利用高频GPS资料研究2016年新西兰凯库拉地震的地表形变及预警震级

Surface deformation and early warning magnitude of 2016 Kaikoura(New Zealand)earthquake from high-rate GPS observations

2016年11月13日,新西兰凯库拉地区发生了M_w7.8级地震.本文利用1 Hz高频GPS观测数据,基于GAMIT track解算模块,采用主分量分析(PCA)空间滤波方法获取了地震地表形变.同时从trackRTr模拟实时解算的动态位移中,提取P波5秒峰值位移(P_d)和地面峰值位移(PGD),并根据震级统计回归模型计算预警震级.结果表明:测站的动态形变时间长达2 min,距震源最近的HANM和KAIK站出现二次剧烈形变,震源北部测站的形变幅度大于南部,而高频GPS静态同震形变场表现出先逆冲后走滑的震源机制特征.不同GPS台站的P_d预警震级相差较大,最大震级差为M_w 2.5.综合考虑预警震级发布的时效性和可靠性,采用顾及空间分布的四台站PGD联合预警方法,其预警震级在震后23 s达到初始稳定(M_w7.56),在震后110 s达到最终稳定(M_w7.78),该震级与USGS矩张量反演震级(M_w7.8)基本一致.

On 13th November 2016, the Kaikoura region of New Zealand was struck by a major MW7.8 earthquake. In this study, coseismic deformation field is derived from 1 Hz high rate GPS observations based on the GAMIT track solution module, combining with PCA spatial filtering method firstly. Then the 5 s peak displacement of P wave （Pd） and the peak ground displacement （PGD） are extracted from the real-time simulated kinematic displacement of the trackRTr module. Finally, the warning magnitude is calculated from the statistical regression model. Our results indicate that the duration time of the kinematic deformation is up to 2 min. The KAIK and HANM stations, which are closest to the epicenter, have secondary severe deformation. And the deformation amplitude of the north stations of the epicenter is larger than that of the south. The static coseismic deformation field from high-rate GPS observations shows the characteristics of the focal mechanism of strike-slip after thrust. In addition, the Pd warning magnitudes from different stations have a significant difference, with the maximum magnitude difference of MW2.5. Considering the timeliness and reliability of the warning magnitude jointly, the warning magnitude from the four-station PGD joint warning method of reasonable spatial distribution can reach its initial stability （MW7.56） at 23 s after the event, while final stability （MW7.78） at 110 s, which is consistent with the USGS moment tensor magnitude （MW7.8）.