Earthquake activity in the Aswan region,Egypt

The November 14, 1981 Aswan earthquake (M _L= 5.7), which was related to the impoundment of Lake Aswan, was followed by an extended sequence of earthquakes, and is investigated in this study. Earthquake data from June 1982 to late 1991, collected from the Aswan network, are classified into two sets on the basis of focal depth (i.e., shallow, or deeper than 10 km). It is determined that (a) shallow seismicity is characterized by swarm activity, whereas deep seismicity is characterized by a foreshock-main shock-aftershock sequence; (b) the b value is equal to 0.77 and 0.99 for the shallow and deep sequences, respectively; and (c) observations clearly indicate that the temporal variations of shallow seismic activity were associated with a high rate of water-level fluctuation in Lake Aswan; a correlation with the deeper earthquake sequence, however, is not evident. These features, as well as the tomographic characteristics of the Aswan region (Awad andMizoue, this issue), imply that the Aswan seismic activity must be regarded as consisting of two distinct earthquake groups.We also relocated the largest 500 earthquakes to determine their seismotectonic characteristics. The results reveal that the epicenters are well distributed along four fault segments, which constitute a conjugate pattern in the region. Moreover, fault-plane solutions are determined for several earthquakes selected from each segment, which, along with the 14 November 1981 main shock, demonstrate a prominent E-W compressional stress.