Reprlnted from

PHYSICSOFTHEEARTH

ANDPLANETARYINTERIORS

Physics of the Earth and Planetary Interiors 84 (1994) 235-246

Seismogenic zone survey by Algerian Telemetered SeismologicalNetwork; case-study of Rouina earthquake, 19 January 1992

M. Bezzeghoud*, A. Ayadi, A. Seba"i,H. BenhallouDepartment ESS, CRAAG, BP 63, 16340 Bouzaréah-Alger, 'Algeria

(Received 1 January 1993; revision accepted 20 December 1993)

=--=- "'----

PHYSICS OF THE EARTH AND PLANETARYINTERIORS

Editors

O. GubbinsOepartment of Earth SciencesUniversity of LeedsLeeds LS2 9JTUnited Kingdom

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O.E. LoperFlorida State UniversityGeophysical Fluid Oynamics Institute18 Keen BuildingTallahassee, FL 32306USA

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J.-P. PoirierInstituI de Physique du Globe4, Place JussieuF-75252 Paris, Cedex 05France

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Founding Editors

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Honorary Editors

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T. Lay, Santa Cruz, CA, USAS. Mackwell, University Park, PA, USAB.O. Marsh, Baltimore, MO, USAH. Mizutani, Kanagawa, JapanJ.-P. Montagner, Paris, FranceH.C Nataf, Paris, FranceJ. Neuberg, Leeds, UKRK O'Nions, Cambridge, UKW. O'Reilly, Newcastle upon Tyne, UKG.O. Price, London, UKV. Rama Murthy, Minneapolis, MN, USAP. Rochette, Marseille, FranceT. Shankland, Los Alamos, NM, USAF.O. Stacey, St. Lucia, Qld., AustraliaD.L. Turcotte, Ithaca, NY, USAS. Uyeda, Tokyo, JapanK Whaler, Leeds, UKB. Wood, Bristol, UK

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ELSEVIER

PHYSICSOFTHEEARTH

ANDPLANETARYINTERIORS

Physics of the Earth and Planetary Interiors 84 (1994) 235-246

Seismogenic zone survey by Algerian Telemetered SeismologicalNetwork; case-study of Rouina earthquake, 19 January 1992

M. Bezzeghoud*, A. Ayadi, A. Seba"i,H. BenhallouDepartment ESS, CRAAG, BP 63, 16340 Bouzaréah-Alger, Algeria

(Received 1 January 1993; revision accepted 20 December 1993)

Abstract

A new telemetered seismological network has been recently installed in northern Algeria. At present, this newseismic network includes 30 stations, with a final goal of 32 stations connected by radio and dedicated telephonelines to a centre located at the CRAAG headquarters in Alger-Bouzaréah. The Algerian Telemetered SeismologicalNetwork (ATSN) stations are ali equipped with short-period seismometers. Monitoring by this network will allow amore precise knowledge of the seismicity in Algeria and southern Europe. As an example, the sequence of theRouina earthquake (M = 5.2) of 19 January 1992 recorded by the ATSN is described.

1. Introduction

Algeria is known as one of the most activeseismogenic zones in the western Mediterraneanbasin (Figs. 1 and 2). This activity is characterizedby three major events which occurred during thelast decade: El Asnam (lO October 1980, Ms =7.3; e.g. Ouyed, 1982; Deschamps et aI., 1982;Yielding et aI., 1989), Constantine (27 October1985, Ms = 5.9; e.g. Bounif, 1990; Deschamps etaI., 1991) and Mont Chenoua- Tipasa (29 October1989, Ms = 6.0; Bezzeghoud et aI., 1990; Mrounand Azizi, 1992; Mroun et aI., 1992). Many otherevents have been reported by several workers(e.g. Rothé, 1950; Roussel, 1973a,b; Benhallou,1985; Ambraseys and Vogt, 1988; Bezzeghoud etaI., 1994); some of these events are historical

* Corresponding" author.

0031-9201/94/$07.00 @ 1994 EIsevier Science H.V. AlI rights reservedSSDI 0031-9201(94)05036-W

(1365-1910) and others are instrumental recentevents that were recorded by teleseismic stationsand by a few Algerian stations including Alger-Bouzaréah (ABA), which was installed in 1910and is the oldest in the region.

Since 1910 many other seismological stationshave been deployed in Algeria (Fig. 1b, Table 1).Among these, two international stations, belong-ing to the GEOSCOPE (Romanowicz et aI., 1991)and MedNet (Giardini et aI., 1992) networks, arerecording digital seismograms; these stations areequipped with three-component broadband seis-mometers.

