Tsunami Scenarios Based on Interseismic Models Along the Nankai Trough, Japan, From Seafloor and Onshore Geodesy

Abstract

The recent availability of Global Positioning System‐Acoustic seafloor geodetic observations enables us to resolve the spatial distribution of the slip deficit rate near the Nankai trough, southwestern Japan. Considering a tectonic block model and the transient deformation due to the major earthquakes in this area, the slip deficit rate between the two relevant blocks can be estimated. In this study, we remove the time‐dependent postseismic deformation of the 2004 southeastern off the Kii Peninsula earthquakes (MJMA 7.1, 7.4), which had led to the underestimation of the slip deficit rate in earlier studies. We model the postearthquake viscoelastic relaxation using the 3D finite element model with bi‐viscous Burgers rheology, as well as the afterslip on the finite faults. The corrected Global Positioning System‐Acoustic and land‐based Global Navigation Satellite Systems data are aligned to the existing tectonic model and used to estimate the slip deficit rate on the plate boundary. We then calculate the coseismic displacements and tsunami wave propagation with the simple assumption that a hundred years of constant slip deficit accumulation was released instantaneously. To evaluate the influence of uncertainties in the plate interface geometry on a tsunami model for the Nankai trough, we investigated two different geometries and performed checkerboard inversion simulations. Although the two models indicate roughly similar results, the peak height of the tsunami wave and its arrival time at several points are significantly different in terms of the expected hazard.

Probabilistic tsunami inundation assessment of Kuroshio Town,Kochi Prefecture, Japan considering the Nankai-Tonankai megathrust rupture scenarios

“…The earthquake slip distributions of the 2012 CDMC models are spatially broader than inverted source models for the 2011 Tohoku earthquake and tsunami that show more concentrated 45 slips (Iinuma et al, 2012;Satake et al, 2013), and are consistent with current geodetic estimates of inter-seismic coupling (e.g. Baranes et al, 2018;Watanabe et al, 2018). It is noteworthy that the 2012 CDMC models are intended for representing extreme rupture scenarios at national scale and are not sufficient for encompassing the variability of tsunami hazards at regional and local scales.…”

Interplate Coupling State at the Nansei‐Shoto (Ryukyu) Trench, Japan, Deduced From Seafloor Crustal Deformation Measurements

“…• Seafloor crustal deformation measurements were performed at two stations along the Nansei-Shoto (Ryukyu) Trench, Japan • Strong interplate coupling was estimated from our measurements, whereas it had been thought to be weak at the Nansei-Shoto Trench • The coupled segment coincides with the source area of the 1791 event and is isolated from the area of short-term slow slip activity crustal deformation has been carried out with an observation network spanning from the Japan Trench to the Nankai Trough (Fujita et al, 2006;Kido et al, 2011;Sato et al, 2013Sato et al, , 2011Tadokoro et al, 2012;Tomita et al, 2017;Watanabe et al, 2015;Yokota et al, 2015). Interplate coupling states have been derived from the monitoring results of seafloor crustal deformation in the whole Nankai Trough subduction zone (Nishimura et al, 2018;Yokota et al, 2016) and for improving tsunami scenarios (Watanabe et al, 2018). In contrast, there had been no station along the Nansei-Shoto Trench before this study.…”

“…Long‐term monitoring of seafloor crustal deformation has been carried out with an observation network spanning from the Japan Trench to the Nankai Trough (Fujita et al, ; Kido et al, ; Matsumoto, Ishikawa, et al, ; Sato et al, , ; Tadokoro et al, ; Tomita et al, ; Watanabe et al, ; Yokota et al, ). Interplate coupling states have been derived from the monitoring results of seafloor crustal deformation in the whole Nankai Trough subduction zone (Nishimura et al, ; Yokota et al, ) and for improving tsunami scenarios (Watanabe et al, ). In contrast, there had been no station along the Nansei‐Shoto Trench before this study.…”

Self-similar stochastic slip distributions on a non-planar fault for tsunami scenarios for megathrust earthquakes

“…In recent decades, to allow earlier and more precise issuance of earthquake and tsunami warnings, dense offshore seismic and OBP networks have been deployed on the ocean floor above the source areas of expected large earthquakes; these include DONET along the Nankai trough (Kaneda et al 2015;Kawaguchi et al 2015) and S-net along the Japan Trench (Kanazawa et al 2016;Mochizuki et al 2016;Uehira et al 2016). Yamamoto et al (2016b) developed a method to rapidly estimate initial tsunami heights by using dense OBP networks.…”