Simulating big earthquakes Accessing the inaccessible with models

Subduction zone earthquakes Two stories of deformation and stress

Pacific Ocean

Eurasia NorthAmerica

1: 1995 M8 Jalisco, Mexico quake 2: 2004 M9

Sumatra-Andaman quake

NorthAmerica

PacificOcean

North AmericanPlate

MexicoM

idd

leAm

erica

Trench

Pacific Ocean

Mid

dle

America

Trench

0 100 200

kilometers

N

4 cm

/yr

RiveraPlate

1. The M8 Jalisco Earthquake: A natural laboratory for stress-triggering

M8 Jalisco Quake

Subduction zone Converging tectonic plates

North AmericanPlate

MexicoM

idd

leAm

erica

Trench

Pacific Ocean

Mexico

4 cm

/yr

North AmericanPlate

Mid

dle

America

Trench

0 100 200

kilometers

N

Pacific Ocean

North AmericanPlate

Mexico

Mexico

RiveraPlate

Rivera Plate North American Plateoceanic crust continental crust

M8 Jalisco Quake

Earthquakes Release of built-up tectonic stress

Rivera Plate North American PlateRivera Plate North American Plate

cross-section

oceanic crust continental crust

M8 Jalisco Quake

Study site 1995 Jalisco earthquake

RiveraPlate

North AmericanPlate

MexicoM

idd

leAm

erica

TrenchPacific Ocean

Mid

dle

America

Trench

0 100 200

kilometers

N

1995 Feb, GPS sites installed

Oct 9, M=8

Dec 11, M=6

GPS site

0.5 m

4 cm

/yr

NorthAmerica

PacificOcean

M8 Jalisco Quake

Observations Earthquakes close together in both space & time

October 9, M=8

December 11, M=6

0 100 200

kilometers

63 d

ays

* earthquakes linked together

rupture plane

M8 Jalisco Quake

Storage and release of elastic energy • Tectonic stresses load fault • Rocks store elastic energy • Frictional resistance of fault is overcome

Stress-triggering 101: The interaction of earthquakes

M8 Jalisco Quake

Storage and release of elastic energy • Tectonic stresses load fault • Rocks store elastic energy • Frictional resistance of fault is overcome

Stress-triggering 101: The interaction of earthquakes

M8 Jalisco Quake

Storage and release of elastic energy • Tectonic stresses load fault • Rocks store elastic energy • Frictional resistance of fault is overcome

Stress-triggering 101: The interaction of earthquakes

M8 Jalisco Quake

tectonicstress

normalstress

friction

Storage and release of elastic energy • Tectonic stresses load fault • Rocks store elastic energy • Frictional resistance of fault is overcome

Stress-triggering 101: The interaction of earthquakes

M8 Jalisco Quake

tectonicstress

normalstress

friction

tectonicstress(winch)

normalstress

(gravity)

friction(sandpaper)

Storage and release of elastic energy • Tectonic stresses load fault • Rocks store elastic energy • Frictional resistance of fault is overcome

Stress-triggering 101: The interaction of earthquakes

M8 Jalisco Quake

Earthquake coupling • Stress release from loads other faults • Quake 1 may trigger Quake 2

fault 1quake 1

fault 2quake 2

Stress-triggering 101: The interaction of earthquakes

M8 Jalisco Quake

Earthquake coupling • Stress release from an earthquake loads other faults • Quake 1 may trigger Quake 2

1

stresstransfer

friction

normalstress

2

tectonicstress

normalstress

Stress-triggering 101: The interaction of earthquakes

M8 Jalisco Quake

1

stresstransfer

friction

normalstress

2

tectonicstress

normalstress

tectonicstress(winch)

normalstress

(gravity)

friction(sandpaper)

normalstress

(gravity)

stresstransfer

(elastic material)

2 2

1

Stress-triggering 101: The interaction of earthquakes

Earthquake coupling • Stress release from an earthquake loads other faults • Quake 1 may trigger Quake 2

M8 Jalisco Quake

What about the time lag? A good model must also account for the 63-day lag

October 9, M=8

December 11, M=6

0 100 200

kilometers

63 d

ays

* earthquakes linked together

rupture plane

lag

M8 Jalisco Quake

Hypothesis

October 9, M=8 0 100 200

kilometers

fault

stress

(from M=8 quake)

pore pressure along fault slowly increases after M=8 quake

pore pressure

(along fault of M=6 quake)

triggered M=6 quake

+

pore pressure: pressure of water in the pores of the rock.

definition

M8 Jalisco Quake

Poroelastic mechanics Physical interaction of rock and pore water

saturated

rockrock matrix

fluid-filledpore

0– +

pore pressure

tension

0– +

pore pressure

compression

M8 Jalisco Quake

Earthquake mechanics The meaning of and

pore pressure tension

0– +

pore pressure tension

0– +

compression

0– +

pore pressure

compression

0– +

pore pressure

fault

M8 Jalisco Quake

Rivera plate North American plate

M = 8( t = 0 )

M = 6( t = 63 days )

tension

tension

compression

compression

cross-section ofsubduction zone

pore pressure near M=6 fault0

– +

t = 63 days

fluid flow0– +

t = 0+

Conceptual model Earthquake released stress and pore pressure

M8 Jalisco Quake

* Coulomb stress along fault can change due to fluid flow changing pore pressure

Coulomb stress tendency for slip to occur along a fault

definition0

– +

shearstress

normalstress

pore pressure

faultpore pressure

shear stress

normal stress

friction

Fault stability: Coulomb stress Combination of stress, pore pressure, and friction