The Centre de Recherche en Astronomie, As-trophysique et Géophysique (CRAAG), moti-vated by interest in monitoring seismic hazardand surveying seismogenic zones, suggested thecoverage of northern Algeria, which is the mostactive zone, by a telemetered seismological net-work. This network enables us to record the

236 M. Bezzeghoud et aI. / Physics of the Earth and Planetary lnteriors 84 (1994) 235-246

seismic activity in this region. As an example ofsuch activity, we describe the sequence of theRouina earthquake (19 January 1992, M = 5.2),for which all the foreshocks (eight events with2.3 ~ M ~ 4.7) and aftershocks (26 events with1.5 ~ M ~ 5.2 were recorded by the telemeteredstation network.

2. Seismicity and instrumental history in Algeria

Algeria has experienced several strong earth-quakes during the last century (e.g. Rothé, 1950;Roussel, 1973a,b; Benhallou, 1985; Ambraseysand Vogt, 1988; Ait Messaoud and Mokrane,1992; Bezzeghoud et aI., 1994). The regional seis-micity is, more or less, well known for the lastdecade. This activity is the strongest in the west-em Mediterranean region, as a result of thecollision between the African and Eurasian plates.Many seismic events have occurred in many parts

o(a)

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of northem Algeria (Fig. l(a)), especially in theChellif basin (Fig. 2). The largest events duringthis century are those of 1954 (M = 6.7) and 1980(M = 7.3), which caused extensive material dam-age and thousands of casualties.

Algeria has a long seismological tradition ow-ing to the seismic activity, and the destructiveevents that have occurred have been reported inofficial documents or newspapers, as well as bymany researchers (e.g. Rothé, 1950; Benhallou,1985; Bezzeghoud et aI., 1994). This tradition wascharacterized by the installation of the Alger-Bouzaréah station (ABA) in 1910 by the ServiceMétéorologique d' Algérie.

For many years (1910-1990), Algerian seismic-ity was monitored by very few seismological sta-tions, which constituted the old seismological sur-vey network. These stations were analog record-ing stations, and data were recorded either inphotographic mode or using ink pen on paper.The eight stations of this network were equipped

3 6

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~(!) . ,l)!.,C9 .

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Fig. 1. (a) Instrumental seismicity map of Algeria between 1910 and 1990 for events of M> 4.0. (b) National and internationalseismological stations (see Table 1). Â Long-period stations which are operational in 1992. TAM and MBA (.)are respectivelyGEOSCOPE and MedNet stations. O, Older stations.

M. Bezzeghoud et ai. / Physics of the Earth and Planetary lnteriors 84 (1994) 235-246

with different types of instruments (Table 1). Theconfiguration of this network (Fig. l(b), Table 1)induced inhomogeneous recording of microactiv-ity in time and space owing to the poor stationcoverage. Nevertheless, some of these stationshave been regularly maintained up to the present,and arrival time reading taken for teleseismic,regional and local events. These data have con-tributed to hypocentral determination, adding ob-servations on the African continent, where therewere always few stations. Data at Tamanrassetwere particularly important for global seismicitydetermination, and data from the northern Alge-rian stations provide information on the westernMediterranean activity. However, local and nearregional activity were poorly determined.

In co-operation with the Institut de Physiquedu Globe de Paris (IPGP) and recently with the

(b) 389-4

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BABO

23

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Fig. 1 (continued).

11

237

Istituto Nazionale di Geofisica (ING), theCRAAG offered two sites, one for a GEO-SCOPE station in Tamanrasset (from May 1984;see Romanowicz et aI., 1991) and the other for aMedNet station in Médéa (from June 1992; seeGiardini et aI., 1992); the latter is a part of abroad regional network covering the Mediter-ranean region. These stations are equipped withvery-broadband seismometers and are maintainedby the Department of Studies and SeismologicalSurvey (ESS-CRAAG) in co-operation with theIPGP-INSU and ING.

