‘triggering’ = a perturbation in the loading deformation that leads to a change in the...
TRANSCRIPT
‘Triggering’ = a perturbation in the loading deformation that leads to a change in the
probability of failure.
How do we know it happens?
‘Triggering’ = a perturbation in the loading deformation that leads to a change in the
probability of failure.
How do we know it happens?
Measure or infer a loading perturbation, & observe a change in
seismicity rate (fault population or single fault recurrence),possibly its spatial variation too.
The ‘Reference’ State
Central California Ambient Seismicity
The Perturbation
Coyote Lake Mainshock & Ambient Seismicity
The Perturbation & Response
Coyote Lake Mainshock & Aftershocks
Dynamic loads:• Seismic waves (oscillatory, transient)
Dynamic loads:• Seismic waves (oscillatory, transient)
• Aseismic slip (not oscillatory, may be permanent)
Dynamic loads:• Seismic waves (oscillatory, transient)
• Aseismic slip (not oscillatory, permanent)
• Solid earth tides and ocean loading (oscillatory, ongoing)
Dynamic loads:• Seismic waves (oscillatory, transient)
• Aseismic slip (not oscillatory, permanent)
• Tides (oscillatory, ongoing)
• Surface/shallow: snow and ice, reservoir filling/draining, mining, ground water, fluid injection or withdrawal (localized)
• Magma movement (temperature, pressure, and chemical changes too)
What’s unique about dynamic loads?
What’s unique about dynamic loads?
They’re transient!
shea
r st
ress
shea
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failure threshold
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Static Load Change
shea
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shea
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failure threshold
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Static Load Change
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shea
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failure threshold
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Dynamic Triggering
shea
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Dynamic Triggering
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failure threshold
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t
What’s unique about dynamic loads?
They’re transient; the failure conditions must change!
What’s unique about dynamic loads?
They’re transient; the failure conditions must change!
They’re oscillatory, but they only enhance failure probability (ASSUMPTION); no stress shadows.
What’s unique about dynamic loads?
They’re transient; the failure conditions must change!
They only enhance failure probability (ASSUMPTION); no stress shadows.
Slower distance decay than static stress changes.
Dynamic Triggering Observations (by load type)
Seismic waves (transient, oscillatory)Remote (many source dimensions)Near-field (few source dimensions)
Distance-independent Quasi-seismic responsesLaboratory
Aseismic slip (slow, permanent)
Tides (oscillatory, ongoing)
Surface/Shallow: snow and ice, reservoir filling/draining, mining, ground water, fluid injection or withdrawal (localized)
Dynamic Triggering Observations (by loading type)
Seismic wavesRemote (many source dimensions)
Seismicity rate increases following large earthquakes.
Dynamic Triggering Observations (by loading type)
Seismic wavesRemote (many source dimensions)
Seismicity rate increases following large earthquakes.
Dynamic Triggering Observations (by loading type)
Seismic wavesRemote (many source dimensions)
Seismicity rate increases following large earthquakes.
Dynamic Triggering Observations (by loading type)
Seismic wavesRemote (many source dimensions)
Seismicity rate increases following large earthquakes.Missing? rate increases.
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Correlation of spatial rate increase with directivity.
Pollitz & Johnston, 2007
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Correlation of spatial rate increase with directivity. Correlation of (no) rate change with co-located seismic & aseismic events.
Pollitz & Johnston, 2007
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Correlation of spatial rate increase with directivity. Correlation of (no) rate change with co-located seismic & aseismic events.
Ma et al., 2005
Chi-Chi earthquake shadows start with 3-month rate increases.
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Correlation of spatial rate increase with directivity. Correlation of (no) rate change with co-located seismic & aseismic events. Early excess of aftershocks. Rate increases in stress shadows.
1998 1999 2000 2001 2002 1998 1999 2000 2001 2002
“Observed seismicity rate decreases in the Santa Monica Bay and along parts of the San Andreas fault are correlated with the calculated stress decrease.” Stein, 1999
“Observed seismicity rate decreases in the Santa Monica Bay and along parts of the San Andreas fault are correlated with the calculated stress decrease.” Stein, 1999
Time history of seismicity from Santa Monica Bay (Marsan, 2003).
“The [Stein, 1999] interpretation is made difficult by the fact that the transient activity modulation by the 1989 M5 Malibu earthquake was still ongoing….the quiescence observed after 1994 can be tracked back several months before Northridge, the latter main shock actually triggering seismicity in the region at the very short (i.e. days) timescale. Marsan, 2003
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view
Measured Linear Aftershock Densities
Felzer & Brodsky, 2006
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view
Modeled Linear Aftershock Densities
=[N(r, D)Δr
]P(r,D)
number of aftershocks at distance r
number of potential nucleation sites per unit distance
probability of nucleation
ρ(r,D) = C10− Mmin D2r−γ constant!
