‘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!
Static Load Change
Dt
shear stress
failure threshold
time
Static Load Change
Dt
Dt
shear stress
failure threshold
time
Dynamic Triggering
shear stress
failure threshold
time
Dynamic Triggering
Dt
shear stress
failure threshold
time
What’s unique about dynamic loads?
They’re transient; the failure conditions must change!
Dt
shear stress
failure threshold
time
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 responses
Laboratory
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 waves
Remote (many source dimensions)
Seismicity rate increases following large earthquakes.
Dynamic Triggering Observations (by loading type)
Seismic waves
Remote (many source dimensions)
Seismicity rate increases following large earthquakes.
Dynamic Triggering Observations (by loading type)
Seismic waves
Remote (many source dimensions)
Seismicity rate increases following large earthquakes.
Dynamic Triggering Observations (by loading type)
Seismic waves
Remote (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.
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.
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.
Early excess of aftershocks.
Rate increases in stress shadows.
Chi-Chi earthquake
shadows start with
3-month rate
increases.
Ma et al., 2005
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
(r,D)  C10
Mmin
N(r,
D)
[
number of
aftershocks
at distance r
2   constant!
Dr
Dr
]P(r, D)
number of
probability of
potential
nucleation
nucleation sites
per unit distance
Dynamic Triggering Observations (by loading type)
Seismic waves
Remote (many source dimensions)
Near-field (few source dimensions)
Distance-independent view
D
‘Linear density’ = number of aftershocks within a volume defined by
surface S everywhere at distance r and width Dr
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)
(r, D)  [
Dr
]P(r, D)
N(r, D)  [  F(r)ds] Dr
S
 [4 A{1  ( D )  ( 1 )( D )2}r (d 1) ] Dr
r
2
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
N(r,
D)
(r, D)  [
P(r, D)  D
P(r)  1
2
[ D  r ]
2
[  r ]
2
2
or
Dr
]P(r, D)
or D
1
2
[ D  r]
2
[  r]
2
r r
D
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)
(r, D)  [
P(r, D)  D
P(r)  1
2
[ D  r ]
2
[  r ]
2
2
or
Dr
]P(r, D)
or D
1
2
[ D  r]
2
[  r]
2
r r
D
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
Are dynamic deformations consistent with these
probabilities?
Peak Velocities vs r, M5.5-7.0
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?
Peak Velocities vs r, M5.5-7.0
perhaps!
Peak Velocities vs r/D, M5.5-7.0
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
Denali surface waves in Japan,
Correlation with Love waves - Shear Load!
High-passed Sumatra surface waves in Japan
Correlation with Rayleigh waves - Dilatation & Fluids
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)
H
H
Glowacka et al., 2002
Dynamic Triggering Observations (by loading type)
Seismic waves
Remote (many source dimensions)
Near-field (few source dimensions)
Distance-independent view
Quasi-seismic responses
Laboratory
Granular surface quasi-static experiments.
“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
Dynamic Triggering Observations
delayed
failure
Seismic waves
Remote (many source dimensions)
Near-field (few source dimensions)
Distance-independent view
Quasi-seismic responses
Laboratory
delayed
failure
Granite surface
stick-slip experiments.
Sobolev et al., 1996
Dynamic Triggering Observations
delayed
failure
Seismic waves
Remote (many source dimensions)
Near-field (few source dimensions)
Distance-independent view
Quasi-seismic responses
Laboratory
Vibration Clock-advances Failure
delayed
failure
Granite surface, shear
vibration, stick-slip
experiments.
Sobolev et al., 1996
Dynamic Triggering Observations
Seismic 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 Observations
Seismic waves
Remote (many source dimensions)
Near-field (few source dimensions)
Distance-independent view
Quasi-seismic responses
Laboratory
Granular surface,
acoustic vibration,
stick-slip experiments.
triggered ‘new’
seismic events
triggered ‘new’
seismic events
clock-delayed
failure
Dynamic Triggering Observations
Seismic waves
Remote (many source dimensions)
Near-field (few source dimensions)
Distance-independent view
Quasi-seismic responses
Laboratory
Granular surface,
acoustic vibration,
stick-slip experiments.
triggered ‘new’
seismic events
memory
clock-delayed
failure
Dynamic Triggering Observations (by loading type)
Seismic waves
Aseismic slip
Earthquakes
Number of earthquakes & displacement
Hawaii Slow Slip & Earthquakes
Dynamic Triggering Observations (by loading type)
Seismic waves
Aseismic slip
Earthquakes
Tremor
Geodetic Displacement (mm east)
Cascadia Slow Slip & Tremor
Dragert et al., 2002
General features:
•apparent more commonly in areas of
•geothermal & Quaternary to recent volcanism,
•extensional regimes,
•high strain rates,
•seismic strains required ~mstrains,
•sometimes instantaneous but also delayed.
Models
Coulomb-Navier failure: no delays
Frictional:
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 )
Models
Coulomb-Navier failure: no delays
Frictional:
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 )
Dynamically reduced contact area (i.e. critical slip distance)
Power-law distribution of contact areas.
Parsons, 2005
Dynamically reduced contact area (i.e. critical slip distance)
Power-law distribution of contact areas.
Number of ‘events’ vs clock-advance for
10% reduction in critical slip distance.
Parsons, 2005
Dynamically reduced contact area (i.e. critical slip distance)
Power-law distribution of contact areas.
Number of ‘events’ vs clock-advance for
10% reduction in critical slip distance.
Perturbed
failure rate.
Parsons, 2005
Models
Coulomb-Navier failure: no delays
Frictional:
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 )
Models
Coulomb-Navier failure: no delays
Frictional:
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?
Pulse Experiments, Glass Beads
Elastic moduli decrease
(soften) with increasing
dynamic load amplitude
-> weakening mechanism?
sinusoid amplitude (strain)
Sinusoid Experiments, Rocks
Pulse Experiments, Glass Beads
Models
Coulomb-Navier failure: no delays
Frictional:
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 QuestionsIs our sampling biased (e.g., best monitoring in high strain rate
and/or geothermal areas)?
-Outstanding QuestionsIs 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 QuestionsIs 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
Velocity
Strengthening,
Slip Weakening
Friction
Theoretical
Frequency
Sensitivity
Non-Linear,
Slip Weakening
Friction
Dynamically
Induced
Pore Pressure
Change
-Outstanding QuestionsIs 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?