3. The Algerian Telemetered Seismological Net-work

Since the EI Asnam earthquake (10 October1980, M = 7.3), to eliminate the various deficien-

6 1138

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A

33

28

TAM

6 18

238 M. Bezzeghoud et ai. / Physics of the Earth and Planetary lnteriors 84 (1994) 235-246

cies and limitations of the old network, theCRAAG took the initiative of deploying regionalarrays of telemetered seismological short-period

stations over northern Algeria, considering areaswhere the seismic risk is the highest. The Alge-rian Telemetered Seismological Network (ATSN)

1.0 2. O

M

C) 7

C) 6

C9 5

CJ 4

Fig. 2. The El Asnam thrust fault and the seismicity of the Chellif basin between 1716 and 1992, with different symbols forhistorical (square for lo (maximal observed intensity)) and instrumental (circle for M) events. Size is proportional to maximumintensity or magnitude.

Table 1National and international seismological stations in Algeria (see Fig. l(b))

Station Code Period in Latitude Longitude Elevation Component Typeoperation (m)

Alger-Bouzaréaha ABA 1910-1949 36°48'04"N 03°02'06" E 332 SP, z n e Photo.

1980 to present MP, z n e InkOued Fodda OFD 1935-1982 36°04'N 0l036'E 380 SP, z Therm.Tamanrasset (GEOSCOPE) a TAM 1948-1987 22°47'30"N 05°31'24"E 1395 SP, z n e Photo.

1984 to present VBB, z n e Magn.Université d'Alger ALG 1949-1982 36°46'18"N 03°O3'30"E 59 SP, z n e Photo.

MP,zSétif a SET 1958-1977 36°12'N OSO24'E 1000 SP, z n e Photo.

1978 to present MP, z n e InkBeni-Abbes BAB 30°07' 17" N 02°11'1O"W SP, z n e Photo.Relizane REL 1955-1961 35°35'N 00°35'E 75 SP, z n e Therm.Tlemcen TEC 34°51'N On7'W SP, z Therm.Médéa MedNet a MBA June 1992 36°18'1O"N 02°43'50"E 1105 VBB, z n e Magn.

a Still in operation. Photo., photographic mode recorde r; Therm., thermic mode recorder; Magn., magnetic mode recorder.

MEDITERRANEAN SEA

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M. Bezzeghoud et ai. / Physics o[ the Earth and Planetary lnteriors 84 (1994) 235-246

consists of four sub-nets, with a planned total of32 stations (Fig. 3, Table 2). It covers the regionsof Oran, Beni-Rached (Chellif basin), Alger-Bouzaréah and Constantine. Each regional sub-net has seven field stations which send data byUHF radio telemetry links, either directly to theregional centre or by a relay station to avoidtopographic obstacles. The sites were chosen toobtain the lowest possible noise leveI; the stationsare far away from industrial disturbances andhuman activity. Also, the regional sub-net centreis equipped with a three-component short-periodstation. The gain is such that events of magnitudelarger than 1.0 are detected at 10 km. The 90 dBdynamic owing to analog telemetry ensures ab-sence of saturation for events of magnitude lessthan 4.5 at the same distance. A magnitude 3.0event which occurs in northern Algeria is gener-aly detectable on seven stations. The installationof the ATSN is totally sponsored by the AlgerianMinistry of Interior, and the Department of Stud-ies and Seismological Survey (ESS-CRAAG) isresponsible for the deployment and maintenanceof the ATSN stations and data collection.

Each ATSN field station is a vertical-compo-nent (SZ) station consisting of a 1 Hz SS-l Kine-metrics (Pasadena, CA, USA) seismometer based

382 o 2

239

on a spring-mass instrument with electromagnetictransduction. Two circular flexural springs sup-port the seismometer mass. The telemetry hous-ing contains a TH-ll module with amplifier-filtercard, calibrating and multiplexer cards, and thereceiver and transmitter module connected toreceiver or transmitter antennas. A power supplybattery is connected to a solar panel; all thisequipment is mounted on a pylon. The ASTNcomprises 28 vertical-component field stations.

The telemetered network has four regionalcentres-Oran Gn the western part of Algeria),Beni-Rached Gn the Chellif basin), AIger-Bouzaréah and Constantine Gn the eastern partof Algeria). Each regional centre consists of ashort-period three-component station and a UHFreceiving system linked with a telemetry cabinetcontaining discriminators, four direct-write drumrecorders (VR-2, Pasadena, CA, USA) and aKinemetrics / Truetime Omega (Pasadena, CA,USA) synchronized time code receiver. The Nor-way signal is received perfectly, ensuring a timeprecision of 1 ms.

