Maria C Arango

Fleur O Strasser

Dr Julian J Bommer
email: j.bommer@imperial.ac.uk

Ruben Boroschek

Diana Comte

Hernando Tavera

D Comté

& H Tavera

A strong-motion database from the Peru-Chile subduction zone

Keywords: Peru-Chile subduction zone, strong-motion database, ground-motion processing, site classes, source and path parameters Peru-Chile subduction zone, strong-motion database, ground-motion processing, site classes, source and path parameters

published or not. The documents may come   L'archive ouverte pluridisciplinaire

This point is very well taken and we realise that the paper would fall short of its objectives if it did not indicate the availability of the dataset. Therefore, we have added a column to Table 1 in which we indicate the source from where the records may be accessed, which in some cases is by request to the 4 th and 6 th authors who manage strong-motion networks in Chile and Peru respectively.

2. The paragraph starting on line 14 of page 7 seems to indicate that focal mechanism data are presented in Table 1, but this data is not present in the table. This is another valuable suggestion, which we have responded to by adding this information to Table 1. 1, the useful metadata is incomplete. I suggest that the authors add the following information: epicenter location, dip of the selected fault model, top and bottom depths of the selected fault model used to compute rupture distances, mechanism (see comment 2).

With regard to Table

All of this information has also been added to Table 1, as suggested by the reviewer.

Minor comments:

There are a few acronyms used without definition (e.g. PGA). Although their meaning is generally clear, they should be defined.

We agree with this comment and have added definitions for acronyms where they first appear in the text.

The paper needs some editorial review, there are a number of miss-spellings (e.g. storeys) and Table 2 is labeled as Table 3.

The labelling of Table 2 has been corrected and the paper has been carefully proof-read in order to correct a few errors, but with regards to the specific example given (storeys) we have used UK rather than US English throughout the paper. Since this is a European rather than North American journal, we believe that the use of UK English is acceptable.

INTRODUCTION

The development of a strong-motion database from subduction events along the Peru-Chile trench is an essential step for ground-motion prediction in this region as well as other subduction zones in the world where there is a significant hazard from earthquakes along the interface between the subducting and overriding plates and within the subducting slab. The tectonic setting of the Peru-Chile region is characterised by the subduction of the relatively young (~50 My) Nazca plate beneath the continental South American plate (Figure 1), which takes place at a convergence rate of 7-9 cm/year in the N78°E direction [START_REF] Demets | Current plate motions[END_REF]. Along the Peru-Chile subduction zone, two main types of seismicity can be identified: firstly, earthquakes occurring at the seismically coupled interface between the Nazca and South American plates (interface earthquakes) and secondly, seismicity related to the zone of extension in the interior of the descending Nazca plate (intraslab earthquakes). The Peruvian-Chilean subduction zone has frequently ruptured in great (M ≥ 8.0) destructive earthquakes during the last centuries, many of which have been thrust-faulting events occurring along the interface between the Nazca and South American Plates, although there have also been a number of damaging intraslab events. An example of the latter is the great event (M W 8.1) that occurred on 25 January 1939, near the city of Chillán, which killed approximately 28,000 people and is amongst the most damaging events that have occurred in the seismic history of Chile [START_REF] Beck | Source characteristics of historic earthquakes along the central Chile subduction zone[END_REF].

The occurrence of great subduction events along the Peruvian-Chilean subduction zone is quite frequent, with 17 events of magnitude M W ≥7.5 registered during the last 50 years. In central Chile, the historical record of earthquakes starts with an event of magnitude M 9.4 in 1575 followed by great events in 1647 (M 8.4), 1730 (M 8.2), 1822 (M 8.4) and1906 (M 8.3) (Comté et al., 1986).

For instance, the great Valparaiso event of 17 August 1906 (M 8.3) caused widespread damage in central Chile and claimed thousands of lives. In recent years, the central Chile segment ruptured in a large interface earthquake on 3 March 1985 (M W 8.0), which killed 177 people and caused extensive damage in the cities of Valparaiso and Viña del Mar. This latter event ruptured along a previously identified seismic gap in central Chile with high probabilities of recurrence for a large earthquake (e.g., [START_REF] Nishenko | Seismic potential for large and great interplate earthquakes along the Chilean and southern Peruvian margins of South America: A quantitative reappraisal[END_REF]. The north-central Chile segment of subduction has also ruptured in great events in 1922 (M W 8.7), 1943 (M W 8.2) and 1995 (M W 8.0). The south-central Chile segment, between 35ºS and 37ºS, is another identified seismic gap, referred to as the Concepción-Constitución seismic gap, which has been extensively studied following the 1939 Chillán event. This segment ruptured in a great (M 8.5) earthquake in February 1835, which completely destroyed the city of Concepción. The last great earthquake in this region was the magnitude M W 8.8 interface event that occurred on 27 February 2010, whose epicentre was located at 100 km from the city of Concepción. Preliminary reports indicated that this latter event had a death toll of more than 500 people and caused extensive damage to the cities of Concepción, Arauco and Coronel, affecting over 2 million people. South of this region, between 37ºS and 46ºS, a great M W 9.5 underthrusting event occurred on 22 May 1960, causing 1660 deaths and leaving 2 million people homeless. This event, the largest instrumentally-recorded in the world during the 20 th Century, had an estimated rupture length of about 1000 km [START_REF] Cifuentes | The 1960 Chilean earthquakes[END_REF] and also induced a tsunami that spread across the Pacific.

In the southern Peru and northern Chile segment of subduction, major interface events occurred in 1868 (southern Peru) and 1877 (northern Chile) with magnitudes estimated between 8.5 and 9.0 [START_REF] Lomnitz | Major earthquakes of Chile: A historical survey, 1535-1960[END_REF][START_REF] Kausel | Los Terremotos de Agosto de 1868 y Mayo de 1877 que afectaron el Sur del Peru y Norte de Chile[END_REF][START_REF] Dorbath | Assessment of the size of large and great historical earthquakes in Peru[END_REF]. This region had been identified as a seismic gap with a high potential of occurrence of a great earthquake [START_REF] Lomnitz | Major earthquakes of Chile: A historical survey, 1535-1960[END_REF][START_REF] Kelleher | Rupture zones of large South American earthquakes and some predictions[END_REF][START_REF] Nishenko | Seismic potential for large and great interplate earthquakes along the Chilean and southern Peruvian margins of South America: A quantitative reappraisal[END_REF]Comté & Pardo, 1991;[START_REF] Delouis | The Andean subduction zone between 22 and 25°S (northern Chile): precise geometry and state of stress[END_REF]. The southern part of this region ruptured in a large interface event in July 1995 (M W 8.0), which occurred south of the rupture zone of the 1877 event. Large intraslab-type events have also occurred in northern Chile in December [START_REF] Tavera | Spatial distribution of rupture areas and seismic gaps in western Peru. Special Volume N6 commemorating Alberto Giesecke[END_REF], had also been identified as another seismic gap. This gap last ruptured in a M W 8.0 event on 17 August 2007 in the Pisco region of Central Peru, causing 595 deaths and extensive damage in the cities of Pisco, Chincha and Cañete [START_REF] Tavera | Ground motions observed during the 15 August 2007 Pisco, Peru, earthquake[END_REF].

In view of the threat that both interface and intraslab-type events pose to the Peru-Chile region, the compilation of a strong-motion database of subduction events that can be the basis of future ground-motion prediction studies is of prime relevance. In Chile, the first strong-motion instruments This paper presents the work performed in order to develop a database of strong-motion records from events along the Peru-Chile subduction zone and associated information (metadata). The strong-motion data recorded by the different networks operators in Peru and Chile have been compiled and processed in a uniform manner, and information on the source parameters of the causative earthquakes, fault-plane geometries and local site conditions at the recording stations has been collected and reviewed. Earthquake parameters from different reporting agencies and published studies were examined to define reliable source parameters, fault-plane geometries and distance metrics. Additionally, geological and geotechnical information at the recording sites was collected from different sources and sites were classified according to various schemes.

