Citation: | Shao, X. H., Yao, H. J., Liu, Y., Yang, H. F., Tian, B. F., and Fang, L. H. (2022). Shallow crustal velocity structures revealed by active source tomography and fault activities of the Mianning–Xichang segment of the Anninghe fault zone, Southwest China. Earth Planet. Phys., 6(2), 204–212. doi: 10.26464/epp2022010 |
The Anninghe fault is a large left-lateral strike-slip fault in southwestern China. It has controlled deposition and magmatic activities since the Proterozoic, and seismic activity occurs frequently. The Mianning−Xichang segment of the Anninghe fault is a seismic gap that has been locked by high stress. Many studies suggest that this segment has great potential for large earthquakes (magnitude >7). We obtained three vertical velocity profiles of the Anninghe fault (between Mianning and Xichang) based on the inversion of P-wave first arrival times. The travel time data were picked from seismograms generated by methane gaseous sources and recorded by three linearly distributed across-fault dense arrays. The inversion results show that the P-wave velocity structures at depths of 0−2 km corresponds well with the local lithology. The Quaternary sediments have low seismic velocities, whereas the igneous rocks, metamorphic rocks, and bedrock have high seismic velocities. We then further discuss the fault activities of the two fault branches of the Anninghe fault in the study region based on small earthquakes (magnitudes between