The 2003 Boumerdes, Algeria Earthquake: Regional Moment Tensor Analysis

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°) of 24 thrust and four strike-slip events is consistent with Africa-Eurasia plate motion (330°). The main shock hypocenter at 8–10 km depth at the coastline and its shallow southward dip (25° ± 5°) 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.