5:15 PM - 6:45 PM
[U15-P67] Effects of possible three-dimensional heterogeneity on future postseismic deformation of the 2024 Noto Peninsula Earthquake
Keywords:Crustal movement, The 2024 Noto Peninsula Earthquake, Post-seismic deformation, Viscoelastic relaxation
This study focuses on the crustal deformations precipitated by the Mj 7.6 Noto Peninsula Earthquake, which struck Ishikawa Prefecture on January 1, 2024. The peninsula is distinguished by its extensive marine terraces, evidencing long-term uplift and sudden seismic events (e.g., Hiramatsu et al., 2008). Despite this, the intricacies of its formation remain obscure. Discerning the impacts of gradual movements, notably postseismic deformation, through field geological explorations is problematic. Moreover, the genesis of inland earthquakes is uncertain, especially where the temporal and spatial evolution of stress and strain is concerned, with heterogeneous viscosity structures playing a critical role (Yamasaki and Seno, 2005).
To address this, the present study undertakes model computations that incorporate the subsurface's three-dimensional heterogeneous field to forecast the viscoelastic relaxation subsequent to the 2024 Noto Peninsula Earthquake. Utilizing the semi-analytical boundary element method (Barbot and Fialko, 2010), this research simulates Maxwell viscoelastic relaxation, calculating a decade of viscoelastic relaxation displacement resulting from stress perturbations induced by rectangular fault models disseminated by the Geospatial Information Authority of Japan. This model includes a one-dimensional stratification of the upper crust, lower crust, and mantle and integrates a three-dimensional heterogeneous model that accounts for low-viscosity zones, drawing on the existence of a fluid-rich lower crust as reported in preceding studies (Nakajima et al., 2022; Nishimura et al., 2023).
The initial computations of the one-dimensional stratified model disclosed that the northern segment of the Noto Peninsula, alongside its adjacent maritime zones, is anticipated to subside approximately ten centimeters, a finding starkly contrasting with the displacement observed during the earthquake. A comparative analysis between the three-dimensional heterogeneous model and the one-dimensional stratified model revealed that incorporating low-viscosity zones induces a relative uplift trend directly above these regions. The extent and magnitude of uplift are proportional to the area covered by the low-viscosity zones. Suppose the low-viscosity zone extends along the southern side of the coseismic fault (i.e., the hanging wall side of the reverse fault). It will result in the inland side of the northern Noto Peninsula experiencing an uplift of several tens of centimeters relative to the offshore areas, with a similar deformation pattern with the coseismic time period. In such a case, the impact of postseismic deformation could be simple, amplifying the displacement patterns of coseismic.
To address this, the present study undertakes model computations that incorporate the subsurface's three-dimensional heterogeneous field to forecast the viscoelastic relaxation subsequent to the 2024 Noto Peninsula Earthquake. Utilizing the semi-analytical boundary element method (Barbot and Fialko, 2010), this research simulates Maxwell viscoelastic relaxation, calculating a decade of viscoelastic relaxation displacement resulting from stress perturbations induced by rectangular fault models disseminated by the Geospatial Information Authority of Japan. This model includes a one-dimensional stratification of the upper crust, lower crust, and mantle and integrates a three-dimensional heterogeneous model that accounts for low-viscosity zones, drawing on the existence of a fluid-rich lower crust as reported in preceding studies (Nakajima et al., 2022; Nishimura et al., 2023).
The initial computations of the one-dimensional stratified model disclosed that the northern segment of the Noto Peninsula, alongside its adjacent maritime zones, is anticipated to subside approximately ten centimeters, a finding starkly contrasting with the displacement observed during the earthquake. A comparative analysis between the three-dimensional heterogeneous model and the one-dimensional stratified model revealed that incorporating low-viscosity zones induces a relative uplift trend directly above these regions. The extent and magnitude of uplift are proportional to the area covered by the low-viscosity zones. Suppose the low-viscosity zone extends along the southern side of the coseismic fault (i.e., the hanging wall side of the reverse fault). It will result in the inland side of the northern Noto Peninsula experiencing an uplift of several tens of centimeters relative to the offshore areas, with a similar deformation pattern with the coseismic time period. In such a case, the impact of postseismic deformation could be simple, amplifying the displacement patterns of coseismic.