Collaborative Research: Reconciling Geologic and Geodetic Rates of Deformation: The Role of Distributed Strain in the Upper Crust

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Understanding the spatial and temporal distribution of surface deformation over various timescales can yield insight into lithospheric rheology, rupture behavior, and nature of slip transfer along fault networks. However, new insights provided by GPS bring new challenges: in particular, how does elastic strain accumulation measured over geodetic timescales (less than 10 yr) relate to geologic slip inferred over longer timescales (10,000 - 1,000,000 yr)? Over the past few years, much effort has been focused on an apparent discrepancy between geodetic rates of surface deformation and geologic rates of fault slip across the Eastern California Shear Zone. Recent hypotheses for this discrepancy center on temporal variations in the strain field which result from: 1) clustering of seismic strain release, 2) oscillatory strain release on conjugate fault systems, or 3) viscoelastic deformation following recent earthquakes. In order to fully understand the pace and tempo of variations in fault system behavior, however, a complete characterization of fault slip over geologic time is required.This investigator team is collecting the basic geologic and geomorphic data necessary to critically assess rates of fault displacement across Owens Valley, California. In particular, the project is aimed at understanding the role played by diffuse arrays of small faults in accommodating strain across the region. The hypothesis that these fault networks may account for a significant component of geologic slip not considered by current interpretations of geodetic data is being tested by determining fault slip rates (exploiting geomorphic markers such as glacial moraines, river terraces and alluvial fans) on numerous fault arrays distributed throughout central and northern Owens Valley. Moreover, an alternative hypothesis holds that the discrepancy between geologic and geodetic data may reflect temporal variation in the rate of strain release. A refined understanding of the pace and tempo of distributed faulting across the region is being developed by exploiting sites with offset markers of varying age.This project contributes towards larger goals articulated by the broader geologic/geophysical community by improving interpretations of geodetic data across the diffuse North American - Pacific plate boundary, and by developing new insight into the problem of temporal variations in fault slip.