Crustal movements before and after several earthquakes in Chile and its neighborhood detected by GPS observations
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摘要: 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GeoffreyBlewitt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。Abstract: 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 websitehttp://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. -
图 1 智利近海及其邻近区域的大地震 （大蓝点），附近的GPS连续观测站 （小的彩色点）。图右侧是表示GPS观测站大地高程的色码。黑色站名是本文位移时间序列所显示的12个GPS连续观测站
Figure 1. Large earthquakes (big blue dot) and GPS stations of continuous observations (small color dot) in Chile and its neighborhood near the events. On the right side is the color bar for the geodetic heights at the GPS stations. 12 GPS stations of continuous observations with displacement time series shown in this paper are marked with station code in black color
图 2 智利近海及其邻近区域多次大地震同震水平 （左图）与垂直 （右图）位移。各图左下角为位移向量比例尺
Figure 2. Coseismic horizontal displacements (left figure) and vertical displacements (right figure) of the large earthquakes in Chile and its neighborhood. The displacement vector scale is shown at the bottom left of each figure
图 3 智利2010年8.8级大地震的同震水平位移。左下角为水平位移向量比例尺
Figure 3. Coseismic horizontal displacements of the 2010 earthquake of M8.8 in Chile. The displacement vector scale is shown at the bottom left of the figure
图 4 智利近海等多次大地震附近南美洲12个GPS连续观测站3个位移分量和水平位移向量时间序列，位移单位均为mm。左图为3个分量，即水平位移东西 （E，棕色） 和南北 （N，红色） 分量与垂直 （U，蓝色） 位移时间序列，图上方标出了有明显同震位移的地震震级和相应的以km为单位的震中距。右图为水平位移向量时间序列，图右侧为用GPS周表示日期的色码
Figure 4. Time series of 3 displacement components (left figure) and horizontal displacement vectors (right figure) in mm at 12 stations of continuous GPS observations in South America near the large earthquakes in Chile and its neighborhood. The 3 displacement components are the east horizontal component E in brown, north horizontal component N in red and vertical component U in blue. At the top of the figures of 3 displacement components, the magnitudes of the earthquakes and the epicentral distances of the stations in km are shown. On the right side of each vector figure the color bar shows the date in GPS week for time series of the horizontal displacement vectors
表 1 2001年至今智利近海多次大地震统计
Table 1. Statistics of earthquakes occurred in Chile and its neighborhood since 2001
发震日期 震级 南纬/° 西经/° 震源深度/km 2001-06-23 8.4* 16.265 73.641 33.0 2007-11-14 7.7 22.247 69.890 40.0 2010-02-27 8.8 35.846 72.719 35.0 2012-03-25 7.1* 35.200 72.217 40.7 2014-04-01 8.2 19.610 70.769 25.0 2015-09-16 8.3 31.573 71.674 22.4 2016-12-25 7.6* 43.406 73.941 38.0 2017-04-24 6.9* 33.038 72.062 28.0 2019-09-29 6.7* 35.476 73.163 11.0 2020-09-01 6.8 27.969 71.306 21.0 2021-01-19 6.4* 31.833 68.799 20.8 *表示地震附近仅有一个GPS连续观测站有显著的同震和震前水平位移 
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表 2 12个GPS连续观测站得到的不同地震同震水平位移
Table 2. Coseismic horizontal displacements observed at 12 stations of continuous GPS observations for earthquakes of different magnitudes
站名 震级 震中距/km 同震水平位移/mm 站名 震级 震中距/km 同震水平位移/mm CONS 8.8 64 4712.7 CSLO 8.3 226 102.6 CONS 7.1 17 61.1 CSLO 6.4 48 20.2 CONS 6.7 70 10.6 VALN 8.3 161 13.3 MAUL 8.8 171 1054.5 VALN 6.9 40 51.2 ANTC 8.8 197 779.5 AREQ 8.4 231 507.3 SANT 8.8 353 283.0 PTRE 8.2 201 76.0 SANT 8.3 199 25.6 CDLC 7.7 15 128.9 LSCH 8.3 189 200.2 TPYU 7.6 153 20.7 CSLO 8.8 550 33.6 LLCH 6.8 33 16.3
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