Geodesy for understanding seismic hazard

Eileen Evans

USGS Menlo Park

Date & Time
Building 3, Rambo Auditorium

Inputs into seismic hazard models include 1) fault slip rates, 2) their uncertainties, and 3) off-fault deformation rates. Fault slip rates can be estimated by modeling fault systems, based on space geodetic measurements of active surface ground displacement, such as Global Navigation Satellite Systems (GNSS) and interferometric synthetic aperature radar (InSAR). Geodetic slip rate estimates may vary widely due to measurement and epistemic (model) uncertainties, presenting a challenge for both estimating slip rates and accurately characterizing uncertainties: models may vary in the number of faults represented and the precise location of those faults. I address this ambiguity in California in two ways.

First, I address the potential role of fault system geometry in the eastern California shear zone with an L1 regularization method that allows for an algorithmic assessment of the best-fitting block model geometry based on geodetic observations. This approach permits fault system geometries with many densely spaced active faults (analogous to distributed interseismic deformation), and so is uniquely capable of addressing the nature of on- vs. off-fault tectonic deformation. Second, I combine 33 published geodetic slip rate estimates on a georeferenced grid and find an average standard deviation on slip rate of ~1.5 mm/yr, which I consider proxy for model uncertainties in geodetic slip rates. Both approaches independently assess geodetic constraints on fault slip, and systematically identify regions that may require more careful consideration in terms of modeling the complex set of faults in California.

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