a seasonal basis and are unable to influence strategic changes to livestock systems, they were not interviewed in this prospective phase.

The choice of time horizon raised another difficulty: set at 25-30 to reflect forest development cycles and climatic impacts, but we also had to precise the scenarios in concrete outcomes for the next 4 to 5 years and apply the 2013 CAP reform to this period because it is very hard for farmers to plan projects on a longer time horizon, due to a context of great uncertainty.

Results

After presenting the reactions to the recent droughts, we shall describe the adaptations envisaged by the farmers.

Farmers' reactions to the recent droughts

The means of leverage activated by the farmers and shepherds aimed to offset the drop in forage resources as well as prevent or limit damage to alpine vegetation (which could undermine the renewal of pastoral resource over several years). On the Alpine pastures, it was found that the farmers generally managed to overcome the dry summers by making contextual adjustments: the shepherds' know-how made it possible to optimise use of the grazing resource (exploration of new sectors, better use of plant phenological differences, etc.). In 7 cases out of 18 alpine pastures, a structural decrease in the stocking rate was nevertheless decided upon in order to face possible future droughts. To really understand the farmers' reactions, it seemed essential to reposition the farms in their pedo-climatic context. This context conditions adaptation possibilities as well as the functioning of forage systems and their sensitivity to drought. Three main types of farming contexts were identified on the sites studied (table 3). The farms displayed considerably different reactions in the face of droughts:

Farm types

• Due to long winters and limited surface areas on which machines could be used, "highmountain" livestock systems were highly sensitive to a drop in hay production. But thanks to oversized grazing land in relation to herd needs, they had few problems during grazing season. Purchasing of hay is generally the unique reaction. Some of the farmers also made some "relocations" on small surfaces (e.g. making hay in the valley, making it also possible to extend the vegetation period and spread out harvesting).

• "Fodder" type farms have a higher proportion of surface areas suitable for machines, but generally few grazing surfaces. They reacted to droughts with grazing of meadows initially to be mowed, or distribution of hay during grazing period, and consequently a drop in hay stocks. Most autonomous farms carried over hay stocks from one year to the next, whereas some others have to purchase hay.

• In the "pastoral" type systems (with a shorter wintering period and hence less need for stock), the farmers used the flexibility of their rangelands and "adjustment" pastoral areas: grazing of young cereal crops, undergrowth, acorns, etc. Hay purchasing are also observed, but with small needs. On contrary to the two other types, structural changes to grazing systems were observed (surface area extensions, woodland surface grazing agreements, or herd livestock reductions).

Many of these farms were found to be run by households with multiple off-farm activities and were therefore able to cope with hard times. It was thought that hay purchases would undermine the viability of the system if they were repeated year after year. No diversification activities on the farms surveyed were observed.

Possible adaptations envisaged by livestock farmers for the different scenarios

For the farmers in the Vercors, the intermittent climate context seemed to reflect the situation experienced over the last few years and to which they had been obliged to adapt. They therefore believed that they would be able to "bounce back" and that their forage system was adapted to face the situation. As was their habit, they intended to make the most of the flexibility of their forage system: adjust grazing or wintering dates, adjust dates for taking animals up to or down from the alpine pastures in relation to the pastoral resource available, use reserve sectors (rangelands outside of the farm parcel or grass regrowth in fields not grazed during normal years), alternate between the use of hay and grazing meadows during the pastoral period and, if possible, carry over hay stock from one year to the next by making the most of wet years or buying additional hay if fodder stocks were not sufficient to cover livestock needs. In a context of intermittent drought, structural changes would only be introduced in response to the socioeconomic context. For the shock climate context where forage resources would be insufficient, they would reduce their herds to match the available resource and attempt to offset loss of income through off-farm work, in the case of the global socio-economic context, or through better use of the remaining animals (farm processing activities, short distribution channels, etc.), or even through additional tourist activities (farms open to the public) in the case of the territorial context for some farmers (Table 4).

"Intermittent" climate context Adapt to the situation as in the past = leveraging system flexibility to limit fodder purchases (increase surfaces, improve meadow productivity, set up carry-over stocks from one year to the next) According to the farmers, changes to the socio-economic context were also a determining factor, owing notably to the importance of public aid in the make-up of their income and to a concern for their work to be recognised by society. They considered agri-environmental measures (AEM) to be a concrete reflection of this recognition. This explains why the AEM provisions included in the "territorial" context were clearly preferred, in spite of the necessity to commit to results, than those envisaged in the "global" context (and based on a best practices obligation). The latter appeared to the farmers to work against their very profession (e.g. the bonus for planting trees on farming land was decried).

Although some main trends emerged for each scenario, the farmers did not apply the same reasoning to adaptation possibilities. While they all strove to think of ways to keep their livestock activity, three different adaptation strategies were identified: "I would reduce the economic impact of droughts by diversifying my production and my activities" (cereals, poultry workshops, agritourism and city work according to the case and socio-economic context); "I would adapt but without diversifying my production because I want to keep my livestock farmer identity" (possible direct sales of meat, even salaried work but in connection with breeding, shepherding work for instance, etc.); "I wouldn't change my system because it's already robust enough" (oversized haymaking surfaces or main source of income from an activity other than livestock).

The adaptations of the Villar d'Arène livestock farmers reflected this kind of reasoning. The intermittent context was considered part of the daily routine with which the farmers had had to cope for several years already. They said they would call on the same solutions as they had used for past droughts (mainly purchasing of hay). Breaks in their tradition were considered for the "shock + global" scenario: older farmers considered putting an early stop to their activity while others said they would stop cutting meadows to ensure animals had enough grazing and send the animals to winter in the valley. However, like the Vercors livestock farmers who preferred the second strategy and did not envisage giving up their animals, for most of the Villar d'Arène livestock farmers, meadow cutting seemed to be an essential component of their job conception. They did not wish to stop haymaking and considered this only as a last resort. The approach implemented at Villard d'Arène made it possible to take into account farmer interactions in the adaptation strategies. Thus, the eldest farmers who would put an end to their activity would free up mechanized land for their neighbours, hence limiting the purchasing of hay.

