Influence of the 2011 Tohoku-oki earthquake on the strain-rate field around the Noto Peninsula

Abstract Before the M7.6 Noto Peninsula earthquake on 1 January 2024, which caused severe damage, an earthquake swarm started from May 2018 and became very active after December 2020 in the northeastern tip of the Noto Peninsula. It is widely considered that the swarm activity was triggered by upward migration of fluids with a large volume, as exemplified by Global Navigation Satellite System (GNSS) data that showed horizontal inflation and uplift around above the swarm area. However, the cause of the upward fluid migration has hardly been discussed. In this study, we consider this problem focusing on geodetic data. By applying a geodetic data inversion method based on basis function expansion to GNSS data in central Japan, we estimate the temporal change of strain-rate fields before and after the 2011 Tohoku-oki earthquake. Because of the postseismic deformation of the 2011 Tohoku-oki earthquake, the estimated strain-rate fields show a drastic change before and after the 2011 Tohoku-oki earthquake: dilatation rates and EW contraction rates reversed from contraction to extension in a wide area including the Noto Peninsula. The obtained strain-rate fields are further converted to the stress-rate fields under the condition of an isotropic elastic medium. The resulting extensive stress-rate field is likely to have facilitated the upward fluid migration, which would trigger the swarm activity in the Noto Peninsula since 2018. Graphical Abstract