Collaborative Research: : Co-evolution and Dynamic Interplay of the San Jacinto and Southernmost San Andreas Fault Zones

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The PI's request funds to analyze the dynamics of fault interaction between the San Jacinto (SJFZ)and southernmost San Andreas (SAFZ) fault zones in southern California. They seek to address whether there has been a decrease in the slip rate along the Indio segment of the SAFZ related to the birth and continued maturation of the SJFZ, and/or whether these two fault zones alternatively assume dominant roles in accommodating relative plate motion across the region over any time scales. These questions have proven difficult to address with any one geological/geophysical technique or data type. They will therefore employ an integrated, cross-disciplinary approach to investigate the evolution, present-day behavior,and dynamics of these active faults. Specifically, the PI's propose to:- Investigate trade-offs between fault model parameter estimates derived from geodetic observations. They will use the SCEC and SCIGN data sets together with inverse elastic faultmodels and more realistic visco-elastic finite element forward models to perform resolutionand covariance analyses to explore the trade-offs between slip rate, locking depth, creep, andseismic cycle effects on these faults. They will (1)determine marginal confidence bounds on therange of present-day boundary conditions on fault evolution models, and (2)determine whatimprovements in geodetic coverage (e.g.,PBO station locations and station density)will benecessary in order to further narrow the class of admissible fault evolution models.- Investigate the relative importance of, and feedbacks between, fault zone geometry, and lithospheric rheology by numerical simulations using a 3-D visco-elastic finite element modelingapproach. Their investigations will include an assessment of how the presence of the restrainingbend in the SAFZ affects partitioning of strain between the SJFZ and SAFZ, how the easternCalifornia shear zone affects this partitioning, and whether there are resolvable differences infault zone strength between the SAFZ and the SJFZ.- Determine the age of offset alluvial deposits using cosmogenic dating techniques which werenot available ten years ago, at the present-day precision. The order-of-magnitude increase inprecision of the offset alluvial fan ages will allow the PI's to discriminate between competing models for fault zone evolution over the 10 to 100 ka time scale. These new cosmogenic dating measurements will be made at no additional cost under this proposal. Rather, funds to cover thecosts of this component of our research are anticipated from Deutsche Forschungsgesellschaft(DFG proposal pending, Prof. Friedrich, P.I.).- Construct a model for the co-evolution of the SJFZ and SAFZ incorporating an aggregationof new and existing displacement history data sets across a broad range of time scales forboth fault zones, as well as dynamical considerations. Our integrated approach will providea more comprehensive test of fault slip dependence between these fault systems than anyindividual technique could possibly provide on its own.The strength of our proposal is that our multidisciplinary research will be coordinated by theover-riding goal of testing competing hypotheses for the evolution of this complex fault system.