Discussion -Conclusion

Thanks to coherent storylines, illustrative drawings and graphs, farmers easily succeed to appropriate the four successive scenarios. When the scenarios were explained, some of the farmers did not agree with some of the assertions, which they nevertheless believed to be plausible. This was especially true for some of the global context measures. For example, one interviewee said, "I like this one less than the other, that's for sure. But it's true that we might have to face such a scenario." The high number of parameters to be considered, and which belonged to different registers, was found to be disturbing by some farmers. However, as some pointed out, this was also something they had to take into account.

The building of a participatory scenario approach combining factor-based climatic and socioeconomic contexts highlighted the relative role of these two dimensions in farmers' adaptation methods. Generally speaking, their proposed adaptations reflected their response to the recent droughts or the forward thinking that these generated. More radical change possibilities underlined their attitude in the face of unexpected events but included other factors too, especially those relating to a changing socio-economic context.

Concerning the scope of the results, some of the adaptations envisaged may appear to be fairly specific to the sites studied, especially the idea to diversify activities and set up direct sales, drawing impetus from the high level of tourists in the area and the closeness of the cities. However, the whole French Alpine range, especially in the north, can be considered as an urbanised mountain area. We identified three main adaptation strategies in response to scenarios. Whereas reactions to past recent droughts were conditioned to pedoclimatic contexts, adaptation strategies depend more on sociological considerations. These can be compared with the logics highlighted by [START_REF] Lémery | La flexibilité des élevages allaitants face aux aléas de production et aux incertitudes de la filière[END_REF] in suckler farmers in Burgundy (France) when facing a situation of uncertainty (during the mad cow crisis), or by [START_REF] Girard | Modéliser une représentation d'experts dans le champ de la gestion de l'exploitation agricole[END_REF] concerning the attitudes of sheep farmers when confronted with unexpected climatic events. Thus, the first two strategies seem to exemplify the idea of "making do" described by [START_REF] Lémery | La flexibilité des élevages allaitants face aux aléas de production et aux incertitudes de la filière[END_REF], or that of "mitigating the impacts of unexpected events" described by [START_REF] Girard | Modéliser une représentation d'experts dans le champ de la gestion de l'exploitation agricole[END_REF], while the aim of the third strategy is to "move outside of the range of impact of the climatic hazard".

Many of the farmers interviewed were ready to take out further commitments in order to enhance the value of their livestock products (meat-cutting, cheese-making, setting up of short distribution channels, etc.). Observed across a small sample, this trend surprised the local experts who nevertheless realised that such changes were in fact already emerging locally. While the farmers surveyed mentioned the limits of an approach based on individual interviews and the adjustments necessary according to local area and sector of activity (not everybody would be able to sell directly), the local experts believed that local authorities should look into the possibility of collective facilities in order to support the farmers: maintaining local abattoirs, creating meatcutting rooms and sales outlets to support the development of farm processing activities and short distribution channels; equipments on Alpine pastures to facilitate and secure pastoral management.

Several public action frameworks could facilitate the preventive adaptation of the livestock farmers. A number of regulatory provisions would remove obstacles and provide leverage: facilitating the exercise of multiple activities, boosting access to land use, adjusting public subsidies criteria in relation to the actual potential and capacity of areas (e.g. recognition of the eligibility of all surfaces with grazing potential, including wooded areas, and adapting stocking rate criteria). Management and training measures could strengthen public action: coordination of farmers to improve access to resources, promotion of products, structuring of short distribution channels, technical advice (practices and production modes adapted to increasing drought periods), setting up of observation and warning systems to plan ahead for the adjustment of practices.

Intervention contexts differed substantially according to the scenario. For the "global" context, each crisis would necessitate the mobilisation of support on a case-by-case basis, as well as financial and social help with changes to area and livestock farmer orientation. The "territorial" context would appear to offer a better resistance thanks to adaptations reducing system vulnerability. The ability to adapt would be facilitated by the organisation of the profession, by local thinking about the multifunctional management of farming, forest and grazing areas, by the development of additional activities to reduce the dependence of livestock farmers on their main activity during drought periods, and by strengthening solidarity.

Table 1 .

 1 Main provisions in the two climate contexts selected.

	Shock

Table 2 .

 2 Main provisions in the two socio-economic contexts selected.

	Global	territorial

Table 3 .

 3 Main characteristics of the surveyed farming systems.

		High mountain	"fodder"	"pastoral"
	Number of	9 (Villar d'Arène)	7 (plateau and foothills of	11 (Diois to the south of
	farms		the Vercors)	the Vercors and
				transhumants in the
				Mediterranean region)
	Livestock	ewes, cattle	suckler ewes and cows	suckler ewes
	farming		dairy cows
	systems
		Long winter (more than	Higher proportion of	Many grazing surfaces.
		6 months) and limited	surface areas suitable for	Shorter wintering period.
	System	mechanised surfaces.	machines. Variable level	Surfaces to be cut
	characteristics	Oversized grazing land.	of fodder autonomy. Few	sometimes limited in
			grazing surfaces.	relation to livestock's
				winter needs.

Table 4 .

 4 Summary of possible adaptations envisaged by livestock farmers in relation to the different scenarios and specific adaptations for each context.