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view
‘Linear density’ = number of aftershocks within a volume defined by
surface S everywhere at distance r and width r
D
trigg
erin
gfa
ult
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view
Modeled Linear Aftershock Densities
ρ(r, D) = [N(r,D)Δr
]P(r,D)
N(r,D) =[ F (r)ds] rS∫
=[4π A{1+ (Dr ) + ( 12π)(Dr )2}r (d−1) ] r
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view
Modeled Linear Aftershock Densities
ρ(r, D) = [N(r,D)Δr
]P(r,D)
P(r, D) ≈D2
[αD2 + r2 ]or D2
[αD+ r]2
P(%r) ≈ 1[α + %r 2 ]
or 1[α + %r]2
%r = rD
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view
Modeled Linear Aftershock Densities
ρ(r, D) = [N(r,D)Δr
]P(r,D)
P(r, D) ≈D2
[αD2 + r2 ]or D2
[αD+ r]2
P(%r) ≈ 1[α + %r 2 ]
or 1[α + %r]2
%r = rD
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view
Are dynamic deformations consistent with these probabilities?
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view
Peak Velocities vs r, M5.5-7.0
Are dynamic deformations consistent with these probabilities?
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view
Peak Velocities vs r, M5.5-7.0 Peak Velocities vs r/D, M5.5-7.0
perhaps!
Are dynamic deformations consistent with these probabilities?
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view Quasi-seismic responses ‘Low-frequency’ events
Sumatra surface waves in Japan
High-passed Sumatra surface waves in Japan
Correlation with Rayleigh waves - Dilatation & Fluids
Miyazawa & Mori, 2006
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view Quasi-seismic responses ‘Low-frequency’ events
Sumatra surface waves in Japan
High-passed Sumatra surface waves in Japan
Correlation with Rayleigh waves - Dilatation & Fluids
Denali surface waves in Japan,Correlation with Love waves - Shear Load!
Miyazawa & Mori, 2006 Rubinstein et al., 2007
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view Quasi-seismic responses ‘Low-frequency’ events Creep and tilt
Response to Hector Mine waves on Imperial Fault
(260 km)
Glowacka et al., 2002
H
H
Dynamic Triggering Observations (by loading type)
Seismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view Quasi-seismic responses Laboratory
“Our results predict that a transient dynamic normal load during creep can strengthen a fault…gouge particles become compacted into a lower energy configuration.” Richardson and Marone, 1999
Granular surface quasi-static experiments.
Sobolev et al., 1996
Granite surface stick-slip experiments.
Dynamic Triggering ObservationsSeismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view Quasi-seismic responses Laboratory
delayed failure
delayed failure
Sobolev et al., 1996
Granite surface, shear vibration, stick-slip experiments.
Dynamic Triggering ObservationsSeismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view Quasi-seismic responses Laboratory
delayed failure
delayed failure
Vibration Clock-advances Failure
Dynamic Triggering ObservationsSeismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view Quasi-seismic responses Laboratory
Granular surface, acoustic vibration,stick-slip experiments.
Dynamic Triggering ObservationsSeismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view Quasi-seismic responses Laboratory
Granular surface, acoustic vibration,stick-slip experiments.
acou
stic
tran
sien
t
acou
stic
tran
sien
t
triggered ‘new’ seismic events
triggered ‘new’ seismic events
clock-delayedfailure
Dynamic Triggering ObservationsSeismic waves Remote (many source dimensions) Near-field (few source dimensions)
Distance-independent view Quasi-seismic responses Laboratory
Granular surface, acoustic vibration,stick-slip experiments.
acou
stic
tran
sien
t
acou
stic
tran
sien
t
triggered ‘new’ seismic events
clock-delayedfailure
memory
Dynamic Triggering Observations (by loading type) Seismic wavesAseismic slip Earthquakes
Hawaii Slow Slip & Earthquakes
Num
ber
of
eart
hqua
kes
& d
ispl
acem
ent
Dynamic Triggering Observations (by loading type) Seismic wavesAseismic slip Earthquakes Tremor
Dragert et al., 2002
Cascadia Slow Slip & TremorG
eode
tic
Dis
plac
emen
t (m
m e
ast)
Trem
o r Acti vity ( hrs in 10 days)
General features:
•apparent more commonly in areas of •geothermal & Quaternary to recent volcanism,
•extensional regimes,
•high strain rates,
•seismic strains required ~strains,
•sometimes instantaneous but also delayed.
ModelsCoulomb-Navier failure: no delaysFrictional:
traditional clock-advance models can’t explain long delays, require high (near lithostatic) pressures or critical conditions, changing frictional properties or stability regime.
