Simulation_Tohoku
A conceptual earthquake cycle simulation of the Tohoku-Oki, Japan area. The M9 megathrust event occurs on a large asperity with a recurrence time of ~600 years. Deep brittle asperities produce high-frequency slip during the M9 event and also M7+ earthquakes recurring every several decades.
The M9 2011 Tohoku Great Earthquake featured outstanding characteristics including large shallow slip (> 50 m near the trench) and deep high frequency radiation. Such megathrust events have a long recurrence time (~1000 years). Numbers of M7+ earthquakes occur in the deeper part of the megathrust between the M9 events. Here we develop 3D quasi-dynamic simulations that reproduce these key features.
To save computational cost, we first perform 2.5D multi-cycle simulations based on a fault grid with a single cell along-dip and multiple cells along-strike. We assume a velocity-weakening zone from 10 to 32 km depth. The effective normal stress increases linearly from 0 to 20 km depth and is constant below 20 km depth. The characteristic slip distance (Dc) is 0.4 m. The model parameters are tuned to get multi-cycle megathrust events with recurrence time of ~1000 years and large slip near the trench.
Figure 1: Simulation of multiple subduction earthquake cycles in 2D. (a) Assumed depth-dependent distribution of rate-and-state friction parameters (a-b) and effective normal stress (σ). (b) Evolution of cumulated slip over several earthquake cycles. Each curve shows the slip as a function of depth at a certain time. The time intervals are irregularly sampled and longer than dynamic rupture time scales. The widely spaced profiles correspond to large megathrust earthquakes. (c) Evolution of slip during a megathrust earthquake. Same representation as in (b), but with shorter time intervals. (d) Moment rate as a function of time over 10 earthquake cycles.
Figure 2: 3D simulation with deep brittle asperities. Left: spatial distribution of logarithmic slip rate normalized by plate velocity at selected times during and between two M9 megathrust events. Snapshot times are indicated by red circles in the right panel. Right: Peak slip rate as a function of time.
Animation: 3D simulation with deep brittle asperities. Top: Logarithmic slip rate normalized by the plate velocity. Bottom: Peak slip rate as a function of time.