HR: 14:25h
AN: S22C-04    [PDF]
TI: New Evidence for Strong Lithospheric Mantle: Mantle Earthquakes beneath the Himalayan-Tibetan Collision Zone
AU: * Chen, W
EM: wpchen@uiuc.edu
AF: Dept. of Geology, University of Illinois, Urbana, IL 61801 United States
AU: Yang, Z
EM: zyang1@uiuc.edu
AF: Dept. of Geology, University of Illinois, Urbana, IL 61801 United States
AB: The mechanical strength of lithospheric mantle beneath continents has far-reaching implications for understanding continental dynamics. For two decades, one of the key evidence for a strong lithospheric mantle is the occurrence of intra-continental earthquakes in the mantle, originally discovered beneath southern Tibet in 1981 (Chen et al., JGR, p. 2863). To a large extent, recent debate on this issue hinges on whether BOTH focal depths and crustal thickness are well enough determined in the same region to resolve if earthquakes near the Moho occurred in the mantle. We present a significant amount of new data and a comprehensive compilation of focal depths, fault plane solutions, and crustal thickness in and around the Himalayan-Tibetan collision zone to show that there are a number of mantle earthquakes, reaching a body-wave magnitude of 6, beneath the western Himalayan syntaxis, the western Kunlun, and southern Tibet (near Xigaze). Focal depths for some of these earthquakes reach over 100 km, as evidenced by matching broadband (high-resolution) waveforms. Frequent occurrence of intra-continental earthquakes in the mantle is clear, in situ, evidence that the lithospheric mantle is strong enough to accumulate elastic strain under geological strain rates. (Supported by NSF Continental Dynamics Program, Project Hi-CLIMB.)
UR: http://www.uiuc.edu/~wpchen
DE: 7218 Lithosphere and upper mantle
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
DE: 8159 Rheology--crust and lithosphere
DE: 8162 Rheology--mantle
SC: Seismology [S]
MN: 2003 Fall Meeting