The data in digital form will be continouslysent in real time from each individual sub-net(Oran, Beni-Rached and Constantine) to theheadquarter (Alger-Bouzaréah) via dedicated

4 6 8 38

MEDITERRANEAN S E A

36

31.2 o 2

36

4 346 8

Fig. 3. Algerian Telemetered Seismological Network (see Table 2); geographical location of the stations installed in northernAlgeria. Full and dashed !ines represent, respectively, UHF radio telemetry links and future telephone links. -, Regional centres(equipped with a three- component short-period seismometer); ., field stations (equipped with one vertical-component seismome-ter); O non-operational field stations.

240 M. Bezzeghoud et aI. / Physics of the Earth and Planetary lnteriors 84 (1994) 235-246

telephone lines. A specific data-recording systemwas instaIled in February 1994.

To facilitate the rapid determination of epi-centres, a Kinemetrics numerical Data Acquisi-tion System DATASEIS 11wiII received the datastreams. The system software provides real-time,continuous monitoring, or is triggered by anLTA/ STA ratio, and records up to 64 channelsof data with a pre-event memory of at least 60 ssynchronized on the Omega receiver. The datawiII be stored on 40 Mb Plus Passport (QuantumCorporation, CA, USA) removable hard disks

instead of a nine-track tape drive. A second mi-crocomputer (4 Mb of RAM, 300 Mb of hard diskand an 80387-25 coprocessor) wiII be integratedwith the DATASEIS 11 for automatic analysisand output of magnitude and location. The datawiII be stored on 2.2 Gb external removable disks.

The main goal of this network is to survey theseismic activity in AIgeria, with the aim of assess-ing seismic hazard and reducing seismic risk inthis region. The ASTN data may also provideinformation on the activity of the Mediterraneanbasin. The ASTN configuration aIlows us to

Table 2

Algerian Telemetred Seismological Network (see Fig. 4); the names in roman, non-Ítalic characters correspond to the stationswhich have been operational since October 1993

Station Code Latitude Longitude Elevation Component(m) (SSI, 1 Hz)

BENI-RACHED EBER 36°17.43'N 01°31.81'E 636 Spz n eDj. Bou Maâd EBOM 36°25.33'N 02°12.77'E 1225 SpzDj. Bou Yalou EBYL 36°25.45'N 01°49.95'E 1051 SpzDj. Tachoubent ETHB 36°01.47'N 01°43.80'E 1070 SpzDj. Bou Ahmed EBHM 36°22.63'N 01 °04.55' E 829 SpzDj. Saâdia ESAD 35"55.00'N 01°21.43'E 890 SpzDj. Mahouada EMHD 36°12.05'N 02°57.18'E 1250 SpzDj. Tanoua ETAN 35°54.50'N 02°20.15'E 1595 Spz

ALGER-BOUZARÉAH AABA 36°48.1O'N 03°02.1O'E 345 Spz n eDj. Djouab ADJB 36°09.46'N 03°26.28'E 1140 SpzDj. Ketaf AKET 36°02.82' N 03°52.93'E 1428 SpzDj. Tarf ATAF 35°52.42'N 04°16.63'E 1000 SpzMt. Rhoder AMRH 35°51.43'N 04°56.33'E 1530 SpzKef Ayad AKAY 36°18.38'N 04°56.12'E 1485 SpzAzrou n'taguat AAZO 36°28.18'N 04°05.32'E 1920 Spz

CONST ANTINE CCST 36°22.20' N 06°36.75'E 680 Spz n eDj. Djama Kebir CDKB 36°50.00'N 06°46.62'E 620 SpzDj. Manchoura CMAH 36°37.50'N 07°25.18'E 795 SpzDj. Ababsia CABS 36°16.40'N 07°28.67'E 1025 SpzDj. Teioualt CTEI 36°O3.78'N 06°24.38'E 1285 SpzKef el Ahmar CKHR 36°01.00'N 05°30.73'E 1280 SpzBou Andas CBND 36°31.65' N 05°07.53'E 1575 SpzDj. Bou Afroun CDFR 36°32.70'N 05"52.62' E 1187 Spz

ORAN-SANTA CRUZ OSCZ 35°42.60'N 00039.60'W 405 Spz n eDj. Kef Guellal OKGL 36°02.28' N 00038.58'E 560 SpzDj. Guires OJGS 35°30.27'N 00044.98'E 920 SpzDj. Berber OJBR 35°35.01'N 00020.70'E 800 SpzDj. Kodjel OKJL 35"02.43' N 00009.88'E 1075 SpzDj. Midouna OMID 35°16.80'N 00011.40'W 745 SpzDj. Bou letas a OBLS 34°58.50'N 00026.52'W 1053 SpzDj. Tessala OTSS 35°16.90'N 00047.65'W 1055 Spz

a Not operational.

