Off Sumatra Island Tsunami on April 11, 2012  


 

We have simulated the tsunamis generated from the Off Sumatra Island, Indonesia earthquake ( 2.311°N, 93.063°E, Mw=8.6 at 8:38:37 UTC, from USGS ) on April 11, 2012. The assumed tsunami sources cover the aftershock area during a half day after the mainshock (Fig. 1). The fault sizes and average slips are 300 km × 30 km and 15 m, respectively, for the both cases. Top depths of the faults are 0 km. The focal mechanism are strike=199º, dip angle=80º and slip angle=3º for the Case 1, and strike=108º, dip angle=87º and slip angle=170º for the Case 2 from the USGS's WPhase Moment Tensor solution. As the initial condition for tsunami, static deformation of the seafloor is calculated for a rectangular fault model [Okada, 1985] using the source model. We used a 2' grid interval bathymetry data from GEBCO . To calculate tsunami propagation, the linear shallow-water, or long-wave, equations were numerically solved by 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 data from NOAA's website and compared the simulated tsunami waveforms and observed ones (Fig. 2). We can see the tsunami propagation in the Indian ocean (Fig. 3).


 

Fig.1 Tsunami Source Model Fig.1 Tsunami Source Model

Fig.1 Tsunami Source Models
 The red contours indicate uplift, while the blue contours indicate subsidence with the contour interval of 0.4 m.
Blue and red stars show the epicenter and centroid, respectively.


 

Fig.2 Maximum Height of Tsunami

Fig.2 Computed Maximum Tsunami Height (Case 1)
 Solid line in red indicates the observed tsunami waveforms. Solid lines in blue and green indicate the synthtic ones for Case 1 and Case 2, respectively.


Fig.3 Tsunami propagation

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)
 
 
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 2012/4/13