Off Niigata Tsunami on July 16, 2007

We have simulated the tsunami generated from the earthquake off Niigata (37.570°N, 138.478°E, Mw = 6.6 at 01:13:22 UTC according to USGS) on July 16, 2007. The assumed tsunami source is based on the aftershock distribution by Hi-net, NIED and the focal mechanism by NEIC, which is strike = 41º, dip angle = 49º and slip angle = 86º. The fault size is 30 km × 15 km. Top depth of the fault is 10 km. Average slip on fault is 1 m. The seismic moment is 2.3 x 10**19 Nm (Mw = 6.8) assuming the regidity of 5 x 10**10 N/m**2. As the initial condition for tsunami, static deformation of the seafloor is calculated for a rectangular fault model [Okada, 1985] using the source model. The used bathymetry data is JTOPO30 with 30" grid interval. We have adopted finer grid intervals of 6" around the tide gauge stations shown in Fig. 2. To calculate tsunami propagation, the linear shallow-water, or long-wave, equations were numerically solved by finite-difference method [Satake, 1995]. We have downloaded the tide gauge data from GSI's wes site and compared the simulated tsunami waveforms and observed ones. We can see the tsunami propagation in Japan Sea (Fig. 3).

Fig.1 Tsunami Source ModelThe red contours indicate uplift, while the blue contours indicate subsidence with the contour interval of 0.05 m. Aftershocks distribution automatically determined by Hi-net, NIED are also shown.

Fig.2 Maximum Height of Computed Tsunami and Tsunami WaveformsSolid lines in red and purple indicate observed tsunami waveforms and synthetic ones, respectively.

Fig.3 Tsunami Propagation (Click to start GIF 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 (GSJ, AIST)

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 2007/7/19