	"Global" socio-economic context Offset loss of income through an activity outside the farm, or even stop the farm	Scenario "Intermittent" + "Global" Leverage system flexibility, increase surfaces, decrease livestock as a last resort Scenario "Shock" + "Global" Decrease livestock and take on off-farm activity to	Scenario "Intermittent" + "Territorial" Leverage system flexibility and increase surfaces + develop direct sales Scenario "Shock" + "Territorial" Decrease livestock,	"Territorial" socio-economic context Farm processing activities + short distribution channels Agri-tourism Subscribe to agri-
		offset the reduction; put a	increase surfaces +	environmental
		stop to the farm in some	develop direct sales +	contracts
		cases	agri-tourism
		Decrease livestock to reduce sensitivity to drought
		"Shock" climate context

Nettier, B. ; Dobremez, L. ; Lamarque, P ; Eveilleau, C ; Quétier, F. ; Véron, F. ; Lavorel, S. How would farmers in the French Alps adapt their systems to different drought and socio-economic context scenarios? The 10th European IFSA Symosium, 1-4 jul. 2012, Aarhus, Denmark.

Acknowledgements

This work was carried out with the financial support of the French Ministry of the Environment (GICC-2 research program) and was conducted on the long-term socio-ecological research site 'Zone Atelier Alpes', which is a member of the ILTER-Europe network, publication n°21.


H Haessler

R Gaulon

L Rivera

R Console

M Frogneux

G Gasparini

L Martel

G Patau

M Siciliano

A Cisternas

THE PERUGIA (ITALY) EARTHQUAKE OF 29, APRIL 1984: A MICROEARTHQUAKE SURVEY

A field study after the Perugia earthquake of 29 April 1984 provided more than 300 well-recorded events concentrated within two parallel clusters separated by 2 km and trending along the Apenninic direction. The length of the aftershock area is 14 km, focal depths being shallower than 8 km. Relocation of the main event places the epicenter at the southern end of the aftershock zone, suggesting a rupture propagation from SE to NW. Most focal mechanisms are consistent with normal faulting. The spatial distribution of seismicity suggests that the Gubbio normal fault was activated during the main shock. This earthquake, together with the Norcia 1979 and the Abruzzi 1984 shocks, is typical of the extension in the high Apennines generated by the flexure of the mountain chain in response to regional compression. The Parma 1983 event, a thrust, belongs to the compression zone at the eastern flank of the chain. These results are consistent with the EW continental collision along the Apennines.

INTRODUCTION

A magnitude 5.3 (NEIC) earthquake struck the region of Perugia in Central Italy on 29 April 1984 (Lat. 43.25 ° N, Long. 12.52 ° E, depth 7 km, mb= 5.1, Ms = 5.2; ISC). The seismic moment was 3.4 10 ~4 dyne-cm (HRVD). It was widely felt, the epicentral intensity being VII to VIII. Many buildings suffered damage, 1200 were declared unsafe, 36 people were injured, and 7500 were homeless.

A French-Italian cooperation permitted the detailed study of the aftershocks of this earthquake. A similar joint field operation had already been conducted for the Norcia 1979 earthquake, situated in the same tectonic province some 70 km to the SE [START_REF] Deschamps | The Umbrian earthquake (Italy) of 19 September 1979[END_REF].

Several other events accompanied the Perugia crisis: in October 1982, a seismic cluster of earthquakes with magnitude smaller than 4.5 had affected the region of Assisi, at 20 km to the SE of the Perugia main shock; in November 1983 an earthquake of magnitude 5.0 was felt in Parma at 255 km to the NW of Perugia; and finally, 1 week after the Perugia earthquake a strong event (M = 5.8) struck the Abruzzi, 200 km to the SE.

Hence, a period of intense seismic activity permitted the collection of an important amount of precise data about the seismotectonics of central Italy. Seismic information is important in this region since almost nothing (except the recent work by [START_REF] Westaway | The earthquake of 1980 November 23 in Campania-Basilicata (Southern Italy)[END_REF] has been reported in Italy up to now, in relation to surface breaks clearly associated to earthquake faulting.

This paper is devoted to the study of the Perugia earthquake and its aftershock sequence in relation with the regional tectonics of the central Apennines.

TECTONIC SETTING

One of the main features of the tectonics of the Western Mediterranean area is the collision (Fig. 1) of the Italo-Adriatic promontory against the European continental region [START_REF] Tapponnier | Evolution tectonique du syst~me alpin en M~diterran~e: poin~onnement et ~crasement rigide-plastique[END_REF]. The Alps result from this convergence. On the other hand, the Apennines (Fig. 1) belong to a rather different structural context where we may distinguish three main geodynamic units:

1. A collision-subduction boundary bordering the Apennines (shown by filled triangles in Figure 1), going from the SW border of the Po plain, through Ancona and the Bradonian trough, down to the Calabrian-Sicilian subduction. The presentday subduction is what remains from an ancient one that has been closed from north to south and replaced by the actual continental collision [START_REF] Bousquet | Neotectonics of the Calabrian arc and Apennines (Italy): an example of plio-quaternary evolution from island arcs to collisional stages, in The Origin of Arcs[END_REF][START_REF] Malinverno | Extension in the Tyrrhenian sea and shortening of the Apennines as result of arc migration driven by sinking of the lithosphere[END_REF]. The thrust surface (and the plane of subduction) dips towards the Apennines. Earthquakes are crustal in northern and central Italy while intermediate and deep events are observed in the Calabrian arc [START_REF] Anderson | The deep seismicity of the Tyrrhenian sea[END_REF].

2. The back-arc region, formed by the Tyrrhenian basin, Corsica, Sardinia and the western coast of Italy. This region is mainly formed by thinned continental crust (a similar situation exists in the Aegean Sea, Le [START_REF] Le Pichon | The Hellenic Arc and Trench System: A key to the Neotectonic evolution of eastern Mediterranean area[END_REF].