M8 Jalisco Quake

Fault Stability: Coulomb Stress Experiment apparatus

0– +

shearstress

normalstress

water pressure

fault

shearstress

normalstress

water pressure

fault

M8 Jalisco Quake

Fault Stability: Coulomb Stress Experiment apparatus

normalstress

fault

water pressure = 0

shear stress = 0

normal stress 0

initial conditions

M8 Jalisco Quake

Fault Stability: Experiment Earthquake changes Coulomb stress

earthquake

shear

stress

normal

stress

fault

M8 Jalisco Quake

Fault Stability: Experiment Pore pressure changes Coulomb stress changes

earthquake

shear

stress

normal

stress

fault

water pressureexcess water pressure induction device

M8 Jalisco Quake

Fault Stability: Experiment Pore pressure changes Coulomb stress changes

shear

stress

normal

stress

fault

water pressureexcess water pressure induction device

M8 Jalisco Quake

- GPS station

1800

km

1300 km

250

km

220 km

oceanic crustcontinental crust

mantle

FEM: numerical model; predicts deformation, stress, and pore pressure due to earthquakes.

definition

Method: Construct deformation models Finite Element Model (FEM)

M8 Jalisco Quake

M=6epicenter

(pore pressure initially drops after M8 quake)

1800

km

1300 km

oceanic crust

continental crust

10 5 0 -5 -10po

re p

ress

ure

(kP

a)

North

days after M=8 earthquake:

Predicted pore pressure Initial conditions following M8 earthquake

M8 Jalisco Quake

1800

km

1300 km

oceanic crust

continental crust

10 5 0 -5 -10po

re p

ress

ure

(kP

a)

North

days after M=8 earthquake:

Predicted pore pressure Gradual recovery to pre-earthquake equilibrium

M=6epicenter

(pore pressure slowly increases after M8 quake)

M8 Jalisco Quake

The M=8 earthquake triggered the M=6 earthquake, fluid flow accounts for the delay

the M=6 earthquake was a predictable event !

stress

(from M=8 quake)

pore pressure

(along fault of M=6 quake)

triggered M=6 quake

+

Conclusions Recall the hypothesis…

M8 Jalisco Quake

0.3

0.2

0.1

0.0

stress (MPa)

- GPS station

220 km

years after M=8 earthquake

The Project Continues Predicting deformation & stress evolution

brittle upper crust(stress accumulates)

ductile mantle(stresses relax)

M8 Jalisco Quake

Earthquake coupling • Stress release loads mantle• Flow relaxes stresses in mantle (silly putty) and transfers stress to fault 1

1

stresstransfer

friction

normalstress

2

tectonicstress

normalstress

Stress-triggering: Viscoelastic relaxation

viscous silly putty(slowly flows & relaxes stress)

M8 Jalisco Quake

M9 earthquake

tsunami

IndianOcean

Sumatra

India

Australia

2. Applying the lessons learned 2004 M9 Sumatra-Andaman earthquake & tsunami

M9 Sumatra-Andaman Quake

Indo-Australian Plate

Eurasian Plate

6 cm/yr

9.2

Rupture & deformation 2004 M9 Sumatra-Andaman earthquake & tsunami

Dec 262004

M9 Sumatra-Andaman Quake

Indo-Australian Plate

Eurasian Plate

6 cm/yr

9.2

Sumatra-Andaman FEM 1) Simulate poroelastic stress-triggering

6 cm/yr 8.7

9.2 Mar 282005

Dec 262004

M9 Sumatra-Andaman Quake

Are the aftershocks predictable in space and time?

not yet, but…we are working on it!

Coupling the 2004 & 2005 quakes What if models in place prior to these events?

M9 Sumatra-Andaman Quake

up

down

Indo-Australian Plate

Eurasian Plate

6 cm/yr

9.2

Dec 262004

Sumatra-Andaman FEM 2) Simulate seafloor deformation tsunamigenesis

M9 Sumatra-Andaman Quake

Predicting seafloor deformation Changes overlying water column

seafloor

ocean surface

cross-section

wat

er c

olu

mn

Indo-Aust Plate Eurasian Plate

fault

M9 Sumatra-Andaman Quake

Predicting seafloor deformation Changes overlying water column

seafloor

ocean surface

cross-section

wat

er c

olu

mn

Indo-Aust Plate Eurasian Plate

fault

M9 Sumatra-Andaman Quake

seafloor

cross-section

wave propagation

earthquakedeformation

India andSri Lanka

Sumatra &Thailand

Predicting seafloor deformation Drives tsunami propagation models

M9 Sumatra-Andaman Quake

seafloor

cross-section

wave propagation

Sumatra &Thailand

India andSri Lanka

M9 Sumatra-Andaman Quake

Predicting seafloor deformation Drives tsunami propagation models

seafloor

cross-section

earthquakedeformation

cross-section

ocean surface

wave propagation:velocity is a

function of depthslow fast fast slow

M9 Sumatra-Andaman Quake

Predicting seafloor deformation Drives tsunami propagation models run-up

seafloor

cross-section

earthquakedeformation

cross-section

wave propagation:velocity is a

function of depthslow fast fast slow

M9 Sumatra-Andaman Quake

Predicting seafloor deformation Drives tsunami propagation models run-up

In progress: Virtual Sumatra-Andaman subduction zone

M9 Sumatra-Andaman Quake

M9 Sumatra-Andaman Quake

In progress: Virtual Sumatra-Andaman subduction zone

M9 Sumatra-Andaman Quake

In progress: Virtual Sumatra-Andaman subduction zone

seafloordeformation

M9 Sumatra-Andaman Quake

In progress: Virtual Sumatra-Andaman subduction zone

seafloordeformation

Imagine the possibilities…

• deformation predictions (tsunami sources)

• stress evolution predictions ultimately, earthquake predictions