GPS观测到的智利及其邻区多次大地震前后地壳运动

Crustal movements before and after several earthquakes in Chile and its neighborhood detected by GPS observations

2001年以来,智利及其邻区发生了3次7.1-7.7级和4次8级以上大地震,其震中附近至少有一个甚至多个GPS连续观测站观测到地震前后的地壳运动。从http://geodesy.unr.edu网站可获得Geoffrey Blewitt教授用GIPSY软件处理得到的南美大量GPS连续观测站南美板块(SA)区域参考框架位移时间序列,获得的这些大地震同震、震前位移积累和震后位移,特别是同震水平位移和震前水平位移积累,为探索地震预测,增添了更多有意义的震例。研究表明,这些大地震的同震水平位移也是震前水平位移积累的回跳或弹性回跳,同样也证明了震前存在前兆地壳形变;这些大地震前震中及其附近也无明显的垂直位移积累,由此证明了板块运动或地壳水平运动就是地震成因。尽管东日本和智利近海大地震的构造环境不同,日本2011年9级和智利2010年8.8级巨大地震前的地壳运动都清楚显示太平洋海底扩张。这些地震的同震水平位移回跳或弹性回跳的规律一致,地震成因都是水平挤压。智利多次大地震GPS观测到的最特殊现象是,在2015年8.3级地震震中以北,2010年8.8级地震的同震水平位移量值偏小,且方向异常一致向北,可认为是8.3级地震的前兆形变现象。临近智利的南美地区应是全球最利于地震预测探索的地区之一。

Since 2001,3 earthquakes of magnitudes of 7.1 to 7.7 and 4 earthquakes of magnitudes over 8.0 occurred offshore Chile and its neighborhood.There are at least one or several GPS stations of continuous observations near these events and they detected crustal movements for these earthquakes.Based on the time series of displacements in the regional reference frame of South America(SA)at more than 70 stations of continuous GPS observations,downloaded from the website http://geodesy.unr.edu,the accumulated preseismic horizontal displacements,coseismic and post seismic displacements of these earthquakes are obtained.Therefore,more earthquake cases with GPS observations have been collected in this study for the benefit of exploring earthquake predictions.The study shows that the coseismic horizontal displacements of these events are rebound or elastic rebound of the accumulated horizontal displacements at the GPS stations and they are the evidences of the precursory crustal deformations.There were no significant accumulated vertical displacements at or near the epicenters before these events.These facts demonstrate that the earthquakes were originated from plate motion of horizontal crustal movements.Both the 9.0 earthquake in 2011 in Japan and the 8.8 earthquake in Chile in 2010 showed clearly the spreading of the bottom of the Pacific Ocean.Though the tectonics in both countries are quite different,the rebound or elastic rebound shown by coseismic horizontal displacements of the 2 earthquakes are of the same pattern and they were the results of horizontal compression.It should be noted that the coseismic horizontal displacements of the 8.8 eathquake in 2010 were significantly smaller and in almost same abnormal direction at GPS stations north of the 8.3 earthquake in 2015.This was the most obvious and particular case from the GPS observations for the earthquakes in Chile and may be considered as the crustal motion precursory to the 8.3 event.The area near Chile in South America is one of the areas in the world,most favorable for the exploration of earthquake predictions.