M. Bezzeghoud et aI. / Physics of the Earth and Planetary Interiors 84 (1994) 235-246

record local activity such as the Rouina earth-quake described below. AlI the foreshocks andaftershocks, even those of weak magnitude, havebeen recorded and the resolution of the epicen-traI determination was satisfactory. The magni-tude of a seismic event is calculated using thesignal duration and the epicentral distance withthe formula (CRAAG, unpublished, 1981)

M = -1.9 + 2.8 log T for D smaller than 40 km

M = 1.2 + 2.210g T + 0.0033D

for D ranging between 40 and 200 km

where T is the signal duration in seconds and Dis the epicentral distance.

4. Case-study of Rouina earthquake

The Rouina earthquake which occurred at20:21 h GMT on 19 January 1992 had M = 5.2and a hypocentral depth of 9 km. This seismicevent was recorded clearly by the eight stations ofthe Chellif sub-net centred at Beni-Rached (seeFig. 5 below), and the location was given as36°12.74'N,Olo51.55'E.

4O

Velocity (km/s)5 6

241

Table 3Velocity models used in this study; r.m.s., erh and erz valuesare mean errors computed from ali Rouina seismic events

The events of this earthquake were locatedusing the HYPOINVERSE program (KIein,1978), based on an appropriate seismic velocitystructure and using data from the local networks.The velocity models for the EI Asnam regiondetermined by Djeddi (1987) and Ouyed et ai.(1981), denoted Model A and Model B, respec-tively, are presented in Fig. 4. First, we haveprocessed the Rouina seismic crisis using ModelsA and B, and obtained high values for the meanroot mean square (Lm.s.), epicentral error (erh)and particularly for the mean depth error (erz)(see Table 3). These errors were due to thedifferences in the network size between our re-gional network and those used by Ouyed (1982)and Djeddi (1987). To take into account the re-

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Fig. 4. Velocity models used jn this study. The details are given in the texto

Velocity model r.m.s. erh erz

B (Ouyed, 1982) 0.4 6.5 24.9A (Djeddi, 1987) 0.2 5.7 45.6C (this study) 0.1 2.2 10.0D (this study) 0.1 3.3 7.0

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M. Bezzeghoud et aI. / Physics of the Earth and Planetary lnteriors 84 (1994) 235-246

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M. Bezzeghaud et ai. / Physics af the Earth and Planetary lnteriars 84 (1994) 235-246

1.5°

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2.0° 2.5°

Tipasa

36.5°

2 3 4 5 6

~ ~ illIIll1 ESJ ~........ ::::::::::::::

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Fig. 6. Geological map. 1, Faults; 2, Cretaceous; 3, Oligocene; 4, Miocene; 5, Jurassic; 6, Pliocene; white are as, Quaternary(modified from Ouyed, 1982). The El Asnam thrust fault (continuous line) and Rouina earthquake epicentre (full star) are alsoincluded.

gional aspect of our network, we locate the events

in a velocity model with a two-Iayer crust (Vp 5.5km s-1 to 12 km depth, and 6.5 km s-1 at greaterdepths) over a Moho at 30 km depth compatiblewith Models A and B. The velocity for the lowerlayer is fixed at 8 km s-1. Various tests have beenperformed on these parameters, with the aim ofminimizing r.m.s. and errors in the location pro-cedure for the 33 events of the sequence.

Several studies (Lyon-Caen et aI., 1988; Dor-

bath et aI., 1992) have shown that the locations ofepicentres are not very dependent on the velocitymodel if the network covers the epicentral zonereasonably welI. As this is the case in our configu-ration (Fig. 5), we are confident in the results onlocation and uncertainties on location, but depthis poorly constrained, probably owing to lack of Swaves. The crustal velocity model determinedfrom the first ATSN data would be improvedusing alI the data of future seismic events.

Fig. 5. Epicentrallocations of main shock (full star, ATSN location; open star 1, NEIC location; open star 2, EMSC location), andof foreshocks and aftershocks. (a) Map view and focal mechanism of the main shock «1>1= 277, 1i1= 85, AI = 11; <1>2= 186, 1i2= 79,A2= 175; <1>1'1i1 and AI represent the focal plane close to the direction given by the distribution of aftershocks). The lowerhemisphere is shown; o, -, dilatational and compressional first-motion readings, respectively. The refracted P waves are indicatedby stars. The upper right box shows the Beni-Rached sub-net used in this study; the full square represents the epicentral region. (b)Cross-section of the distribution of foreshocks and aftershocks; line af view is along the strike determined in this study. (c)Cross-sectian of the distributian af fareshacks and aftershacks; line af view is perpendicular ta the strike determined in this study.(d) Beni-Rached sub-net used in this study; ., epicentral regian.

