HR: 14:10h
AN: S22C-03    [PDF]
TI: Depths of Earthquakes in the Central Tien Shan
AU: * Roecker, S
EM: roecks@rpi.edu
AF: Dept Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180 United States
AU: Pavlis, G
EM: pavlis@geology.indiana.edu
AF: Dept. Geological Sciences, Indiana University, Bloomington, IN 47405 United States
AU: Vernon, F
EM: flvernon@ucsd.edu
AF: IGPP, UC San Diego, La Jolla, CA 92093 United States
AB: Using a variety of techniques, we relocated local and regional events recorded by the GHENGIS deployment of Broad Band sensors in the central Tien Shan from 1997-2000 in order to determine the extent to which earthquakes occur within the lower crust in the Tien Shan and surrounding regions. We generated probability density functions using a new spherical coordinate adaptation of the Eikonal Equation solver in combination with refined tomographic images which should provide accurate estimates of travel time in this complicated structure. We also used a new algorithm based on the Progressive Multiple Event Location $($PMEL$)$ that associates each event in the catalog with one or more control points in a 3D grid and locates these events with PMEL. The implementation allows us to resolve the traditional bias problem by folding in anomalies computed from a 3D model through a set of matrix projectors. These relocation efforts significantly improve the spatial resolution of the GHENGIS catalog. We find that while hypocenters from some regions where lower crustal earthquakes were previously reported were in fact poorly constrained, there appear to be several well constrained depths in the central Tien Shan south of Lake Issyk-Kul, and a large number near the Jiashi region of western China. A combination of tomographic and receiver function images suggests that these events are clearly located in the lower crust.
DE: 7205 Continental crust (1242)
DE: 7215 Earthquake parameters
DE: 7218 Lithosphere and upper mantle
DE: 7230 Seismicity and seismotectonics
DE: 8102 Continental contractional orogenic belts
SC: Seismology [S]
MN: 2003 Fall Meeting