3. The fore-arc region, formed by the Po plain and the Adriatic basin. This sedimentary basin is asymmetric, being deeper next to the Apennines where it reaches a thickness of 8 km [START_REF] Ogniben | Structural Model of Italy[END_REF] while thinning gently toward the east. It corresponds to the accretion prism in front of the Apennines. The convergence is characterized by east-west tectonic shortening, by uplifting and substantial thickening of the Apenninic belt and nappe thrusting over the Adriatic foreland. Thrusting on the eastern flank of the belt is certainly active at present [START_REF] Elter | Tensional and compressional areas in the recent (Tortonian and present) evolution of the northern Apennines, Boll[END_REF].

The back-arc or internal region (the Tyrrhenian Sea and western Italy) is characterized by an extensional state of stress with R = (azax)/(ay -ax) > 1 (R is the shape of the deviatoric stress obtained from the eigenvalues, R > 1 when az > ay > ax, see [START_REF] Armijo | The inverse problem in microtectonics and the separation of tectonics phases[END_REF]. There we observe normal faulting, crustal thinning, volcanism (alcaline to the north and calco-alcaline in front of the Calabrian-Sicilian arc), uplift, and positive gravity anomalies. Actually, the regional extension ceased to be active to the north of the basin, at the places where oceanic subduction stopped. Young, normal faulting occurs only at the flexure ("extrados") related to the thrust at the boundary of continental collision.

The forearc or external region (the Po plain, the Adriatic Sea and the Bradanic basin) shows compressional tectonics with R < 0 (az < a~ < ay), reverse faulting and nappes, crustal thickening, subsidence, and accretion of sediments and negative gravity anomalies.

The epicenter of the Perugia earthquake is located to the north of the back arc basin, near the transition from extensional to compressional tectonics. The relief of the Apennines is related to thrusting and flexuring of the upper crust [START_REF] Philip | Le tectonique actuelle et r~cente dans le domaine M~diterraneen et ses bordures, ses relations avec la sismicit~[END_REF]. A simplified geological map (Fig. 2) shows a series of elongated sedimentary basins along a NNW direction. These valleys are controlled by normal faults, and are filled with Plio-quaternary deposits. We may notice, for example, the small valley at Gubbio, and the larger one that extends to the NW next to Perugia, while bifurcating towards the SE. A schematic block diagram through Perugia (Fig. 3, modified after [START_REF] Bousquet | Neotectonics of the Calabrian arc and Apennines (Italy): an example of plio-quaternary evolution from island arcs to collisional stages, in The Origin of Arcs[END_REF] illustrates the region of extension with normal faulting, the transition to compression with reverse faulting, the thickening of the crust under the Apennines, and the Adriatic sedimentary basin related to the accretion prism of the older subduction.

FIELD WORK

The Perugia earthquake was one of a series of events that affected central Italy in recent years. Figure 4 illustrates the seismic activity from 1976 to 1985 according to the data file of the Euro-Mediterranean Seismological Center (EMSC). The clusters of seismicity correspond to the aftershocks of these earthquakes. The Parma 1983, Perugia 1984, Norcia 1979, Abruzzi 1984, and the Irpinia 1980 event to the south are clearly seen. The seismic cluster (M < 4.5) near Assisi in October 1982, 18 months before the Perugia event and 20 km to the south of it, is easily distinguishable too.

Two days after the main shock (see Table 1 for focal parameters) a team of seismologists from the Institutes of Physics of the Earth of Paris and Strasbourg set up a local seismic network around the epicentral area. The network, formed by 5 MEQ 800 Sprengnether analog recorders with WWV time control, and four portable 3-components digital records (GEOSTRAS) with automatic gain and DCF time signals, operated during 7 days. Several hundreds of microearthquakes (ML < 3.5) were recorded and about 300 among them, having more than five arrivals, P or S, were selected as reliable. [START_REF] Bousquet | Neotectonics of the Calabrian arc and Apennines (Italy): an example of plio-quaternary evolution from island arcs to collisional stages, in The Origin of Arcs[END_REF]. Crosses correspond to crustal material and dots to the lithospheric mantle• The Moho level shows crustal thickening at the collision front. On the contrary, the crust is thinner where extension took place. An accretion prism is observed in the Adriatic basin. The star shows the relative position of the Perugia earthquake•

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I_ 1

: ~-'~."-..,- . ~ ..,~ ..' .. o | am | i "' PO Valley , ' , I_N e • i'., |l, • . • ~: : ,I~"~.,~ • '% Adriatic ,, • |a ~ a • " ,,~ ' ,,' ',% ' , Sea '~." | i• . • • | • • ' 43, . . ~ _
.-.,, .. , ...,,, . of 1982.3. Parma 1983. 4. Perugia 1984. 5. Abruzzi 1984. not considerably change the distribution of epicenters. The frequency distribution of the standard errors of horizontal and vertical focal coordinates (Fig. 5 a,b) shows accuracies of the order of 0.5 and 1.0 km, respectively. The magnitude was obtained from the coda length t<: of the MEQ-800 records through the following formula: M = 2.5 log tc -1.9• The spatial distribution of aftershocks and the location of the seismic stations are shown in Figure 6. The epicenters follow a N140E direction and lie within a domain of about 20 km long and 6 km wide. They show a remarkable agreement with the direction of the major tectonic features of the region (Fig. 2). The same orientation was also obtained in the case of the Norcia earthquake [START_REF] Deschamps | The Umbrian earthquake (Italy) of 19 September 1979[END_REF]. The epicentral distribution seems to follow two parallel linear clusters, the denser one being to the southwest. It is interesting to observe that the aftershocks lie in between the valleys of Gubbio and Perugia. As we have mentioned, these valleys are formed by normal faulting and filled with Quaternary sediments. The Gubbio valley is an elongated basin, limited to the east by a fault scarp, 20 km long, dipping to the west. Since no surface rupture was observed, it is not certain that this is the fault responsible for the earthquake. Nevertheless, the geometrical distribution of aftershocks suggests that either its prolongation in depth or an equivalent en-echelon fault system are involved (see Figs. 2 and7c). A cross-section along the strike of the clusters (Fig. 7b) shows that the depth of aftershocks is smaller than 8 km, namely they are shallower than those of the Norcia sequence (h 3) and (4), of magnitude higher than 4 relocated using the 10 May 1984, 9:45 hrs shock (M = 4.0) as master event (5). Open circles with letters are main shock locations given by the international agencies, E: EMSC, N: NEIC, S: ISC. Open triangles are the MEQ stations and filled triangles are the GEOSTRAS digital stations. The aftershocks are distributed along two parallel clusters striking NW.

< 15 km) [START_REF] Deschamps | The Umbrian earthquake (Italy) of 19 September 1979[END_REF]. The cross section in the direction NE-SW (Fig. 7c) shows a separation of about 2 km between the clusters.

FOCAL MECHANISM AND RELATED EARTHQUAKES

The focal mechanism of the Perugia earthquake is presented in Figure 8, together with those of the Norcia (September 19, 1979, Ms = 5.9), Abruzzi (May 7, 1984, Ms = 5.8) and Parma (November 9, 1983, Ms = 4.9) earthquakes.

The Norcia mechanism, determined by Deschamps et al. (1984) from the analysis of long period P-wave forms (Fig. 8a), showed a normal fault with an important right lateral shear component. The others (Figs. 8b,c,d) were obtained by us on the basis of ISC bulletin readings of the initial motion of short-and long-period body waves. We adopted the following selection criteria: a reading was acceptable either if it was from a short-period wave closer than 10 ° to the epicenter, or from a long-period, pure-mantle-path, direct P wave observation. The maximum likelihood algorithm of Brillinger et al. (1980) was used in order to obtain the best nodal solution in each case.

The Perugia event, with a WNW strike, has a small left lateral shear component (Fig. 8c). An independent calculation, the HARVARD solution (Fig. 8e) from longperiod surface waves inversion, gives an almost pure normal fault, one of the planes being parallel to the Apenninic direction as in our mechanism.

The Abruzzi mechanism (Fig. 8d,f) also shows normal faulting with one nodal plane oriented along the Apenninic direction. We observe here a small clockwise rotation of the axis of the chain and of the azimuth of the fault plane, with respect to Perugia.

The Parma mechanism (Fig. 8b) represents a reverse fault almost without shear and therefore differs from that of the other three shocks. This mechanism shows that this event is within the compression region, and indeed its epicenter and its strike correspond well to the Apenninic thrust. Hence it is likely that the fault plane is that pointing to the southwest.

Stress-compatible focal mechanisms of 65 aftershocks (Table 2) of the Perugia earthquake are shown in Figure 9a,b,c,d. In our case, we have five or more polarities for each event. Evidently, individual solutions cannot be obtained by the usual methods. Therefore, we need to make some assumptions in order to deal with the total number of earthquakes in a collective way. The hypothesis is that the same regional stress tensor acts on each fault plane. The stress tensor (more exactly, its orientation and shape) and the different fault planes are jointly estimated, by a maximum likelihood procedure (Rivera and Cisternas, Submitted for publication). The method permits, in general, the discrimination of the fault plane from the auxiliary plane under the assumption of a single stress tensor acting on the faults. (1984). The Parma (b), Perugia (c) and Abruzzi (d) mechanisms were obtained from first motion body wave readings (short and long period) by using the maximum likelihood algorithm of Brillinger et al. (1980). Confidence regions for P and T axes correspond to one standard deviation. The Parma shock is the only one showing a reverse fault. The Perugia (e) and Abruzzi (f) nodal solutions determined by Harvard on a routine basis (NEIC, monthly listing), using a long-period body and mantle wave tensor inversion. At the same time, it is possible to estimate confidence ellipses around the poles of the fault planes. Even in the case when each individual shock has few polarities, the total data set may still enable us to constrain the parameters of the stress tensor.

The stress tensor (Fig. 10) depends on the polarity data set as a whole. It has the ~1 axis almost vertical, the ~2 axis trending in an EW direction and the a3 axis with a NS orientation. Confidence regions correspond to one standard deviation: the a3 axis is better constrained than al or ~2, and these are better determined in the NS than in the EW direction. The shape factor R is equal to 1.1, corresponding almost to a uniaxial extension [START_REF] Armijo | The inverse problem in microtectonics and the separation of tectonics phases[END_REF].

The slip direction (Fig. 9a,b,c,d) is not discriminated in this case because of the ambiguity inherent to an almost axially symmetric tensor. At the same time, fault and auxiliary planes cannot be distinguished. Error ellipses are shown for the pole of one of them, except when errors are too large and the mechanism is not well constrained (dotted lines). Normal faulting dominates in most of the solutions and 94 per cent of the observed polarities are correctly predicted by the model. This stress state is also compatible with the mechanism of the main earthquake.

DISCUSSION AND CONCLUSIONS

The analysis of the data from recent seismic events recorded in central Italy shows a remarkable agreement between the fault mechanisms and the mechanical models deduced from neotectonic information [START_REF] Bousquet | Neotectonics of the Calabrian arc and Apennines (Italy): an example of plio-quaternary evolution from island arcs to collisional stages, in The Origin of Arcs[END_REF]. The region of the Perugia (1984), Parma (1983), Norcia (1979), and Abruzzi (1984) earthquakes is situated at the north-eastern border of the Tyrrhenean basin, where continental collision takes place. We observe that thrusts occur very close to normal faults, and that the strike of both is parallel to the main Apenninic direction. Reverse faulting is present at the eastern flank of the mountains (Parma) while normal faulting dominates around the axis of the chain (Perugia, Norcia, Abruzzi). This situation is not unusual in tectonics; for instance, the E1 Asnam 1980 earthquake showed normal faulting next to the main thrust that was interpreted as being due to an "extrados" flexure on the hanging wall [START_REF] Cisternas | Models of the complex source of E1 Asnam earthquake[END_REF]. Bousquet The precision obtained by using a local network displayed over the hypocentral region allows us to map in detail the structure of the ruptured zone. In the case of the Perugia aftershocks, we obtained a distribution into two clusters, each one having an elongated shape parallel to the Apenninic direction with individual depths ranging from 2 to 8 km. The orientation of the clusters provides sufficient evidence to select the fault plane in the mechanism of the main shock. Moreover, the epicenter of the main shock is located at the SE edge of the large cluster, hence showing a rupture that propagated toward the NW. The application of the method of Rivera and Cisternas (submitted for publication) to obtain stress-consistent focal mechanisms to the Perugia aftershocks shows that they are compatible with an almost uniaxial extensional state of stress with the a3 axis oriented NS. This confirms the stress regime inferred from the main shock.