244 M Bezzeghoud et ai. / Physics of the Earth and Planetary lnteriors 84 ([994) 235-246

Eight events occurred before the main shock;two of them had a magnitude greater than 4.0(Fig. 5(a)), the first at 12:25 h GMT (M = 4.7),and the second at 13:00 h GMT (M = 4.3). Themain shock was followed by a total of 26 after-shocks (1.5 « M « 5.2), until 23 January. The con-

ofiguration of the Chellif sub-net gives very goodprecision in the location of the main shock(36°12.74'N, Olo51.55'E, depth 9 km, withr.m.s. = 0.12s, erh 0.7 km and erz 1.1 km), andmost of the epicentres of foreshocks and after-shocks are given with an r.m.s. « 0.17 s, erh « 2.5km and erz « 3.7 km. The epicentres of the mainshock given by the European Mediterranean Seis-mological Center (EMSC) and the NationalEarthquake Information Center (NEIC) are about10 km away from that obtained with the ATSNand from the distribution of aftershocks (Fig.5(a)). This demonstrates rather well the impor-tance of local networks for improving locationprecision. This is fundamental for any furtherseismotectonic interpretation of the seismic activ-ity in northern AIgeria and to darify the complexboundary of Mrican and European plates.

Fig. 5 presents a map view with horizontal andvertical cross-sections of the spatial distributionof foreshocks and aftershocks. This figure showsan elongated zone of about 4 km length trendingSE-NW apparently at about 65°W (Fig. 5(a)).The entire sequence of events shows a patternwith activity at depth between 5 and 10 km (Figs.5(b) and 5(c)). We note that no seismic eventsappear above 5 km depth.

The mechanism of the main shock determinedfrom P-wave first motion indicates a thrust faultwith a large component of strike-slip movementrotated towards the west (Fig. 5(a)). This mecha-nism is poorly constrained because the first mo-tion determinations are based on a few P* waves(P waves refracted at the first discontinuity). Nev-ertheless, this focal mechanism is in agreementwith the stress direction (P-axes) deduced fromanalysis of aftershocks and the focal solution ofthe M = 7.3 EI Asnam earthquake of 10 October1980 (e.g. Ouyed et aI., 1981; Ouyed, 1982; De-schamps et aI., 1982) and the M = 6.0 Tipasa-Chenoua earthquake of 29 October 1989 (Be-zzeghoud et aI., 1990; Mroun and Azizi, 1992;

Mroun et aI., 1992). The P-axes are nearly nor-mal to a plate boundary, with a NNW-SSE direc-tion, as shown recently by Udias and Buforn(1991) for the western Mediterranean region. Thisdirection is compatible with the convergence ofthe European and Mrican plates. The stressregime of this region deduced from the focalsolutions (for the EI Asnam, Tipasa-Chenoua andRouina events) is of NW-SE horizontal compres-sional stresses, generated from the collision ofthe Mrican and European plates, and is consis-tent with a pole of rotation for Mrica of 22.7°N,28.9°W (from McKenzie, 1972).

The Rouina seismic activity seems to be re-lated to a fault trending N1O0W dose to theRouina earthquake epicentre, as shown on thegeological map presented in Fig. 6. This activefault (lhe Rouina fault) is situated about 70 kmeast of the EI Asnam thrust fault. The seismicactivity in this region (Fig. 2) and this preliminarystudy of the Rouina aftershocks show that it ispossible that the Rouina system of blind faultscrosses the EI Asnam major fault.

5. Conclusion

The ATSN needs further expansion and im-provement to enhance our assessment and under-standing of Algerian seismicity and seismotecton-ics. For instance, the present configuration of theATSN needs additional stations in the south,along the South Atlas "Flexure". In addition toland-based stations, seismological coverage ofvarious parts of the region would be greatly im-proved by indusion of four ocean bottom seismo-graphs (OBS) to the national network along thecoastal margin, as proposed by Adams andBarazangi (1984). This offshore network will helpus to locate correctly the numerous recordedmarine seismic events. Most of them are of mag-nitude less than 4.5 and occur along tectonicaccidents that are prolongations of land struc-tures (Bezzeghoud et aI., 1990; Mroun and Azizi,1992; Mroun et aI., 1992).

