Alaska Tsunami on Jan. 23, 2018  


 

We have simulated the tsunami generated from the Alaska earthquake (56.046N, 149.073W, depth = 25.0 km, M = 7.9 at 09:31:42 UTC according to USGS) on January 23, 2018 (Fig. 1). The assumed tsunami source is located within the aftershock area (Fig. 1). The fault length and width are 80 km 20 km. The focal mechanism is strike:259, dip:74, slip:10 from the USGS's W-phase moment tensor solution. The top depth of the fault was assumed to 5 km. The average slip on the fault is 10 m. The seismic moment is 8.0 x 10**20 Nm (Mw = 7.9) assuming the rigidity 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 the 30 arc-second grid data from GEBCO, 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 applied the phase correction method [Watada et al., 2014] to the calculated tsunami waveforms. We have downloaded the DART data and Tide gauge data from 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

Fig.1 Tsunami Source Model
The red lines indicate uplift with the contour interval of 0.2 m, while the blue dotted lines indicate subsidence with the contour interval of 0.2 m. Aftershocks determined by USGS are shown by red circles. The focal mechanism determined by USGS is also shown.


 

Fig.2 Maximum Height of Tsunami

Fig.2 Maximum Height of Simulated Tsunami and Tsunami Waveforms
Solid lines in red and blue indicate the observed tsunami waveforms and calculated ones, respectively.
Purple lines show the synthetic tsunami waveforms by applying the phase correction method [Watada et al., 2014].


 


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.
Watada, S., S. Kusumoto and K. Satake (2014), Traveltime delay and initial phase reversal of distant tsunamis coupled with the self-gravitating elastic Earth, J. Geophys. Res., 119, 4287-4310.


Last Updated on 2018/2/2