Off Tohoku-Pacific Tsunami on March 11, 2011

We have simulated the tsunami generated from the the Off Tohoku-Pacific earthquake (38.322°N, 142.369°E, Mw = 8.9 at 5:46:23 UTC according to USGS) on March 11, 2011. The assumed tsunami source is located within the aftershock area (Fig. 1). The fault length and width are 400 km × 150 km. The focal mechanisms are strike:193º, dip:14º, slip:81º from the USGS's Wphase moment tensor solution. The top depth of the fault was assumed to 3 km. The average slip on the fault is 20 m. As the initial condition for tsunami, static deformation of the seafloor is calculated for a rectangular fault model [Okada, 1985] using the source models. The used bathymetry data are 30 arc-second grid for tide gauges in Japan and 2 arc-minute grid for off shore, resampled from GEBCO_08 30 arc-second grid data. To calculate tsunami propagation, the linear shallow-water, or long-wave, equations were numerically solved by using a finite-difference method [Satake, 1995]. The maximum heights of simulated tsunami indicate that the tsunami energy is concentrating to directions perpendicular to the strike of fault (Fig. 2). We have downloaded the DART and tide gauges data from NOAA's and JCG's web sites and compared the simulated tsunami waveform and the observed one (Fig. 2). We can see the tsunami propagation around the coasts in Japan (Fig. 3).

Fig.1 Tsunami Source ModelThe red contours indicate uplift with the contour interval of 0.5 m, while the blue contours indicate subsidence with the contour interval of 0.5 m. Aftershocks (determined by USGS) during about one day after the mainshock are also shown by red circles.

Fig.2 Maximum Height of Simulated TsunamiSolid lines in red and blue indicate the observed tsunami waveform and synthtic ones, respectively.

Fig.2 Maximum Height of Simulated TsunamiSolid lines in red and blue indicate the observed tsunami waveform and synthtic ones, respectively.

Fig.3 Tsunami Propagation (Click to start animation)The red color means that the water surface is higher than normal sea level, while the blue means lower.

by Yushiro Fujii (IISEE, BRI) and Kenji Satake (ERI, Univ. of Tokyo)

ReferencesOkada, Y. (1985), Surface Deformation Due to Shear and Tensile Faults in a Half-Space, Bull. Seismol. Soc. Am., 75, 1135-1154.

Satake, K. (1995), Linear and Nonlinear Computations of the 1992 Nicaragua Earthquake Tsunami,Pure and Appl. Geophys., 144, 455-470.

Last Updated on 2011/3/12