SCEC Award Number 11150 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Characterizing the regional pattern of post-earthquake deformation associated with the 4 April 2010 Mw 7.2 Sierra El Mayor-Cucapah earthquake using campaign GPS
Name Organization
Rick Bennett University of Arizona Falk Amelung University of Miami
Other Participants Christina Plattner
Javier Gonzalez-Garcia
SCEC Priorities A1, A2, C SCEC Groups Geodesy, Geology, Seismology
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
This project utilized GPS data from the SCIGN, EarthScope Plate Boundary Observatory (PBO), and campaign GPS networks in southern California and northern Baja California Mexico, including six new PBO stations located in northern Baja California, Mexico. The objective of the project was to utilize both continuous and campaign GPS data to assess the co-seismic and postseismic deformation following the El Mayor-Cucapah earthquake. Originally we planned a campaign occupation of existing stations in Baja California Mexico. However, we were unable to achieve that goal, due to a health related issue with our collaborator at CICESE (Javier Gonzalez)(Alejandro Gonzalez, personal communication). In the end, we turned our focus to an analysis of crustal motions associated with the 1999 Mw7.1 Hector Mine and 2010 Mw7.2 El Mayor-Cucapah earthquakes. These earthquakes were of very similar size, geometry, and slip mechanism. We sought to compare and contrast the postseismic responses to these events, which should tell us something important about lithospheric rheology variations throughout a large portion of southern California and northern Mexico. We began our investigation by assessing the resolving power of the GPS time series for determining the decay times of postseismic deformation transients. Rapid short-time scale motions are apparent for both earthquakes. But there is a longer-term effect that seems to have a characteristic time in the wide range of 200 to 700 days. In order to better resolve these long-term variations, particularly for the new stations in Baja installed following the El Mayor-Cucapah earthquake, we have begun to develop a model for pre-earthquake crustal velocity. This model is being used to compare with ongoing post-earthquake motions observed at the existing stations. The model is based on existing campaign and continuous GPS measurements collected over the past two decades in southern California and northern Baja California Mexico. We anticipate that the changes in crustal velocities in the far-field of the Hector Mine and El Mayor-Cucapah earthquakes will form the basis for an evaluation of crust and mantle rheology and the role that postseismic processes play in the evolution of crustal stresses in southern California and Baja California, with implications for hazards assessment.
Intellectual Merit Postseismic deformation may be caused by relaxation of viscoelastic materials in the lithosphere, afterslip, or poroelastic response. Our data-driven approach will allow us to address the critical question of model parameter estimate resolution and uncertainty, prerequisite for discriminating among competing hypotheses for postseismic mechanisms, and lithospheric rheology. Accurate knowledge of postseismic deformation mechanisms and lithospheric rheology are prerequisite to an accurate description of the evolution of stress in the crust.
Broader Impacts Precise measurements of deformation following these earthquakes will contribute to several basic-research foci of SCEC, including (1) stress transfer from plate motion to crustal faults, (2) long-term fault slip rates, (3) possible causes of earthquake clustering, and (4) the causes and effects of transient crustal deformations. The results of this project should contribute to future modeling exercises that target these research foci. This project also provided stipend support for a PhD student at the University of Arizona, Mr. Joshua Spinler.
Exemplary Figure Figure 2. . Estimates for decay time for El Mayor-Cucapah and Hector Mine earthquakes determined using constrained random search algorithm, compared with strong crust and weak crust models filtered through the constrained random search algorithm. The strong crust model represents the case where the lower crust has a viscosity that is higher than the underlying upper mantle. The weak crust model represents the case where there is a relatively weak lower crust between strong upper crust and upper mantle. Despite significant scatter and large uncertainties, the estimates for decay time derived from GPS time series for both earthquakes seem most consistent with the strong lower crust model.