Given recent advances in geodetic data, interseismic locking models along the megathrust now become useful to qualitatively evaluate future earthquake potential. However, an individual earthquake's true rupture potential is challenging, as it depends on more than just a static image of prior locking. Here, we test the determinism of interseismic locking models using spontaneous rupture simulations and the well-resolved processes associated with the 2012 moment magnitude (Mw) 7.6 Nicoya earthquake. To do so, we estimate initial megathrust stress from locking by assuming that the entire slip deficit will be released in the next megathrust earthquake. Then we initiate spontaneous ruptures at the hypocenter of the 2012 Nicoya earthquake. We find scenarios that approximate the same coseismic slip distribution and final earthquake moment magnitude as obtained from seismic and geodetic observations, demonstrating that deriving potential rupture scenarios from interseismic locking is feasible. We also find that spontaneous rupture scenarios from different locking models differ in moment rate duration and thus ground motion prediction, although the final slip distribution and moment magnitude were similar. The results highlight that quantifying rupture scenarios and ground motions from reliable locking models by dynamic rupture simulations can be an effective tool for seismic hazard assessment in subduction zones.
Key Points:• We conduct numerical simulations of rupture scenarios based on interseismic locking models • Our simulated earthquake scenario is well consistent with kinematic models of the 2012 Mw 7.6 Nicoya earthquake • Details of rupture process and synthetic waveforms depend on the choice of the input locking model
Supporting Information:• Supporting Information S1• Movie S1Note that the dynamic cohesive zone size is smaller than the static one (Day et al., 2005). Therefore, we tested mesh grid sizes of 400, 300, 250, and 200 m on the fault interface during dynamic rupture simulations. The results show that the final slip patterns are stable for 300, 250, and 200 m, while the slip amplitudes and moment magnitudes slightly differ ( Figure S2). Based on the grid size test, we select 250 m as the
Frictional properties on subduction interfaces are essential for understanding earthquake nucleation, rupture propagation, and tsunami generation during megathrust earthquakes. Because they cannot be directly observed, they have been inferred from different approaches. However, none of them have reported constraints immediately before a megathrust earthquake. Here we quantify the frictional strength on the megathrust prior to the 2012 Mw 7.6 Nicoya earthquake by conducting spontaneous rupture simulations with constraints from near‐field observations. Our preferred dynamic rupture model shows a remarkable fit on the near‐field data. The simulation results indicate an average strength drop of <5 MPa. Considering typical ranges for the dynamic friction coefficient fd ≤ 0.2 and the static friction coefficient fs = 0.6, we infer that the average strength on the megathrust is ≤7.5 MPa. Such low strength is attributed to the near‐lithostatic pore pressure along the subduction interface, which is implied by seismic studies in this region.
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