[S-CG40] Science of slow-to-fast earthquakes

[SCG40-P51] An interpretation of gravity changes caused by the Noto Peninsula Earthquakes based on a fault model

*Maki Oshida¹, Yoshiyuki Tanaka¹ (1.Department of Earth and Planetary Science, The University of Tokyo )

Keywords:Noto Peninsula Earthquake, Gravity, fluid, crustal deformation, earthquake swarm

Gravity at Earth's surface changes due to fault movement. Fault movement causes mass redistributions due to surface uplift/subsidence and density change underground. On May 5, 2023 and January 1, 2024 M6.5 and M7.6 earthquakes occured in Noto Peninsula, respectively. The GNSS network has detected crustal deformations associated with these earthquakes, and gravity changes have also been measured with terrestrial campaign observations. From inversion of the crustal deformation data a fault model can be estimated, based on the elasticity dislocation theory of a homogeneous half-space medium. The fault mechanism is reverse fault for both earthquakes. Using a fault model obtained we calculated gravity change based on the same dislocation theory. A comparison between the theoretical and observed gravity changes shows that, for both events, there is disagreement exceeding ~10%. Therefore, to account for gaps, we are considering the following possible mechanism; effects of a local crustal density difference, poroelastic rebound, and a tensile component into which water comes. The influence of the first two factors is considered to be small, compared with the third factor. We are trying to construct a fault model including a tensile component. For this, we will perform inversion that includes gravity observations as well as crustal deformation.