Spatiotemporal crustal strain distribution around eastern Hokkaido measured by GEONET

The crustal deformation field in eastern Hokkaido is affected by a little complex tectonic system, such as the interplate coupling between the Pacific plate and the Okhotsk plate, deformable volcanic front, local volcanism, and inland seismic activity. In order to confirm spatiotemporal change of the crustal strain distribution in this area, GNSS daily coordinates obtained from GEONET are analyzed. The 41 of data sets made by three-years daily coordinate time series shifting 0.5 years since 1996.5 are prepared after elimination of coseismic steps induced by several large earthquakes. Then, velocity and strain tensors are calculated. It is clear that the 2003 Tokachi-oki earthquake and the 2011 Tohoku-oki earthquake generated temporary strain disturbances at this study area. However, most of strain fields indicate NW-SE contractional maximum strain through all period. This contractional direction corresponds to the Pacific plate convergence or orthogonal direction with respect to the Kurile Trench axis. It is thought that the plate convergence effect is working in this area even though disturbances receives, such as large earthquakes. The high strain rate field around volcanic front exists through the whole period. The strain field calculated from simulated interseismic velocity data provided by Itoh et al. (2019), which assumes thinner elastic layer with lower rigidity in the volcanic front region than forearc and backarc regions, also reproduces high strain rate field at this area. Around each volcano, the crustal deformation field is probably composed of this regional heterogeneous structure effect and local volcanic activities