Seismicity and state of stress in NE Arabia

Abstract

Eastern Arabia exhibits low seismic activity although damaging earthquakes are historically known. Despite the proximity to convergent plate boundaries in the Arabia–Eurasia collision zone, the state of stress in northern Oman with its persistent topography of the Oman Mountains (OM) remains enigmatic. We have revised the earthquake catalogue of northern Oman and confirm the detection and location accuracy of the permanent network by comparison with a temporarily densified network across the OM. For the first time, we infer focal mechanisms (FM) for earthquakes in Oman from P-wave polarities. Seismic activity is high in the Northern OM but diminishes rapidly south of 24.5° N. In the Central and Eastern OM, low-magnitude earthquakes occur along topography bounding faults with mostly transtensional FM. Offshore, seismicity follows NE-trending lines in extension of the Semail Gap and the Masirah Fault Zones, up to the Makran trench. Except for an isolated patch of repeated small-magnitude earthquakes, the western Makran trench is seismically quiet. Inversion of FM confirms a NE–SW direction of maximum horizontal stress that aligns with Arabia–Eurasia convergence. In the Central and Eastern OM, maximum horizontal and vertical stresses are balanced. The topography of the OM appears, therefore, not to be generally sustained by compressional forces.