RSQSim
Jim Dieterich
Keith Richards-Dinger
UC Riverside
Funding:
USGS NEHRP
SCEC
6/9/2011
UCERF3 / EQ Simulators Workshop
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Representation of Fault Friction
• Constitutive relation:
• State evolution:
• Stress evolution:
•
•
•
•
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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
UCERF3 / EQ Simulators Workshop
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Representation of Fault Friction
• Constitutive relation:
• State evolution:
• Stress evolution:
State 0: locked fault
State 1: nucleation
State 2: seismic slip
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UCERF3 / EQ Simulators Workshop
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Representation of Fault Friction
• No predetermined failure stress or stress drop
• Stress drop scales roughly as
6/9/2011
UCERF3 / EQ Simulators Workshop
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Representation of Fault Friction
• No predetermined failure stress or stress drop
• Stress drop scales roughly as
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UCERF3 / EQ Simulators Workshop
5
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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UCERF3 / EQ Simulators Workshop
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Effect of Overshoot on Rupture Characteristics
Large overshoot (13%)
Small overshoot (1%)
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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)
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Representation of Viscoelasticity afterslip
• 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)
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Representation of Viscoelasticity afterslip
Penetration of slip of large events into creeping zone
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Representation of Viscoelasticity afterslip
Fraction of moment release in creeping section
Aftershocks
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Representation of Viscoelasticity afterslip
Small repeating
earthquakes
Simulation
Omori' s law

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Rt
1989 Loma Prieta Earthquake
1
Omori' s law
Rt
1

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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
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Dieterich and Richards-Dinger, PAGEOPH, 2010
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Power-law temporal clustering
Interevent Waiting Time Distributions
California Catalog 1911 – 2010.5
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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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UCERF3 / EQ Simulators Workshop
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Earthquake cluster along San Andreas Fault
M7.2
All-Cal model – SCEC Simulator Comparison Project
6/9/2011
UCERF3 / EQ Simulators Workshop
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Colella et
al.,
submitted
6/9/2011
Slow-slip events
UCERF3 / EQ Simulators Workshop
•
•
slip ~2.3 - 4.0 cm
•
inter-event time ~10-19 months
•
simultaneous slip in
different areas
•
•
no Omori clustering
duration ~10-40
days
spontaneous
segmentation
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Summary or Conclusions (if appropriate or desired)
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