5:15 PM - 6:30 PM
[SSS05-P11] Crustal movements due to the seismic motions observed in Kobe
Keywords:crustal movements, source process
Strain changes due to the source processes of the 2011 off the Pacific coast of Tohoku earthquake (M9.0) and the 2018 northern Osaka earthquake (M6.1) were observed by using the Ishii-type three-component strainmeter at Rokko-Takao station of Kyoto University in Kobe (Mukai et al., 2020). This station is equipped with the extensometers as well as the strainmeter, and one extensometer is installed at the nearby Rokko-Futatabi station. Strain changes observed by those extensometers significantly contained the changes due to the source processes as well. We can get some information about a source process by investigating the observational data of strainmeters and extensometers installed in an underground tunnel away from the focal region.
Rokko-Takao station passes through the fracture zone of Manpukuji fault. In this station, the continuous observation of crustal movements have been performed by using the Ishii-type three-component strainmeter, the extensometers, the water-tube tiltmeters, the pore pressure meters and so on. The maximum principal strain of extension in the east-northeast direction increased at nearly constant rate for about 30 seconds just after the arrival of the seismic waves of the 2011 earthquake. In addition, just after the arrival of the seismic waves of the 2018 earthquake, the maximum principal strain in the east-northeast direction increased for about one second and kept constant for the following two seconds. These principal strain changes agreed with the calculated ones based on the source processes reported by the Meteorological Agency and Disaster Prevention Research Institute, Kyoto University (Mukai et al., 2020). It is considered that we could detect the strain changes due to the time development of co-seismic fault slips, that is, the source process by using the strainmeter.
Three extensometers in the direction of N69oE are installed in Rokko-Takao station. Rokko-Futtabi station about 0.5km south of Rokko-Takao station is equipped with one extensometer in the direction of N9oW. These extensometers observed the increase of the strain changes at nearly constant rate just after the arrival of the seismic waves of the above earthquakes as the case of the strainmeter, and the observed strain changes agreed with the calculated ones based on the source processes. This shows that we can confirm a source process by using the crustal movements observed by strainmeters and extensometers installed in the underground tunnel.
Rokko-Takao station and Rokko-Futatabi station are equipped with some water-tube tiltmeters as well. Although these tiltmeters respond slowly to the inclined ground, the tilt changes at nearly constant rate could be observed with the water-tube tiltmeters for several 10 seconds just after the 2011 earthquake as a result of the long source process. In this study, I investigated the crustal movements due to the source processes observed by the water-tube tiltmeters as well as the strainmeter and the extensometers.
Rokko-Takao station passes through the fracture zone of Manpukuji fault. In this station, the continuous observation of crustal movements have been performed by using the Ishii-type three-component strainmeter, the extensometers, the water-tube tiltmeters, the pore pressure meters and so on. The maximum principal strain of extension in the east-northeast direction increased at nearly constant rate for about 30 seconds just after the arrival of the seismic waves of the 2011 earthquake. In addition, just after the arrival of the seismic waves of the 2018 earthquake, the maximum principal strain in the east-northeast direction increased for about one second and kept constant for the following two seconds. These principal strain changes agreed with the calculated ones based on the source processes reported by the Meteorological Agency and Disaster Prevention Research Institute, Kyoto University (Mukai et al., 2020). It is considered that we could detect the strain changes due to the time development of co-seismic fault slips, that is, the source process by using the strainmeter.
Three extensometers in the direction of N69oE are installed in Rokko-Takao station. Rokko-Futtabi station about 0.5km south of Rokko-Takao station is equipped with one extensometer in the direction of N9oW. These extensometers observed the increase of the strain changes at nearly constant rate just after the arrival of the seismic waves of the above earthquakes as the case of the strainmeter, and the observed strain changes agreed with the calculated ones based on the source processes. This shows that we can confirm a source process by using the crustal movements observed by strainmeters and extensometers installed in the underground tunnel.
Rokko-Takao station and Rokko-Futatabi station are equipped with some water-tube tiltmeters as well. Although these tiltmeters respond slowly to the inclined ground, the tilt changes at nearly constant rate could be observed with the water-tube tiltmeters for several 10 seconds just after the 2011 earthquake as a result of the long source process. In this study, I investigated the crustal movements due to the source processes observed by the water-tube tiltmeters as well as the strainmeter and the extensometers.