Abstract:
Objective The Tangra Yumco Rift (TYR) area, located in the central Qinghai-Xizang Plateau, is characterized by unique tectonic features and frequent seismicity. This study aims to determine the focal mechanism, focal depth, characteristics of the regional tectonic stress field, and the seismogenic dynamic background of the Ms 3.2 earthquake (Event ID: 20231023224722) that occurred at the intersection of the Zhala Fault and the N−S striking normal fault in this region.
Methods The Cut−and−Paste (CAP) method was employed to invert the focal mechanism solution, revealing a strike−slip mechanism with a normal faulting component. The focal depth was estimated to be 8 km (measured from the surface) using the sPL depth phase.
Results The calculated azimuths of the P− and T−axes for this earthquake are concentrated in the N−S and E−W directions, respectively. The principal compressive and extensional stress axes inverted from historical earthquakes align well with the N−S compression and E−W extension of the regional tectonic stress field. The occurrence of upper−to−middle crustal earthquakes in the TYR is controlled not only by the N−S normal fault system within the rift but also decisively by the regional tectonic stress field of the rift and its adjacent areas.
Conclusions Integrating geological and geophysical observations, we conclude that the regional tectonic stress field and deep structures jointly play a dominant role in the seismogenic process within the TYR. These findings provide crucial seismological evidence for understanding the Cenozoic E−W extensional mechanism in this region.
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