| This article is for a master degree. An earthquake with magnitude Ms 5.6 hit the place from Pucun village to XituanPu village, Datong county, Shanxi province in the first of November, 1999. An aftershock sequence followed the main event. The location and mechanism of partial aftershocks were illustrated in this paper. We located 31 events, which are well recorded, and 18 of them, which have clear waveform, were chosen to calculate the mechanism. We use the software "Seismic Handler" and HYP071 program for location. And we use the moment tensor inversion program to calculated focal mechanism. The process of moment tensor inversion is in frequency domain. The location result shows that the aftershock sequence is at an intercourse of EW striking Liulengshang fault, the NE striking Dawang fault and NW striking TuanBao fault. The mechanism shows that the movement of aftershock is on strike-slip fault. But the strikes of different events are not at same orientation. This is why the location was in the fault intercourse place.Chapter one describes the location process. Staff of the institute of geophysics set up a temporal digital seismic network around the meizoseismal region after the magnitude 5.6 earthquake of November 1st, 1999. We sort out the record of the aftershock sequence began from the eleventh of November to eighteenth, using the software of "Seismic Handler" for phase time picking and HYPO71 program for calculating the hypocenter location. We get the velocity model by refence from "rupture activities of Datong in Oct., 1989 and Mar., 1991" ( Wang and Stammler, 2001., in Chinese). The epicenter distribution map shows that the location of aftershock is fit for the activity of faults locating in Datong, Shanxi area.Chapter two describes the way to use the moment tensor inversion program to calculating the focal mechanism of 18 events, which have clear waveform among the well located 31 events. The resolution of mechanism shows that the movement of aftershock event is on strike-slip fault. But the strikes are not at same orientation. This is why the location was in the fault intercourse place.The results of the location calculating and focal mechanism show that the aftershocks were not occurred at same fault, which the main shock occurred on it, but at several faults around main fault. It means when main shock happened the stress on the fault changed, this effect the stress balance of other faults around it. Some of the aftershock is just for adjusting the balance of stress on the faults. |
