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m ss= = t/s= m * +(a-b) ln(V/V * )PowerPoint Presentation

m ss= = t/s= m * +(a-b) ln(V/V * )

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Rate-and-State Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Rate-and-State Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Rate-and-State Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Stationary State Frictional Sliding

mss== t/s= m*+(a-b) ln(V/V*)

a-b < 0

slip is potentially unstable

a-b > 0

stable sliding

a-b

Correspond to

T~300 °C

For Quartzo-Feldspathic rocks

(Blanpied et al, 1991)

from Rate-and-state friction

(e.g., Tse and Rice, 1986)

Slip as a function of depth over the seismic cycle of a strike–slip fault, using a frictional model containing a transition from unstable to stable friction at 11 km depth

(Sholz, 1998)

Model of afterslip

Evolution of afterslip on BCFZ with time

Slip velocity (or slip rate) on BCFZ

background loading rate

afterslip duration

Figure 2, 2004

Model of aftershock rate

Key assumption: seismicity rate is proportional to the stress rate (time derivative of applied stress, or loading)

slope of 1/t

C = 100

Figure 4, 2004

Note: the decrease in seismicity rates lasts longer than increase in seismicity rate.

Postseismic Displacements following the Mw 7.2 1992 Landers Earthquake

CPA analysis show that all GPS stations follow about the same time evolution f(t)

Modeling Landers afterslip

Step 4: Compute displacement U(r,t) in a bulk:

Modeling Landers afterslip

Step 5: Find the best-fitting model parameters to the geodetic data

maybe due to dynamic stress change

too small: maybe due to high pore-pressure

Figure 4, 2007

DCFF on 340ºE striking fault planes

at 15 km depthdue to afterslip

6 yr

6 months

Figure 9, 2007

DCFF (bar)

Aftershocks tend to fall preferentially in area of static Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Aftershocks follow the Omori Law (seismicity rate decays as 1/t)

>> the stress history at the location of each aftershocks is a step function and a static Coulomb failure criterion is rejected. Failure needs being a time depend process.

OR

>> the postseismic stress is time dependent in a way that controls the seismicity rate.

Ge277-Experimental Rock Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stressimplication for Aftershocks triggering

Dieterich, J. H. (1994). A constitutive law for rate of earthquake production and its application to earthquake clustering. JGR 99, 2601–2618.

Gomberg, J. (2001), The failure of earthquake failure models, Journal of Geophysical Research-Solid Earth, 106, 16253-16263.

Gross, S., and C. Kisslinger (1997), Estimating tectonic stress rate and state with Landers aftershocks, Journal of Geophysical Research-Solid Earth, 102, 7603-7612.

King, G.C.P., and M. Cocco (2001). Fault interaction by elastic stress changes: New clues from earthquake sequences. Adv. Geophys. 44.

Perfettini, H., J. Schmittbuhl, and A. Cochard (2003a). Shear and normal load perturbations on a two-dimensional continuous fault: 1. Static triggering. JGR 108(B9), 2408.

Perfettini, H., J. Schmittbuhl, and A. Cochard (2003b). Shear and normal load perturbations on a two-dimensional continuous fault: 2. Dynamic triggering. JGR 108(B9), 2409.

Time Delay Explanations Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

- Failure model involving a nucleation phase (rate-and-state friction, static fatique)
- fluid flow
- postseismic relaxation / creep in the crust, either on faults or distributed through a volume
- viscoelastic relaxation of the lithosphere and asthenosphere
- continued progressive tectonic loading adding to postearthquake stresses

Rate-and-State Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

King & Cocco (2001)

- Constitutive laws can be described by two coupled equations:
- the governing equation, which relates sliding resistance (or shear stress) to slip velocity V and state variables i :
= F (V, i, a, b, 0, n)

where a and b are positive parameters, 0 is a reference friction,and n is normal stress

- the evolution equation, which provides time evolution of the state variable:
/t = G (V, L, , b)

- the governing equation, which relates sliding resistance (or shear stress) to slip velocity V and state variables i :
- Dieterich (1994) uses :

Rate-and-State Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Dieterich (1994)

- Dieterich derives two likely equations to describe seismicity rate as a function of time:

- Note that (13) has the form of Omori’s law:
R = K / (c + t)

- Similarly (12) gives Omori’s law for t/ta<1 but seismicity rate merges to the steady state background rate for t/ta>1
- This makes (12) preferable in general

The inferred value of a is around 3-6 10 Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress-4

For a small stress change : Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Rate-and-State Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Perfettini et al. (2003a,b)

Rate-and-State Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Perfettini et al. (2003a,b)

Rate-and-State Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Perfettini et al. (2003a,b)

Perfettini et al. (2003a,b)

Perfettini et al. (2003a,b)

Perfettini et al. (2003a,b)

Rate-and-State Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Perfettini et al. (2003a,b)

- In the previous figures, Perfettini et al. considered permanent variations of the normal stress (loading or unloading step)
- Perfettini et al. show more generally that all stresses for whichCFF(,) are the same are equivalent for this purpose

Rate-and-State Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Perfettini et al. (2003a,b)

- Except near the end of the earthquake cycle, the prediction of the Coulomb failure criterion, in terms of clock advance/decay, agrees to the first order (i.e., neglecting the small oscillations)
- This agreement may explain the success of the Coulomb failure criterion in modeling many earthquake sequences
- The discrepancy at the end of the cycle comes from the fact that varies significantly at the end of the cycle
- The departure from a Coulomb-like behavior later in the cycle is the self-accelerating phase
- The transition from the locked to the self-accelerating phase occurs when the state variable becomes greater than its steady state value, i.e., when > ss = Dc/V or when > ss

Rate-and-State Friction Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Perfettini et al. (2003a,b)

- One major difference between the Coulomb failure model and their results is that, at the end of the earthquake cycle, the clock delay due to unloading steps drops to zero; one example of such an effect is the 1911 Morgan Hill event occurring in the 1906 stress shadow
- In other words, a fault at the end of its cycle seems to be only slightly sensitive to external stress perturbations, the nucleation process being underway

Influence of Pulse Duration in Dynamic Triggering Coulomb stress increase but there are also earthquakes in area of decrease Coulomb stress

Perfettini et al. (2003a,b)

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