2016年日本本州东岸近海MS7.2地震前后的地壳运动

Crustal movements of the eastern Honshu offshore MS7.2 earthquake in Japan in 2016

  • 摘要: 2016年11月22日日本本州东岸近海发生东日本MW9.0大地震的MS7.2强余震。本文利用美国内华达大学内华达大地测量实验室网站获得此次大地震周围共30多个GPS连续观测站及其它台站的IGS08全球参考框架坐标时间序列,采用北京附近的GPS连续观测站BJSH作为区域位移参考框架的核心站,获取了此次MS7.2强余震的同震水平位移和区域参考框架位移时间序列,得到了此次强余震前后的位移时空变化图像。结果显示:尽管本州东岸近海MS7.2地震作为东日本MW9.0地震的强余震,受其震后形变的影响强烈,但其地壳水平形变的前兆规律与已观测到的大地震一致;不同的是东日本MW9.0地震前的垂直位移无积累,而本州东岸近海MS7.2地震前后的垂直位移保持MW9.0地震后均匀而缓慢的衰减变化;临震前震中附近的GPS连续观测站的东西分量明显减速,有的甚至减至零,是明显的短期前兆异常。此外,本文还进一步讨论了两种同震位移及其成因,并推断地壳水平运动挤压是此次地震的成因。

     

    Abstract: In Japan, on November 22, 2016, occurred the eastern Honshu offshore MS7.2 earthquake, which was the aftershock of the 2011 Tohoku MW9.0 earthquake. Time series of coordinates of a large number of GPS stations in the world are available at the website of the Nevada Geodetic Laboratory of the Nevada University. Based on the time series of coordinates in the global reference frame of IGS08 at more than 30 stations of continuous GPS observations, downloaded from the website and with the station of continuous GPS observation BJSH near Beijing used as the core station in the regional reference frame, the coseismic displacements and time series of horizontal displacements before and after the earthquake are analyzed in time and space. The results show, though the eastern Honshu offshore MS7.2 earthquake, as the aftershock of the 2011 Tohoku MW9.0 earthquake, was intensely affected by the postseismic crustal deformation of the main shock, the precursory horizontal deformations were in good agreement with those of other large earthquakes. The prominent feature of the Tohoku earthquake is that there was no significant preseismic vertical displacement accumulation, whereas the vertical displacements before and after the eastern Honshu offshore MS7.2 earthquake show slow and uniform decaying as those after the main shock. Shortly before the earthquake, the stations of continuous GPS observations near the epicenter showed significant decrease in velocities or even zero as for the east component, which were short term precursory anomalies. Moreover, two types of coseismic displacements and their cause were discussed, and the horizontal compression in the crust was the cause of the aftershock.

     

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