Fault-Slip Potential near the Deadly 8 September 2023 Mw 6.8 Al Haouz, Morocco, Earthquake

Abstract

Thousands were killed by the 8 September 2023 Mw 6.8 Al Haouz, Morocco, earthquake in the western High Atlas (WHA) Mountains. To identify the faults and fault orientations most likely to host aftershocks and future large earthquakes, regional crustal stress is estimated from focal mechanism inversions, and the associated slip potential of known and suspected active faults is modeled. North–south shortening is accommodated by a mix of reverse, oblique-reverse, and strike-slip motion. As such, many fault orientations are well aligned for slip: steep north-northeast-, south-southwest-, southeast-, or northwest-strik-ing planes, gently (∼15°–50°) dipping east-and west-striking planes, and all orientations between. Nearly all mapped regional faults have high slip potential. By contrast, steep east–west and nearly all north–south faults are relatively stable, although low friction in the anomalously hot lower crust of the WHA, such as due to partial melt, could allow slip on these suboptimal faults as well.