Focal mechanism and seismogenic mechanism of recent small and medium earthquakes in Tangra Yumco Rift

Earthquakes are common in the Tangra Yumco Rift (TYR), situated in the central Tibetan Plateau, exhibiting typical seismic structural features. An M 3.2 seismic event (20231023224722) was observed by broadband seismic stations at the site of the intersection of the Zhala Fault and the NS-trending normal fault in the northern section of the TYR. The CAP method was employed to identify the seismic mechanism of this earthquake as a strike-slip. The depth of the seismic source was estimated at 8 km (from the surface) using sPL depth phases. The orientations of the earthquake's P and T axes are concentrated in the NS and EW directions, aligning with the principal stress axes derived from historical earthquake inversions and the regional tectonic stress field, characterized by NS compression and EW extension. Subsurface NS faults beneath the TYR also influence seismic event occurrence in the middle and upper crust of the region. The regional tectonic stress field frequently exerts a significant influence on seismic activity, whereas the complex fault intersection also affects seismic activity. Our belief, supported by comprehensive geological and geophysical observations, is that the regional tectonic stress field and deep structure in the TYR predominantly govern the seismic processes in this region. This presents vital seismic evidence for comprehending the east-west extension mechanism in TYR since the Neogene epoch.