资源环境科技发展态势分析平台

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 M-w 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 f(d) <= 0.2 and the static friction coefficient f(s) = 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.

Plain Language Summary Subduction zones host a preponderance of great earthquakes that are sometimes accompanied by destructive tsunamis. The frictional resistance (strength) on subduction interfaces, termed megathrusts, plays critical roles in controlling earthquake rupture process and thus significantly impacts the ground motion intensity and the tsunamigenic potential during earthquakes. However, the strength on the megathrust is difficult to estimate directly and evolves over time. Here, we constrain the strength on the Nicoya megathrust shortly before the 2012 Nicoya M-w 7.6 earthquake with constraints from near-field observations. Based on the simulation results, we infer the strength on the megathrust prior to the earthquake to be less than 7.5 MPa. Such low strength at similar to 25 km in depth indicates the existence of compacted fluids with a high pore pressure.