A micro-scale perspective on a km-scale problem Microphysically - - PowerPoint PPT Presentation

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A micro-scale perspective on a km-scale problem Microphysically - - PowerPoint PPT Presentation

May 31, 2023 174 likes •633 views

200 m A micro-scale perspective on a km-scale problem Microphysically based modelling of friction and earthquakes Brace & Byerlee (1966) Dieterich (1972) Dieterich (1978) Rate & State Friction Scholz (2002) # + - ln # % #

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A micro-scale perspective on a km-scale problem

Microphysically based modelling of friction and earthquakes

200 µm

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Dieterich (1972) Brace & Byerlee (1966) Dieterich (1978)

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Rate & State Friction

!(#, %) = !∗ + * ln # #∗ + - ln #∗% ./ 0% 01 = 2(%, #, … )

Scholz (2002)

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!"" = !∗ + & − ( ln + +∗

& − ( = −0.005

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!"" = !∗ + & − ( ln + +∗

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SLIDE 7

!"" = !∗ + & − ( ln + +∗

& − ( > 0 & − ( < 0 & − ( > & − ( < 0

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SLIDE 8

Quick summary

  • Modelling and analysis relies on rate-and-state friction
  • RSF is empirical formulation => problem for extrapolation
  • We need models based on physical principles
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Coming up…

  • 1. Lab observations of fault friction, micro-scale processes
  • 2. Basic concepts behind microphysical models
  • 3. Applications in seismic cycle modelling
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Part 1: Lab observations

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Velocity-step tests

Velocity Shear stress

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Velocity-step tests

Velocity Shear stress !

"

!

#

$" $#

% ln !

#

!

"

( ln !

#

!

"

∆$ = % − ( ln !

#

!

"

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Velocity-step tests

Chester (1994)

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Microstructures

Shimamoto (1986)

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Microstructures

Bos et al. (2000)

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Microstructures

Niemeijer & Spiers (2007)

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Microstructures

Dynamic weakening

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Micro-scale processes

Pressure solution

Barker & Kopp (1991)

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Micro-scale processes

Pressure solution

Bos et al. (2000)

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Micro-scale processes

Granular flow

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Recap Part 1

  • Velocity dependence of friction is not a constant
  • Several deformation regimes
  • Microstructural changes between deformation regimes
  • At least 2 micro-scale processes
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Part 2: Microphysical models

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Basic ingredients

  • 1. Pressure solution

=> Time-dependent compaction

  • 2. Granular flow

=> Slip-dependent dilatation

  • 3. Microstructure

=> Porosity

  • 4. Boundary conditions

=> Constant !", #

$%

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Model geometry (CNS model)

Niemeijer & Spiers (2007) Chen & Spiers (2016)

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Model equations

!" !# = % &

'( − ℎ

̇ ,(- + ̇ ,/0 !1 !# = − 1 − 1 ̇ 3(- + ̇ 3/0

̇ ,(- = 4"5(1) ̇ ,/0 = ̇ ,/0

∗ exp " 1 − <∗ tan @ − A <∗ + tan @

B C A + " tan @ ̇ 3(- = 4A5(1) Pressure solution: Granular flow: ̇ 3/0 = − tan @ ̇ ,/0

Main ODE

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Steady-state behaviour

Ductile creep

(zero porosity)

Increasing porosity

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Transient behaviour

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Recap Part 2

  • Quantified micro-scale processes
  • Incorporated constitutive relations into spring-block model
  • Steady-state and transient frictional behaviour = OK
  • Microphysical model explains lab results
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Part 3: Seismic cycle modelling

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Skipping 6 orders

github.com/ydluo/qdyn

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Earthquakes!

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Earthquakes!

Van den Ende, Chen, Ampuero, Niemeijer (2018, Tectonophysics) See:

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Into the field

Faulkner et al. (2003) Fagereng (2011a,b) Kimura et al. (2012) and others…

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Back to safety…

Asperities: “slow” pressure solution Matrix: “fast” pressure solution

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Earthquakes!

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Earthquakes!

“Regular” earthquakes (Mw < 6) Slow slip events “Anomalous” earthquakes

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Why anomalous earthquakes?

Stable creep Unstable slip

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Why anomalous earthquakes?

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Why anomalous earthquakes?

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Recap Part 3

  • Interplay between pressure solution and granular flow gives

earthquakes

  • Variations in pressure solution kinetics leads to complex slip behaviour
  • Massive instability facilitated by flow-to-friction transition
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Perspectives

1.

Microphysically-based (numerical) modelling offers new avenues for studying earthquake and slow slip mechanics

2.

Incorporating micro-scale processes and physical principles facilitates collaboration between experimental- and field geologists, and modellers

3.

Far future: earthquake hazard assessment and forecasting based on physical/chemical considerations