14:00 〜 14:15
[J05-5-03] Crustal deformation in and around the Atotsugawa fault before and after the Tohoku-Oki earthquake
The 2011 Tohoku-Oki earthquake (Mw9.0) provides us the first opportunity to examine the responses of strain accumulation zones and active faults to megathrust earthquakes with dense permanent GPS network. In this presentation, we report the differences and/or similarities between pre, co, and post seismic crustal deformation of the earthquake using GPS data in and around the Atotsugawa fault, located at the central part of Niigata-Kobe Tectonic Zone (Sagiya et al., 2000).
We used daily coordinates obtained from the GPS stations operated by university group in addition to GEONET. For the pre- and post-seismic period, we estimated the velocity fields by removing annual and semi-annual components. For the co-seismic displacement, we calculated 5 days average of the coordinates before and after the earthquake, respectively, and subtracted each other. From the velocities and displacements, we calculated the strain rates following the method of Shen et al. (1996).
Spatial pattern of the co-seismic strain, which is the elastic response, is completely different from the pre and post seismic strain rates pattern. Therefore we conclude that the pre and post seismic strain concentration, similar to each other, is mainly caused by the inelastic straining (e.g. viscous flow) which is essentially driven by the absolute stress. The absolute stress accumulated over a long time scale is far larger than the stress change by one earthquake, which explains the similarity between pre and post seismic strain rates.
Looking in detail, the sense of pre- and post-seismic strain rates reverse in the south of the Hida mountain range and to the east of Mt. Ontake. Both regions are known as thermally active areas and many small earthquakes have been occurring frequently. Therefore, the change in the strain rates in these regions might be related to the volcanic activities.
We used daily coordinates obtained from the GPS stations operated by university group in addition to GEONET. For the pre- and post-seismic period, we estimated the velocity fields by removing annual and semi-annual components. For the co-seismic displacement, we calculated 5 days average of the coordinates before and after the earthquake, respectively, and subtracted each other. From the velocities and displacements, we calculated the strain rates following the method of Shen et al. (1996).
Spatial pattern of the co-seismic strain, which is the elastic response, is completely different from the pre and post seismic strain rates pattern. Therefore we conclude that the pre and post seismic strain concentration, similar to each other, is mainly caused by the inelastic straining (e.g. viscous flow) which is essentially driven by the absolute stress. The absolute stress accumulated over a long time scale is far larger than the stress change by one earthquake, which explains the similarity between pre and post seismic strain rates.
Looking in detail, the sense of pre- and post-seismic strain rates reverse in the south of the Hida mountain range and to the east of Mt. Ontake. Both regions are known as thermally active areas and many small earthquakes have been occurring frequently. Therefore, the change in the strain rates in these regions might be related to the volcanic activities.