Summary. This project supported a component of the rapid geologic, geodetic and seismological field studies following the 2019 Ridgecrest earthquake sequence in the Eastern California Shear Zone (ECSZ) and Southern Walker Lane (SWL), which included M6.4 and M7.1 events and numerous aftershocks that extended northward toward the Owens Valley and to the south toward the Garlock fault. The rapid studies collected data that  measured the seismic and geodetic displacement fields, and fragile geological evidence that decayed rapidly with time and will eventually become obscure. The studies included field data gathering, instrumentation deployment, remote sensing and imaging surveys. The component of this collaborative work presented in this report includes data collection and processing of GPS observations in the Mobile Array of GPS for Nevada Transtension (MAGNET) semi-continuous GPS network that covers the western Great Basin in eastern California and western Nevada. This component supported for 1 year surveying MAGNET stations near the earthquakes that were displaced by the Ridgecrest sequence. MAGNET, operated by the Nevada Geodetic Laboratory (NGL) at the University of Nevada, Reno, has observations starting in January 2004. Thus, long time series of high-precision observations are available prior to the earthquake, providing strong geodetic constraint and the means for measuring and separating interseismic, coseismic and postseismic deformation associated with the Ridgecrest earthquakes.  The data and follow up studies clarify earthquake processes and structures in the highly active and complex ECSZ and SWL east of the Sierra Nevada.  NGL activities included rapid processing of GPS data from all continuous stations such as those from NSF’s Network of the Americas operated by UNAVCO, as well as data retrieved from MAGNET over the one year course of this project.  

Intellectual Merit. Geodetic observation of the coseismic movement from the Ridgecrest sequence reveals that a very large proportion of California and Nevada permanently moved because of the event. The observations show a NNE contraction and WNW extension consistent with the strike and style of the dextral slip, with the movement extending hundreds of kilometers to the north, south, east and west.   For example, to the south in southern California GPS station CAT2 on Catalina Islands moved a little over 3 mm northward, while the town of Tonopah in central Nevada moved ~4 mm south.  Stations in the San Francisco Bay Area moved 2 mm ~west.  Thus the area that shifted is that within 500 km of the epicenter, near one million square kilometers.  Measuring these movements allows better understanding of the earthquake processes, its impacts, the seismic cycle, its relation to tectonic loading prior to the event, and how postseismic deformation plays a role in changing stresses in the Earth. 

Broader Impacts. The data collection facilitated by this RAPID project serves a very broad set of communities of scientists working on earthquake processes and effects. The obtained multi-disciplinary observations address numerous outstanding issues associated with earthquake ruptures, spatio-temporal seismicity patterns, fault zone and crustal structures, intensity of ground shaking and postseismic deformation. The recorded data and follow up studies contribute broadly to improved understanding of tectonic deformation in the ECSZ and SWL.  The MAGNET GPS component of the response provided valuable experience for students who contributed to the field deployment, and many opportunities for other scientists to perform original research using the GPS data that was collected.  GPS data products generated by NGL, including time series files, plots and tables of the estimates of coseismic offsets, were made available through our website and updated periodically following the earthquake.  Having data on the coseismic offsets from the Ridgecrest events contributed directly to our ability to have high precision coseismic offsets for the next significant earthquake: the Monte Cristo Range, Nevada Earthquake that hit on May 15, 2020 that also struck within the footprint of the MAGNET GPS Network.  The field work and derived results generated excellent material for the NSF and SCEC E&O activities and media outreach.

Last Modified: 10/11/2020
Modified by: William C Hammond