HR: 1340h
AN: S43B-1315    [Abstracts]
TI: Calculation of focal loci used for locating an earthquake in complex media
AU: * Zhao, A
EM: ahzhao123@yahoo.com
AF: Institute of Geophysics, China Earthquake Administration, 5 Minzu Xueyuan Nanlu Street,Haidian District, Beijing, 100081, China
AU: Ding, Z
EM: ding@cdsn.org.cn
AF: Institute of Geophysics, China Earthquake Administration, 5 Minzu Xueyuan Nanlu Street,Haidian District, Beijing, 100081, China
AU: Wang, C
EM: wangcy@cea-igp.ac.cn
AF: Institute of Geophysics, China Earthquake Administration, 5 Minzu Xueyuan Nanlu Street,Haidian District, Beijing, 100081, China
AU: Sun, W
EM: sunwg3s@yahoo.com.cn
AF: Institute of Geophysics, China Earthquake Administration, 5 Minzu Xueyuan Nanlu Street,Haidian District, Beijing, 100081, China
AB: Focal loci are often required in earthquake location. However, It is extremely difficult to analytically express them when the earthquake lies in a complex model. Therefore, the calculation of focal loci is usually limited to simple media. In this paper, we put forward a method for calculating focal loci in complex media by means of a minimum travel time tree algorithm for tracing rays. The focal locus is constrained with differential arrival time so that the problem of origin time is avoided. From all the model nodes, we select a small part with smaller absolute residuals between observed and calculated travel time differences (or double-differences) as representative points of the focal locus. The representative point with minimal double-difference is assigned as an initial point. Ray paths from the initial point to the other selected representative points in the double-difference field actually represent the focal locus, and are calculated with a minimum travel time tree algorithm. When the obtained focal locus is rather rough due to the excessive amount of selected representative points, it can be improved by removing some ray paths to the representative points that there are less rays go through. In addition, we modified the stop condition in the minimum travel time tree algorithm in order to reduce computational time. Our method is applied to calculating focal loci of an earthquake in a complex model in different cases including velocity perturbations and noisy arrival data. The calculation results show that the method is feasible.
DE: 7200 SEISMOLOGY
SC: Seismology [S]
MN: 2007 Fall Meeting