DATABASE DESCRIPTION

The compiled database consists of 98 triaxial ground-motion recordings from 15 subduction-type events with moment magnitudes ranging from 6. 1970, 1971 and 1974 Peruvian events available at the COSMOS Virtual Data Centre (http://db.cosmos-eq.org) were also included in this database (48 records). The location of the strong-motion stations operating along the Peru-Chile subduction zone, from which recordings are presented in this study, is shown in Figure 2. The majority of the data from these agencies have been released in unprocessed format; however, in a few cases strong-motion records to which some level of processing has already been applied were also included. All strong-motion data included in this database are from either from free-field stations or instruments at the base of structures, at a total of 56 sites. In the context of this study, free-field recordings are defined as those obtained at stations in small shelters, isolated from any building influence. The other recordings are obtained from instruments at the basement of structures up to three storeys in height, although five recordings obtained at stations located at the basement of structures with more than 3 storeys were included in this database.

Figure 3 displays the distribution of the data in terms of magnitude, distance, focal depth, event type, and NEHRP (National Earthquake Hazards Reduction Program) site class. The methodology used in the determination of the seismological parameters, computation of distance metrics and assignment of sites is discussed in the following sections of this paper. Overall, all strong-motion data available are from moderate-to-large events (6.3≤M W ≤8.4) recorded at distances of about 25-420 km from the fault plane. Approximately half of the entire dataset was recorded at short distances (R rup ≤100 km) and consequently, a significant number of the ground motions are of large amplitudes; the level of peak ground acceleration (PGA) recorded during these events varies within a range of approximately 20-700 cm/s 2 . Similarly, most of the data included in the dataset come from events with magnitudes M W 8±0.3 and M W 7±0.2. The distribution of focal depth with respect to rupture distance for recordings from both interface and intraslab-type events is shown in the upper right panel of Figure 3. The majority of the data from interface events was recorded at distances ranging from about 30 to 200 km, while the intraslab dataset includes ground motions recorded at distances R rup greater than 100 km. The lower panels of Figure 3 show the distribution of the data for interface and intraslab events by NEHRP site class. As seen from this figure, most of the strong-motion records available are from sites classified as NEHRP class C, C/D and D.

Only one record from a NEHRP class D/E site is available and no data was recorded at very soft sites (NEHRP class E).

The effort has been focused on compiling and reviewing the available metadata, which entailed an evaluation of the earthquake-related parameters (i.e., magnitude, location and fault mechanism), classification of subduction events by type (i.e., interface or intraslab), computation of source-tosite distance metrics and characterisation of site conditions at recording stations using different parameters (i.e., surface geology descriptors, shear-wave velocity profiles, natural site period and normalised response spectra shapes). Site classes were assigned to the stations in Peru and Chile following various classification schemes used in ground-motion prediction equations (GMPEs) for subduction-zone environments, such as the NEHRP classification used by [START_REF] Atkinson | Empirical ground-motion relations for subduction-zone earthquakes and their application to Cascadia and other regions[END_REF][START_REF] Boore | TSMMP Suite of Programmes for time series processing[END_REF], the New Zealand site classification scheme used by [START_REF] Mcverry | New Zealand acceleration response spectrum attenuation relations for crustal and subduction zone earthquakes[END_REF] and the scheme used by Zhao et al. (2006b).

Earthquake-related parameters

The earthquake-related information was collected from various reporting agencies and publications and ranked by preferred importance order. The epicentral locations and depths of the events used in this study were selected as follows: special studies of mainshock and aftershock sequences with accurate relocations, determinations published in the Centennial catalogue [START_REF] Engdahl | Global Seismicity:1900-1999[END_REF] and locations and depths determined by the ISC. For the more recent events not included in the ISC catalogue, the location estimated by NEIC was adopted. Regional determinations reported by local agencies (e.g., Department of Geophysics, University of Chile, GUC; Geophysical Institute of Peru, IGP) were also used in this study when appropriate. The moment magnitude (M W ) estimates and focal mechanism solutions for the earthquakes whose data are used in this study were obtained from the Harvard Centroid Moment Tensor database (CMT) when available, which was generally the case for the large earthquakes included herein with magnitude greater than 6.0 which occurred after 1976. For all pre-1976 events, moment magnitudes and focal mechanism solutions were collected from individual studies (e.g., [START_REF] Hartzell | Importance of model parameterization in finite fault inversions: Application to the 1974 M w 8.0 Peru earthquake[END_REF]Pacheco & Sykes, 1992;[START_REF] Abe | Mechanics and tectonic implications of the 1966 and 1970 Peru earthquakes[END_REF]. Other instrumental measures of magnitude were collected from the onlinecatalogues of the different reporting agencies (i.e., International Seismological Centre, ISC and National Earthquake Information Center, NEIC) and were also included in the metadata. Surface wave magnitude (M S ) and body-wave magnitude (m b ) estimates of the Peruvian-Chilean earthquakes determined by the ISC were collected; however, in cases where ISC magnitude determinations were not available, those estimated by NEIC were used instead. No estimates of moment magnitude (M W ) were available for the 5 January 1974 (M S 6.6) event and the 3 March 1985 (M S 6.4) aftershock. It was therefore assumed that M S estimates for these events were equivalent to moment magnitude estimates (M W ). This approximation was validated by plotting moment magnitude values against the different magnitude scales for the events with M W , M S and m b data reported. The characteristics of the events contributing data to the present study are listed in Table 1; their locations and focal mechanisms are shown in Figure 2.

Additionally, the earthquake events were classified in terms of the physical processes with which they were associated (i.e., interface or intraslab activity). The earthquake classification was made on the basis of focal mechanism, epicentral location, depth, and relative position with respect to trench axis. The dominant mechanism of interface-type earthquakes corresponds to thrust faulting on shallow-dipping planes that are oriented approximately parallel to the trench axis. At depths greater than the coupled plate interface, the stress regime changes from compressional to tensional, and thus normal faulting prevails. These normal mechanism events are associated with intraslab activity occurring within the subducted Nazca slab, at some distance down-dip from the seismically coupled interface. At intermediate depths, two types of intraslab earthquakes have been identified in this region (e.g., [START_REF] Lemoine | Slab-pull and slab-push earthquakes in the Mexican, Chilean and Peruvian subduction zones[END_REF]: slab-push and slab-pull, which are associated with down-plate compression and extension, respectively. Along the Peru-Chile subduction zone, the occurrence of slab-pull events is relatively common in comparison with slabpush events, although some slab-push events have been occurred in north-central Chile (the 15 October 1997 Punitaqui earthquake) and central Peru (the 5 and 29 April 1991 earthquakes).

