Off-Fukushima Tsunami on Oct. 25, 2013  


 

We have simulated the tsunami generated from the Off-Fukushima Japan earthquake (37.149°N, 144.679°E, depth=26.1km, M=7.1 at 17:10:18 UTC according to USGS) on October 25, 2013 (Fig. 1). The assumed tsunami sources are based on the USGS's W-phase moment tensor solution of the earthquake.

Case 1: strike = 180°, dip angle = 46º and slip angle = -100º.
Case 2: strike = 15º, dip angle = 45º and slip angle = -79º.
The fault size is 50 km × 25 km for both cases. Top depth of the fault is assumed to 5 km. An average slip on fault is 1 m. The seismic moment is 6.3 x 10**19 Nm (Mw = 7.1) assuming the regidity of 5 x 10**10 N/m**2.

As the initial conditions for tsunami, static deformations of the seafloor are calculated for a rectangular fault model [Okada, 1985] using the source models (Fig. 2). The used bathymetry data is 2 arc-minute grid data resampled from GEBCO 30 arc-second grid data for the DART buoys in the open ocean. For the tide gauges along the coast, we used the bathymetry data of J-EGG500 with 12 arc-second grid interval. To calculate tsunami propagation, the linear shallow-water, or long-wave, equations (for DART buoys) and non-linear shallow-water equations (for tide gauges) were numerically solved by using a finite-difference method [Satake, 1995]. The maximum heights of simulated tsunami are shown with the calculated tsunami waveforms at coastal tide gauges and DART buoys in Fig. 3. We downloaded the DART data from NOAA's web site and compared the observed tsunami waveforms and simulated ones.


 

Fig.1 Mainshock and stations
Fig.1 Epicenter of the earthquake, USGS's W-phase moment tensor solution and locations of tide gauges and DART buoys.


 

Fig.1 Tsunami Source Model USGS1 Fig.1 Tsunami Source Model USGS2
Fig.2 Tsunami source models of Case 1 (left) and Case 2(right).
The red contours indicate uplift with the contour interval of 0.02 m., while the blue contours indicate subsidence with the contour interval of 0.1 m.
Blue star and red circles show the mainshock and aftershocks, respectively, which were determined by USGS.


 

Fig.3 Tide gauges Fig.3 Maximum Height of Simulated Tsunami Fig.3 DART buoys
Fig.3 Distribution of maximum height of the simulated tsunami (Case 2) and comparison of tsunami waveforms
 Solid lines in red indicates the observed tsunami waveforms. The blue and green lines are synthtic tsunami waveforms for Case 1 and Case 2, respectively.


 

by Yushiro Fujii (IISEE, BRI) and Kenji Satake (ERI, Univ. Tokyo)
 
 
References
Okada, 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 2013/11/13