‘triggering’ = a perturbation in the loading deformation that leads to a change in the...

‘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)


• Aseismic slip (not oscillatory, may be permanent)


• Aseismic slip (not oscillatory, permanent)

• Solid earth tides and ocean loading (oscillatory, ongoing)


• 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?


They’re transient!

shea

r st

ress

shea

r st

ress

failure threshold

time

t

Static Load Change

shea

r st

ress

shea

r st

ress

failure threshold

time

Static Load Change

t

t

shea

r st

ress

failure threshold

time

Dynamic Triggering

shea

r st

ress

failure threshold

time

Dynamic Triggering

t

shea

r st

ress

failure threshold

time

t


They’re transient; the failure conditions must change!



They’re oscillatory, but they only enhance failure probability (ASSUMPTION); no stress shadows.



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.


Seismic wavesRemote (many source dimensions)

Seismicity rate increases following large earthquakes.Missing? rate increases.


Seismic waves Remote (many source dimensions) Near-field (few source dimensions)

Correlation of spatial rate increase with directivity.

Pollitz & Johnston, 2007



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.



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



Distance-independent view

Measured Linear Aftershock Densities

Felzer & Brodsky, 2006




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!




‘Linear density’ = number of aftershocks within a volume defined by

surface S everywhere at distance r and width r

D

trigg

erin

gfa

ult





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





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




Are dynamic deformations consistent with these probabilities?




Peak Velocities vs r, M5.5-7.0





Peak Velocities vs r, M5.5-7.0 Peak Velocities vs r/D, M5.5-7.0

perhaps!




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



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



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



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)


delayed failure

delayed failure

Sobolev et al., 1996

Granite surface, shear vibration, stick-slip experiments.



delayed failure

delayed failure

Vibration Clock-advances Failure



Granular surface, acoustic vibration,stick-slip experiments.




acou

stic

tran

sien

t

acou

stic

tran

sien

t

triggered ‘new’ seismic events


clock-delayedfailure




acou

stic

tran

sien

t

acou

stic

tran

sien

t


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 )

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.


Parsons, 2005

Power-law distribution of contact areas.Number of ‘events’ vs clock-advance for 10% reduction in critical slip distance.

Perturbed failure rate.





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 )




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




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)?



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




What are the important characteristics of the dynamic field (frequency/rate, duration, max. value)?

How does delayed failure happen?

Thanks!

Comments?

‘triggering’ = a perturbation in the loading deformation that leads to a change in the...

Documents

transient slide

permanent slide

ongoing slide

dynamic loads

seismic waves oscillatory

withdrawal localized

probability of failure

theyre oscillatory