To modernize the ATSN, we have recentlyreceived financial support from the World Labo-ratory (WorldLab) to equip our network with a

M. Bezzeghaud et ai. / Physics ai the Earth and Planetary lnteriars 84 ([994) 235-246

data acquisition system, which will provide uswith easy and rapid epicentre location.

The case-study of the Rouina earthquake pre-sented above (for the foreshocks in particular) isan example of the performance of a telemeteredseismological network. Seismic activity studiesperformed by the ATSN can contribute to solveseismotectonics analysis in northem Algeria; forexample, seismic events can be more preciselylocated, and can be related to mean tectonicfeatures. However, the ATSN will also constitutea good support to the European networks interms of constraint of events that occur in South-em Europe, and particularly in the westemMediterranean Sea.

Acknowledgements

We thank Anne Deschamps for her reviewsand recommendations during the preparation ofthis manuscript. We are grateful for the benefi-cial suggestions of Raul Madariaga and MarkNoble. We also thank the network team-D.Alni, F. Chaoui, A. Deramchi, A. Ferkoul, S.Haned, R. Izarar, K. Lammali, M. Oudahmane,H. Sefta and K. Talbi-for their technical sup-port. We are indebted to the the Arab Fund forEconomic and Social Development and the Is-lamic Development Bank for the Programme forAssessment and Mitigation of Earthquake Risk inthe Arab Region (PAMERAR) on behalf of UN-ESCO as the executing agency. This work wassupported by the Algerian Ministry of the Inte-rior. Special thanks are due to A. Mekki andS.M.S. Si Ahmed from the Ministry of the Inte-rior.

References

Adams, R.D. and Barazangi, M., 1984. Seismotectonics andseismology in the Arab region: a brief summary and futureplans. Buli. Seismol. Soc. Am., 74: 1011-1030.

Afroun, N. and Azizi, D. 1992. Analyse des répliques duséisme du Mont Chenoua (Algérie) du 29 Octobre 1989(M = 6.0). Mémoire d'lngénieur d'Etat en Géophysique,Université des Sciences et de Ia Technologie HouariBoumedienne (USTHB), AIger, 54 pp.

245

Afroun, N., Azizi, D., Bezzeghoud, M., Bounif, M.A andBoughacha, M.S., 1992. Le séisme du Mont Chenoua(AIgérie) du 29 Octobre 1989 (M = 6.0). Analyse du chocprincipal et des répliques. geme Séminaire National desSciences de Ia Terre, 25-27 October 1992, Université deTlemcen, Algeria, p. 8.

Ait Messaoud, A and Mokrane, A, 1992. Contribution à Iaconnaissance de Ia macrosismicité de l'AIgérie de 1971 à1989. Mémoire d'lngénieur d'Etat en Géophysique,USTHB, Alger, 138 pp.

Ambraseys, N.N. and Vogt, J., 1988. Material for the investi-gation of the seismicity of the region of AIgiers. Eur.Earthquake Eng., 3: 16-29.

Argus, D.F., Gordon, R.G., DeMets, C. and Stein, S., 1989.Closure of the Africa-Eurasia-North America plate mo-tion circuit and tectonics of the Gloria fault. J. Geophys.Res., 94: 5585-5602.

Benhallou, H., 1985. Les catastrophes seismiques de Ia régiond'Echelif dans le contexte de Ia seismicité historique del'Algérie. These es-Sciences, USTHB, Alger, 295 pp.

Bezzeghoud, M., Bounif, A, Boughacha, M.S. and Benhallou,H., 1990. Résultats préliminaires du séisme du MontChenoua (Algérie, M = 6.0) du 29 Octobre 1989. 8emeSéminaire National des Sciences de Ia Terre, 16-18Décember, Constantine, Université de Constantine, Alger,p.9.

Bezzeghoud, M., Ayadi, A, Séba"i, A, Ait Messaoud, M.,Mokrane, A and Benhallou, H., 1994. Seismicity of Alge-ria between 1365 and 1989: map of maximum observedintensities (MOI). Rev. Geofis., in press.

Bounif, MA., 1990. Etudes sismotectoniques en Algérie dunord: contribution a I'étude d'un tronçon de Ia chainetelienne à partir des répliques du séisme de Constantinedu 27 Octobre 1985. These de Magister, USTHB, Alger,155 pp.

