SCEC Award Number 12179 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Collaborative Research: Relating fault-slip gradients to distributed deformation in the Eastern California Shear Zone
Investigator(s)
Name Organization
Michael Oskin University of California, Davis Michele Cooke University of Massachusetts Amherst
Other Participants
SCEC Priorities 4b, 4c, 4e SCEC Groups Geology, USR, Geodesy
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 We combine modeling and observational approaches to better understand how permanent off-fault deformation contributes to the strain budget and seismic hazard of southern California, focusing on the well-exposed fault-system of the Mojave Desert portion of the ECSZ. Our objective is to quantify how slip-gradients at the ends of faults are accommodated by deformation in the surrounding volume of crust. The ECSZ is an ideal region to investigate this off-fault deformation because: (1) the fault system is well exposed, as attested by the numerous minor fault traces contained within the USGS Quaternary fault database; (2) the region shows a discrepancy between geologic slip rates on the major faults and slip rates from geodetic inversions that may be at least in part due to unaccounted off-fault deformation; (3) faults within the ECSZ are generally parallel to one another, and appear to rupture from end-to-end in single M7+ earthquakes - a geometry and rupture behavior that lends itself well to the Boundary Element Method modeling approach; and (4) substantial near-field (<1 km) off-fault deformation has already been quantified from geodetic, seismic and geologic studies of fault damage-zones. Our study compliments this research by quantifying the along-strike trade-off between on- and off-fault deformation, and relating this to field observations of strain and long-wavelength vertical motions off of the main faults.
Intellectual Merit Because the Earth’s crust is not purely elastic, it can accrue permanent deformation between earthquakes. This permanent off-fault deformation is expressed in damaged, folded and uplifted rocks between active faults in southern California. Because permanent off-fault deformation is not accounted for in most geodetic inversions for fault slip rates, these inversions may over-estimate seismic hazard if this deformation accrues between earthquake events. Hazard may also be under-estimated away from known fault traces if some off-fault deformation is released by rare, seismogenic slip events on unrecognized secondary structures. This study combines modeling and observational approaches to better understand how permanent off-fault deformation contributes to the strain budget and seismic hazard of southern California, focusing on the well-exposed fault-system of the Mojave Desert portion of the ECSZ. Our objective is to quantify how slip-gradients at the ends of faults are accommodated by deformation in the surrounding volume of crust.
Broader Impacts The most significant broader impact of this research is quantify deformation that may not be accrued via damaging earthquakes, reducing overall hazard. This project also involves two graduate students (Jacob Selander at UCD, and Justin Herbert at UMass) and two undergraduates (Difo Ohida and Karl Grette, both at UMass; Difo is an underrepresented minority student). Undergraduate students are leading various components of the modeling efforts and are participating in the publication of our results.
Exemplary Figure Figure 2. Strike slip rates along faults of the ECSZ. A) model strike slip rates using the CFM geometry for active faulting in the region and geologic slip rate (stars infilled with color of slip rate). The model overpredicts slip rates along the Helendale, Lenwood and Camprock faults. The model underpredicts slip rate on the Calico fault. B) Revised fault model incorporates fault geometry that better relfects the mapped fault geometry. The revised model much better matches observed right-lateral strike-slip rates on all faults.
Linked Publications

Add missing publication or edit citation shown. Enter the SCEC project ID to link publication.