The Al Hoceima earthquake of May 26, 1994 and its aftershocks: a seismotectonic study

Abstract

The present paper focuses on the moderate earthquake that occurred on May, 26, 1994, at 8 h 27 min, which caused great damage and two deaths. The epicentre of the main shock was located at 35.280N, 3.990W. The focal depth was 13 km, and the magnitude (Md) attained 5.6. A field survey of the earthquake effects showed that the maximal intensity (VIII-IX EMS) follows an elongated corridor trending NNE-SSW, where 80% of the constructions were destroyed. During the 14-day survey carried out with the help of the temporary network established in the area, 512 shocks were located. The best constrained epicentres (68) are shallow and are largely distributed over a NNE-SSW trending cluster along an almost-vertical plane. Focal mechanisms determined for the main shock and for the 7 largest aftershocks, correspond to strike-slip faulting with a reverse (main shock and one aftershock) or normal component (6 events). The P axes have a NNW-SSE trend, with variable plunge, whereas the T axes are ENE-WSW with a slight plunge. The state of stress determined with the help of these mechanisms corresponds to a strike-slip regime with s1 oriented NNW-SSE and s3 ENE-WSW, which is in conformity with previous studies. The present study also shows that the Nekor fault remained inactive during the seismic crisis of 1994, as during the previous surveys, and this casts some doubt on the present-day role of this major fault. Instead, as proposed by some authors, a seismic zone trending NNE-SSW may be related to the faults of the same trend that appear to cross the Al Hoceima area towards the Alboran Sea.