Time-dependent creep model of the central creeping section of the San Andreas Fault from 21 years of InSAR GPS and repeating earthquakes

Overview: Page A The proposed work will address the advanced analysis, full integration, and careful interpretation of space-geodetic and seismic data over the central creeping section of the San Andreas. To this end, three time series of the surface deformation, using C-Band, L-Band and X-band SAR data and spanning period 1992-2013, will be generated. The SAR images are acquired by ERS1, 2, Envisat and ALOS satellite and Cosmo-SkyMed satellites, which will be jointly explored with a dense network of GPS data and catalogue of repeating earthquakes, through a time-dependent inverse modeling scheme. The ultimate research goals of this project are to evaluate in more detail the spatiotemporal distribution of creep on the Central San Andreas Fault (CSAF) and understand the characteristics and evolution of creep pulses. These findings have implications for the frictional parameters of this fault segment and improve knowledge of the fault-rheological properties at the creeping portions of the fault. This will allow us to infer to what degree the creeping portions participate in dynamic rupture events. This also helps to improve hazard probability estimates and aid in constructing dynamic earthquake scenarios. This information can be integrated into updated forecast models of the Working Group on California Earthquake Probabilities, which are used by local communities, and the California Earthquake Authority in their earthquake risk estimates and earthquake mitigation effort. Intellectual Merit : An improved understanding of the spatially and temporally varying deformation field of fault zones to great depth is critically important for understanding active tectonics, fault-fault interaction and the occurrence of large earthquakes. Unique to the Central Creeping Segment of the San Andreas is the combination of a rich historic data set, the recent deployment of EarthScope instrumentation, fault complexity, and a variety of natural transient phenomena occurring throughout the crust that, in effect, make this section of the San Andreas fault system a natural laboratory for attaining this objective. The proposed research effort will comprehensively analyze, integrate and interpret geodetic and seismic data in this region to investigate the underlying architecture and mechanics of the faulting process. Joint inverse modeling of the GPS, InSAR and repeating earthquake data will be used to resolve the 4-dimensional distribution of slip in the upper crust. We will conduct a systematic and detailed study of the spatial and temporal association of the aseismic slip pulses and events. Characteristic repeating earthquakes will provide unique information on transient activity in the Earth?s crust. This project, in particular, is focused on exploring the nature of interactions between seismic and aseismic deformation processes that occur in the fault zone and characterizing the kinematic models of creep pulses along the CSAF. Fault slip is tied to the mechanical properties of the fault zone rocks and adjoining crustal blocks and the proposed activity can also evaluate the first order changes of crustal properties. Time-dependent kinematic modeling of transient slip will be employed to investigate possible relationships among long-term, and short-term transient behavior. Broader Impacts : Results from this work will allow us to assess the role of aseismic fault slip transients in earthquake occurrence and clustering. Long-term societal benefits might ultimately arise from improved understanding of aseismic slip transients, their relation to regional strain anomalies, and improved models of the earthquake cycle that should improve earthquake forecasts and intermediate to longer-term predictions. This project will provide partial support for an early-career geophysicists. It will also provide valuable research experience for a postdoc and a graduate student who are planned to directly involve in this project. For this purpose two sub-projects have been developed. PI Shirzaei will incorporate issues and results from this work in his undergraduate teaching, including Physical Geology (this course includes sections on fault mechanics and seismicity), as well as a graduate course Crustal Deformation and Remote Sensing which includes numerous case examples from the San Andreas fault zone and lectures on crustal deformation and seismicity.