HR: 0800h
AN: S51B-0511    [Abstracts]
TI: Source mechanism of the 2006 M5.1 Wen'an Earthquake determined from a joint inversion of local and teleseismic broadband waveform data
AU: * Huang, J
EM: jh11@rice.edu
AF: University of Science and Technology of China, 96th Jingzhai Road, Hefei, Anh 230026, China
AU: * Huang, J
EM: jh11@rice.edu
AF: Rice University, 6100 main street, Houston, TX 77005, United States
AU: Ni, S
EM: sdni@ustc.edu.cn
AF: University of Science and Technology of China, 96th Jingzhai Road, Hefei, Anh 230026, China
AU: Niu, F
EM: niu@rice.edu
AF: Rice University, 6100 main street, Houston, TX 77005, United States
AU: Fu, R
EM: frs@ustc.edu.cn
AF: University of Science and Technology of China, 96th Jingzhai Road, Hefei, Anh 230026, China
AB: On July 4th, 2006, a magnitude 5.1 earthquake occurred at Wen'an, {~}100 km south of Beijing, which was felt at Beijing metropolitan area. To better understand the regional tectonics, we have inverted local and teleseismic broadband waveform data to determine the focal mechanism of this earthquake. We selected waveform data of 9 stations from the recently installed Beijing metropolitan digital Seismic Network (BSN). These stations are located within 600 km and cover a good azimuthal range to the earthquake. To better fit the lower amplitude P waveform, we employed two different weights for the P wave and surface wave arrivals, respectively. A grid search method was employed to find the strike, dip and slip of the earthquake that best fits the P and surface waveforms recorded at all the three components (the tangential component of the P-wave arrivals was not used). Synthetic waveforms were computed with an F-K method. Two crustal velocity models were used in the synthetic calculation to reflect a rapid east-west transition in crustal structure observed by seismic and geological studies in the study area. The 3D grid search results in reasonable constraints on the fault geometry and the slip vector with a less well determined focal depth. As such we combined teleseismic waveform data from 8 stations of the Global Seismic Network in a joint inversion. Clearly identifiable depth phases (pP, sP) recorded in the teleseismic stations obviously provided a better constraint on the resulting source depth. Results from the joint inversion indicate that the Wen'an earthquake is mainly a right-lateral strike slip event (-150°) which occurred at a near vertical (dip, 80° ) NNE trend (210°º) fault. The estimated focal depth is {~}14- 15km, and the moment magnitude is 5.1. The estimated fault geometry here agrees well with aftershock distribution and is consistent with the major fault systems in the area which were developed under a NNE-SSW oriented compressional stress field. Key word: waveform modeling method, source mechanism, grid search method, cut and paste method, aftershocks distribution
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
SC: Seismology [S]
MN: 2007 Fall Meeting