Integrated Simulation of Earthquake and resulting Ground Motion and Tsunami Generation for Understanding the Nankai Trough Megathrust Earthquakes

Abstract:

In order to examine how the diversity in the earthquake fault-rupture scenario alters the ground motion and tsunami generation, we have conducted an integrated simulation of earthquake, and resulting seismic ground motion and tsunami generation. The result of earthquake simulation is used as an input for ground motion and tsunami simulation. Here, we examined how the frictional property used in the earthquake simulation affects the fault rupture propagation process and the resulting ground motion and tsunami generation.

In this study, a large fault rupture area with different frictional properties was used for representing the diversity of large earthquake (~ Mw 8.5-8.8) scenarios. The rupture area is commonly spread from Shikoku Island to Suruga Bay along the Nankai Trough. A crack propagation model based on the quasi-dynamic approach, where the frictional property of the fault in a plate boundary in a fully-dynamic approach can be expressed by energy dissipation in each small fault unit, is used. The target volume for ground motion simulation is 1,200 km (EW) x 1,000 km (NS) x 250 km (depth). The equations of motion for viscoelastic body were solved by means of finite-difference method with discretization of 0.5 km and 0.25 km in horizontal and vertical direction, respectively.

As a result, energy dissipation mainly affects the fault rupture propagation speed resulting in several types of seismic ground motions and tsunamis. As energy dissipation decreases, the rupture propagation speed becomes lower and seismic ground motion dramatically becomes weak, characterized by decay in amplitude and shift in frequency. Unlike ground motion, tsunami does not dramatically attenuate, sometimes leading to tsunami earthquake, which is apparent from the difference between the maximum velocity range of ~ 6 – 0.5 m/s and tsunami height range of ~ 6.5 – 3 m. The relation between the generation of earthquake, and that of seismic ground motion and tsunami was clarified in this simulation.