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

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 fault

models and more realistic visco-elastic finite element forward models to perform resolution

and covariance analyses to explore the trade-offs between slip rate, locking depth, creep, and

seismic cycle effects on these faults. They will (1)determine marginal confidence bounds on the

range of present-day boundary conditions on fault evolution models, and (2)determine what

improvements in geodetic coverage (e.g.,PBO station locations and station density)will be

necessary 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 modeling

approach. Their investigations will include an assessment of how the presence of the restraining

bend in the SAFZ affects partitioning of strain between the SJFZ and SAFZ, how the eastern

California shear zone affects this partitioning, and whether there are resolvable differences in

fault zone strength between the SAFZ and the SJFZ.

- Determine the age of offset alluvial deposits using cosmogenic dating techniques which were

not available ten years ago, at the present-day precision. The order-of-magnitude increase in

precision 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 the

costs 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 aggregation

of new and existing displacement history data sets across a broad range of time scales for

both fault zones, as well as dynamical considerations. Our integrated approach will provide

a more comprehensive test of fault slip dependence between these fault systems than any

individual technique could possibly provide on its own.

The strength of our proposal is that our multidisciplinary research will be coordinated by the

over-riding goal of testing competing hypotheses for the evolution of this complex fault system.