Le séisme du 21 mai 2003 de Zemmouri : Résultats sismotectoniques (Seismotectonics and aftershocks

sequence relocation of the 2003 Zemmouri earthquake)

Ayadi, C. Dorbath, A. Harbi, S. Maouche, A. Bounif & H. Beldjoudi

-10°

-10°

-5°

-5°

0°

0°

5°

5°

10°

10°

15°

15°

35° 35°

40° 40°

1 cm/yr.

TheThe Tell Atlas of Tell Atlas of AlgeriaAlgeria

0.5°

0.5°

1° 1.5°

1.5°

2°

2°

2.5°

2.5°

3°

3°

3.5°

3.5°

4°

4°

4.5°

4.5°

5.5° 35.5

36° 36°

6.5° 36.5

37° 37°

7.5° 37.5

081894 111582 101080

110880101080

110581

120580021481 020181

101380 103188

020990

102989 090496 052903 052703052103

052203 052203

5.0 5.8 6.8 4.7 4.8

5.8 5.0 6.1

5.1 7.3 5.0

5.0 4.8 5.7

5.2 5.6

4.4

6.0 5.8

Mediterranean Sea

Cheliff

Bas

in

El Asn

am

Mitidja

Kabylie

Alger

High Plateaux

17161365

HistoricalHistorical SeismicitySeismicity of of AlgeriaAlgeria

(Rothé, 1950; Benouar 1994)

Major earthquakes near Algiers: 1365, 1716 (seismic sequence)

The ZemmouriEarthquake of 21 May 2003

Mw = 6.8Fault length = 50 kmHypocentral depth = 7 kmMo = 2.86 1026 dyne.cmN 54° 47°SE, 88 rake (NEIC)

Severe damage inland

Coastal uplift

3 2°

3.2°

3 6°

3.6°

4°

4°

36.6° 36.6°

36.8° 36.8°

37° 37°

52103

52103

52103

52103

52203

5220352203

52203

52203

52303

52403

52403

52403

52703

52803

52903

MainshockMainshock & main & main aftershocksaftershocks relocationrelocation21 21 –– 30 May 200330 May 2003

EMSC

USGSCRAAG

AlgerAlger

Baraki

Meftah

ReghaiaBoumerdes

S. El Had

Draa el Mizan

Zemmouri

Cap Djinet

DellysDellys

Relocation Relocation procedureprocedure

2. HypoDD (Waldhauser & Ellsworth, 2000)

Seismic records of Italian, Southern France, Spanish,& Algerian permanent and portable stations

Three master events 27, 28 and 29 May 2003

1. Simple double difference method

Δ = 0.02° from hypoDD relocation and permanent-portable stations relocation

P

S

S

Selected events: Rms < 0.2 sec, Erh < 2 km, Erz < 2 km

~ 1000 events25 – 30 May 2003

557 selected events

μ for all events: Rms < 0.09 sec , Erh < 1.32 km, Erz < 1.91 km

ReadingsReadings of of selectedselected seismicseismic recordsrecords

Aftershocks distribution following the Zemmouri earthquake of may 21st 2003. More than 500 events have been used.

Cross Section showing the distribution with depth of the aftershocks sequence along the azimuth N150°perpendicular to the direction of the considered fault and the N60° along the considered fault.

Dellys Tigzirt

BoumerdesAlgiers

Tipaza

M i t

i d

j a

B a s i

n

M e d e a B a s i n

T i z i o u z o u B a s i n

B l i d

a m

o u n t s

Zemmouri

Blida

ArbaaBoufarik

Thenia

K a b y l i e b a s e m e n t

21/05/2003

N 3° 4°

37°

36°3

0’

VI

VII

IXX X

X

X

X

VIII

25 km

M e d i t e r r a n e a n

sea

B.El Bahri

Basement Flysh Ante-Neogene Miocene Volcanism Pliocene Quaternary Marine terraces

The Zemmouri earthquake (Mw 6.8) has a coastal epicentral relocation obtained from three master events

ConclusionConclusion

Fault geometry, focal depth and seismic moment suggest a fault trace between 5 and 8 km from the coastline

Aftershocks distribution indicates a thrust faultgeometry with deeper seismic events in the NE faultsection

Seimic events distribution and faulting geometry are consistent with the coastal uplift and regional active tectonics

Relocation of the main shock (white star: using mater event (may 27, 28 and 29), large circle: using HypoDD program) and the major aftershocks (Ml >3) from may 21st to May 30th. Black stars: international institutions locations. Insert (lower right corner) shows the western Mediterranean seismic stations used for relocation. Errors on the relocation using Singular Value Decomposition method are shown by ellipses