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RSQSim. Jim Dieterich Keith Richards-Dinger. UC Riverside. Funding: USGS NEHRP SCEC. Representation of Fault Friction. Constitutive relation: State evolution: Stress evolution: Terms in red are additional ones due to normal stress variations (Linker and Dieterich, 1992)

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Rsqsim

RSQSim

Jim Dieterich

Keith Richards-Dinger

UC Riverside

Funding:

USGS NEHRP

SCEC


Representation of fault friction

Representation of Fault Friction

  • Constitutive relation:

  • State evolution:

  • Stress evolution:

  • Terms in red are additional ones due to normal stress variations (Linker and Dieterich, 1992)

  • Interaction coefficients, K, calculated from the dislocation solutions of Okada, 1992

  • Tectonic stressing rates derived from backslipping the model

  • Numerical integration too slow for the scale of problems we would like to address


Representation of fault friction1

State 0: locked fault

State 2: seismic slip

Representation of Fault Friction

  • Constitutive relation:

  • State evolution:

  • Stress evolution:

State 1: nucleation


Representation of fault friction2

Representation of Fault Friction

  • No predetermined failure stress or stress drop

  • Stress drop scales roughly as


Representation of fault friction3

Representation of Fault Friction

  • No predetermined failure stress or stress drop

  • Stress drop scales roughly as


Approximations to elastodynamics

Approximations to Elastodynamics

Parameters that influence the rupture process:

  • Slip speed during coseismic slip determined from shear impedance considerations

  • Reduction of a on patches nearby to seismically slipping patches

  • Stress overshoot during ruptures


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Effect of Overshoot on Rupture Characteristics

Large overshoot (13%)

Small overshoot (1%)


Approximations to elastodynamics1

Approximations to Elastodynamics

Values for rupture parameters determined by comparison with fully dynamic rupture models

DYNA3D – Fully dynamic finite element simulation

Propagation time 14.0 s

RSQsim – Fast simulation

Propagation time 14.3 s


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Smooth Initial Stress (w/ block of higher normal stress)


Representation of viscoelasticity afterslip

Representation of Viscoelasticityafterslip

  • Rate-strengthening (a > b) patches

    • Approximated as always sliding at steady-state

    • Distributed as

      • Deep creeping extensions to major faults

      • Shallow creep on major faults

      • Entire creeping sections (e.g. SAF north of Parkfield)

        • Possibly with small imbedded stick-slip patches

      • More complicated mixed stick-slip and creeping areas (e.g. Hayward Fault)


Representation of viscoelasticity afterslip1

Representation of Viscoelasticityafterslip

Penetration of slip of large events into creeping zone


Representation of viscoelasticity afterslip2

Representation of Viscoelasticityafterslip

Fraction of moment release in creeping section

Aftershocks


Representation of viscoelasticity afterslip3

Representation of Viscoelasticityafterslip

Small repeating earthquakes

Simulation

1989 Loma Prieta Earthquake


Power law temporal clustering

Power-law temporal clustering

Stacked rate of seismicity relative to mainshock origin time

Decay of aftershocks follows Omori power law t -p with p = 0.77

Foreshocks (not shown) follow an inverse Omori decay with p = 0.92

Dieterich and Richards-Dinger, PAGEOPH, 2010


Power law temporal clustering1

Power-law temporal clustering

Interevent Waiting Time Distributions

California Catalog 1911 – 2010.5


Power law temporal clustering2

Power-law temporal clustering

Space – Time Distributions


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Earthquake cluster along San Andreas Fault

M7.3

43 aftershocks in 18.2days

All-Cal model – SCEC Simulator Comparison Project


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Earthquake cluster along San Andreas Fault

M6.9

Followed by 6 aftershocks in 4.8 minutes

All-Cal model – SCEC Simulator Comparison Project


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Earthquake cluster along San Andreas Fault

M7.2

All-Cal model – SCEC Simulator Comparison Project


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Colella et al.,

submitted

Slow-slip events

  • slip ~2.3 - 4.0 cm

  • duration ~10-40 days

  • inter-event time - ~10-19 months

  • simultaneous slip in different areas

  • no Omori clustering

  • spontaneous segmentation


Summary or conclusions if appropriate or desired

Summary or Conclusions (if appropriate or desired)


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