Project Abstract
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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.
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