A Fractal Future for Earthquake Slip Inversions
Abstract
Spatial patterns of coseismic slip offer valuable insight into earthquake and faulting processes, and are commonly used to infer the geometry of causative faults, crustal stress changes, fault frictional properties and even potential future hazard.
These slip distributions at depth are normally inferred from inversion of seismological and geodetic data, but such inversions require regularization to obtain a stable, unique solution. Common regularisation approaches such as minimizing the second spatial derivative of slip (the Laplacian), have little physical basis and potentially bias the slip distribution, as well as any further inference based on the estimated pattern of slip. A growing body of evidence, including analysis of surface slip observed after earthquakes, the roughness of fault surfaces and analysis of published seismological slip inversions, suggests that fault slip shows fractal properties. In light of this we incorporate fractal properties into geodetic earthquake slip inversions, using the von Karman regularisation to capture the self-affine nature of faulting. In this talk we present a newly-developed Bayesian approach to solve for slip incorporating von Karman regularization. In synthetic tests, our approach retrieves fractal slip better than Laplacian smoothing, as expected, but even performs comparably, or better, when the input slip is not fractal. We apply this to the 2014 Mw 6.0 Napa Valley earthquake on a two-segment fault using InSAR and GPS data. We find the von Karman and Laplacian inversions give similar slip magnitude but in different locations, and the von Karman solution has much tighter confidence bounds on slip than the Laplacian solution. We further improve this method by solving for the size of the fault during the inversion to remove any bias caused by fault size. This is achieved by defining a slipping area using circular harmonics and we incorporate it using a trans-dimensional Bayesian approach. Differences in earthquake slip due to the regularization technique could have important implications for the interpretation and modeling of stress changes on the causative and neighbouring faults. We therefore recommend that choice of regularization method should be routinely made explicit and justified and that von Karman regularization is a better default than Laplacian.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.G21A..04A
- Keywords:
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- 1207 Transient deformation;
- GEODESY AND GRAVITYDE: 1211 Non-tectonic deformation;
- GEODESY AND GRAVITYDE: 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICSDE: 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS