Present-day state of stress in northern Morocco from focal mechanism analysis

The use of focal mechanisms of micro-earthquakes and moderate teleseisms in the Al Hoceima area (northern Morocco) enables the determination of the state of stress in the southern part of the Gibraltar arc. Two different states of stress were determined: (1) a ENE-WSW extension in the Imzouren area (probably with similar magnitudes of σ2 and σ1) which may be controlled by pre-existing structures, and (2) a strike-slip regime in Beni Boucetta, Tamassint and Beni Abdallah areas (σ1 NNW-SSE, σ3 ENE-WSW in the two first areas and σ1 NE-SW, σ3 NW-SE in the latter). Contrary to recently proposed ideas, the mean state of stress determined with the help of moderate teleseisms corresponds to a strike-slip regime with a NNW-SSE oriented main compressional axis and a ENE-WSW horizontal extension, similar to the stress field determined from neotectonic studies, and somewhat different from that determined from the El Asnam aftershock sequence of 1980.