Researchers: Yuehua Zeng, U.S. Geological Survey and Zheng-Kang Shen, University of California, Los Angeles.
Written by Linda Rowan
28 February 2018
A crustal deformation model developed for the Western United States fits a growing body of observations and shows where major changes in the crust are occurring. The model combines geodetic data from GPS sites (many are part of UNAVCO's Plate Boundary Observatory) with geologic observations to determine how six major crustal plate blocks are moving and interacting in the Western United States from the Rocky Mountains to the west coast. Such modeling is critical for earthquake hazard assessments and for understanding Earth processes.
The U.S. Geological Survey (USGS) is responsible for earthquake hazard information for the United States. The USGS has encouraged researchers to develop new models of crustal deformation in the Western U.S. with all of the available data, especially with the growing body of geodetic data. Here the authors combine geodetic and geologic observations gathered for more than a decade to develop a new deformation model.
The geologic data are a compilation of all of the geologic slip rates measured along known faults in the Western United States. The USGS asked researchers to update their National Seismic Hazard Map Project by combining the most up-to-date compilation of geologic slip rates with the expanding and accurate geodetic measurements of current slip rates.
Here the authors chose to use a block-like model that assumes most of the slip occurs at or near the block boundaries. The model is divided into 6 major blocks: Pacific, North American, Juan de Fuca, San Jacinto, Hayward-Maacama and Bartlett Springs-Green Valley. Deformations around smaller faults within these blocks are also considered in the model.
The crustal deformation model shows that the geodetic and geologic data are consistent for some faults in California and most of the rest of the western U.S. faults. There are discrepancies between the geodetic and geologic data for some California faults especially, the Mojave to San Bernardino section of the San Andreas fault, the western Garlock fault and the southern segment of the Wasatch fault. The model highlights the compression across Washington and Oregon, the extension in the Basin and Range, the contraction around Big Bend and the Transverse Ranges and the high expansion near Yellowstone and Long Valley calderas. The model enhances the USGS National Seismic Hazard Map (NSHM) and Contributes to the 2014 and 2018 NSHM updates.
A Fault-Based Model for Crustal Deformation in the Western United States Based on a Combined Inversion of GPS and Geologic Inputs, Yuehua Zeng and Zheng-Kang Shen, Bulletin of the Seismological Society of America, 2017, doi:10.1785/0120150362.
geologic slip rate, geodetic slip rate
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