Abstract
This paper selects the waveform records of 16 broadband digital seismic stations in the regional seismic network of Gansu province, Qinghai province, and Sichuan province involved inversion, use CAP focal mechanism solution method to calculate the Ms 5.2 earthquake which occurred in Qilian County, Qinghai Province, November 23, 2015. Obtained the focal mechanism solution of this earthquake is a strike-slip fault with thrust property. The inversion results show the optimal double couple solution is nodal plane I: The strike is 112°, the dip, 51.7°; and the rake, 24.5°. Nodal plane II: The strike is 7°, the dip, 71°; and the rake, 139°. Earthquake moment magnitude isMw5.2 and the optimal depth solution is 8km, which is consistent with the results of IGP-CEA. We calculate focal depth with the arrival time difference between sPn and Pn phases, the results is 6.6km, which agree with the CAP method results and verify the feasibility of this method.
Highlights
Focal depth is one of the most difficult parameters to accurately measure as a basic parameter of seismic space-time parameters
The focal mechanism solution with the smallest global difference between synthetic seismogram and observed seismogram is searched in an appropriate time range, which enhances the weight of Pnl and has better constraints on seismic depth
The transverse axis is coming into a line according to Pn phase, longitudinal axis distribution according to epicentral distance; it can be seen from the Fig 6 that the average the arrival time difference between sPn and Pn is about 2.4S
Summary
Focal depth is one of the most difficult parameters to accurately measure as a basic parameter of seismic space-time parameters. Because there are fewer seismic stations in the upper and lower directions, depth positioning is not as accurate as horizontal positioning and focal depth is a relatively difficult quantity to determine in earthquake location. The regional seismic network is usually based on a onedimensional velocity model, using Pg (Sg) and Pn (Sn) phases to locate earthquakes. Seismic location based on Pg (Sg) phase can only obtain high precision focal depth when the number of near stations is sufficient and the station azimuth coverage is good. Under the circumstances of the seismic network relatively sparse, due to the lack of sufficient near station data, the accuracy of focal depth determined by conventional positioning methods is low. The layout of most stations in China is relatively sparse, so the deep seismic phase method will have a better effect. Earthquakes occurred in the Qilian fault zone and its styles mainly are large sinistral strike-slip faults
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