Elizabeth H. Hearn, UBC, Vancouver, CANADAin collaboration withSemih Ergintav, Marmara Research Centre, Gebze, TURKEYRobert Reilinger, MIT, Cambridge MA, USASimon McClusky, MIT, Cambridge MA, USARoland Bürgmann, UC Berkeley, Berkeley CA, USA

Elizabeth H. Hearn, UBC, Vancouver, CANADAin collaboration withSemih Ergintav, Marmara Research Centre, Gebze, TURKEYRobert Reilinger, MIT, Cambridge MA, USASimon McClusky, MIT, Cambridge MA, USARoland Bürgmann, UC Berkeley, Berkeley CA, USA

Numerical models of the North Anatolian Fault Zone in TurkeyNumerical models of the North Anatolian Fault Zone in Turkey

University of Southern California - March 5, 2007University of Southern California - March 5, 2007

The North Anatolian Fault Zone in Turkey: Continental transform

plate boundary

The North Anatolian Fault Zone in Turkey: Continental transform

plate boundary

19991999

‘rigid’ down to asthenosphere with

localized shear zones?

creeping below mid-crust?

How does the aseismic relative motion of plates occur? Are plates thick or thin?How does the aseismic relative motion

of plates occur? Are plates thick or thin?

e.g., Jimenez-Munt and Sabadini, 2002e.g., Jimenez-Munt and Sabadini, 2002

e.g., Provost et al. 2003e.g., Provost et al. 2003

block figure courtesy Michael Rymerblock figure courtesy Michael Rymer

Vauchez et al., 1998Vauchez et al., 1998

...or a hybrid?...or a hybrid?

Today: What do models of postseismic and interseismic deformation tell us about the NAFZ plate boundary?

Today: What do models of postseismic and interseismic deformation tell us about the NAFZ plate boundary?Postseismic deformation: perturbation to GPS velocities caused by the 1999 Mw = 7.5 and 7.2 Izmit and Düzce earthquakes

Postseismic deformation: perturbation to GPS velocities caused by the 1999 Mw = 7.5 and 7.2 Izmit and Düzce earthquakesInterseismic deformation: GPS velocities around central NAFZ segments that last failed from 1700’s to the early 1940’s

Interseismic deformation: GPS velocities around central NAFZ segments that last failed from 1700’s to the early 1940’s

coseismiccoseismic////postseismicpostseismic interseismicinterseismic

Snapshots: GPSSnapshots: GPS

Today: What do models of postseismic and interseismic deformation tell us about the NAFZ plate boundary?

Today: What do models of postseismic and interseismic deformation tell us about the NAFZ plate boundary?Postseismic deformation: perturbation to GPS velocities caused by the 1999 Mw = 7.5 and 7.2 Izmit and Düzce earthquakes

Postseismic deformation: perturbation to GPS velocities caused by the 1999 Mw = 7.5 and 7.2 Izmit and Düzce earthquakesInterseismic deformation: GPS velocities around central NAFZ segments that last failed from 1700’s to the early 1940’s

Interseismic deformation: GPS velocities around central NAFZ segments that last failed from 1700’s to the early 1940’s

Simple models can explain each, but not both!Simple models can explain each, but not both!

episodic earthquakesepisodic earthquakes

elastic upper crustelastic upper crust

transient lower crust?transient lower crust?

transient upper mantletransient upper mantle

(mantle asthenosphere)

(mantle asthenosphere)

LCLC

UMUM

RS friction or (at greater depths) viscous shear zone

RS friction or (at greater depths) viscous shear zone

Today: What do models of postseismic and interseismic deformation tell us about the NAFZ plate boundary?

Today: What do models of postseismic and interseismic deformation tell us about the NAFZ plate boundary?

Postseismic deformation modeling approach

Postseismic deformation modeling approach

GPS siteGPS site

epicentreepicentre

modeled rupturesmodeled ruptures

1000 x 1000 x 300 km

1000 x 1000 x 300 km

Free surface,fixed sides and

base

Free surface,fixed sides and

base

3D viscoelastic finite-element

model

3D viscoelastic finite-element

model

Izmit and Düzce

earthquake slip

are imposed

Izmit and Düzce

earthquake slip

are imposed Model calculates

stresses and velocities at requested

time intervals

Model calculates

stresses and velocities at requested

time intervals

Postseismic deformation modeling approach

Postseismic deformation modeling approach

GPS siteGPS site

epicentreepicentre

modeled rupturesmodeled ruptures

We are less sure about rheology of aseismically deforming

material (i.e. viscosity) and its distribution:

vary these parameters

We are less sure about rheology of aseismically deforming

material (i.e. viscosity) and its distribution:

vary these parameters

We think we know elastic

structure, coseismic slip

We think we know elastic

structure, coseismic slip

WRSS at a particular time is WRSS*WRSS at a particular time is WRSS*

Find parameters that minimizemisfit of modeled GPS site velocities to

observations

Find parameters that minimizemisfit of modeled GPS site velocities to

observations

viscoelastic relaxation: lower crust (Newtonian)viscoelastic relaxation: lower crust (Newtonian)

afterslip: viscous creep along shear zone (Newtonian)afterslip: viscous creep along shear zone (Newtonian)

