Going to Any Lengths: Solving for Fault Size and Fractal Slip for the 2016, M-w 6.2 Central Tottori Earthquake, Japan, Using a Transdimensional Inversion Scheme

摘要

Many earthquake properties, including slip, show self-similar (fractal) features. We can incorporate self-similarity into Bayesian slip inversions via von Karman correlation, so that the regularization applied is representative of observed fault features. In von Karman regularization, each slip patch has a relationship to every other patch. This means that von Karman regularization only has meaning when applied to patches that actually slipped; if applied to nonslipping patches, spurious slip can be added to meet the von Karman correlation criteria. Additionally, the fault size, usually chosen in advance, also affects the von Karman correlation lengths meaning that the final slip solution may be biased by initial geometry choices. Here we present a method for solving for the size of the fault plane during the slip inversion process, as well as slip, rake, and a hyperparameter controlling slip variance. We use a transdimensional Bayesian inversion scheme constrained by geodetic surface displacements and regularized using von Karman correlation. We use circular harmonics to solve for the size of the slipping area, to allow for a complex shape that is connected and continuous across the fault. We apply this method to the 2016 M-w 6.2 Central Tottori earthquake, Japan, constrained by interferometric synthetic aperture radar InSAR (Sentinel-1 and ALOS-2) and Global Navigation Satellite System data (GNSS). We find an area of slip extending from approximately 2- to 10-km depth, with the slipping area elongated in the downdip direction. In contrast to some seismic studies, we find slip ruptured most of the seismogenic layer.