Preliminary Tsunami Simulation of the M 7.5 – 78 km N of Palu, Indonesia

We have simulated the tsunami generated from the M 7.5 – 78km N of Palu, Indonesia (0.178°S, 119.840°E, depth=10.0 km, M = 7.5 at 10:02:43 UTC according to USGS) on September 28, 2018. The assumed tsunami sources cover the aftershock area for 2 hours after the mainshock (Fig. 1). The fault size and average slip are 120 km × 20 km and 3.1 m. The focal mechanism is strike=350º, dip=67º, and slip=-17º from the USGS’s W-phase moment tensor solution. The top depth of the fault was assumed to 5 km. The seismic moment is 2.497 x 1020Nm (Mw = 7.5) assuming the rigidity of 5 x 1010N/m2.


Figure 1. Tsunami source model, the red lines indicate uplift with the contour interval of 0.2 m, while the blue contours indicate subsidence with the contour interval of 0.1 m. The epicenter is shown by the blue star. The focal mechanism defined by USGS is also shown.

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 12 arc-second grid data from GEBCO. To calculate tsunami propagation, the linear shallow-water, or long-wave, equations were numerically solved by using a finite-difference method [Adriano et al., 2018].


Figure 2. Maximum Height of Simulated Tsunami. The epicenter is shown by the blue star.

by Bruno Adriano and Shunichi Koshimura (IRIDeS, Tohoku University) 

Okada, Y. (1985), Surface Deformation Due to Shear and Tensile Faults in a Half-Space, Bull. Seismol. Soc. Am., 75, 1135-1154.

Adriano, B., Fujii, Y., Koshimura, S. et al. (2018), Tsunami Source Inversion Using Tide Gauge and DART Tsunami Waveforms of the 2017 Mw8.2 Mexico Earthquake, Pure Appl. Geophys. 175, 35-48.