Miyazaki Earthquake on Aug. 8, 2024  


 

We have simulated the tsunami generated from the Miyazaki earthquake (31.719°N, 131.527°E, depth = 25.0 km, M = 7.1 at 7:42:55 UTC according to USGS) on Aug. 8, 2024 (Fig. 1). Fig. 1 shows the assumed tsunami source model. The fault length and width are 40 km x 20 km. The focal mechanism is strike: 203°, dip: 19°, slip:72° from the USGS's W-phase moment tensor solution (NP1). The top depth of the fault was assumed to 20 km. The average slip on the fault is 1.2 m. The seismic moment is 4.80 x 1019 Nm (Mw = 7.1) assuming the rigidity of 5 x 1010 N/m2.
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 is the 15 arc-second grid data from GEBCO_2023, which was resampled to 12 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]. We have downloaded the DART and Tide gauge data from the NOAA's and UNESCO/IOC's web sites, respectively, and compared the simulated tsunami waveforms and the observed ones (Fig. 2). We can see the tsunami propagation in the Pacific Ocean (Fig. 3).


 

Fig.1 Tsunami Source Model Case1

Fig.1 Tsunami Source Model
 The red and blue lines indicate uplift and subsidence, respectively, with the contour intervals of 0.05 m. The focal mechanism of the mainshock and aftershocks (red circles) determined by USGS are also shown.


 

Fig.2 Maximum Height of Tsunami

Fig.2 Maximum Height of Simulated Tsunami and Tsunami Waveforms
 Solid lines in red indicate the observed tsunami waveforms. The blue lines are calculated tsunami waveforms.


 




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.
GEBCO Compilation Group (2023) GEBCO 2023 Grid (doi:10.5285/f98b053b-0cbc-6c23-e053-6c86abc0af7b)


Last Updated on 2024/8/8