GPS观测得到的大地震前兆地壳形变震例

Case studies on GPS observations and crustal deformation precursors to strong earthquakes

综合介绍2008年汶川大地震以来,GPS观测得到的国内外10多次6—9级,不同构造、不同类型的大地震前兆地壳形变震例:2008年汶川8级大地震、2011年东日本9级巨震、2013年芦山7级,直至2020年6月墨西哥7.4级地震和7月美国阿拉斯加州以南海域7.8级地震等。利用GPS连续观测站区域参考框架水平位移时间序列和水平位移场,特别是水平位移向量时间序列的研究证明,同震水平位移是研究地震前兆形变存在的关键;利用垂直位移和水平位移向量时间序列、同震垂直位移及同震水平位移向量的分解,揭示地震弹性回跳真实方式;提出了符合GPS观测和岩石破裂试验结果的地震压-剪弹性回跳模型;根据已有震例,提出预报不同震级地震的可能性和监测临震前兆形变的GNSS站布设设想。

Studies on cases of more than 10 strong earthquakes of M6.0 to M9.0 since the 2008 Wenchuan earthquake around the world with GPS observations and crustal deformation precursors are reviewed.These earthquakes occurred in regions of different tectonic movements and of different types.They are the M8.0 Wenchuan earthquake in 2008,the M9.0 Tohoku earthquake in 2011 in Japan,the M7.0 Lushan earthquake in 2013 and so on until the recent earthquake of M7.4 in Mexico in Jun.,2020 and the southern Alaska offshore earthquake of M7.8 in Jul.,2020.Based on the time series of horizontal displacement components and horizontal displacement field,particularly the time series of horizontal displacement vectors,in the regional reference frames,studies have shown that the coseismic displacements are the keys to the confirmation of the existence of crustal deformations precursory to earthquakes.The time series of vertical displacements and horizontal displacement vectors,the coseismic vertical displacements and decomposition of the coseismic horizontal displacement vectors have revealed the real pattern of elastic rebound.A model of rebound or elastic rebound of(preseismic)compression-(coseismic)shear strain is proposed in agreement with results of rock failure tests and the GPS observations.Based on the studies of the earthquake cases,a layout of stations of continuous GNSS observations of monitoring precursory crustal deformations for possible predictions of earthquakes of different magnitudes is proposed.