a post-loma prieta progress report on earthquake triggering by a continuum of deformations
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A Post-Loma Prieta Progress Report on
Earthquake Triggering by a Continuum of Deformations
Presented By
Joan Gomberg
Response of Regional Seismicity to Static Stress Change Produced by the Loma Prieta Earthquake.
Reasenberg & Simpson, 1992
A pleasingly simple correlation….
Stress transfer by the 1988-1989 M=5.3 and 5.4 Lake Elsman foreshocks to the Loma Prieta fault: Unclamping at the site ofpeak mainshock slip.
Perfettini et al., 1999
When should correlation imply causation?Normal Stress Change
Right-lateral Stress Change
Reverse Stress Change
Coulomb Stress Change
shear stress
shear stress
failure threshold
time
t
One End Member - Static Load Change
shear stress
shear stressfailure threshold
time
t
t
One End Member - Static Load Change
shear stress
failure threshold
time
The Other End Member - Dynamic Load Change
shear stressfailure threshold
time
t
Static Triggering -> Load or Strength ChangeDynamic Triggering -> Strength Change
The Picture Post-Loma Prieta:
A wide spectrum of triggers between the end members:
The Picture Post-Loma Prieta:
The ‘Dieterich (1994)’ or ‘Clock-Advance’ Model
A Popular Physical Model:
The ‘Dieterich (1994)’ or ‘Clock-Advance’ Model
Stress -> Rate Change Highly Non-linear.
Afterslip and Aftershocks in the Rate-state Friction Law.Helmstetter & Shaw, 2009
Rate
Change
Frictional Model Rate Change Predicted for Stress Step
background
perturbed
Other Slowly-Developing, Permanent Load Changes:
Afterslip and Aftershocks in the Rate-state Friction Law.Helmstetter & Shaw, 2009
Rate
Change
Frictional Model Rate Change Predicted for Stress Step & Afterslip
background
perturbed
Modeling Afterslip and Aftershocks Following the 1992 Landers EarthquakePerfettini & Avouac, 2007
Cumulative # of
Aftershocks
Post-seismic
Deformation
Time after Landers (yr)
Measured Afterslip Deformation & Aftershock Rate -> Linear Relationship
Oscillatory, continuous loads:
Seasonal Variations of Seismicity and Geodetic Strain in the Himalaya Induced by Surface Hydrology
Bettinelli et al., 2008
Earthquake Rate
Geodetically Measured Displacement
River Elevation
Rainfall Modulated Seismicity
+2-4 kPa
Seasonal Variations of Seismicity and Geodetic Strain in the Himalaya Induced by Surface Hydrology
Bettinelli et al., 2008
Earthquake Rate
Geodetically Measured Displacement
River Elevation
Lack of tidal modulation constrains nucleation time.
‘Dynamic’ Triggering (by seismic waves).
The ‘Dieterich (1994)’ or ‘Clock-Advance’ Model
The Failure of Earthquake Failure Models. Gomberg, 2001
A Few More Outstanding Questions…
Measured Linear Aftershock Densities
Felzer & Brodsky, 2006
Aftershock Scale Independence -> Large & Small Earthquakes Triggered Identically
Evidence for Mogi Doughnut Behavior in Seismicity Preceding Small Earthquakes in Southern CaliforniaShearer & Lin, 2009
Foreshock Scale Dependence -> Large & Small Earthquakes Begin Differently
M3 source dimension
M4 source dimension
The Response of Seismicity to Coulomb Stress Triggers & Shadows of the 1999 Mw=7.6 ChiChi Earthquake. Ma et al., 2005
1998 1999 2000 2001 20021998 1999 2000 2001 2002
Complex Aftershock Behaviors: Rate Increases Precede Quiescences
background rate
background rate
background rate
background rate
quiescence
quiescence
quiescence
quiescence
Can Coseismic Stress Variability Suppress Seismicity Shadows? Insights from a Rate-State Friction ModelMarsan, 2006
Complex Aftershock Behaviors Reflect Stress Heterogeneity
seismicity rate change
time (ta units)
background rate
Complex Aftershock Behaviors Reflect Fault Patch Depletion
A Frictional Population Model of Seismicity Rate ChangeGomberg et al., 2005
Thank You!
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