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Epistemic uncertainty in California-wide simulations of synthetic seismicity
Fred Pollitz, USGS Menlo Park
Acknowledgments: David Schwartz, Steve WardAcknowledgments: David Schwartz, Steve Ward
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Ward (2000)Ward (2000)
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Rundle et al. (2008)Rundle et al. (2008)
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Capabilities ofCapabilities ofthis simulatorthis simulator
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• Inherently discrete fault zoneInherently discrete fault zone
(Ben-Zion and Rice model)(Ben-Zion and Rice model)
• Homogeneous, planar faultsHomogeneous, planar faults
• Viscoelasticity of lower crust/upper mantleViscoelasticity of lower crust/upper mantle
--> loading through backslip in the--> loading through backslip in the
fully relaxed limitfully relaxed limit
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• Fault network and slip rates courtesy of Steve Ward (June, 2009)
• Original set of ~4 x 3 km2
patches are re-grouped and subdivided into set of smoothly-connected, non-overlapping ~1 x 1 km2 patches
• 101208 fault patches
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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)
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Simulator parameters
Dynamic overshoot parameter:
Stress reduction parameter: = s - a
D = s - a)/(s - d)
Shape of slip-weakening curve
Mantle viscosity m
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Twenty consecutive M>6.7 ruptures
M6.9M6.9
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M7.2M7.2
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M7.0M7.0
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M7.6M7.6
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M6.7M6.7
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M7.5M7.5
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M7.6M7.6
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M7.2M7.2
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M6.7M6.7
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M6.7M6.7
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M7.7M7.7
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M7.3M7.3
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M7.5M7.5
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M7.3M7.3
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M7.3M7.3
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M7.2M7.2
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M6.7M6.7
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M7.2M7.2
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M7.3M7.3
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M7.5M7.5
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• mean recurrence interval (for given magnitude threshold)
• magnitude-frequency statistics, e.g. b-value
• coefficient of variation
• conditional rupture probability
Simulator results
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Hanks and Bakun (2007Hanks and Bakun (2007))
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Magnitude-frequency statistics
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magnitude
log10
[earthquakeproduction rate (yr-1)]
With slip weakeningD=1.25m= 1.2 x 1019 Pa s
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With slip weakeningD=1.25m= 1.2 x 1019 Pa s
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Low Mantle Viscosity
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High Mantle Viscosity
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magnitude
log10
[earthquakeproduction rate (yr-1)]
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• 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