A quantitative comparison and validation of finite-fault models: The 2011 Tohoku-Oki earthquake

Abstract

Large earthquakes rupture faults over hundreds of kilometers within minutes. Finite-fault models elucidate these processes and provide observational constraints for understanding earthquake physics. However, finite-fault inversions are subject to non-uniqueness and substantial uncertainties. The diverse range of published models for the well-recorded 2011 M_w 9.0 Tohoku-Oki earthquake aptly illustrates this issue, and details of its rupture process remain under debate. Here, we comprehensively compare 32 finite-fault models of the Tohoku-Oki earthquake and analyze the sensitivity of three commonly-used observational data types (geodetic, seismic, and tsunami) to the slip features identified. We first project all models to a realistic megathrust geometry and a 1-km subfault size. At this scale, we observe poor correlation among the models, irrespective of the data type. However, model agreement improves significantly when subfault sizes are increased, implying that their differences primarily stem from small-scale features. We then forward-compute geodetic and teleseismic synthetics and compare them with observations. We find that seismic observations are sensitive to rupture propagation, such as the peak-slip-rise time. However, neither teleseismic nor geodetic observations are sensitive to spatial slip features smaller than 64 km. In distinction, the synthesized seafloor deformation of all models exhibits poor correlation, indicating sensitivity to small-scale slip features. Our findings suggest that fine-scale slip features cannot be unambiguously resolved by remote or sparse observations, such as the three data types tested in this study. However, better resolution may become achievable from uniformly gridded dense offshore instrumentation.