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Predictive Modeling of Seismicity Sequences in Southern California Julia Clark David D. Bowman California State University, Fullerton

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Schematic Diagram of the Seismic Cycle from Ellsworth et al., 1981

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Many current models of Accelerating Moment Release fit seismicity data to an analytic function Accelerating Seismicity Function One of the most commonly used functions is the Power-Law time-to-failure equation Bufe and Varnes (1993); Sornette and Sammis (1995) Where (t) is the seismic energy release at time t, t f is the time of the earthquake, and A,B and m are fitted parameters describing the shape of the function This function takes the form: (t ) = A - B(t f -t) m

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325 km 600 km 325 km RMS Residuals 200 km 1952 Kern County Earthquake Selecting a circular region Bowman et al., 1998

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All California Earthquakes M≥6.5 1950-1995 Bowman et al., 1998

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Critical Regions Circular Regions A simple systematic method to calculate critical regions using an arbitrary shape that is easy to program, but is not based on geology. A New Method The idea is to model critical regions as the region of stress accumulation before an earthquake. Stress Accumulation Regions The stress field from loading a locked fault patch is the same as the stress field created by slipping the fault backwards. This permits us to calculate the Coulomb Stress Change for the future earthquake, and look for accelerating seismicity in the regions of increased stress.

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What is “Coulomb Stress Change”? From King et al., 1994

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Slipping Fault Seismic Slip Creep at Depth Future Earthquake Calculate from motion on all adjacent faults plus creep at depth Stress Change From Loading a Locked Patch on a Simple Fault

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Negative Slip Future Earthquake Creep at Depth = Where are pre-earthquake stresses?

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Accelerating Seismicity in Stress Accumulation Regions Bowman and King, 2001

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No? Yes? Future California Earthquakes?

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Fault Senerios Coulomb Stress Region Seismicity Analysis Southern California Faults Summer Project

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