11:45 AM - 12:00 PM
[SGD02-10] An Apparent Reduction of Crustal Activity in GNSS data before Great Earthquake
Keywords:Reduction of Crustal Activity, GNSS data, Great Earthquake
Harada and Fujita JpGU 2022 compared F3 and new F5 solutions of GEONET(GSI) from 2000 to 2021, and calculated displacement vectors of about 1300 GNSS sites for examining the crustal activity of Japan. The 30 days running means and standard deviations for the 3-components of F3 and F5 solutions were calculated and the 30 days term displacement vectors were produced for all GEONET sites from 2000 to 2021. The large differences were noted of the positions and the displacement vectors between F3 and F5 solutions. Those differences were largely disappeared after the calculation of displacement vectors with center-of-mass-system of coordinates. Also the sum of the lengths of each displacement vectors were calculated to investigate overall amount of crustal activity of Japan. The 10 years term decreasing trends of the crustal activity are shown before the 2011 off the Pacific coast of Tohoku Earthquake.
In this study, we used the global GNSS data analysed by the Nevada Geodetic Laboratory ("Nevada" for short) and examined whether the same decreasing trends of the crustal activity before big Earthquake will appear or not. The similar differences were noted of the positions and the displacement vectors between F5 and Nevada solutions. And with center-of-mass-system of coordinates the differences were disappeared. However more significant decreasing trends appeared for the sum of the lengths of each displacement vectors from 2008 to 2011. The three year data length is too short to conclude that obvious reduction of crustal activity before the 2011 off the Pacific coast of Tohoku Earthquake is shown. Next we tried to analyse the 2010 Chile earthquake using the same method. A gradual decreasing trend of the sum of the lengths of each displacement vectors from 2005 to 2010 is noted. More importantly, the reduction of crustal activity in the area is considered to occur now after 2021.
In this study, we used the global GNSS data analysed by the Nevada Geodetic Laboratory ("Nevada" for short) and examined whether the same decreasing trends of the crustal activity before big Earthquake will appear or not. The similar differences were noted of the positions and the displacement vectors between F5 and Nevada solutions. And with center-of-mass-system of coordinates the differences were disappeared. However more significant decreasing trends appeared for the sum of the lengths of each displacement vectors from 2008 to 2011. The three year data length is too short to conclude that obvious reduction of crustal activity before the 2011 off the Pacific coast of Tohoku Earthquake is shown. Next we tried to analyse the 2010 Chile earthquake using the same method. A gradual decreasing trend of the sum of the lengths of each displacement vectors from 2005 to 2010 is noted. More importantly, the reduction of crustal activity in the area is considered to occur now after 2021.