The differentiation between interface and intraslab events was performed using the definitions of style of faulting of [START_REF] Wells | New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement[END_REF] and the event depth and location with respect to the trench axis. As seen in Table 1, the interface events in this catalogue have a reverse mechanism and are limited to a maximum depth of 40 km, which is consistent with the maximum depth extent of the seismically coupled zone found along different segments of the Peru-Chile subduction zone (e.g., Comté et al., 1994;Comté & Suárez, 1995;[START_REF] Tichelaar | Seismic coupling along the Chilean subduction zone[END_REF]. On the other hand, intraslab-type events in Table 1 have a normal mechanism and occur within the Nazca slab at depths from about 60 km to 110 km. The location of these events in 3D space combined with information regarding their focal mechanism (Figure 1 and lower left panel of Figure 2) allows a fairly unambiguous classification between interface and intraslab events, particularly since the geometry of the subducting Nazca slab has been extensively documented. The geometry of the subducting Nazca plate is characterised by variations in the dip angle along the strike of the trench [START_REF] Barazangi | Spatial distribution of earthquakes and subduction of the Nazca plate beneath South America[END_REF][START_REF] Jordan | Andean tectonics related to geometry of subducted Nazca plate[END_REF][START_REF] Cahill | Seismicity and shape of the subducted Nazca plate[END_REF]. Between latitude 2°S and 45°S, the subducting Nazca plate is divided into four segments: northern and central Peru, from 8°S to 15°S, where the subducted Nazca plate has a shallow dip of about 10°; southern Peru and northern Chile, from 15°S to 27°S, where the Nazca Plate descends with a dip of 25° to 30°. In Central Chile, from 27°S to 33°S, the slab is again relatively flat, with a shallow dip angle of about 10°, and in southern Chile, from 33°S to 45°S, the dip of the subducted slab increases to 30°.

The depth extent of the seismically-coupled plate interface along the Peru-Chile subduction zone is similarly well-documented. It has been estimated from the maximum depth of shallow-dipping reverse events (e.g., [START_REF] Tichelaar | Seismic coupling along the Chilean subduction zone[END_REF]Suárez & Comté, 1993;Comté et al., 1994;Comté & Suárez, 1995) and from the depth transition from compressional to extensional stress regime (e.g., Comté & Suárez, 1995;[START_REF] Pardo | Seismotectonic and stress distribution in the central Chile subduction zone[END_REF]. Based on the maximum depth of large (M W >6) underthrusting events located teleseismically, [START_REF] Tichelaar | Seismic coupling along the Chilean subduction zone[END_REF] suggested that the maximum depth of the seismically coupled zone between plates along Chile extends down to 48-53 km and that there is a change in the maximum depth north of latitude 28°S, where the coupled zone extends to depths of 36-41 km. In contrast, studies using both locally and teleseismically recorded data in Northern Chile (Comté et al., 1994;Comté & Suárez, 1995) suggest that the coupling zone, as defined by the maximum depth observed for shallow-dipping reverse events, extends consistently to about 40±10 km and no variations along the strike of the trench are appreciable.

The maximum depth of the coupling zone may, however, extend up to 60±10 km, if the depth transition from compressional to tensional stress regime observed along the upper part of the subducting slab is considered (Comté & Suárez, 1995). This transition of stress field along Northern Chile segment occurs at depths greater than the maximum depth at which shallowdipping reverse events are observed (~40 km). Along the Central Chile segment of the subduction zone, the maximum depth of the plate interface has also been estimated to be about 60 km [START_REF] Pardo | Seismotectonic and stress distribution in the central Chile subduction zone[END_REF], which is in agreement with the above mentioned studies along different segments of the Chilean subduction zone.

Station information and assignment of site conditions

The coordinates of the stations used in this study, type of instruments and instrument housing are listed in Tables 2 and3 and their geographical distribution is shown in Figure 2. For the stations in Central Chile that recorded the 1985 Valparaiso earthquake sequence, some of which are no longer in operation, the station coordinates listed correspond to those reported by [START_REF] Campbell | Processed strong-motion data for the Central Chile earthquake of March 3, 1985: Fifteen accelerograph sites owned by CHILECTRA, ENDESA, and the Department of[END_REF][START_REF] Campbell | Processed strong-motion data for the Central Chile aftershock of April 9, 1985: Nine accelerograph sites owned by CHILECTRA, ENDESA, and the Department of[END_REF], which were validated against satellite imagery (i.e., Google Earth) to ensure accuracy. Information on the type and location of instrument (i.e., type of building) was also obtained from these references, from the accelerogram headings and from the websites of the network operators (IGP, CISMID, RENADIC and DGF-DIC). Information on the majority of the Peruvian stations included herein has already been presented in [START_REF] Tavera | Ground motions observed during the 15 August 2007 Pisco, Peru, earthquake[END_REF].

Tables 2 and 3 also summarise all geological and geotechnical information collected for the sites contributing data to this study. Site conditions assigned to the stations in Central Chile were based on information collected from a number of references including descriptions of the surface geology [START_REF] Eeri | The Chile Earthquake of March 3, 1985 -EERI Reconnaissance Report[END_REF][START_REF] Çelebi | Topographical and geological amplifications determined from strong-motion and aftershock records of the 3 March 1985 Chile earthquake[END_REF][START_REF] Çelebi | Processed Chile earthquake Records of 3 March 1985 and Aftershocks[END_REF][START_REF] Campbell | Processed strong-motion data for the Central Chile earthquake of March 3, 1985: Fifteen accelerograph sites owned by CHILECTRA, ENDESA, and the Department of[END_REF][START_REF] Campbell | Processed strong-motion data for the Central Chile aftershock of April 9, 1985: Nine accelerograph sites owned by CHILECTRA, ENDESA, and the Department of[END_REF][START_REF] Midorikawa | Strong-motion accelerograph array in Santiago, Chile, and preliminary evaluation of site effects[END_REF][START_REF] Midorikawa | Site effects on strong-motion records of the 1985 Chile earthquake and their non-linear behaviour[END_REF], the site categories following the Chilean seismic design code assigned by [START_REF] Riddell | Inelastic design spectra accounting for soil conditions[END_REF] and NEHRP site classes assigned by [START_REF] Atkinson | Empirical ground-motion relations for subduction-zone earthquakes and their application to Cascadia and other regions[END_REF] to the Chilean sites whose data were included in the regression database for subduction-zone events. Shear-wave velocity (V S ) profiles obtained by [START_REF] Araneda | Project of geological survey of strong motion site in Central Chile[END_REF], [START_REF] Midorikawa | Strong-motion accelerograph array in Santiago, Chile, and preliminary evaluation of site effects[END_REF] and [START_REF] Midorikawa | Site effects on strong-motion records of the 1985 Chile earthquake and their non-linear behaviour[END_REF] in addition to the natural period of the Chilean sites determined by [START_REF] Luppichini | Interpretación de los acelerogramas del terremoto de Chile Central de 1985 considerando ondas sísmicas de alta frecuencia[END_REF] using the records of the 1985 Valparaiso earthquake, were also used. Site conditions at the strong-motion stations in northern Chile are still under investigation and geological and geotechnical information for a number of these stations has not yet been made available to the wider engineering community. It is believed, however, that recording sites in northern Chile can be classified as NEHRP class C, with an average shear-wave velocity over the top 30 m, V S30 , between 400 and 600 m/s (Boroschek & Comté, 2006). Therefore, site conditions assigned to these sites were only based on information from descriptions of the local geology (SNGM, 1982), V S profiles obtained from SASW (spectral analysis of surface waves) measurements at the stations in Arica and Poconchile [START_REF] Cortez-Flores | Site response of the 2001 Southern Peru earthquake[END_REF], and natural site periods estimated by site response analysis for the Arica and Poconchile stations [START_REF] Cortez-Flores | Site response of the 2001 Southern Peru earthquake[END_REF].

Site conditions assigned to the stations in Central and Southern Peru were based on descriptions of the surface geology [START_REF] Eeri | Learning from earthquakes: The Pisco, Peru, Earthquake of August 15[END_REF]Bernal & Tavera, 2007a, 2007b) and the site category (i.e., rock, soil or firm ground) assigned by [START_REF] Rodriguez-Marek | Preliminary Reconnaissance Report on the Geotechnical Engineering Aspects of the August 15, 2007 Pisco, Peru Earthquake[END_REF]. Shear-wave velocity (V S ) profiles obtained from SASW measurements at the stations in Ica [START_REF] Rosenblad | Shear wave velocity profiles determined from SASW measurements at sites affected by the August 15 th , 2007 earthquake in Peru[END_REF] and the stations in Moquegua and Tacna [START_REF] Cortez-Flores | Site response of the 2001 Southern Peru earthquake[END_REF], as well as the V S profiles estimate by Bernal & Tavera (2007a, 2007b) using an infinite flat-layered half-space model were also used.

