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

摘要：

2021年5月21日青海玛多7.4级地震导致玛多县及其周边地区受灾严重。为了快速获取GNSS同震位移场服务于震情快速研判, 文中采用多种方法对玛多地震的同震位移开展了针对性研究。采用1Hz高频动态差分、 震后5h静态解算及多天静态解算3种方法获取了同震位移, 经对比分析发现GAMIT/GLOBK的动态差分TRACK模块在利用高频数据获取同震形变时适用于近场形变量较大的测站, 对远场形变量小的测站则适用性不强; 震后5h静态解算获得的同震位移与多天静态解算结果相比时效性更强, 两者的数值相差1~4mm, 所反映的位移大小、 方向及影响范围都保持较强的一致性。综合GNSS资料分析表明, 本次地震的发震断层为昆仑山口-江错断裂, 且震源机制以左旋走滑为主, 距离震中区约40km的QHMD站(青海玛多)的W向位移约为24cm, N向位移约为8cm。从近场震后5h静态解和多天静态解的结果分析可知震后变形显著, 仍需持续关注。

关键词: 青海玛多7.4级地震, GNSS, 同震位移