[M-TT37] New Developments in Earth Science Explored by Dense GNSS Observation Networks

[MTT37-P03] Postseismic deformation of the 2024 M7.6 Noto Peninsula earthquake observed by dense GNSS networks

*Takuya NISHIMURA¹, Yoshihiro Hiramatsu², Yusaku Ohta³ (1.Disaster Prevention Research Institute, Kyoto University, 2.Faculty of Geosciences and Civil Engineering, Institute of Geosciences and Engineering, Kanazawa University, 3.Graduate School of Science, Tohoku University)

Keywords:GNSS, Noto Peninsula, Earthquake, Postseismic deformation

We analyzed GNSS data by SoftBank, GSI(Geospatial Information Authority of Japan), and universities to clarify the deformation related to the 2024 M7.6 Noto Peninsula earthquake. The observed postseismic displacement for about one year shows northeastward displacement in the southeastern side of the mainshock fault, including the Noto Peninsula (Fig. 1), which is similar to the coseismic displacement. However, there are two distinctive differences between coseismic and postseismic displacement patterns. One is postseismic subsidence in the Noto Peninsula, which contrasts with coseismic uplift. The other is a rather gradual spatial decay of postseismic horizontal displacement from the mainshock fault. These observations suggest that viscoelastic relaxation is the main source of the observed displacement. We modeled the postseismic deformation assuming an elastic plate overlying a viscoelastic half-space using VISCO1D code (Pollitz, 1997). The elastic thickness, the Maxwell viscosity, and the Kelvin viscosity are 27 km, 1.7x10¹⁹ Pa s, and 8.5x10¹⁷ Pa s. A deep afterslip at the downdip extension of the mainshock fault is another minor source for the postseismic displacement. The viscoelastic model predicts a significant postseismic deformation around the source areas for several decades. It is consistent with the observed postseismic deformation of the other large earthquakes in the back-arc region, including the 1964 M7.5 Niigata and the 1993 M7.8 Hokkaido-nansei-oki earthquakes.

Acknowledgments: 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". We are also grateful to GSI for providing us with GNSS data.