Subcritical crack growth: same behavior as rate-state friction. Dynamic nonlinear softening.Fluid and pore pressure mechanisms:
decrease effective normal stress,local, fluid-driven deformationdisruption of clogged fractures and hydraulic fracturingbubbles
rectified diffusion (volatiles selectively pumped into bubbles during the dilatation) advective overpressure (rising of loosened bubbles within magma body )
ModelsCoulomb-Navier failure: no delaysFrictional:
traditional clock-advance models can’t explain long delays, require high (near lithostatic) pressures or critical conditions, changing frictional properties or stability regime.
Subcritical crack growth: same behavior as rate-state friction. Dynamic nonlinear softening.Fluid and pore pressure mechanisms:
decrease effective normal stress,local, fluid-driven deformationdisruption of clogged fractures and hydraulic fracturingbubbles
rectified diffusion (volatiles selectively pumped into bubbles during the dilatation) advective overpressure (rising of loosened bubbles within magma body )
Parsons, 2005
Power-law distribution of contact areas.
Dynamically reduced contact area (i.e. critical slip distance)
Parsons, 2005
Power-law distribution of contact areas. Number of ‘events’ vs clock-advance for 10% reduction in critical slip distance.
Dynamically reduced contact area (i.e. critical slip distance)
Parsons, 2005
Power-law distribution of contact areas.Number of ‘events’ vs clock-advance for 10% reduction in critical slip distance.
Perturbed failure rate.
Dynamically reduced contact area (i.e. critical slip distance)
ModelsCoulomb-Navier failure: no delaysFrictional:
traditional clock-advance models can’t explain long delays, require high (near lithostatic) pressures or critical conditions, changing frictional properties or stability regime.
Subcritical crack growth: same behavior as rate-state friction. Dynamic nonlinear softening.Fluid and pore pressure mechanisms:
decrease effective normal stress,local, fluid-driven deformationdisruption of clogged fractures and hydraulic fracturingbubbles
rectified diffusion (volatiles selectively pumped into bubbles during the dilatation) advective overpressure (rising of loosened bubbles within magma body )
ModelsCoulomb-Navier failure: no delaysFrictional:
traditional clock-advance models can’t explain long delays, require high (near lithostatic) pressures or critical conditions, changing frictional properties or stability regime.
Subcritical crack growth: same behavior as rate-state friction. Dynamic nonlinear softening.Fluid and pore pressure mechanisms:
decrease effective normal stress,local, fluid-driven deformation,disruption of clogged fractures and hydraulic fracturing,bubbles
rectified diffusion (volatiles selectively pumped into bubbles during the dilatation) advective overpressure (rising of loosened bubbles within magma body).
Elastic moduli decrease (soften) with increasing dynamic load
amplitude
-> weakening mechanism?
Rel
ativ
e C
hang
e in
Mod
ulus
Pulse Experiments, Glass Beads
Elastic moduli decrease (soften) with increasing dynamic load amplitude
-> weakening mechanism?
Rel
ativ
e C
hang
e in
Mod
ulus
% Relative C
hange in Resonant
Frequency %R
elat
ive
Cha
nge
in M
odul
us
sinusoid amplitude (strain)
Pulse Experiments, Glass Beads
Sinusoid Experiments, Rocks
ModelsCoulomb-Navier failure: no delaysFrictional:
traditional clock-advance models can’t explain long delays, require high (near lithostatic) pressures or critical conditions, changing frictional properties or stability regime.
Subcritical crack growth: same behavior as rate-state friction. Dynamic nonlinear softening.Fluid and pore pressure mechanisms:
decrease effective normal stress,local, fluid-driven deformation,disruption of clogged fractures and hydraulic fracturing,bubbles
rectified diffusion (volatiles pumped into bubbles during the dilatation), advective overpressure (rising of loosened bubbles within magma body),
liquefaction.
-Outstanding Questions-
Is our sampling biased (e.g., best monitoring in high strain rate and/or geothermal areas)?
-Outstanding Questions-
Is our sampling biased (e.g., best monitoring in high strain rate and/or geothermal areas)?
How important are local conditions; are multiple mechanisms at work?
-Outstanding Questions-
Is our sampling biased (e.g., best monitoring in high strain rate and/or geothermal areas)?
How important are local conditions; are multiple mechanisms at work?
What are the important characteristics of the dynamic field (frequency/rate, duration, max. value)?
Strain Rate(acceleration)
Strain (velocity)
Displacement
Theoretical Frequency Sensitivity
DynamicallyInduced
Pore PressureChange
Velocity Strengthening,
Slip Weakening Friction
Non-Linear, Slip Weakening
Friction
-Outstanding Questions-
Is our sampling biased (e.g., best monitoring in high strain rate and/or geothermal areas)?
How important are local conditions; are multiple mechanisms at work?
What are the important characteristics of the dynamic field (frequency/rate, duration, max. value)?
How does delayed failure happen?
Thanks!
Comments?