Additionally, the natural site period as interpreted from the microzonation map of Lima (Aguilar [START_REF] Aguilar Bardales | Seismic microzonation of Lima[END_REF] and that estimated by site response analysis for the Moquegua and Tacna sites (Cortez-Flores, 2004) were included. Information on the site conditions of the majority of the Peruvian stations included herein has been also been reported in [START_REF] Tavera | Ground motions observed during the 15 August 2007 Pisco, Peru, earthquake[END_REF].

Besides the site information collected, the spectral shapes of the records were considered by normalising the response spectra by their PGA value (for all records) and by dividing the spectra recorded at soil stations by the spectrum obtained on rock, for stations sufficiently close to one another. The natural period for each site computed from earthquake records, T 0 , REC , was also estimated and used as a guide for the assignation of site classes, following the empirical site classification approach (JP) adopted by Zhao et al. (2006a) which defines the site period as that corresponding to the highest H/V response spectral ratio. Tables 2 and 3 also list the site classes assigned to the different stations following several classification schemes: the NEHRP site classification, which is based on the average shear-wave velocity over the top 30 m; the New Zealand classification scheme used by [START_REF] Mcverry | New Zealand acceleration response spectrum attenuation relations for crustal and subduction zone earthquakes[END_REF], which classifies sites on the basis of the surface geology, geotechnical properties, site period and depth to bedrock; and the scheme used by Zhao et al. (2006b), which uses the predominant site period from H/V response spectral ratios Due to the inherent limitations of some of site data collected, the same level of priority was not given to all the various pieces of information in the assignment of site classes. For instance, only V S profiles determined from measurements of shear-wave velocity conducted in the field have been used for the direct assignment of site classes, and profiles reported in inversions (e.g., Bernal & Tavera, 2007a;2007b) have only been used to distinguish between shallow and deep soil sites since in several instances these profiles have been found to be biased towards low values, leading to site classifications that are inconsistent with other geological and geotechnical descriptions.

Similarly, the V S30 values listed in Table 2, calculated from the V S profiles estimated by [START_REF] Araneda | Project of geological survey of strong motion site in Central Chile[END_REF] at a number of sites in central Chile (i.e., LLAY, MEL, ISI), were found to be biased towards high values. As no information as to the manner in which the V S values published in [START_REF] Araneda | Project of geological survey of strong motion site in Central Chile[END_REF] were obtained (i.e., in situ measurements or numerical modelling), these V S profiles have only been used to identify different soil depths. In addition, the natural period (T 0, CIS ) derived using ambient noise measurements mapped in the microzonation map of Lima [START_REF] Aguilar Bardales | Seismic microzonation of Lima[END_REF], was generally the preferred input for assigning the JP site classes to the Peruvian sites as the predominant period calculated directly from the records (T 0 , REC ) could be biased due to non-linearity effects. In some instances, however, it was found that mapped period was inconsistent with other site descriptors, possibly due to limitations of the mapping resolution. For the stations in Chile, natural periods estimated by site response analysis [START_REF] Cortez-Flores | Site response of the 2001 Southern Peru earthquake[END_REF] were the preferred input.

Most of the stations in central

Record information

Processing was performed with the suite of programmes for processing and manipulation of time series developed by Dr David Boore from United States Geological Survey (USGS) [START_REF] Boore | TSMMP Suite of Programmes for time series processing[END_REF].

The ground-motion recordings were reformatted and converted into SMC-format files (see http://nsmp.wr.usgs.gov/smcfmt.html for details). When necessary, unevenly sampled data were interpolated and resampled at 200 samples per second. Before the application of any processing procedure, non-standard noise (i.e., spurious spikes) encountered in digitized records from analogue instruments [START_REF] Douglas | What is a poor quality strong-motion record[END_REF] was identified by visual inspection of the jerk (derivative of the acceleration trace). Spikes identified as erroneous, were removed by replacing the acceleration ordinate of the spike with the mean of the preceding and proceeding accelerations values. For some of the analogue recordings included in this database, instrument correction has been already applied by the data provider and thus not applied here. Instrument corrections were not applied to the remaining records from analogue instruments in this database as, in some cases, complete information on the instruments response was not available and additionally, the application of an instrument correction can result in amplification of high-frequency noise introduced during the digitization process [START_REF] Boore | Processing of strong-motion accelerograms: needs, options and consequences[END_REF]. As a result of the dynamic range of the digital instruments (natural frequencies of 100 Hz or higher) corrections for instrument characteristics were not applied to the digital recordings included in the database The records were processed in a consistent manner, with individual components individually filtered. Before performing the actual filtering of the record, an initial baseline correction was applied to the raw accelerogram (zero th -order correction). The mean determined from the pre-event portion of the record, or the mean computed from the whole record if the pre-event portion was not available, was subtracted from the entire acceleration time series. After making this initial baseline correction, the acceleration traces were integrated without filtering, to check for long-period drifts that could indicate the presence of offsets in the reference baseline. In most cases baseline offsets were small and the long-period noise was removed by filtering. The records were then filtered using an acausal bi-directional, eighth-order Butterworth filter. For digital records, low-cut filter frequencies were determined by considering the signal-to-noise ratio between each channel and a model of the noise obtained from the pre-event memory. Since this type of model does not account for "signal-generated" noise [START_REF] Boore | Processing of strong-motion accelerograms: needs, options and consequences[END_REF], the results were checked through visual inspection of the velocity and displacement traces obtained from integration of the filtered acceleration record. Visual inspection of these traces was also the basis for the selection of the low-cut filter frequency when no pre-event memory of digital records was available. For analogue records, fixed traces were not available to allow the identification of low-frequency noise.

Therefore, the Fourier Amplitude Spectrum (FAS) of the unfiltered accelerogram was compared with the noise spectrum estimated from studies of instruments and digitising apparatus such as those proposed by [START_REF] Lee | Automatic digitization and processing of accelerograms using PC[END_REF] and [START_REF] Skarlatoudis | Determination of noise spectra from strong motion data recorded in Greece[END_REF], which were used as guide for the selection of low-cut filters. Since these studies correspond to a particular combination of accelerograph and digitiser, which does not correspond to that of data being processed, visual examination of the velocity and displacement traces was also used as a basis for the selection of the low-cut filter frequency.

In selecting low-cut filter frequencies, the filter parameter was chosen to give a signal-to-noise ratio of 2. It is noted that the comparison of the Fourier Amplitude Spectrum (FAS) of the record with that of the noise indicates the ratio of signal-plus-noise to noise, hence if the desired target is a signal-to-noise ratio of 2, the ratio of the record FAS to that of the noise model should be 3. The maximum usable period of the spectrum was then defined as 0.8 times the low-cut filter period, as suggested by [START_REF] Abrahamson | Empirical response spectral attenuation relations for shallow crustal earthquakes[END_REF], which is broadly consistent with the limits suggested by [START_REF] Akkar | Influence of long-period filter cut-off on elastic spectral displacements[END_REF]. On this basis it was decided that, for about 85% of the records included in the database, the spectral ordinates could be reliably calculated up to 3 sec (or up to 4 sec or longer for digital records), although for a few analogue accelerograms, the usable period range could only be extended up to 2 sec. Finally, removal of high-frequency noise was achieved by using high frequency cut-off filters at 25 Hz for records from analogue instruments and 50 Hz for records from digital instruments. Peak values of acceleration and velocity and acceleration response spectra values for 5% of the critical damping were then obtained from the processed data.

