Tsunami earthquakes are defined as the events that rupture near the trench and characterised by longer source duration and large tsunami waves following the earthquake. Despite the hazard imposed by tsunami earthquakes, physical processes (e.g. duration) of tsunami earthquakes and the underlying mechanisms of both earthquake and tsunami generations have not been well-understood. The complexity of near trench structure, including steep bathymetry, water layer, and highly heterogeneous velocity structure, is a key barrier to better understand tsunami earthquakes.
With my collaborator Dr Wu Wenbo, we have developed a SEM-DSM hybrid numerical simulation code (Wu et al., 2018), that computes the 3D wavefields in the earthquake source region with Spectral-Element-Method (SEM) and then propagates the wavefield to the rest of the spherical earth with Direct-Solution-Method (DSM). The SEM can handle any structure complexity in the source region, including velocity heterogeneity, topography/bathymetry, anisotropy, and solid/fluid coupling. The application of this numerical method to two Mw6.8 earthquakes in the central Chilean subduction zone has shown substantial improvement to the teleseismic waveform modelling when bathymetry/topography and water layer were considered in teleseismic wavefield simulations. The highly accurate wavefield simulations had led to ~5km uncertainty in horizontal and ~2km uncertainty in vertical for the refined source location (Qian et al., 2018). Such a level of uncertainty is much better than that in the global earthquake catalogues (e.g. ~20km/10km in USGS and GCMT catalogues). We show that the apparently ultra-long duration of the mainshock as proposed by a previous study (Lee et al., 2016) was likely an artefact from structure (Qian et al., 2018). Based on the high-resolution seismic profiles, we also propose a pull-up structure model to explain the mechanism of tsunami earthquakes in the Mentawai region (Hananto et al., 2020).
- Earth Observatory of Singapore