Izmit postseismic deformation prior to the Düzce earthquake: three

hypotheses

Izmit postseismic deformation prior to the Düzce earthquake: three

hypotheses

afterslip: velocity-strengthening frictionafterslip: velocity-strengthening friction

(earlier study: Hearn et al., 2002)

(earlier study: Hearn et al., 2002)

Velocity-strengthening friction primer

Velocity-strengthening friction primer

equation applies after some small threshold slip distanceequation applies after some small threshold slip distance

(a-b) = velocity-strengthening parameter(a-b) = velocity-strengthening parameter

• this leads to stable sliding along the fault instead of earthquakes,

and accelerated postseismic slip

• this leads to stable sliding along the fault instead of earthquakes,

and accelerated postseismic slip

• at some depths (~0 to 2 and 10+ km), the friction coefficient increases with sliding velocity V• at some depths (~0 to 2 and 10+ km), the friction coefficient increases with sliding velocity V

34 mm/yr (model)34 mm/yr (model)

vs. 28 mm/yr(GPS and 1000-yr

paleoseismic;Titus et al. 2006)

vs. 28 mm/yr(GPS and 1000-yr

paleoseismic;Titus et al. 2006)

incr

easi

ng

t/T

incr

easi

ng

t/T

Creeping sections of NAFZ and SAFZ may also be explained with velocity-

strengthening friction

Creeping sections of NAFZ and SAFZ may also be explained with velocity-

strengthening friction

What about the later postseismic deformation?

What about the later postseismic deformation?

New GPS postseismic data*New GPS postseismic data*

7 years of postseismic GPS site velocity data7 years of postseismic GPS site velocity data50+ GPS sites with at least 6 occupations during that time50+ GPS sites with at least 6 occupations during that timeDisplacements are fit to functions of time, so velocities may be calculated at any timeDisplacements are fit to functions of time, so velocities may be calculated at any time

••

••

••

Can this rich dataset be fit with afterslip alone?

Can this rich dataset be fit with afterslip alone?

*Ergintav et al., 2007, to be submitted this summer*Ergintav et al., 2007, to be submitted this summer

No! Afterslip is insufficient to explain the GPS site velocities after 3 monthsNo! Afterslip is insufficient to explain the GPS site velocities after 3 months

Total modeled afterslip after a yearTotal modeled afterslip after a year

Distance along fault (km)Distance along fault (km)

Depth

(k

m)

Depth

(k

m)

slip (m)slip (m)00

1.21.2

M = 1.07 x 10 Nm

M = 1.07 x 10 Nm

2020oo Not enough! About twice this slip would be required. But all coseismic shear stress

on the fault has been spent.

Not enough! About twice this slip would be required. But all coseismic shear stress

on the fault has been spent.

Afterslip model : GPS velocities too slow at some sites, especially after

several months

Afterslip model : GPS velocities too slow at some sites, especially after

several monthsULUTULUT

DataDataFE ModelFE Model

east

(m

m/y

r)east

(m

m/y

r)n

ort

h

(mm

/yr)

nort

h

(mm

/yr)

time post-Izmit (days)

time post-Izmit (days)

ULUT - zoomedULUT - zoomed

DataDataFE ModelFE ModelKinematic inversionKinematic inversion

east

(m

m/y

r)east

(m

m/y

r)n

ort

h

(mm

/yr)

nort

h

(mm

/yr)

time post-Izmit (days)time post-Izmit (days)

Simplest hybrid model: Afterslip plus Maxwell viscoelastic relaxation

Simplest hybrid model: Afterslip plus Maxwell viscoelastic relaxation

••

••

••

(A-B): 0 to 2 km and 10+ km intervalsheld constant

(A-B): 0 to 2 km and 10+ km intervalsheld constant : lower crust - vary : lower crust - vary

upper crustupper crust

lower crustlower crust

upper mantleupper mantle

(mantle asthenosphere)

(mantle asthenosphere)

: upper mantle - vary : upper mantle - vary

LCLC

UMUMLCLC

UMUM

Geophysical evidence for mantle flow?

