The Zemmouri-Boumerdes Earthquake of May 21st, 2003, Mw=6.8: Source Parameters and Rupture Propagation Study from Teleseismic Data.

Abstract

On May 21, 2003, occurred the Zemmouri-Boumerdes earth- quake (Mw=6.8, depth 7km) in a zone characterized by rela- tively moderate and diffuse seismicity. The main shock have been relocated at Zemmouri el Bahri (36.83N,3.65E) close to the continent and the aftershocks sequence (CRAAG mobile stations) gives a distribution in the NE-SW direction with most of the epicenters located on the continent or near the coast. Source mechanism of this event, including fault plane solutions, waveform inversion, spectral analysis, fault slip distribution and displacement field model, is analysed. The results show pure thrusting motion (plane striking 64o and dipping 50o to the SSE) with a STF formed by two main asperities at shallow depth (7 and 4km respectively) and Mo=1.3x1019Nm. Slip distribution show an E-W asymmetric bilateral rupture process. The rupture front through the region (Zemmouri-Boumerdes) of high slip (206 cm) and maximum moment released (50% of the total Mo), in direction of Algiers, produced a pulse of energy about 8s after the start of the earthquake. This strong subevent located at SW of the hypocenter started at 4.0km depth and probably broke the surface. The vertical displacements estimated from the fault slip distribution model, the main shock relocation and the aftershock distribution suggest a fault close to the coastline as origin of the Zemmouri-Boumerdes earthquake.