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 image these processes and provide
observational constraints for understanding earthquake physics. However,
finite-fault inversions are subject to non-uniqueness and uncertainties.
The diverse range of published models for the well-recorded 2011
$M_w$~9.0 Tohoku-Oki earthquake 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 four commonly-used
observational data types (geodetic, teleseismic, regional
seismic-geodetic, and tsunami) to their slip features. We first project
all models to a realistic megathrust geometry and a 1-km subfault size.
At this scale, we observe low correlation among the models, irrespective
of the data type. However, model agreement improves significantly with
increasing subfault sizes, implying that their differences primarily
stem from small-scale features. We then forward-compute geodetic and
seismic synthetics and compare them with observations available during
the earthquake. We find that seismic observations are sensitive to
rupture propagation, such as the peak-slip rise time. However, neither
teleseismic, regional seismic, nor geodetic observations are sensitive
to spatial slip features smaller than 64~km. In
distinction, the seafloor deformation predicted by 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
four data types tested in this study. However, better resolution may
become achievable from dense offshore instrumentation.