Seismicity in northern Tibetan Plateau (INDEPTH IV)
A total of 400 regional earthquakes were located in northern Tibetan Plateau from data recorded by INDEPTH IV and PKU Eastern Kunlun arrays from May 2007 to June 2009. The distribution of these earthquakes is compatible with a continuously deforming Tibetan lithosphere. Most earthquakes occur at a depth range of 0‐15 km, but no event is deeper than 30 km. This observation strongly supports the existence of a hot and weak lower crust beneath the northern Tibet. The crustal seismogenic zone appears slightly thicker beneath the northern Tibet than in the southern plateau, possibly reflecting a difference in the rheological (dry vs. wet) structure of the crust. The absence of lower crustal and uppermost mantle earthquakes in northern Tibet is consistent with a localized asthenospheric upwelling under the Qiangtang and Songpan‐Ganze terranes. Finally, the lack of mantle earthquakes should be fully addressed in any models of subduction in northern Tibet.
Project INDEPTH (International Deep Profiling of Tibet and the Himalaya) is a multidisciplinary geophysical and geological investigation of the Himalayas and Tibet. The passive seismic array of phase IV consisted 98 PASSCAL instruments deployed from May 2007 to June 2009, covering northern Tibetan Plateau.
The spatial and temporal distribution of earthquakes and their depth extent provides crucial information about active tectonics as well as thermal conditions and the mechanical strength as a function of depth. A total of 592 regional earthquakes were located by Hypoinverse-2000. The HypoDD procedure is designed for the relative relocation of close events. We were able to apply this to a subset of 275 events. By combining results we obtained a catalog of 400 earthquakes with horizontal errors less than 10 km and vertical errors less than 5 km.
Epicenters located by INDEPTH IV and Hi-CLIMB projects (black and cyan dots).
Cross section of seismicity across the southern Tibet (the left panel) and the northern Tibet (the right panel).
Reference:
Wei, S., et al. (2010), Regional earthquakes in northern Tibetan Plateau: Implications for lithospheric strength in Tibet, Geophys. Res. Lett., 37(19), L19307, DOI:10.1029/2010gl044800.
Liang, X., et al. (2008), Earthquake distribution in southern Tibet and its tectonic implications, J. Geophys. Res., 113(B12), B12409, DOI: 10.1029/2007jb005101.