Bayesian Inference of Lower-Crustal Viscosity Near the Kunlun Fault Based on Geologic, Geomorphic, and Geodetic Data
Abstract
Bayesian methods provide the means of integrating geologic, paleoseismic, seismic, and geodetic data to improve estimates of fault zone and lower-crustal properties that are important for predicting the long-term deformation of plate boundary zones, understanding deformation and stress transfer following earthquakes, and estimating future seismic hazard. We developed a Bayesian methodology that integrates geologic, geomorphic, and geodetic data to provide probabilistic estimates of fault-zone and lower-crustal properties. Unlike previous studies that have used a priori information to constrain optimizations, and bootstrapping to assess uncertainty in model parameters, we explicitly employed Bayes' rule in our analysis and estimate model parameters using simulation methods. Our Bayesian methodology provides a means of straightforwardly assessing covariance between and uncertainty within model parameters, and allows geologic and geomorphic information to be used to quantitatively constrain fault-zone and lower crustal properties. Because the methodology casts model parameter estimates in a probabilistic framework, inversions obtained from these methods provide far more information about the behavior of the model parameters inferred from data than do conventional geophysical inversions. Finally, these methods may be modified to incorporate other a priori information (e.g., fault zone geometry from microseismicity, and paleo-eathquake timing and recurrence from paleoseismic excavations), and thus may serve as important tools in seismic hazard assessments that strive to formally incorporate different data types. We applied this methodology to the Kunlun Fault in northern Tibet, where quantitative estimates of lower-crustal viscosity are lacking. Here, geologic and geomorphic information constrains the range of permissible long-term slip rates and coseismically generated offsets. We combined these a priori estimates with GPS velocities using a Bayesian implementation of an elastic-viscoelastic earthquake cycle model to estimate fault-zone and lower crustal properties in the area. We found that the non-dimensional relaxation time varies between 0.04 and 3.25 (95% bounds), implying plastosphere viscosity between 3.8 × 1019 Pa s and 6.7 × 1021 Pa s. These viscosities are large compared to those required by models of mid-crustal channel flow, perhaps suggesting that the mid- to lower-crust underneath northern Tibet is significantly more viscous than previously envisioned.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.G11A0781H
- Keywords:
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- 7221 Paleoseismology;
- 8107 Continental neotectonics;
- 8120 Dynamics of lithosphere and mantle: general;
- 1243 Space geodetic surveys