The orientations of the stresses are in agreement with the overall tectonic scheme already presented, but absolute values of seismic deformations are at odds with those inferred from tectonics. According to [START_REF] Malinverno | Extension in the Tyrrhenian sea and shortening of the Apennines as result of arc migration driven by sinking of the lithosphere[END_REF], the Apennines show a shortening of about 200 to 320 km since some 12 m.y.B.P. These values give an average rate of shortening of 1.6 to 2.6 cm/yr. These numbers are one order of magnitude higher of what may be estimated from earthquake associated deformation during this century (1 to 4 mm/yr; [START_REF] Anderson | Is the Adriatic an African promontory?[END_REF][START_REF] Jackson | The relationship between plate motions and seismic moment tensors, and the rate of active deformation in the Mediterranean and Middle East[END_REF] McKenzie, 1988). Furthermore, strong earthquakes during the last decades seem to be more related to normal faulting in the high Apennines than to thrusts on the eastern flank of the chain. Since thrust should be the main mechanism for shortening, it is likely that aseismic deformation is responsible for most of the effect. It is also possible that recurrence times for large earthquakes associated to thrust are longer than some centuries. In that case, the record would not be complete and large thrust events could occur in the future.

Thus, normal faulting appears to be the most seismogenic feature in the Apennines. Nevertheless, a problem that puzzled seismologists for years in this region was the absence of surface faulting directly related to earthquakes in the Apennines, in spite of the fact that geologists had abundant mapping of Quaternary active faulting [START_REF] Bousquet | Neotectonics of the Calabrian arc and Apennines (Italy): an example of plio-quaternary evolution from island arcs to collisional stages, in The Origin of Arcs[END_REF]. This question seems to be partially answered by the recent mapping of the surface breaks corresponding to the Irpinia earthquake [START_REF] Westaway | The earthquake of 1980 November 23 in Campania-Basilicata (Southern Italy)[END_REF].

  FIG. 1. Generalized tectonic map of the Tyrrhenian basin after Philip (1983). The gray region at the lower right corner is the Ionian basin. Normal faults are represented by indented lines. Dip of reverse faults is indicated by solid triangles, the larger ones corresponding to subduction. The thrust belt divides the area into two parts: the Tyrrhenian internal region to the left and the Adriatic foreland to the right. Shear faulting is shown by arrows parallel to the trace of the faults. Dotted zones are deep oceanic basins. Filled stars are active volcanoes. The open star shows the epicenter of the Perugia earthquake. The large NNE-SSW oriented fault to the south of Perugia is the Anzio-Ancona shear zone. Hatched lines correspond to compressional belts. A block diagram across Perugia is shown in Figure 3.

FIG. 3 .

 3 FIG. 2. Simplified geological scheme of the Perugia region displaying Plio-quaternary basins and recent faulting. Valleys are controlled by normal faulting. Aftershock clusters are located between Perugia and Gubbio and their trend is parallel to the orientation of the valleys and to the strike of the faults. Epicenters are represented by rectangles whose size increases with the magnitude.

  seismicity of centralItaly (1976Italy ( -1985))• Data from the Euro-Mediterranean Seismological Center (EMSC). The focal mechanisms are those of Figure7. 1. Norcia 1979. 2. Assisi sequence

  FIG. 5. a) Frequency distribution of the standard errors ERH = (ERX 2 + ERY2) '~ of the epicenters in km. ERX and ERY are the standard errors in the EW and NS directions respectively. 80 per cent of the ERHs are less than .5 km. b) Frequency distribution of the standard errors ERZ of the focal depths in km. 80 per cent of ERZ are less than 1 km.

  FIG.6. Epicenters of aftershocks (rectangles) recorded from 6 May to 10 May 1984. Open circles with numbers are: the main shock (1), and the aftershocks (2), (3) and (4), of magnitude higher than 4 relocated using the 10 May 1984, 9:45 hrs shock (M = 4.0) as master event (5). Open circles with letters are main shock locations given by the international agencies, E: EMSC, N: NEIC, S: ISC. Open triangles are the MEQ stations and filled triangles are the GEOSTRAS digital stations. The aftershocks are distributed along two parallel clusters striking NW.

  FIG. 7. a) Epicenter distribution showing the orientation of the cross sections, b) Cross section along the strike of the clusters of aftershocks. Depth is smaller than 8 km in general, c) Cross section orthogonal to the strike of aftershocks. Two independent clusters are separated by 2 kin. The topographic scale is exaggerated four times and the surface trace of the Gubbio normal fault plane is shown.