The other relevant parameter for each record is the source-to-site distance. The source-to-site distance was characterised in terms of the closest distance to the earthquake fault plane or rupture distance (R rup ). Fault plane dimensions and orientations were obtained from published finite-source rupture models when available (e.g., [START_REF] Abe | Mechanics and tectonic implications of the 1966 and 1970 Peru earthquakes[END_REF][START_REF] Hartzell | Importance of model parameterization in finite fault inversions: Application to the 1974 M w 8.0 Peru earthquake[END_REF][START_REF] Mendoza | Wide-band analysis of the 3 March 1985 central Chile earthquake: Overall source process and rupture history[END_REF][START_REF] Choy | Rupture process of an extended earthquake sequence: Teleseismic analysis of the Chilean earthquake of March 3, 1985[END_REF][START_REF] Pritchard | Geodetic, teleseismic, and strong motion constraints on slip from recent southern Peru subduction zone earthquakes[END_REF][START_REF] Ji | Preliminary results of the August 15, 2007 M w 8.0 coast of central Peru earthquake[END_REF]. Events for which fault-plane geometries from finite-fault inversion were available have moment magnitudes 7.1≤M W ≤8.4 and contribute 70% of the strong-motion data included in the database. For the 1966 (M W 8.1) and 1970 (M W 8.0) Peruvian earthquakes, the rupture areas assumed for source-to-site distance computations were those estimated by [START_REF] Abe | Mechanics and tectonic implications of the 1966 and 1970 Peru earthquakes[END_REF] based on early aftershocks distributions; these two events only contribute two records. For the aftershocks of the 1985 Valparaiso event, with moment magnitudes 6.3≤M W ≤7.1, the circular rupture geometries determined by [START_REF] Choy | Rupture process of an extended earthquake sequence: Teleseismic analysis of the Chilean earthquake of March 3, 1985[END_REF] were used to estimate the corresponding rupture distances.

For the remaining events, for which neither finite source models nor reliable distribution of early aftershocks were available, an alternative approach was used to estimate the distance metrics.

Fault-rupture dimensions were estimated from empirical relationships between rupture area and moment magnitude (M W ) for interface and intraslab-type events that have been determined in [START_REF] Strasser | Scaling of source dimensions for interface and intraslab subduction-zone earthquakes with moment magnitude[END_REF]. The rupture plane was then located in space, assuming that the epicentre lies above the centre of a dipping plane. The strike, dip and rake of the fault plane were assumed to correspond to the preferred focal plane of the two sets of angles listed in the Harvard CMT catalogue. On the other hand, for intraslab-type events the main focal plane was assumed to be that suggested by individual studies of these events. For instance, for the 15 October 1997 (M W 7.1) Punitaqui event, the orientation of the actual fault plane was estimated to be the almost vertical nodal plane of the two sets of angles reported in the Harvard CMT catalogue, based on the body-wave modelling for this event carried out by [START_REF] Lemoine | Evidence for earthquake interaction in Central Chile: the July 1997-September 1998 sequence[END_REF]. Similarly, the orientation of the preferred focal planes for the 7 November 1981 (M S 6.7) and the 5 January 1974 (M S 6.7) events used herein were those suggested by Astiz & Kanamori (1986) and [START_REF] Langer | The 1974 Peru earthquake series[END_REF] respectively. This approach is expected to be a reasonable approximation for the purpose of source-to-site distance calculations in view of the fact that most of the events for which this assumption was applied correspond to intraslab events with magnitude 5.9≤M S ≤6.8, which were recorded at large distances and thus their fault dimensions are not likely to be very large compared to the source-to-site distances.

CONCLUSIONS

A database of recordings for the Peru-Chile region from 1966 to 2007 has been compiled, with particular emphasis on the quality of both the data and the metadata associated with the recordings. The development of reliable regional strong-motion databases for subduction events is therefore of prime importance as they increase the confidence in the results of both regional and global ground-motion prediction studies for subduction regimes. While the database presented in this study is not sufficient for the derivation of a new predictive equation for ground motions from subduction-type events in the Peru-Chile region, it significantly expands the global database of strong-motion data and associated metadata that can be used in the derivation of predictive equations for subduction environments. Indeed, the compiled database further extends the magnitude range of the currently available global databases for interface events (e.g., [START_REF] Youngs | Strong ground motion attenuation relationships for subduction zone earthquakes[END_REF]Atkison & Boore, 2003;[START_REF] Boore | TSMMP Suite of Programmes for time series processing[END_REF] by the inclusion of data from the 2001 (M W 8.4) Peruvian event and further supplements the global intraslab data by the inclusion of recordings from the 2005 (M W 7.8) Chilean event. Although the database presented in this paper includes strongmotion data recorded from 1966 to 2007, the present work can be easily extended to include more recordings and metadata from this region as they become available, including those from the M w 8.8 that struck Chile on 27 February 2010, as this study was being finalised.

The compiled database will also allow the assessment of the existing predictive models for subduction-type events in terms of their suitability for this region, which directly influences the seismic hazard assessment in this region.

FIGURES

TABLES

Table 1. Summary of the earthquakes recorded In Peru and Chile, whose data is used for this study. M W estimates were obtained from Harvard CMT catalogue, except for those events not included in there, for which M S estimates have been listed instead (values followed by asterisk). The source of the fault geometry used to compute the rupture distance (R rup ) is also listed along with the number of records available from each event and the distance and PGA range. Other parameters listed include the hypocentral location, the style-of-faulting and dimensions of the fault rupture (see notes at foot of table ).

Table 2: Summary of characteristics of Chilean strong-motion stations used in this study.

Table 3: Summary of characteristics of Peruvian strong-motion stations used in this study.

Table 1. Summary of the earthquakes recorded In Peru and Chile, whose data is used for this study. M W estimates were obtained from Harvard CMT catalogue, except for those events not included in there, for which M S estimates have been listed instead (values followed by asterisk). The source of the fault geometry used to compute the rupture distance (R rup ) is also listed along with the number of records available from each event and the distance and PGA range. Other parameters listed include the hypocentral location, the style-of-faulting and dimensions of the fault rupture (see notes at foot of table ). [3] CISMID [4] IGP (upon request)

a Epicentre locations and depths from the following references: [START_REF] Engdahl | Global Seismicity:1900-1999[END_REF] e Fault plane orientation from the selected fault model. Events for which a finite source model is not available, the strike and dip have been selected from the two sets of angles reported in the Harvard CMT catalogue (see text for explanation). Two dip values are reported for hinged fault models. f H top: depth to top, H bottom: depth to bottom. For multi-segment models, the depth to the hinge in the fault is also reported (H hinge). RL; rupture length as measured along the strike [1] ; Soft clay [2] ; Granular fill over fine stratified soils [3] S 75

[5] S 200 c Average shear-wave velocity over the top 30m. For the Ica stations, this is based on the VS profiles obtained by [START_REF] Rosenblad | Shear wave velocity profiles determined from SASW measurements at sites affected by the August 15 th , 2007 earthquake in Peru[END_REF] using SASW. For the Lima stations, the value tabulated is a tentative estimate of VS,30 based on the Vs profile inferred by Bernal and Tavera (2007a,b) using an infinite flat-layered half-space model. d Natural site period (T0 ) inferred from the microzonation map of Lima (Aguilar [START_REF] Aguilar Bardales | Seismic microzonation of Lima[END_REF]. Values are not available for the NNA station in Lima, nor for the Ica stations. e Predominant period calculated from accelerogram by considering the H/V ratio of the response spectra, following the approach of Zhao et al. (2006a). The top value corresponds to the east-west component of motion, while the bottom value corresponds to the north-south component.

f Site class according to the NEHRP (1997) provisions. The number in brackets corresponds to the VS(30) value assumed when explicitly required, following the recommendations of [START_REF] Atkinson | Empirical ground-motion relations for subduction-zone earthquakes and their application to Cascadia and other regions[END_REF].

