The Al Hoceima (Morocco) earthquake of 24 February 2004, analysis and interpretation of data from ENVISAT ASAR and SPOT5 validated by ground-based observations

Abstract

The magnitude Mw = 6.3 earthquake in Al Hoceima, Morocco of 24 February, 2004 occurred in the active plate boundary accommodating the oblique convergence between Africa and Eurasia. Three different sets of estimates of its source parameters have already been published. We try to resolve the discrepancies between them by using additional data including two remote sensing satellite systems (ENVISAT and SPOT5). Using a model with a dislocation in an elastic half-space, we constrain the source parameters. The hypothesis of two subevents on distinct faults as inferred from seismological inversions is confirmed here by adopting a cross-fault mechanism. The rupture began on a left-lateral strike-slip fault striking at N10° azimuth with 90 cm of horizontal slip and then transferred to a right-lateral strike-slip fault striking at N312° azimuth with 85 cm of horizontal slip. The first fault is at 500 m depth from the free surface and the second fault is at 3 km depth. This model is consistent with ground-based observations, including GPS, seismology, and mapped surface fissures. The pair of faults activated in 2004 appears to constitute part of a complex seismogenic structure striking NNE-SSW that separates the Rif tectonic blocks.