Epistemic uncertainty in California-wide simulations of synthetic seismicity Fred Pollitz, USGS Menlo Park Acknowledgments: David Schwartz, Steve Ward

Ward (2000)

Rundle et al. (2008)

Capabilities of this simulator

Inherently discrete fault zone Inherently discrete fault zone (Ben-Zion and Rice model) (Ben-Zion and Rice model) Homogeneous, planar faults Homogeneous, planar faults Viscoelasticity of lower crust/upper mantle Viscoelasticity of lower crust/upper mantle --> loading through backslip in the --> loading through backslip in the fully relaxed limit fully relaxed limit

Fault network and slip rates courtesy of Steve Ward (June, 2009) Original set of ~4 x 3 km 2 patches are re-grouped and subdivided into set of smoothly-connected, non-overlapping ~1 x 1 km 2 patches fault patches

Stress history on a single fault patch Static frictional stress Dynamic frictional stress Arrest stress Dynamic overshoot parameter: Stress reduction parameter:  =  s -  a D =  s -  a )/(  s -  d )

Simulator parameters Dynamic overshoot parameter: Stress reduction parameter:  =  s -  a D =  s -  a )/(  s -  d ) Shape of slip-weakening curve Mantle viscosity  m

Twenty consecutive M>6.7 ruptures M6.9

M7.2

M7.0

M7.6

M6.7

M7.5

M7.6

M7.2

M6.7

M7.7

M7.3

M7.5

M7.3

M7.2

M6.7

M7.2

M7.3

M7.5

mean recurrence interval (for given magnitude threshold) magnitude-frequency statistics, e.g. b-value coefficient of variation conditional rupture probability Simulator results

Hanks and Bakun (2007 )

Magnitude-frequency statistics

magnitude log 10 [earthquake production rate (yr -1 )] With slip weakening D=1.25  m = 1.2 x Pa s

With slip weakening D=1.25  m = 1.2 x Pa s

Low Mantle Viscosity

High Mantle Viscosity

magnitude log 10 [earthquake production rate (yr -1 )]

Fault system behavior is sensitive to simple parameters Simulations capture Gutenberg-Richter and characteristic-earthquake behavior Comparison of slip maps for the southern SAF suggests that the ‘slip barrier’ nature of a segment boundary depends substantially on mantle viscosity Characteristic magnitude and mean recurrence interval may exhibit a systematic dependence on mantle viscosity Conclusions