Assessing Long‐Term Postseismic Transients From GPS Time Series in Southern California
Publisher
AMER GEOPHYSICAL UNIONCitation
Guns, K. A., & Bennett, R. A. (2020). Assessing Long‐Term Postseismic Transients From GPS Time Series in Southern California. Journal of Geophysical Research: Solid Earth, 125(4), e2019JB018670.Rights
© 2020. American Geophysical Union. All Rights Reserved.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
In order to gain insight into long-term plate boundary motion and to shed light on geodetic-based fault slip rates and the seismic hazards they inform, we apply a forward modeling strategy to identify and reduce the short- and long-term effects of viscoelastic postseismic deformation on modern GPS observations following large magnitude earthquakes in Southern California. We assess ongoing postseismic deformation in the southwestern United States by analyzing all magnitude >= M(w)6.0 earthquakes that have occurred there and in Baja California and Sonora, Mexico, since year 1800, finding that ongoing postseismic displacements from 12 events are potentially contributing to the modern day deformation field in Southern California. With a forward modeling step, we calculate postseismic displacements associated with these 12 events using a reference model consisting of a layered, laterally homogeneous, viscoelastic Earth structure; these displacements are then subtracted from processed horizontal GPS coordinate time series data to produce a postseismic-reduced data set. In order to quantify the success of this forward modeling in reducing the postseismic signal, we estimate parameters representing logarithmic decay associated with the 2010 M(w)7.2 El Mayor-Cucapah earthquake using two different time series analysis methods. Variance reduction indicates we were able to reduce postseismic deformation in this test case by up to 60%. Anomaly maps produced using our assessment of deformation around the El Mayor-Cucapah event highlight hot spots in which secondary processes may be occurring or where a more complex viscosity structure may be necessary. Plain Language Summary Earthquakes relieve the shear stresses that build up on crustal faults, but at the same time induce other stresses in the nearby crust and mantle. Relaxation of earthquake-induced stresses can cause Earth's surface to move in predictable patterns for decades or longer. However, the accuracy of such predictions is hampered by our limited understanding of how the lower crust and upper mantle relax as a function of depth and tectonic setting. Here, we apply a regionally optimized Earth model to calculate displacements caused by all historic earthquakes that may be contributing to the contemporary crustal motion field in Southern California. Our modeling assesses all magnitude 6.0 and larger earthquakes since 1800 in California, Nevada, and Baja California, and Sonora, Mexico, to evaluate ongoing relaxation and associated crustal motion. We devise a method for determining ongoing postseismic motions that overcomes limitations in our knowledge of crust and mantle relaxation properties. We discuss the implications of our modeling for crustal strain accumulation and seismic hazards in Southern California. Our new modeling approach may help improve knowledge of the relaxation properties of the lower crust and upper mantle.Note
6 month embargo; first published online 3 March 2020ISSN
2169-9313EISSN
2169-9356Version
Final published versionSponsors
Southern California Earthquake Centerae974a485f413a2113503eed53cd6c53
10.1029/2019jb018670