Seismotectonics and Earthquake Focal Mechanisms of the Kalabsha Fault Zone, Southwest Aswan, Egypt

Most seismic activities took place along the Eastren Kalabsha Fault Zone and ranged from low to moderate magnitudes. Fault geometry, seismic parameters and stress regime are determined using the focal mechanism solutions and the composite focal mechanism. The main goal of this paper is to gather all focal mechanism solutions for events greater than 3.2 ML from previous studies, and to create new solutions for some events using polarities of first arrivals, as well as unravel the relation of seismicity to the structural architecture of the active Kalabsha Fault Zone. Two nodal planes were revealed by the focal mechanism solutions, one with a right-lateral strike-slip component trending E to ENE and the other with a left-lateral motion trending N to NNW. The directions of tectonic compression (P) and extension (T) are respectively, NNW-SSE and ENE-WSW. Such solutions are consistent well with the main surface rupturing trend of the Kalabsha Fault Zone. According to structural investigations, the Kalabsha Fault Zone is a conspicuous dextral transtensional shear zone rather than a simple wrench fault. Along the E-W strike of the Kalabsha Fault Zone and further east to Nasser Lake for about 100 km, surface topographic expressions and remarkable kinematic indicators are evidenced including intensive degree of shearing, overprinted slickenlines, severe fragmentation, and pulverization reflecting recent seismic activity. The frequent surface rupturing and newly formed slickenside kinematic indicators endorse fault reactivation, pointing to an ENE-WSW and NNW-SSE active fault system.