  1950 (M W 8.0) and 13 June 2005 (M W 7.8). The northern part of this seismic gap, ruptured in a great interface event on 23 June 2001 (M W 8.4), along the rupture area associated with great 1868 southern Peru event. The 2001 event had a death toll of 80 causalities and caused severe damage in the cities of Ocoña, Arequipa, Tacna and Moquegua. Along the central region of Peru, the subduction processes have caused great earthquakes in 1746 (M 8.5), 1940 (M W 8.1), 1942 (M W 8.0), 1966 (M W 8.1), 1970 (M W 7.8), 1974 (M W 8.1), 1996 (M W 7.7) and 2007 (M W 8.0), causing thousands of deaths. The Central Peru segment of the subduction zone, between the rupture areas of the 1974 (M W 8.1) Lima event and the 1996 (M W 7.7) Nazca event

  were deployed in 1970s by the Civil Engineering Department of the University of Chile (RENADIC network), which recorded the 3 March 1985 (M W 8.0) Valparaiso events and associated aftershocks amongst other events. Presently, the RENADIC network consists of 20 analogue and 15 digital stations installed in Northern and Central Chile. A second network (DGF-DIC) was deployed by the Departments of Geophysics and Civil Engineering of the University of Chile and the Swiss Seismological Service as a part of a project to study the northern Chile seismic gap and has been in operation since 2001. The DGF-DIC network consists of 11 digital instruments installed in Northern Chile, from Arica to Antofagasta. These two networks have recorded several large events on 13 June 2005 (M W 7.8) and 23 June 2001 (M W 8.4), amongst others. The Geophysical Institute of Peru (IGP) deployed the first strong-motion instruments in Lima, which recorded the 1966, 1970, 1971 and 1974 Peruvian events. Currently, strong-motion networks in Peru are operated by IGP, the Japan-Peru Centre for Seismic Research and Disaster Mitigation (CISMID), the South American Regional Seismological Centre (CERESIS), the Catholic University of Peru (PUCP), and the Peruvian state water company (SEDAPAL). Recent significant events recorded by these networks include the 23 June 2001 (M W 8.4) and 15 August 2007 (M W 8.0) Pisco event.

  3 to 8.4, recorded at 55 different sites in Peru and Chile, between 1966 and 2007. These accelerograms have been made available by local networks in Chile and Peru including the National Accelerographic Network of Chile (RENADIC, 23 records), the DGF-DIC network jointly operated by the Departments of Geophysics and Civil Engineering of the University of Chile (7 records), the Geophysical Institute of Peru (IGP, 8 records) and the Japan-Peru Centre for Seismic Research and Disaster Mitigation (CISMID, 12 records). Additionally, strong-motion records from the 1985 Valparaiso (Chile) sequence and from the 1966,

  Chile are situated on dense alluvial gravel and sand classified as NEHRP class C, C/D and D. There are no stations situated on soft soil (NEHRP E); however, the VMAR and V-ALM stations are on deep sand and artificial fill respectively and therefore exhibit features consistent with soils of medium density. These sites are classified as NEHRP D in view of the large values of the V S30 reported. Only three stations are located on hard rock and rock (NEHRP class A and B), and three sites are on soft/weathered rock classified as NEHRP class C: the RAP, VIL and UTFSM stations are located on rock (NEHRP site class B) and ZAP, QUI, PIC sites are on soft/weathered rock (NEHRP site class C). Stations in Northern Chile are situated on volcanic rock and shallow fill on weathered rock, classified as NEHRP B and C respectively. The most recent material in this region consists of Quaternary alluvial and fluvial deposits and many of the stations are located on such material. These sites are therefore classified as NEHRP C by virtue of the V S30 values estimated for some of those sites (ACA, ACO, POCO1, POCO2) as well as the shape of the normalised spectra (IQU, MEJI, PICA, CUY). The majority of the stations in Peru used in this study are situated on alluvial gravel, sand and silt and have been classified as NEHRP class C and D and only one station (NNA) is situated on rock classified as NEHRP class B. Conversely, the station CAL is located close to the coast in an area of reclaimed land over soft soil, and has been classified as NEHRP class D/E. Another station located on reclaimed land is RIN, which is located on loose granular fill composed of gravel, silt and fine sand.

Figure 1 :

 1 Figure 1: Tectonic setting and distribution of seismicity along the Peru-Chile subduction zone. Seismicity corresponds to that reported in EHB Bulletin for the period 1960-2006. The width and direction of the cross sections of seismicity are indicated by the rectangle in the map.

Figure 2 :

 2 Figure 2: Location of the strong-motion stations used in this study. The panels show the stations located in (a) Central and Southern Peru; (b) Northern Chile; and (c) Central Chile. The locations and focal mechanisms of the events contributing data to this study are also shown.

Figure 3 :

 3 Figure 3: Distribution of the dataset in terms of magnitude, distance, focal depth, event type, and NEHRP site class.

  [Events 1,2,6,8],Larger and Spence (1995) [Events 3,4,5],[START_REF] Choy | Rupture process of an extended earthquake sequence: Teleseismic analysis of the Chilean earthquake of March 3, 1985[END_REF] [Events 7,9,10,11], [3]Pardo et al. (2002b) [Event 12],Tavera et al. (2002) [Event 13], Delouis and Legrand [Event 14],[START_REF] Tavera | Ground motions observed during the 15 August 2007 Pisco, Peru, earthquake[END_REF] [Event 15] b Mw estimates are taken form the CMT catalogue. For events earlier than 1976, the values reported come from the following references:[START_REF] Abe | Mechanics and tectonic implications of the 1966 and 1970 Peru earthquakes[END_REF] Stauder (1975) [Events 1, 2],[START_REF] Langer | The 1974 Peru earthquake series[END_REF] [Event 3],Hartzell and Langer (1993) [Events 4,5] c Style-of-Faulting: R (reverse), N (normal) following theWells & Coppersmith (1994) definitions d Fault plane dimensions of events of unknown geometry have been defined using the[START_REF] Strasser | Scaling of source dimensions for interface and intraslab subduction-zone earthquakes with moment magnitude[END_REF] scaling relations for subduction-zone events.

a

  Description of surface geology profile, based on the following references: [1] EERI (2007) [2] Bernal and Tavera (2007a,b) [3] information provided by the strong-motion network in the accelerogram heading [4]Espinosa et al. (1977) [5] Cortez-Flores (2004) b Site class assigned by Rodriguez-Marek et al. (2007).

g

  Site class according to the New Zealand site classification, which is based on surface geology, geotechnical properties and depth to bedrock. See McVerry et al. (2006) for details. h Site class according to the Zhao et al. (2006a) scheme, considering VS,30 and the natural period of the site. i Site class assumed to compute the design loads prescribed by the 1977 and 2003 Peruvian seismic codes.

Table 3 .

