SCEC Award Number 22049 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title GNSS measurements of postseismic deformation and updating of site positions in the Mojave Desert in the aftermath of the 2019 Ridgecrest earthquake sequence for the Community Geodetic Model
Investigator(s)
Name Organization
Gareth Funning University of California, Riverside
Other Participants Mike Floyd (collaborator)
Ryan Rivera (graduate student)
SCEC Priorities 3b, 1a, 2a SCEC Groups Geodesy, SDOT, CXM
Report Due Date 03/15/2023 Date Report Submitted 04/28/2023
Project Abstract
 The primary objective of this project was to extend the time series of GNSS-constrained postseismic deformation at a range of sites in the near and medium field of the 2019 Ridgecrest earthquakes that were previously occupied with survey GNSS receivers. A secondary objective was to start to reoccupy sites in the wider Mojave Desert region, to update positions and velocities following the earthquakes. In total, we made measurements at 22 sites over five visits to the region during the project period. Preliminary processing of the data shows that the postseismic transient may be coming to an end after three years, and that the directions of postseismic motions may be rotating towards the fault-perpendicular direction, suggesting that the primary mechanism driving the displacements is changing from afterslip to viscous relaxation.
Intellectual Merit Measurements of postseismic deformation allow us to constrain the rheology of the lower crust and upper mantle, and understand how faults are loaded, how they fail, and how stress is transferred in the lithosphere. We have added significantly more GNSS data coverage in the near-field area of the 2019 Ridgecrest earthquakes, providing strong constraints on the amount and direction of any associated off-fault deformation, a SCEC priority.
Broader Impacts The survey GNSS data collected in the project will contribute to two community models within SCEC – the data on postseismic deformation will help to constrain the Community Rheological Model, and the updated measurements of sites in the Mojave Desert area will be incorporated into future generations of the Community Geodetic Model. Updated GPS secular velocities are used as inputs for seismic hazard estimation through efforts such as the Uniform California Earthquake Rupture Forecast (UCERF), which are used widely by local governments and the insurance industry to quantify and mitigate risk. The fieldwork was led by Karlee Rivera, a female graduate student from an underrepresented background, and also involved two field assistants from underrepresented backgrounds, Ryan Rivera and Norma Contreras.
Exemplary Figure Figure 1: Map pattern of postseismic displacements as a function of time following the M7.1 July 5th Ridgecrest mainshock. Vectors show surface displacement and are color-coded by time. The NW-striking M7.1 source fault and SW-striking M6.4 source fault are shown as black solid lines. Overall, the pattern of displacements is consistent with deep, right-lateral afterslip on the M7.1 source fault, but rotations of most of the vectors as time increases suggests that a different deformation mechanism may be influencing the later period of displacement. Displacements to the NE of the M7.1 source fault are typically larger in amplitude at a similar distance to the fault compared with sites to the SW of the fault, suggesting a possible influence of the surface elevation – which varies by ~3 km from SW to NE – on the measured displacement.
Figure produced by Gareth Funning and Michael Floyd