SCEC Award Number 18202 View PDF
Proposal Category Workshop Proposal
Proposal Title Toward a SCEC Community Rheology Model (CRM) Workshop on Loading of Southern California Faults: Bulk Lithospheric Deformation and/or Localized Ductile Shear Zone Strain
Name Organization
Wayne Thatcher United States Geological Survey Elizabeth Hearn Independent Contractor Michael Oskin University of California, Davis Greg Hirth Brown University Whitney Behr University of Texas at Austin
Other Participants
SCEC Priorities 1c, 3a, 3b SCEC Groups CXM, SDOT, CISM
Report Due Date 10/08/2018 Date Report Submitted 11/14/2018
Project Abstract
A workshop under the aegis of SCEC’s Community Rheology Model (CRM) effort was held on September 8th 2018 at Palm Springs Its goal was to explore observations and models bearing on the existence (or not) of narrow ductile shear zones and distributed ductile deformation in southern California’s lower crust and upper mantle lithosphere. One session was devoted to examining evidence from lab ductile flow experiments, process-based modeling and the rock record, demonstrating how several weakening mechanisms promote shear localization but also are consistent with bulk ductile flow. A second evaluated geophysical evidence from the niche fields of structural seismology, non-volcanic tremor observations, and tectonic geology that strongly supported shear localization beneath several segments of the San Andreas fault but not excluding distributed deformation in other parts of Southern California. Finally, a third session included two provocative presentations; one showed emerging evidence that bulk ductile rheology may be inferred from tomographic models of P- and S-wave structure in SoCal; the other described a suite of numerical models of strike slip earthquake cycle deformation. Lively discussion followed all workshop presentations, with some arguing for strain localization and others supporting large-scale ductile flow. The meeting was well-attended, with 50-65 participants, and the meeting room was full from start at 9 am to adjournment at 5 pm.
Intellectual Merit The rheology of the ductile lithosphere and its coupling to the seismogenic upper crust strongly influences the deformation and state of stress of the lithosphere, determines the geodetically-measured surface deformation through the earthquake cycle and can affect the geodetic estimates of fault slip rates
Broader Impacts The 2018 CRM workshop attendees included one undergraduate, 8 graduate students and 10 early career scientists, broadening engagement across the SCEC community as well as contributing to the education of young and early career scientist
Exemplary Figure Fig 1