 3 Information on Peruvian strong-motion stations used in this study.

	Code	Name	IT	Lat [ºS]	Lon [ºW]	Loc Surface geology	a		SCRM	VS30 [m/s]	T0, CF	T0, CIS	T0,REC	NH	NZ JP CO
	ANC [IGP]	Ancon	D 11.776 77.150	U	Alluvial gravel (soil)	[2]	S	280 [5]		0.2 -0.3	0.30 0.10	C/D	C	II	II
	ANR [CER]	Asamblea Nacional de Rectores	D 12.123 76.976	B	Alluvial gravel (soil)	[2]	FG	205 [5]		0.2 -0.3	0.50 0.15	D	C	II	II
	CAL [CIS]	Callao	E 12.060 77.150	S	Soft soil

ACKNOWLEDGMENTS

The doctoral research of the first author, on which this paper is based, has been partially funded by the Alβan Programme of the European Union under scholarship E05D053967CO and the COLFUTURO programme; their financial support is gratefully acknowledged. The authors thank Bertrand Delouis for providing information on the source process of the 13 June 2005 Chilean earthquake.

We are grateful to two anonymous reviewers for their constructive feedback that helped to improve the manuscript.

Alluvium [4] ; Soft alluvium [5] ; Dense gravel Granite [4,7] ; Paleozoic intrusive [5] ; Medium density sand Firm gravel [4] ; Alluvium [5] ; Shallow fill on dense gravel [4,5,7] ; Sand Soft alluvium [4,7] ; Gravel and soft lime [4] ; Dense sand [6] ; Granite [4] ; Alluvium [5] ; Sand [6] ; Granite (1991) and [START_REF] Midorikawa | Site effects on strong-motion records of the 1985 Chile earthquake and their non-linear behaviour[END_REF]. e NEHRP site classes assigned by [START_REF] Atkinson | Empirical ground-motion relations for subduction-zone earthquakes and their application to Cascadia and other regions[END_REF][START_REF] Boore | TSMMP Suite of Programmes for time series processing[END_REF]. f Site classes assigned by [START_REF] Cortez-Flores | Site response of the 2001 Southern Peru earthquake[END_REF] following the [START_REF] Rodriguez-Marek | An empirical geotechnical seismic site response procedure[END_REF] site classification scheme: B=Rock; C2=Shallow stiff soil. g Soil classes assigned by [START_REF] Riddell | Inelastic design spectra accounting for soil conditions[END_REF] following the 1993 Chilean seismic design code provisions h Average shear-wave velocity over the top 30m, in m/s, determined from: [1] Vs profiles obtained by Cortez-Flores (2004) using SASW; [2] VS profiles determined by [START_REF] Araneda | Project of geological survey of strong motion site in Central Chile[END_REF]; VS profiles obtained by [START_REF] Midorikawa | Strong-motion accelerograph array in Santiago, Chile, and preliminary evaluation of site effects[END_REF] and [START_REF] Midorikawa | Site effects on strong-motion records of the 1985 Chile earthquake and their non-linear behaviour[END_REF]. For calculation purposes, when VS data were available at depths < 30 m, the VS value of the last layer was assumed constant to 30 m depth. i Predominant site period, in seconds, determined by [START_REF] Luppichini | Interpretación de los acelerogramas del terremoto de Chile Central de 1985 considerando ondas sísmicas de alta frecuencia[END_REF]. Values listed as reported by Ruiz & Saragoni (2005). j Predominant site period determined by [START_REF] Cortez-Flores | Site response of the 2001 Southern Peru earthquake[END_REF]. TS1 was estimated as the period corresponding to the maximum ratio of response spectra at the surface over the response spectra of outcrop input motion and TS2 corresponds to the characteristic site period calculated from the equation TS=4H/VS. k Predominant site period calculated from accelerogram by considering the H/V ratio of the response spectra, following the appr oach of Zhao et al. (2006a). The lower and upper boundaries of the interval reported correspond to the maximum and minimum values of the natural site period found when using multiple records f rom the same station. Values are only listed for those records whose vertical component is available l Average shear-wave velocity over the top 30m, in m/s, used in analyses.


Dr Alan Tang
email: alan.tang@royalberkshire.nhs.uk

How to run a prison STI service

Keywords:

Abstract

Objectives

• The rationale for providing in-reach services for STI and BBV diagnosis and treatment to prisoners • Principles underpinning the design and implementation of these services • Understanding the special considerations needed to accommodate the effects of the prison regime and categories of prison Methods. Recent literature on service delivery and standards were reviewed. Results. There is ample evidence worldwide that STI and BBV infection are more highly prevalent in prison populations than in the outside community. STI diagnosis and treatment services are therefore an essential component of any STI control programme. Conclusion. Services should be commissioned with characteristics of the prison setting in mind and link in with the local health strategy and action plan. Approval of funding is strongly supported by the quick win from diagnosis and treatment of highly prevalent STI. The quality of services must be assured by a monitoring and governance framework grounded on national standards.

Why provide a sexual health service in the local prison? Why should commissioners pay for it?

• It's a great public health opportunity • If you don't, prisoners might be brought out in shackles to your clinic anyway • In the UK, you might be asked, since one of the Prison Health Performance Indicators (PHPI) is 'Access to a GUM Clinic in prison' • It might bring additional income to your service under a contract with commissioners • A well planned, appropriately commissioned service could be a rewarding experience for you and your team

The Public Health Angle There is evidence from studies in the UK and elsewhere that prisoners have higher prevalences of sexually transmitted infections (STI) and blood-borne viruses (BBV) than non-incarcerated populations [1, 2, and 3]. Prisoners are literally a captive audience and many do use (and possibly abuse) opportunities for sex and relationship education (SRE), contraception, screening for STI and BBV, and hepatitis B vaccination during incarceration. Chlamydia screening programmes for prisoners under the age of 25 have been successfully implemented, contributing to local targets in England and Wales [START_REF] Menon-Johansson | The first point prevalence study of genital Chlamydia trachomatis infection in young male inmates in the UK[END_REF]. Partner notification schemes can be set up, and post-release STI care provided, accruing further health gains. In the UK the Genitourinary

Key Messages

• There is ample evidence of the need to provide diagnosis and treatment for Sexually Transmitted Infections (STI) and Blood-Borne Viruses (BBV) in prison populations and prisoners have the right to access these services. • STI and BBV services may be served by a plurality of providers but must be led by specialists to maintain quality and lead service development. • Services must be sensitive to the special needs of the prison population and the particular prison setting • The need for benchmarking of service quality is urgent Medicine Clinic Activity Dataset (GUMCAD) STI surveillance system introduced in 2011 includes a code for prisoners, and this will enhance the monitoring of STI and BBV in prisons on a national level [START_REF]Genitourinary Medicine Clinic Activity Dataset[END_REF]. In the US, the Corrections STI Prevalence Monitoring Project (formerly the Jail STD Monitoring Service) has been collecting such data for many years [START_REF]STD in persons entering corrections facilities[END_REF].

Human Rights and the prisoner The practice of transporting prisoners to access health care outside prisons, shackled to one or more prison officers, is both demeaning and resource-intensive. The BMA has been against this practice for many years [START_REF]Prison Doctors[END_REF]. Lack of provision of health care is an infringement of human rights for the prisoner. "All prisoners have the right to receive health care, including preventive measures, equivalent to that available in the community" (WHO, 1993).Prisons in the UK generally have in-house health care provided by doctors who are usually GPs, and a team of nurses, managed by a health care manager appointed by the commissioners. The National Commission for Correctional Health Care (NCCHC) in the US aims to improve the quality of health care in correctional settings and sets out standards for service provision and provides guidance on management. The NCCHC recommends early detection and treatment for STI for all prisoners, and for youth in prisons this includes education and counselling on STI.

Key Performance Indicators (Table 1). Prisons in the UK have over 30 health indicators including hepatitis B vaccination and sexual health, with the latter containing 5 elements for compliance. The responsibility for ensuring these are achieved rests with the Governor of the prison concerned, who in turn works with the local health commissioners to agree on how services are delivered.

