The 2023 Mw 6.8 Adassil Earthquake (Chichaoua, Morocco) on a steep reverse fault in the deep crust and its geodynamic implications

Abstract

The Mw 6.8 Adassil earthquake that occurred in the High Atlas on September 8, 2023, was a catastrophic event that provided a rare opportunity to study the mechanics of deep crustal seismicity. This research aimed to decipher the rupture characteristics of the Adassil earthquake by analyzing teleseismic waveform data in conjunction with interferometric synthetic aperture radar (InSAR) observations from both ascending and descending orbits. Our analysis revealed a reverse fault mechanism with a centroid depth of approximately 28 km, exceeding the typical range for crustal earthquakes. This result suggests the presence of cooler temperatures in the lower crust, which facilitates the accumulation of tectonic stress. The earthquake exhibited a steep reverse mechanism, dipping at 70°, accompanied by minor strike-slip motion. Within the geotectonic framework of the High Atlas, known for its volcanic legacy and resulting thermal irregularities, we investigated the potential contributions of these factors to the initiation of the Adassil earthquake. Deep seismicity within the lower crust, away from plate boundaries, calls for extensive research to elucidate its implications for regional seismic hazard assessment. Our findings highlight the critical importance of studying and preparing for significant seismic events in similar geological settings, which would provide valuable insights into regional seismic hazard assessments and geodynamic paradigms.

Keywords

• adassil earthquake
• seismogenic fault
• source depth
• interferometric synthetic aperture radar (insar)
• seismic waveform
• joint inversion