FIG. 9

 9 FIG. 9 a,b,c,d. Stress-compatible focal mechanisms of 65 well-recorded aftershocks of the Perugia sequence. Schmidt lower hemisphere projection. The one standard error ellipses correspond to the pole of one of the nodal planes, and they are not shown if the uncertainty is too large. In the latter case the nodal planes are drawn in dotted lines. and Philip (1986) extended this model to a larger scale in order to explain the tectonics of the Apennines. Other cases of extensional tectonics in mountain countries may be found in Tibet and the high Andes (Armijo et al., 1986; Carey-Gailhardis and Mercier, 1987). Nevertheless, the elevation, the areas involved, and

  FIG. 10. Stress tensor orientation and shape factor R, for the Perugia 1984 aftershock sequence. Lower hemisphere Schmidt projection. The stress correspond to almost uniaxial extension with a NS oriented a3 axis. Confidence regions correspond to one standard deviation. The score is the percentage of consistent polarities.

TABLE 1 ISC

 1 Note: all data except Seismic Moment are from ISC Bulletins. The depth of the Parma earthquake is based on both pP-P delays and the normal hypocenter determination.

								1953
				PARAMETERS
	Event	Date Origin Time	Latitude	Longitude	Depth	Mb	Ms	Seismic Moment
	NORCIA	19-09-1979	42.80 N	13.04 E	6 km	5.8	5.9	0.7 1025dyne-cm
		21:35:36.8						(Deschamps)
	PARMA	9-11-1983	44.68 N	10.28 E	38 km	4.9	4.9
		16:29:51.8
	PERUGIA	29-04-1984	43.25 N	12.52 E	7 km	5.1	5.2	3.4 1024dyne-cm
		5:02:59.3						(HRVD)
	ABRUZZI	7-05-1984	41.76 N	13.90 E	16 km	5.4	5.8	7.8 1024dyne-cm
		17:49:42.7						(HRVD)

  Compression readings on short-and long-period records are shown as filled squares and circles, respectively. The Norcia (a) mechanism is taken from Deschamps et al.

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	317' ?8" X PLhHE ~	_.r.~_.. / /			oDILIT.
	289' 55" Y PLfiNE	188								191
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	?"i~~ IN			:r'~.	~llll 198" H' X Pl,nl41 DI~ ...... ~ ~29" 40" Y PLIII	~	L ~--'~-.~-41~-~-~ tBS	;l	I flp. o IILIT.
	PERUGIA 29 APIIL 1984	O		\ (e)	fiBRI.~ZI 7 lily 1994	/-		8	-..
								/	S ~:	\ \	\
		\				L,		t 278				,	X	\ 't /	98
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	386" 148"	* X 21" Y PI~HZ	188				STRlIi DIP 313 ° 66 ° X PlaNE ~ 173* 3t" Y PLANZ	~-~~	.,i -f	/

,,., ,,~,.3 , (b) IN (f) FIG. 8. Focal mechanism of recent Italian earthquakes. Schmidt lower hemisphere projection.

TABLE 2 LIST

 2 OF PERUGIA AFTERSHOCKS WITH FOCAL MECHANISM(FIGURE 9a, b, c, d)

	1957

TABLE 2 -

 2

	N	y	Date m	d	h	Origin Time m sec.	Latitude °N rain.	Longitude Depth ERZ °E min. km kin	MAG	RMS ERX ERY sec km km
	54 84 05 08 18 20	8.59 43 13.79 12 32.82 5.65	0.9	1.1	0.08	0.4	0.4
	55 84 05 08 18 23 40.33 43 13.72 12 33.08 4.81	0.3	0.7	0.05	0.2	0.2
	56 84 05 08 18 48 27.67 43 13.83 12 32.85 4.98	0.4	1.4	0.04	0.3	0.2
	57 84 05 08 18 49 18.62 43 13.73 12 33.15 4.89	0.2	1.5	0.04	0.1	0.1
	58 84 05 08 21	4	4.06 43 15.26 12 32.18 5.86	0.5	1.0	0.04	0.3	0.2
	59 84 05 09	2 37 44.47 43 14.55 12 31.69 5.47	0.4	0.7	0.06	0.3	0.3
	60 84 05 09	2 38 50.87 43 14.63 12 31.65	5.24	0.4	1.1	0.05	0.3	0.3
	61 84 05 10	0 50 58.47 43 17.35 12 32.36 3.26	0.2	2.0	0.01	0.2	0.1
	62 84 05 10	2 10 17.70 43 17.43 12 31.47 4.10	0.3	1.1	0.03	0.2	0.2
	63 84 05 10	5	2	8.91 43 14.92 12 31.17 5.97	0.7	1.4	0.08	0.5	0.4
	64 84 05 10	5 51 58.42 43 16.58 12 30.14 4.78	0.3	0.9	0.03	0.4	0.2
	65 84 05 10	9	5	3.41 43 14.69 12 31.47 6.88	0.7	1.2	0.10	0.5	0.4

-(continued)

HAESSLER ET AL.

ACKNOWLEDGMENTS

The field work was financed by the ATP Sismogen~se de l'Institut National des Sciences de rUnivers (France). We are grateful to Michel Cara for his encouragement and help in preparing the expedition. Herv~ Philip made several important tectonic suggestions and kindly allowed us to use Figures 1 and3. M. Ferretti of Perugia gave us valuable advice. A Cisternas and L. Rivera are associated with the "Centro de Estudios Cient~ficos de Santiago."


Laurent Rodriguez

Benoît Miramond

Fakhreddine Ghaffari

Bertrand Granado

Self-organization in embodied reconfigurable architectures

This paper describes a bio-inspired architectural approach to design highly adaptive and reconfigurable systems in the context of mobile robotics. The purpose is to design the hardware architecture of an intelligent controller for a robot that exhibits several behaviors such as landscape learning, obstacle avoidance, path planning, sensorimotor control. The Embodied Computing approach presented is employed in this context to integrate the reconfiguration management as a part of the behavior of the global system. We propose a hardware implementation of the approach based on artificial neural networks.