Geophysical evidence for mantle flow?

Hearn et al. 1994: (not me!)Hearn et al. 1994: (not me!)Slow Pn beneath AnatoliaSlow Pn beneath Anatolia

• Several seismic studies suggest high T and/or melt• This is consistent with moderate viscosities• Several seismic studies suggest high T and/or melt• This is consistent with moderate viscosities

Sandvol et al., 2001: attenuatedSn (regional seismic phase)

beneath Anatolia

Sandvol et al., 2001: attenuatedSn (regional seismic phase)

beneath Anatolia

Broad backarc with young ‘tectonic age’?

Broad backarc with young ‘tectonic age’?

Currie and Hyndman, 2006Currie and Hyndman, 2006

Anatolia: 13 Ma? and 70-100 mW/m2

Anatolia: 13 Ma? and 70-100 mW/m2

Anatolia: 20 km ?Anatolia: 20 km ?

Anatolia?Anatolia? Black Sea?Black Sea?

Which parameters worked best? Afterslip + viscoelastic relaxation

models

Which parameters worked best? Afterslip + viscoelastic relaxation

modelsNormalized WRSS, t = 0 to 900 daysNormalized WRSS, t = 0 to 900 days

Fit improves for lower crust or upper mantle viscosities of2 - 5 x 10 Pa s

Fit improves for lower crust or upper mantle viscosities of2 - 5 x 10 Pa s1919

Best afterslip + viscoelastic model: 1 yr

Best afterslip + viscoelastic model: 1 yr

Dynamic model WRSS* = 2250 (70% reduction)

Dynamic model WRSS* = 2250 (70% reduction)

September, 2000September, 2000

1080 (85% reduction)1080 (85% reduction)

Best afterslip + viscoelastic model: 3 yrs

Best afterslip + viscoelastic model: 3 yrs

Dynamic model WRSS* = no reduction Dynamic model WRSS* = no reduction (50% reduction)(50% reduction)

Blue = pre-Izmit GPS velocities, 1-sigma errorsBlue = pre-Izmit GPS velocities, 1-sigma errorsPink = block model velocities (Reilinger et al., 2006)Pink = block model velocities (Reilinger et al., 2006)

Is this model compatible with interseismic GPS velocities?

Is this model compatible with interseismic GPS velocities?

DD

D’D’

Blue = pre-Izmit GPS velocities, 1-sigma errorsBlue = pre-Izmit GPS velocities, 1-sigma errorsPink = block model velocities (Reilinger et al., 2006)Pink = block model velocities (Reilinger et al., 2006)

Is this model compatible with interseismic GPS velocities?

Is this model compatible with interseismic GPS velocities?

DD D’D’Reilinger et al., 2006Reilinger et al., 2006

• localized strain around NAFZ: like a 20 km locking depth• insensitive to time since previous major earthquake

(profiles across other NAFZ segments look similar)

• localized strain around NAFZ: like a 20 km locking depth• insensitive to time since previous major earthquake

(profiles across other NAFZ segments look similar)

Interseismic GPS velocitiesInterseismic GPS velocities

Can lower crust or upper mantle with a viscosity of 5 x 10 Pa s produce this? Can lower crust or upper mantle with a viscosity of 5 x 10 Pa s produce this? 1919

Can the postseismic deformation model explain the observed interseismic

deformation?

Can the postseismic deformation model explain the observed interseismic

deformation?Earthquake cycle modeling is required

Earthquake cycle modeling is required

UMUM

LCLC

• impose periodic earthquakes and velocity boundary conditions on 3D finite-element model of NAFZ and lithosphere

• impose periodic earthquakes and velocity boundary conditions on 3D finite-element model of NAFZ and lithosphere

• model several cycles, until cycle invariant status attained• model several cycles, until cycle invariant status attained• compare absolute velocities at appropriate time in the earthquake cycle to GPS velocities

• compare absolute velocities at appropriate time in the earthquake cycle to GPS velocities

periodic coseismic slipperiodic coseismic slip

frictional afterslip:all models to 24 km (some to 32 km)

frictional afterslip:all models to 24 km (some to 32 km)

viscoelastic layers:• linear• nonlinear• transient

viscoelastic layers:• linear• nonlinear• transient

Earthquake cycle modelsEarthquake cycle models

0 km0 km

24 km24 km

32 km32 km

to 300 kmto 300 km

Depth distribution and rate of aseismic slip

Depth distribution and rate of aseismic slip

Afterslip velocity(mm/yr)

Afterslip velocity(mm/yr)

Shear stress perturbation(MPa, relative to 20 MPa background stress)

Shear stress perturbation(MPa, relative to 20 MPa background stress)

3 y3 y

9 y9 y

16 y16 y

42 y42 y

140 y140 y

Aseismic slip rate and shear stress fluctuations over the interseismic interval

Aseismic slip rate and shear stress fluctuations over the interseismic interval

Meanwhile, viscoelastic relaxation is occurring in the upper mantle, and together these processes control

interseismic velocities around the fault.

