Time series of coordinates of a large number of GPS stations in the world,processed by Prof.Geoffrey with GIPSY software are available at http://geodesy.unr.edu.Based on the time series of coordinates in the global reference frame of IGS08 at more than 250 stations of continuous GPS observations,downloaded from the website,the co-seismic displacements of the M7.3 Kyushu earthquake on April 16th,2016 in Japan and the preseismic strain accumulations and displacements in the regional reference frame were obtained.The station of continuous GPS observation at BJFS near Beijing has been quite stable in displacement in the eastern part of China for more than 17 years since the beginning of its operation,and this station is used as the core station in the regional reference frame for the pre-seismic displacements of the Kyushu earthquake of M7.3.The main feature of the pre-seismic displacements of the Kyushu earthquake is characterized by the lock in the crust at and near the epicenter.The anomalous pre-seismic strain accumulation developed in an area of anomalous accumulation of the shear strain component of γ1 on the northeast side of the epicenter,with increasing size of the area and increasing magnitude in γ1.The largest area covered by the anomalous γ1 is about 2 000 km2.The change in E component at BJFS since Nov.26th,2015 was caused by the replacement of the receiver and the antenna at the station.In order to study the short term change in displacements at stations at and near the epicenter,time series at three stations of continuous GPS observations,two at SUWN and DAEJ in south Korea and one at BJSH near Beijing were analyzed and the analysis shows that the displacements at the 3 stations have been quite stable in the same manner in east Asia.So BJSH is used as the core station in the regional reference frame of displacements and the displacement time series show that there were no significant short term anomalies before the earthquake.%从http:∥geodesy.unr.edu网站可获得Geoffrey Blewitt用GIPSY软件处理得到的全球大量GPS站坐标.本文主要利用该网站2012年4月至2016年4月23日日本九州岛及其附近250多个GPS连续观测站及其他站的IGS08全球参考框架坐标时间序列,获取2016年4月16日日本九州岛7.3级地震同震位移、震前水平应变积累和区域参考框架位移.位于中国大陆北京附近的GPS连续观测站BJFS观测结果保持长期稳定,因而主要采用此站作为区域位移参考框架核心站,得到此次日本九州岛7.3级地震震前位移时空变化图像.该地震震前水平位移的主要特征是震源附近地壳运动处于闭锁状态.水平应变积累表明,震前在震中的东北方有第一剪应变γ1积累异常区,震前异常范围不断扩大,幅度逐渐增大,异常范围达到2000 km2.但该网站得到的201 5年11月26日后BJFS站数据处理结果的E分量变化为更换接收机和天线所致.为研究震前短期变化,比较了东亚大陆韩国SUWN和DAEJ这2个GPS连续观测站和北京附近另一个GPS连续观测站BJSH的全球参考框架坐标时间序列,表明这3个站变化一直保持平稳且一致.采用BJSH作为区域位移参考框架核心站得到的位移时间序列表明,此次大地震前位移无明显的短期异常.
展开▼
