Using Geodesy to Separate Transient and Steady Extension in the Basin and Range Province, Western United States

Board Of Regents, Nshe, Obo University Of Nevada, Reno, Reno NV

Investigators

Abstract

The Basin and Range Province is an integral part of the Pacific/North America plate boundary deformation zone, and experiences large earthquakes that can threaten communities in Nevada, Utah, Arizona, Idaho and Oregon. The active deformation of the 800 km wide Province can now be precisely measured with space geodetic methods such as GPS, and thus it is now possible to chart the rates and styles of the slow movements that generate the stresses that cause these earthquakes. However, recent geological and geophysical studies have come to conflicting conclusions about how the deformation across Nevada occurs. Some geodetic studies have suggested that the North American Plate is non-deforming in eastern Nevada, while others have found evidence for episodic, large-scale, but small magnitude deformation events. Geologic evidence suggests that recent normal faulting and extension occurs and is distributed roughly evenly across the Province. These three different views of how the North American plate deforms imply three extremely different dynamic modes of extension of continental lithosphere, and thus it is not possible that all three are correct. The EarthScope Plate Boundary Observatory GPS network was designed with a profile of sites along US Interstate Highway 50, across the entire Basin and Range at a latitude of about 39 degrees N. These GPS sites are now detecting single digit nanostrain/yr deformation rates across eastern Nevada. Therefore PBO is ready to address this new frontier in the science of tectonic geodesy: The slow but active realms that transfer deformation between the major elements of the plate boundary. To distinguish between the three hypotheses we will: 1) process GPS data using the latest software and models, 2) systematically generate a catalog of geodetic transients, 3) develop improved models of the viscoelastic response of 19th and 20th century earthquakes to remove postseismic transient signals from the GPS time series, 4) estimate rates and patterns of long term deformation of eastern Nevada and compare these results to geologic and seismic data. The results of these activities will be an improved understanding of how the contents in active plate boundaries deform. In so doing we will quantify the rate, pattern, and style of background tectonic deformation that drives the occurrence of earthquakes. These rates are increasingly being used in the U.S. National Seismic Hazard Maps that guide building practices. Thus this work will have a direct impact on preparedness for and estimates of future losses from earthquakes.