I. INTRODUCTION

The aim of this work is to design an intelligent embedded controller that will be able to self-organize its elements in order to adapt its architecture to the robot behavior and to its environment. This paper explores the way of biologicallyinspired systems in order to face the complexity of the design of a such systems [START_REF] Compton | Reconfigurable computing: a survey of systems and software[END_REF]. We argue that reconfigurable (or adaptive) computing has to be thought as a part of a global system, composed of sensors, actuators, a source of energy and a controlling unit that implements each processing step of what can appear as the behavior of that artificial entity.

Inspired from psychological models of human visual attention [START_REF] Treisman | A feature-integration theory of attention[END_REF], the controller will lead the robot to focus only on the most outstanding information. It will be able to adapt the allocation of its different processing elements (PEs) according to the saliency of the information from its external and internal environment.

In section II we present the reconfigurable architecture of the controller. This section also provides an analysis of the self-organizing properties of this system and its behavior in the context of robotic applications. Then section III presents the functional results obtained in simulation. We conclude the paper and discuss the future works in section IV.

II. DATA-DRIVEN SELF-ORGANIZED ARCHITECTURE

As introduced in a previous paper [START_REF] Rodriguez | Embodied computing: self-adaptation in bio-inspired reconfigurable architectures[END_REF], the proposed architecture adapts itself to its environment in a data driven way.

This can be done thanks to its layered organization (illustrated in Fig. 1). The first layer is responsible for acquiring the data from the input sensors. Then it leads the primitive signals to the preprocessing layer. This second one processes the information using data parallelism to compute saliency between the different maps and prepares the needed information to the third one. The adaptation layer then implements a Kohonen neural network that learns the data structure (p.119 [START_REF] Kohonen | Self-Organization and Associative Memory[END_REF]) and leads the replication mechanism of the fourth layer. This last one is the high-level computing layer that consists in an array of processing elements. There, the PEs can self-replicate their configuration (functionality) in each others influenced by the dynamics of the previous layer. Then different tasks will compete for the PEs and will colonize different areas. As the SOM learns the data structure and converges to an organization that fits the needs of the application, different areas emerge from it. Each of them are specialized in relation to the different inputs of the system. An illustration of the result of this process is depicted in Fig. 3, the areas represent the sets of winning neurons after having presented several inputs.

In our robotic context, we are designing a sensorimotor application (more described in [START_REF] Rodriguez | Self-organization of reconfigurable processing elements during mobile robots missions[END_REF]). The robot entries are images provided by a camera and proprioceptive information that let the robot know about the position and force given to its own actuators. With the particular preprocessing layer of this application, the SOM converge in three main areas. The first and the second are allocated to compute the static and the dynamic saliency map. The result of these maps is to extract the interest points in the image in relation with the shapes and motions in the visual scene. The third one is used as a sensorimotor map. It will merge the information from the first two areas and from the actuators of the robot in order to learn and to adapt its behavior relatively to its actions and its environment.

III. EXPERIMENTS AND RESULTS

Here we describe the results given by simulation and the dimensioning results of the first hardware implementation.

A. Behavior of the system

The simulator, implemented in C++, exposes a modular design. It is composed of three modules containing an implementation of the first three layers (Fig. 1).

Each layer uses synchronous connections and provides the resulting information frame by frame to connected layers. The reconfiguration process is simulated by a labeling of the cell.

For this first experiment, we use the amount of information in each feature map as an entry for the adaptation layer.

Fig. 2. Evolution of cells colonization by tasks over the time

As we can see in Fig. 2, the maps compete for the resources (PEs) available into the controller according to their inputs. The three stages of the robot mission are clearly visible. From the first to the 200th frame, the robot remains static and a few objects are moving in front of it. From frames 200 to 490, the robot is moving. The motion estimation map takes the space of the static map. This ensures enough computing power to the motion processing tasks. Finally the robot remains stationary, moreover, there is no motion in front of it. Therefore the stationary map is gaining space from the dynamic one.

The profiling of the application behavior resulting from simulation is very promising for the next stages of design.

B. Architecture dimensioning

From the first VHDL implementation results, we can assume that the consumption for a 10x10 map remains easily compatible with the FPGA capacity. For instance, the implementation of the Kohonen neuron model described in Fig. 3 consumes 803 LUTS over the 1507720 available on a VIRTEX 6 LX240 and for the fives states of the cell. But the idea would be in the long term to integrate the preprocessing layer in a real artificial retina that could deal with high-resolution sensors. The Embodied Computing approach exactly allows to totally dissociate the size of the preprocessing map and the size of the high-level processing map.

The behavior of the system obtained in simulation has now to be verified when deployed into the FPGA device.

IV. CONCLUSION AND PERSPECTIVES

We presented in this paper a survey of our design approach for self-adaptive reconfigurable architectures. Inspired from the Embodied Computing theory [START_REF] Pfeifer | How the Body Shapes the Way We Think: A New View of Intelligence[END_REF], the adaptive process is the result of a relationship between the sensors, the actuators and the computing substrata that implements the behavior (the application) of the target system. The method is experimented in the context of mobile robotics where the vision is the main source of perception of the external environment. We demonstrate that the set of resources can be managed in a totally distributed manner following a data driven process tightly coupled to the amount and the nature of the input system sensors.

We are now working on some interesting problems related to the programmability of this architecture. But the access from a reconfiguring PE to the data of the underlying layers is still an open problem since the organization of the computation areas does not respect the input data topology. The Embodied Computing theory has then to be generalized. Finally, with regard to this special use case, the hardware self-configuring architecture has to be refined and optimized to envisage the final deployment onto the robot.

Fig. 1 .

 1 Fig. 1. The layered view of the system architecture.

Fig. 3 .

 3 Fig.3. The Kohonnen neuron is implemented thanks to different VHDL modules. Fd is dedicated to handle the distances computing. Fa handles the activation function. Ws is used to store and compute the synaptic weights. Finally PM is responsible of the replication and configuration of the current program of the cell.