[J07-1] Tracking the sea floor in motion I

[J07-1-02] Interseismic seafloor GPS-A data used for tsunami generation modeling along the Nankai trough, Japan

^○Shun-Ichi Watanabe¹, Yehuda Bock², Diego Melgar³, Tadashi Ishikawa¹, Yusuke Yokota¹, Keiichi Tadokoro⁴ (1.Japan Coast Guard, Tokyo, Japan, 2.Scripps Institution of Oceanography, La Jolla, U.S., 3.University of California, Berkeley, Berkeley, U.S., 4.Nagoya University, Nagoya, Japan)

Dense near-fault GPS-A seafloor geodetic and on-shore GPS GEONET observations provide significantly improved resolution of the interseismic slip deficit in the Nankai trough, Japan [Yokota et al., 2016]. In a previous study, we included additional seafloor data at the Kumano basin collected by Nagoya University [Tadokoro et al., 2012] to estimate expected seafloor deformation during a large subduction zone earthquake as input to tsunami models [Watanabe et al., 2016 AGU]. In order to derive the appropriate model, the displacements caused by episodic events should be quantitatively estimated. Therefore, we first constructed a 3D FEM model to quantify the postseismic displacements following the southeastern off the Kii Peninsula earthquakes (on Sep. 5, 2004 JST, M 7.1, 7.4). Because these events occurred near the trough axis, the larger deformation was caused on the seafloor in the Kumano basin. Our results indicated that the displacements of up to 1 cm/year occurred in the period of July 2006 to July 2009 at the GPS-A sites. The corrected displacements were aligned to the Nankai-block (forearc sliver) to derive the slip deficit from the tectonic model of Loveless and Meade [2010]. For the slip deficit estimation, we modified the static model approach of Melgar and Bock [2013] using Okada's Green's functions. The plate interface was divided into approximately 25 x 25 km rectangular subfaults with displacements constrained to minimize Akaike's Bayesian Information Criterion. We then estimated the coseismic motions assuming that the 100-years of slip deficit was released instantaneously. These were then used as the initial conditions to model the propagation of the subsequent tsunami. In the presentation, we will show the updated distribution of the slip deficit rate in the Nankai trough region and the tsunami model.