Epistemic uncertainty in California-wide simulations of synthetic seismicity

Epistemic uncertainty in California-wide simulations of synthetic seismicity

Fred Pollitz, USGS Menlo Park

Acknowledgments: David Schwartz, Steve WardAcknowledgments: David Schwartz, Steve Ward

Ward (2000)Ward (2000)

Rundle et al. (2008)Rundle et al. (2008)

Capabilities ofCapabilities ofthis simulatorthis simulator

• 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

• 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

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

M6.9M6.9

M7.2M7.2

M7.0M7.0

M7.6M7.6

M6.7M6.7

M7.5M7.5

M7.6M7.6

M7.2M7.2

M6.7M6.7

M6.7M6.7

M7.7M7.7

M7.3M7.3

M7.5M7.5

M7.3M7.3

M7.3M7.3

M7.2M7.2

M6.7M6.7

M7.2M7.2

M7.3M7.3

M7.5M7.5

• 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 (2007Hanks and Bakun (2007))

Magnitude-frequency statistics

magnitude

log10

[earthquakeproduction rate (yr-1)]

With slip weakeningD=1.25m= 1.2 x 1019 Pa s

With slip weakeningD=1.25m= 1.2 x 1019 Pa s

Low Mantle Viscosity

High Mantle Viscosity

magnitude

log10

[earthquakeproduction 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