[S-GD02] Crustal Deformation

[SGD02-01] Modeling for a transient crustal deformation around Kussharo caldera, eastern Hokkaido, Japan

*Mako Ohzono¹, Hiroaki Takahashi¹, Teruhiro Yamaguchi¹ (1.Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University)

The Kussharo caldera in eastern Hokkaido is located on the volcanic front of the island arc where the Pacific plate subducts beneath the Okhotsk (North American) plate. The result of nationwide GNSS observation has reported that the area to the west of Atosanupuri experienced a temporary expansion event in 1993-1995, and a contraction after this event. Because this area has a potential for damaged inland earthquakes and micro-seismic activity rather than other Hokkaido areas, we have installed continuous and campaign GNSS stations around this area since 2003 to grasp the detailed crustal deformation. By the framework of the "Consortium to utilize the SoftBank original reference sites for Earth and Space Science", which is constructed in 2022, we obtained additional GNSS observation data around the Kussharo caldera in September 2020, 2021, and 2022. Therefore, we processed the available data and estimated more detailed recent crustal deformation. As a result, from around the latter half of 2021, the crustal deformation pattern, which had previously shown a contraction trend toward the center of the Atosanupuri volcanoes, changed, and now the trend of divergence (expansion) around the same place has been captured. Following the model to explain the crustal deformation at the 1993-1995 expansion event estimated by Fujiwara et al. (2017), we tried to estimate the deformation source with two models. When the geometry is fixed and only the opening amount is changed (Case 1), the volume change is about 20% of that at the time. On the other hand, when the geometry is freely changed to some extent (Case 2), the volume change is about 40% of that at the time, and the estimated depth of the source becomes shallow, about 2 km. Since this transient deformation has continued even at the end of 2022, it is necessary to pay attention to what kind of transition of this activity will occur in the future.

[Acknowledgements] The SoftBank's GNSS observation data used in this study was provided by SoftBank Corp. and ALES Corp. through the framework of the "Consortium to utilize the SoftBank original reference sites for Earth and Space Science". This study was also supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its The Second Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research).