SCEC Award Number 15073 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Improving the Community Geodetic Model with GPS and InSAR
Investigator(s)
Name Organization
Yuehua Zeng United States Geological Survey David Sandwell University of California, San Diego Javier Gonzalez-Ortega University of California, San Diego Bridget Smith-Konter University of Hawaii at Manoa
Other Participants Javier Gonzalez, CICESE; Daniel Trugman, UCSD
SCEC Priorities 1d, 1e SCEC Groups Geodesy, CME
Report Due Date 03/15/2016 Date Report Submitted 03/06/2016
Project Abstract
 One of the priorities of SCEC4 is to investigate stress transfer from plate motion to crustal faults. Surface crustal velocities are one of the key boundary conditions needed for develop-ing 3-D stress rate models. The quality and quantity of GPS and InSAR data are increasing rapidly and many groups are developing detailed crustal velocity models. Over the past year we have contributed in two areas. 1) We have collaborated with other SCEC and PBO scientists to develop a time-dependent Community Geodetic Model (CGM) at variable spatial resolution. Murray and Sandwell led a Community Geodetic Model (CGM) Workshop, January 28 – 29, 2016, Pomona, CA. The workshop overview, agenda and participants are provided on a SCEC web site https://www.scec.org/workshops/2016/cgm. The workshop report is in press at SCEC. In 2015 Sandwell assembled secular velocity models from 15 groups. These will form the basis for the secular CGM. In addition, the models will be converted to horizontal strain rate for cross comparisons as well as comparison with SHmax from seismic studies.
2) We worked with CICESE scientists to acquire spatially dense GPS velocities across the Imperial and Cerro Prieto Faults. The preliminary results of the analysis of slip rates and locking depths across these two faults are provided in Figure 1. There is a significant step in velocity across the Imperial Fault of 29 + 4 mm/yr with a locking depth of 7.3 km. This rate is somewhat smaller than the slip rate of 35 mm/yr north of the border. More important we find the full plate rate of more than 40 mm/yr is realized between the most distant points across the fault (PJZX – IID2); the sum of the model slip rates is 50 mm/yr.
Intellectual Merit The San Andreas Fault System (SAFS) is a natural laboratory for investigating the physics of the earthquake cycle along a major continental transform boundary. Two of the key parameters that can be used for seismic hazard assessment are seismic moment accumulation rate and strain accumulation rate. The GPS component of the Plate Boundary Observatory (PBO) provides accurate vector velocities (< 1 mm/yr accuracy) at a spacing of 10 to 20 km along the SAFS. However, the velocity gradient (strain rate) varies most rapidly within 20 km of the major faults, so strain rate is not well resolved by the GPS data alone. Radar interferometry (InSAR) provides deformation maps at 100 m spatial resolution, although factors such as temporal decorrelation and atmospheric path errors have made it difficult to achieve this full resolution with sufficient precision to improve upon the GPS measurements. The primary focus of our research is to construct high spatial resolution vector surface deformation measurements by combining the high accuracy point measurements provided by PBO GPS data with the high spatial resolution InSAR measurements.
Broader Impacts These proposed research activities will contribute to the objectives of SCEC by further advancing our understanding of fault system crustal dynamics, earthquake hazards, and data synthesis. The fundamental earthquake science being explored by this research has substantial societal relevance, as earthquake cycle strain rate estimates are poised to help mitigate seismic hazards.
Exemplary Figure Figure 1. (upper) Location map of active strike-slip faults in Northern Baja California. The Im-perial Fault passes through a highly populated area of eastern Mexicali. The Cerro Prieto Fault ends at the geothermal pond of the geothermal power generation plant. Continuous GPS sites are shown as blue dots and campaign GPS monuments are shown as black dots. The velocity vectors are relative to the ITRF. (lower left) Fault-parallel velocity versus distance across the Imperial Fault. The preliminary model has two additional faults to the west to explain the signif-icant changes in velocity. (lower right) Fault-parallel velocity versus distance across the Cerro Prieto Fault. The preliminary model has one additional fault to the west of the Cerro Prieto Fault. We are developing a time-dependent model that includes the postseismic deformation of the El Major-Cucupah earthquake to explain these data.
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