A national survey of STI services in prisons conducted in 2008 showed extreme variation in quality of services and poor monitoring of standards [START_REF] Tang | A survey of sexual health services in UK prisons[END_REF]. The Standards for the management of sexually transmitted infections (STIs) 2010 [START_REF]The Standards for the management of sexually transmitted infections (STIs)[END_REF] have set best practice for all NHS-commissioned services and therefore includes prison STI services. The 2008 survey shows that many services fall short of best practice as currently known, therefore it is urgent that peer review or health needs re-assessment is carried out.

Commissioning and Contracting

There is currently no national guidance for commissioning and service delivery of sexual health services in prisons that prison partnership boards can refer to. Generally, commissioners want services that are broadly equivalent with those in the community and the contract will be monitored for quality and cost effectiveness, while the Governor has to ensure that services can be safely delivered in the prison setting. A good model document to use is a Regional Sexual Health Task Force's Guidance on commissioning sexual health and blood borne virus services in prisons in the South West of England [START_REF]Guidance on commissioning sexual health and blood borne virus services in prisons in the South West of England[END_REF].

The prison partnership board contracts one or more providers to deliver services, for example the local STI service may be contracted to run sessions to diagnose and treat STI while education may be delivered by a voluntary sector organisation. If your service is invited, or is successful in the tendering process, you may consider asking an expert in health care contracting to scrutinise the proposed contract, and decide on the length of the term. and the transport time if using culture media, availability of microscopy and Gram's staining • Results: agree a results notification system with prison staff; best practice is giving all results, be they positive or negative; alternative practice 'no news is good news' system, that must be enforced to avoid repeated enquiries from prisoners • Partner notification: decide who will advise and follow up on partner notification; system for recording this in case records; agreement from prison staff on allowing telephone calls or e-mails or posted mail • Surveillance and monitoring: set up an information collection system to feed into clinical governance meetings and to provide data for annual reports, service reviews, etc. and ensure such data are collected regularly; data are available for contract monitoring by the commissioners; identify responsible staff in prison and also host service • Discharge planning: arrange continuing treatment e.g. anti-retroviral drugs, wart treatment; condoms; location of nearest Level 3 STI service; partner notification Much as the WHO Checklist has transformed patient safety in surgery, a checklist for high quality STI services in prisons may help in the much needed reduction in variability and increase in standards (Table 3).

Conclusions

Sexual health services should be provided for the prison population because of the ample evidence of need and services must be configured according to the prison setting, funding available and epidemiological intelligence. Improved outcomes for sexual health of prisoners may contribute to reduction in re-offending as an aspiration in the Offender Health Strategy for England and Wales. Sexual health if viewed in this wider context would look like a risk-reduction service for teenage conception and acquisition of STI combined with services dealing with ill-health due to STI, and one of a whole package of services to rehabilitate prisoners back into society and reduce re-offending by dealing with the root causes as far as possible. Ultimately monitoring may show improvements in post-release socio-economic parameters and wider gains in society as a whole.

Competing interests: None Funding: None

The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all authors, an exclusive licence (or non exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd to permit this article (if accepted) to be published in STI and any other BMJPGL products and sublicences such use and exploit all subsidiary rights, as set out in our licence http://group.bmj.com/products/journals/instructions-for-authors/licence-forms.

Table 1 .

 1 Prison Health Performance Indicators 2009

	Indicator No. Indicator
	1.30	Hepatitis B Vaccination of Prisoners
	1.32	Sexual Health

• Means of accessing condoms • Access social/life skills modules on SRE education or similar • Access to a GUM Clinic in Prison • Access to Chlamydia screening programme • Access to barrier protection and lubricants

Table 2 .

 2 Typical measures in the contract or service level agreement include number of sessions per year, numbers of prisoners seen, non-attendance figures (with reasons), STI diagnosed and treated. You should work with your host organisation and the commissioner to develop an appropriate contract, bearing the considerations in this article and related references in mind. Commissioning should define core levels of service and areas for future development, appropriate to the type of prison and distribution of resources between services. Health commissioners do not have lead responsibility for sex and relationships education, condom provision and training for prison staff, but these greatly impact the improvement of the sexual health of prisoners and it is essential to collaborate with other related providers. Essential Elements of Commissioning Adapted from Guidance on commissioning sexual health and blood borne virus services in prisons in the South West of England[START_REF] Tang | A survey of sexual health services in UK prisons[END_REF]. link in with providers of sexual health education, ensuring the scope of your service is accurately portrayed • Booking: work out the capacity of the clinic, including extra slots and take into account non-attendance; record reasons for non-attendance e.g. refusal, security, in education • Accommodation: sound attenuated consultation room, undisturbed intimate examination, adequate lighting, space for laying out specimen taking equipment, keeping sharps out of prisoners' reach • Workforce: trained in sexual health and annually appraised; competencies appropriate for the level of service commissioned; communication with prison GP service; guidelines for syndromic management by GP on days between STI sessions; links with education service; chaperones; well-informed prison officers (especially important in high-security prisons, where prisoners are always seen in the presence of a prison officer) • Records management: devise a case note system bearing in mind access, confidentiality, availability for clinical audit, recording of KPI e.g. HIV testing uptake; facilities for locked storage if kept in the prison • Treatment: check arrangements for prescribing, funding for the more expensive drugs (e.g. Imiquimod, Podophyllotoxin), make arrangements for cryotherapy; check means of supply of anti-retroviral drugs if relevant • Diagnostics: ensure specimens are delivered promptly to the pathology service

	Universal access to doctor or nurse trained in sexual health
	All practitioners linked to local sexual health network
	Define level of service e.g. National strategy for sexual health and HIV Level 2
	Access to Chlamydia screening programme if aged under 25
	Confidentiality of consultations and record keeping
	Access to advice and screening for BBV
	Access to treatment for BBV and assurance of continuity of treatment in case of
	transfers or release
	Women's services if relevant -services for abused women, contraceptive advice and
	support, continuity after release
	Surveillance and reporting of STI and BBV data
	Provision of post-exposure prophylaxis for BBV exposure
	Running the service
	There are various models of care, from a traditional consultant delivered service to a
	complete 'patchwork' involving prison nurses, specialist STI health advisors,
	specialist STI nurses, GPs and specialist doctors in STI management each providing a

component of the overall service. A few principles to bear in mind include:

• Referral/triage: agree a referral system, e.g. application slips, or direct referral based on the secondary health screen questionnaire, with the prison health care team and

Table 3

 3 Personal security should always be borne in mind and if available, having breakaway training is a good idea.• Maintaining confidentiality -proximity of prison staff to clinical rooms may compromise the process though personal security may be enhanced. • Access to sexual health information in case notes by prison health care staff should be restricted by keeping separate records. These can be kept locked separately on prison premises or retained in the host GUM service. If the latter notes should be kept in secure container or bag during transportation. • BBV screening nurses are useful allies; collaborate with them for blood tests and management of hepatitis B and C • Provide education and training for prison staff, aiming to inform of standards, raise awareness of the service and needs of prisoners , improve cooperation with running of clinics. • Medicines that are allowed in cells (In Possession Medications) -no glass bottles are usually allowed for security reasons. • Effectiveness of referral systems -Secondary Health Screen question on STI could be supplemented by a referral slip to give multiple opportunities allowing for embarrassment and stress of initial incarceration. • Risk of being moved -fights, court proceedings, age limit (in juvenile and young offender facilities) may make appointments difficult to arrange.

	. STI Management in Prisons (STIMP) Checklist
	1. access
	2. accommodation
	3. diagnostics
	4. treatment
	5. records management

by the British Association for Sexual Health and HIV (BASHH) , including members and officers of BASHH, officials from Prison Health, and the Chief Executive of the Medical Foundation for AIDS and Sexual Health (MedFASH).