Numerical modeling of the subaerial landslide source of the 22 December 2018 Anak Krakatoa volcanic tsunami, Indonesia

The eruption of the Anak Krakatoa volcano (Indonesia) in December 2018 produced a destructive tsunami with maximum runup of 13 m killing 437 people. Since the occurrence of this rare tsunami, it has been a challenge as how to model this tsunami and to reconstruct the network of coastal observations.

A combination of qualitative physical modeling and wavelet analyses of the tsunami as well as numerical modeling to propose a source model is applied. Physical modeling of a volcano flank collapse showed that the initial tsunami wave mostly involves a pure-elevation wave. An initial tsunami period of 6.3–8.9 min was identified through Wavelet analysis, leading to an initial tsunami dimension of 1.8–7.4 km. Twelve source models were numerically modelled with source dimensions of 1.5–4 km and initial tsunami amplitudes of 10–200 m.

Based on the qualities of spectral and amplitude fits between observations and simulations, the tsunami source dimension and initial amplitude in the ranges of 1.5–2.5 km and 100–150 m,was respectively constrained. The best source model involves potential energy of 7.14 × 1013–1.05 × 1014 J equivalent to an earthquake of magnitude 6.0–6.1. The amplitude of the final source model is consistent with the predictions obtained from published empirical equations.