Seismogenic environments of earthquakes on the southeastern margin of the Tibetan Plateau revealed by double-difference tomography

The uplift and expansion of Tibetan Plateau has dramatically changed the tectonics, climate and environment of Asia, and has caused high seismic hazards at its southeastern margin as well. To better understand the generating mechanisms of regional damaging earthquakes and the plateau crustal material expansion, a high resolution crustal P-wave velocity (VP) model is obtained by double-difference tomography using the updated dataset of dense seismic array deployed in the southeastern margin of the Tibetan Plateau (SETP). The results show sig-nificant lateral heterogeneities in the upper crust and two prominent low-VP belts are revealed at mid-lower crust (20-35 km), which has a good correspondence with the major faults and has potential for the mid-lower crustal flow. Although almost all the large earthquakes are located at the boundary between high-and low-VP anomalies related to the two low-VP belts, the seismogenic mechanisms are somewhat different. Ludian and Yiliang earthquakes may be associated with the eastern low-VP anomalies in mid-lower crust, which decouples the upper and lower crust and drags the upper brittle crust leading to sinistral strike slip and thrust accompanied with dextral strike slip earthquakes, respectively. Yangbi earthquake is mainly caused by the upper crustal movement and also probably related to the compressive tectonic loading from western material migration of low-VP anomalies in mid-lower crust. As for Changning earthquake, the seismotectonics are mostly affected by water injection at slat mines. Whether the fluids or low-VP anomalies in mid-lower crust, they may weaken the seis-mogenic layer and make the stress concentration easier. Our results provide a new perspective to study the seismogenesis that the inhomogeneity of upper crust and the mechanically weak materials in mid-lower crust play an important role in triggering and generating crustal damaging earthquakes in SETP, which also helps illuminate the uplift and deformational mode of the plateau.

Automated summary

The uplift and expansion of the Tibetan Plateau have had a significant impact on the tectonics, climate, and environment of Asia, as well as causing high seismic hazards at its southeastern margin. A high-resolution crustal P-wave velocity (VP) model was obtained using double-difference tomography, revealing lateral heterogeneities in the upper crust and prominent low-VP belts in the mid-lower crust. The study provides new insights into the generating mechanisms of damaging earthquakes and the role of crustal inhomogeneity and mechanically weak materials.