Deschamps, A, Gaudemer, Y. and Cisternas, A, 1982. TheEI Asnam, AIgeria, earthquake of 10 October 1980: multi-ple-source mechanism determined from long-periodrecords. BulI. Seismol. Soe. Am., 72(4): 1111-1128.

Deschamps, A, Bezzeghoud, M. and Bounif, A, 1991. Seis-mological study of the Constantine (Algeria) earthquake(27 October 1985). Seismicity, seismotectonics and seismicrisk of the Ibero-Maghrebian region. In: J. Mezcua and AUdias (Editors), Publication I.G.N., Série Monografia No.8. Madrid, pp. 163-173.

Djeddi, M., 1987. Séisme d'Ech-Chllef (10-10-80), études de Iacrofite et de son hétérogénéité à l'aide des répliques.Utilité des stations tridirectionnelles. These de Magister,USTHB, Alger, 180 pp.

Dorbath, L., Dorbath, c., Rivera, L., Fuenzalida, A, Cister-nas, A., Tatevossian, R., Aptekman, J. and Arevief, S.,1992. Geometry, segmentation and stress regime of theSpitak (Armenia) earthquake from the analysis of theaftershock sequence. Geophys. J. Int., 108: 309-328.

Giardini, D., Boschi, E., Mazza, S., Morelli, A, Ben Sari, D.,Najid, D., Benhallou, H., Bezzeghoud, M., Trabelsi, H.,Hfaidh, M., Kebeasy, R.M. and Ibrahim, E.M., 1992. Very

246 M. Bezzeghoud et ai. / Physics of the Earth and Planetary lnteriors 84 (1994) 235-246

broad-band seismology in northern Africa under the Med-Net project. Tectonophysics, 209: 17-30.

Klein, F.W., 1978. Hypocenter location program HYPOIN-VERSE. US Geol. Surv. Open-File Rep. No. 78-694, 102pp.

Lyon-Caen, H., Armijo, R., Drakopoulos, J., Baskoutass, J.,Delibassis, N., Gaulon, R., Kouskouna, V., Latoussakis, J.,Makropoulos, K., Papadimitriou, P., Papanastassiou, D.and Pedotti, G., 1988. The 1986 Kalamata (South Pelopon-nesus) earthquake: detailed study of a normal fault, evi-dences for east-west extension in the Hellenic Arc. J.Geophys. Res., 93: 14967-15000.

McKenzie, D., 1972. Active tectonics of the Mediterraneanregion. Geophys. J.R. Astron. Soc., 30: 109-185.

Ouyed, M., 1982. Le tremblement de terre d'EI-Asnam du 10octobre 1980. Etude des répliques. These de 3eme cycle,Université Scientifique et Médicale de Grenoble, 227 pp.

Ouyed, M., Meghraoui, M., Cisternas, A., Deschamps, A.,Dorel, J., Fréchet, J., Gaulon, R., Hatzfeld, D. and Philip,H., 1981. Sismotectonics of the EI Asnam earthquake.Nature, 292: 26- 31.

Romanowicz, B., Karczewski, J.F., Cara, M., Bernard, P.,

Borsenberger, J., Cantin, J.-M., Dole, B., Fouassier, D.,Koenig, J.-c., Morand, M., Pillet, R., Pyrolley, A. andRouland, D., 1991. The GEOSCOPE program: presentstatus and perspectives. Buli. Seismol. Soc. Am., 81(1):243-264.

Rothé, J.P., 1950. Les séismes de Kherrata et Ia sismicité del'Algérie. Bulletin du Service de Ia Carte Géologique deI'Algérie, 4eme Série, Alger, Géophysique, No. 3, 40 pp.

Roussel, J., 1973a. L'activité sismique en AIgérie de 1951 à1970 incluso Buli. Soc. Hist. Nat. Afr. Nord, 64(3,4): 185-210.

Roussel, J., 1973b. Les zones actives et Ia fréquence desséismes en Algérie (1716-1970). Buli. Soc. Hist. Nat. Afr.Nord, 64(3,4): 211-228.

Udias, A. and Buforn, E., 1991. Regional stress along theEurasia plate boundary derived from focal mechanisms oflarge earthquakes. Pageoph, 136(4): 433-448.

Yielding,G., Ouyed, M., King, G.c.P. and Hatzfeld, D., 1989.Active tectonics of the Algerian Atlas Mountains - evi-dence from aftershocks of the 1980 EI-Asnam earthquake.Geophys. J. Int., 99: 761-788.

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