Kermadec Islands Earthquake on Apr. 24, 2023

We have simulated the tsunami generated from the earthquake at the Kermadec Islands, New Zealand (29.955°S, 177.838°W, depth = 49.0 km, M = 7.1 at 00:41:56 UTC according to USGS) on April 24, 2023 (Fig. 1). The fault length and width are 40 km × 20 km. The average slip on the fault is 1.5 m. The seismic moment is 6.0 × 10

^{19}Nm (Mw = 7.1) assuming the rigidity of 5 × 10^{10}N/m². The focal mechanism is strike: 176°, dip: 27°, slip: 72° from the USGS's W-phase moment tensor solution (NP1). The top depth of the fault was assumed to 40 km.

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 15 arc-second grid data from GEBCO_2022, 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 Tide gauge and DART 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 South Pacific Ocean (Fig. 3).

Fig.1 Tsunami Source ModelThe red lines indicate uplift with the contour interval of 0.02 m, while the blue dotted lines indicate subsidence with the contour interval of 0.02 m. The focal mechanisms determined by USGS are also shown.

Fig.2 Maximum Height of Simulated Tsunami and Tsunami WaveformsSolid 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)

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.

GEBCO Compilation Group (2022), GEBCO_2022 Grid (doi:10.5285/e0f0bb80-ab44-2739-e053-6c86abc0289c).

Last Updated on 2023/4/25