| Earthquake location, as a basic work in seismometry, plays an important role in the studying of active faults. Double-difference earthquake location algorithm (HYPODD) is able to get high-resolution hypocenter location by introducing the residual between observed and calculated travel-time difference between two events. In the paper, the resolution of double-difference location algorithm was analyzed using theoretical data, and the influence from initial location error on relocation result is estimated when the P- and S-waves travel times were correct. Then, the relocation result was gotten from initial hypocenter location parameters which were determined by using HYPO71 with different error data of P- and S-waves travel times. The results show that HYPODD is better than HYPO71.The earthquakes in Fenwei basin from 1990 to 2008 were relocated based on the data recorded by Shaanxi and Shanxi seismic network in China Earthquake Data Center. The results shows that the earthquakes in the basin are all occurred in the middle of great faults lying on the two sides of the basin, and the inner active faults also have an influence on seismicity. Depths of earthquake in Linfen Basin gradually deepen from south to north, and the maximum focus depths in Wehe Basin have the tendency of increase from east to west.Earthquake nucleation is short-time precursor of earthquake, and has an important implication on earthquake prediction. And the foreshocks are the most obvious manifestation of earthquake nucleation. Though double-difference location algorithm, high-resolution hypocenter location parameter can be determined only by using earthquake catalog data, which benefits to analyze the process of earthquake nucleation. The earthquakes in 1981 Westmorland earthquake (ML5.8) sequence, including foreshocks and aftershocks, were relocated by using HYPODD through catalog data from Southern California Seismic Network in this paper. The relocations had uncertainties of 100m horizontally and 200m vertically. These results were used to analyze the nucleation process. The results show that the 363 foreshocks occurred on two different faults planes and the barrier may be lies near the foreshocks, which is consistent with the preslip model in earthquake nucleation process. |