Meanwhile, viscoelastic relaxation is occurring in the upper mantle, and together these processes control

interseismic velocities around the fault.

Best postseismic model is incompatible with interseismic GPS velocities around

the NAFZ

Best postseismic model is incompatible with interseismic GPS velocities around

the NAFZ

Reilinger et al. 2006 interseismic GPS dataNo variation withtime in EQ cycle!

Reilinger et al. 2006 interseismic GPS dataNo variation withtime in EQ cycle!

Model predictionfor 1940’s rupturesegment

Model predictionfor 1940’s rupturesegment

Modeled velocities around fault are very sensitive to time since the last earthquake

Modeled velocities around fault are very sensitive to time since the last earthquake

Explore other mantle rheologies:nonlinearly stress-dependent viscosity

Explore other mantle rheologies:nonlinearly stress-dependent viscosity

interseismic GPS

interseismic GPS

This is a bit better...This is a bit better...

Problem

Differential stress is too low for dislocation creep (nonlinear flow with n > 3)

Problem

Differential stress is too low for dislocation creep (nonlinear flow with n > 3)

Explore other mantle rheologies: Burgers Body rheology (two viscosities)

Explore other mantle rheologies: Burgers Body rheology (two viscosities)

see also Hetland (2005) for 2D analytical models of the NAFZ with transient mantle rheology

see also Hetland (2005) for 2D analytical models of the NAFZ with transient mantle rheology

depends on time since a step in stress ratedepends on time since a step in stress rate

depend on change in stress rateand on temperature (for dunite,

Chopra, 1997)

depend on change in stress rateand on temperature (for dunite,

Chopra, 1997)

andand

interseismic GPSinterseismic GPS

= 10= 10 = 2 to 5 x 10 Pa s= 2 to 5 x 10 Pa s = 10 years= 10 years1919

This is good - little variation in strain rates for most of the interseismic

interval

This is good - little variation in strain rates for most of the interseismic

interval

upper crustupper crust

trans. lower crust?trans. lower crust?transient upper mantletransient upper mantle

(mantle asthenosphere)

(mantle asthenosphere)

LCLC

UMUM

episodic earthquakesepisodic earthquakes

RS friction or (at greater depths) viscous shear zone

RS friction or (at greater depths) viscous shear zone

What do models of postseismic and interseismic deformation tell us about the NAFZ plate boundary?

What do models of postseismic and interseismic deformation tell us about the NAFZ plate boundary?

Work in progress - improved EQ cycle models

Work in progress - improved EQ cycle models

(A) irregular interevent times (B) finite rupture segments (C) transient effect superimposed on nonlinear rheology as

Chopra intended(D) biviscous rheology (Ivins and Sammis 1996) in lower

crust models, if admissible(E) 3D viscoelastic structure: contrast in effective plate

thickness across the NAFZ? Tethyside accretionary complexes?

(A) irregular interevent times (B) finite rupture segments (C) transient effect superimposed on nonlinear rheology as

Chopra intended(D) biviscous rheology (Ivins and Sammis 1996) in lower

crust models, if admissible(E) 3D viscoelastic structure: contrast in effective plate

thickness across the NAFZ? Tethyside accretionary complexes?

Sengor, 2005Sengor, 2005

Sandvol et al., 2001Sandvol et al., 2001

SummarySummary

“Later” postseismic and interseismic deformation suggest viscoelastic relaxation of upper mantle or lower crust, but a transient rheology is required

“Later” postseismic and interseismic deformation suggest viscoelastic relaxation of upper mantle or lower crust, but a transient rheology is required

Early postseismic deformation is compatible with velocity-strengthening afterslip along the NAFZ, driven by coseismic stresses. (At depth the NAFZ could be a viscous shear zone.)

Early postseismic deformation is compatible with velocity-strengthening afterslip along the NAFZ, driven by coseismic stresses. (At depth the NAFZ could be a viscous shear zone.)

Istanbul, August 2006Istanbul, August 2006