Source mechanisms of recent earthquakes in southern Saudi Arabia: New seismic sources to update the Saudi Building Code

Abstract

Abstract Recently in 2020, in southern Saudi Arabia three felt earthquakes occurred in Asir region, in the Khamis Mushait, Ahad Rafidah, and AL-Shuqiq area, of magnitude 3.45, 3.1, and 3.5, respectively, and no large damages were recorded. The most interested event was the earthquake that occurred in Khamis Mushait area, along a lake formed behind the Tadhah Dam (~ 7 km), fearing any damage to the dam's body and the consequent destruction. Moment tensors for each event were computed for determining fault plane solutions, seismic moment, moment magnitude (Mw) and the CLVD ratio, in addition to determining the frequency contents in the waveforms of each event. The obtained focal mechanisms represent different styles of faulting, normal movement with strike slip and strike slip with reverse. These tectonic movements on faults parallel to the Red Sea refer to the tensional forces due to the Red Sea rift system. To identify the reasons behind the occurrence of these events, more than one factor was taken into consideration, which indicated to a natural tectonic movement, with considering the Khamis Mushait event as an induced event due to the lake formed behind the Tandaha Dam. Many previous seismic hazard assessment studies have been conducted in the southern part of the Kingdom, but the locations of these recent seismic sources have not been taken in account in their calculations. Thus, our study provides additional new information related to detecting of new seismic sources in the south of the Kingdom, which contributes to updating studies of seismic risk assessment in this region. In addition, our study pushing us to establishing other additional seismic stations, especially around new seismic sources, which in turn will play a pivotal role in reassessing the seismic hazard in the Kingdom and then updating the Saudi Building Code to mitigate the seismic risk.