[S-GD01] Geodesy and Global Geodetic Observing System

[SGD01-10] An Apparent Reduction of Crustal Activity before the Great East Japan Earthquake

*Yasushi Harada¹, Yuka Murai¹ (1.School of Marine Science and Technology, Tokai University)

Keywords:GEONET, The Great East Japan Earthquake, Reduction of Crustal Activity

We used F3 solutions of GEONET(GSI) from 2000 to 2020, and calculated displacement vectors of about 1300 GNSS sites. First we created grid files for 3-components of the displacement vectors, and created animations for the deformation of Japan for the 3-components. We also calculated the length of the displacement vectors to investigate overall amount of crustal activity distribution of Japan. We noted the significant changes of regions where the length of the displacement relatively small and those changes of pattern are partly related to the previous block model of Japan. To quantify the long-term change of the crustal activity, we summed up every length of the displacement vectors, and made a time-series plot of the amount of crustal activity of Japan (See figure). The 10 years term decreasing trends are noted both before and after the Great East Japan Earthquake. It is natural that the decreasing trend appeared after the earthquake, but we found 10 years term decreasing trend for the crustal deformation of whole Japan even before the great earthquake. The rate of decrease is about 50% higher for after the earthquake than before. Further analyses are needed to be specify the cause of the reduction of the crustal activity before very large earthquake like the Great East Japan Earthquake.