关键词: 青海玛多7.4级地震, GNSS, 同震位移

Abstract:

The May 21, 2021, Maduo M_S7.4 earthquake in Qinghai Province caused serious disasters in Maduo County and its surrounding areas. The GNSS co-seismic displacement field data can play a key role in quickly determining the influence range of the earthquake and serving for the rapid investigation. After the earthquake, we immediately collected the data of 18 GNSS stations surrounding the epicenter, including 7 stations that recorded 1Hz high-frequency observation data. Various data were used to rapidly obtain the GNSS co-seismic displacements, such as, the 15-minute high-frequency data, 5 hours after earthquake and multi-day displacement data. In this paper, we used three methods to obtain the co-seismic displacement, including the dynamic difference method for 1Hz frequency data by GAMIT/GLOBK Track module, and the static difference method for the post-seismic 5-hour data and for the pre- and post-seismic multi-day data by GAMIT/GLOBK. The results are shown as follows:
(1)The dynamic difference method for 1Hz frequency data by GAMIT/GLOBK Track module has ability to quickly process the data and acquire the co-seismic displacement. When using the high-frequency data to obtain co-seismic displacement by Track module, it is suitable for the near field stations which have a large value of co-seismic deformation. However, in the far field, the accuracy of the solution is at cm level restricted by the distance of stations. In addition, the result of the Track is influenced by the stability of reference station. Although the results obtained by Track are not accurate, it can be used as a method to quickly judge the characteristics and amount of coseismic surface motion.
(2)Comparing the results obtained from the post-seismic 5-hour data and the pre- and post-seismic multi-day data, the GNSS stations’ displacements have good consistency in the magnitude, direction and influence range, especially in the near field. The difference of the results by the two methods is from 1mm to 4mm. Considering the processing accuracy of the GAMIT/GLOBK, the value of the difference is not unreasonably high. When the displacement value is small, it is difficult to obtain accurate results. In addition, the direction of the pre- and post-seismic multi-day result is consistent with that from the post-seismic 5-hour data, and the value increased. If we regard the result of the pre- and post-seismic multi-day data as the result of one day data after the earthquake which is included in the post-seismic displacement, this phenomenon coincides with the afterslip deformation, and the difference may be caused by the afterslip, especially in the near field. Although the difference exists, taking into account the timeliness and the overall consistency, we believe that using the postseismic 5-hour data to quickly obtain the co-seismic displacement is credible in an emergency.
(3)Based on the analysis of various results, it is preliminarily judged that the Maduo earthquake is dominated by left-handed strike-slip. The maximum displacement at the station QHMD, which is about 40km from the epicenter, is about 24cm to the west and 8cm to the north. The earthquake affected the area around epicenter including Maduo, Xining, Dulan, Delingha in the north, and Zebra and Ganzi areas in the south. From the comparison of the results of the static difference method for the 5 hours and multi-day data, it is believed that the post-seismic deformation taking place in the near field is significant, and continuous attention is required in the later stages.

Key words: the Maduo M_S7.4 earthquake in Qinghai Province, GNSS, coseismic displacement