超导重力数据检测到的2011年日本东北大地震(Mw 9.0)震前重力异常及同震重力变化

Pre-seismic anomalies and co-seismic gravity changes of 2011 Tohoku-Oki earthquake(M_(w) 9.0)detected by superconducting gravity data

高精度的超导重力数据已广泛应用于地球动力学的研究,对大地震前重力异常和同震重力变化的探测有助于震源机制和地震预警的研究,同时高精度的同震观测数据可用于断层滑动模型的反演。本文利用日本、中国及欧洲7个超导台站2011年3月的秒采样数据研究日本东北大地震(M_(w) 9.0)产生的重力变化,经潮汐、气压、漂移等预处理改正后,得到改正后的重力变化。对比同时段日本岛附近发生的2861次M_(b)≥4级地震,分析滤波后的重力变化数据,排除非主震的影响,发现0.12 Hz≤f≤0.18 Hz频段显示了明显的震前重力异常扰动信息,所有台站在震前89 h均开始出现重力异常扰动,Medicina站的震前最大异常扰动振幅达到28×10^(-8) m/s^(2)。另外,利用球形位错理论及地震的CMT解计算得到的地表同震重力变化理论值与超导重力观测值非常接近,同震重力变化绝对值与震中距成反比,近场站点的观测值比远场站点更接近于理论计算值,前者可作为断层反演的约束条件。

High-precision superconducting gravity data had been widely used in the study of geodynamics.The detection of the pre-seismic anomalies and co-seismic gravity changes caused by a huge earthquake is helpful to the study of focal mechanism and early warning.Meanwhile,the co-seismic observations can be used in the inversion of fault slip model.We study the gravity changes caused by the Tohoku-Oki earthquake(M_(w) 9.0)using the second sampling data in March 2011 of 7 Superconducting Stations in Japan,China and Europe.We obtained the corrected gravity changes by the preprocessing of tide,air-pressure and drift correction,et al.Comparing the 2861 M_(b)≥4 earthquakes near the Japan island at the same period and analyzing the filtered gravity changes,we can exclude the influence of non-main earthquakes and find the obvious pre-seismic anomalies at frequencies 0.12 Hz≤f≤0.18 Hz.The pre-seismic anomalies occurred 89 h before the earthquake for all the stations.The maximum amplitude of pre-seismic anomalies reaches 28×10^(-8) m/s^(2) at Medicina.Moreover,the theoretical co-seismic gravity changes simulated by the spherical dislocation theory and the CMT solution,are very close to the observed values of superconducting gravimeters.The absolute values of co-seismic gravity changes are inversely proportional to the epicenter distances.The observations at near-field are closer to the theoretical calculations than that at far-field,and the former can be used as the constraints for fault inversion.