The 2003 Boumerdes, Algeria earthquake: Regional moment tensor analysis

[1] We used regional broadband seismograms to determine seismic moment tensors for the destructive May 21, 2003 Boumerdes (Algeria) M-w = 7.0 earthquake and its larger aftershocks. Fully automatic inversions using near-real time data provided solutions for seven M-w >= 4.7 events within 90 minutes after event occurrence. After adding off-line data, we manually obtained 30 solutions (M-w >= 3.8) from May 2003 to January 2004. All have shallow source depths (6-21 km). The median P-axis orientation (338 degrees) of 24 thrust and four strike-slip events is consistent with Africa-Eurasia plate motion (330 degrees). The main shock hypocenter at 8-10 km depth at the coastline and its shallow southward dip (25 degrees +/- 5 degrees) puts the fault surface trace 15-20 km offshore, consistent with documented seafloor deformation at the base of the continental slope. A main shock rupture length of about 50 km is deduced from first day aftershocks and location of strike-slip events. The strike-slip events probably define the western rupture end and indicate a left-step of main convergence. Fault strike variability of thrust events suggests fault orientation changes and possibly fault segmentation.