Focal Depths and Mechanisms of Earthquakes in the Himalayan-Tibetan Region

The complexity of the Himalayan-Tibetan lithospheric deformation is evident from extensive seismicity and diverse focal mechanism solutions. Here we investigate the focal depths and fault plane solutions of moderate earthquakes in the Himalayan-Tibetan region by teleseismic waveform modeling and a multi-scale double-difference earthquake relocation method. Shallow earthquakes are widespread across the whole study region. In the central Tibet, earthquakes are restricted to the upper crust and originate dominantly by strike-slip faulting, in agreement with low velocity layers observed previously in the lower crust and strong S-wave attenuation zones observed in the uppermost mantle. In the northern and southern Tibet, where the Asian and Indian plate subduct beneath the central Tibet, earthquakes appear to be distributed throughout the thickness of the crust and exhibit dominantly reverse faulting (Bai et al., 2015a). Intermediate-depth earthquakes are mostly located at the eastern and western Himalayan syntaxes, which reflect the ongoing deformation along the plate interface. The continental slab beneath the Indian-Eurasian collision zone deforms in a more complex manner than the oceanic slab subduction, combining tension, shearing and oblique convergence with plate subduction (Bai et al., 2015b). References Bai, L., Li, G., Khan, N.G., Zhao, J., and Ding, L., 2015a. Focal depths and mechanisms of shallow earthquakes in the Himalayan-Tibetan region, Gondwana Research, accepted. Bai, L., and Zhang, T., 2015b. Complex deformation pattern of the Pamir-Hindu Kush region inferred from multi-scale double-difference earthquake relocations, Tectonophysics, 638: 177-184, doi:10.1016/j.tecto.2014.11.006.