Simulating big earthquakes Accessing the inaccessible with models.
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Transcript of Simulating big earthquakes Accessing the inaccessible with models.
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