Fialko et al. (2002)

Modeling coseismic deformation of compliant fault zones to estimate stress in the upper crust

Elizabeth Hearn, UBC

Ben Zion et al. 2003

what?where?

There are permanently compliant zones around active faults in the Mojave and elsewhere (e.g., Fialko et al., 2002; Li et al., 1999).

These zones soften slightly (damage increases) in response to local earthquakes (Vidale and Li, 2003).

Idea: compliant zones as stress barometers?

In an earthquake, these zones should strain in response to both the total stress (due to coseismic CZ weakening) and coseismic stress change (due to permanent CZ weakness).

Hearn, E and Y. Fialko, J. Geophys. Res. 2009

1 Compliant zones around faults, coseismic changes to their elastic properties

Today’s talk

4

How we would expect compliant zones to deform in response to a nearby earthquake

How compliant zones actua!y deform and what this says about the state of stress in the upper crust

3 Modeling approach

2

Pockets of damaged material in the uppermost crust around active faults

Concentrated strain shows up as wrinkles on filtered inSAR images of coseismic deformation.

Colors are line-of-sight (LOS) displacements, toward the satellite.

+ is upward and east-southeast.

- is down, west-northwest

243 15 243 30 243 45 244 0034 00

34 15

34 30

34 45

Cam

p Rock

Pinto Mountain

HM

0 1 2 3

mm

243˚30' 243˚35' 243˚40' 243˚45' 243˚50' 243˚55'

34˚05'

34˚10'

B

B!

Pinto Mountain

243˚15' 243˚20' 243˚25' 243˚30' 243˚35'

34˚15'

34˚20'

34˚25'

34˚30'

34˚35'

34˚40'

A

A!

Cam

p Rock

Johnson Valley

Johnson Valley

from Hearn and Fialko, 2009

B

B’

-8

-6

-4

-2

0

2

-12

-10

Distance from center of CZ (km)

0 2 4 6-2-4-6

Models

LO

S d

isp

lacem

en

t (m

m)

RC Data

B B’

Damaged material in the uppermost crust around active faults: past models

Models suggest ~1-2 km wide zones, 3-15 km deep, with G about 50% of host rock value (varies).

Seismic studies show these low-strength zones, but ~100 m wide.

1-2 km wide compliant zoneconcentrates strain and is observed in interferograms

A ~100 m wide, highly damaged zone (which traps seismic waves) may extend down to 10-15 km

InSAR (Cochran et al., 2009) suggests lateral tapering of elastic

properties.

Likely features of highly damaged (compliant) zones around faults

geodetic and seismic data and static deformation models(e.g. Cochran et al., 2009, Fialko et al., 2002, Vidale and Li, 2001, 2003, and others)

damage rheology models of fault formation and models of dynamic rupture propagation with

plastic strain (Finzi et al., 2009; Ma et al., 2008)

Typical FE deformation

model

This study and Fialko group CZ models

width = 400 m to km’sdepth = 1 km to 15 km

Our taperedCZ models

Our models: softened continuum surrounding faults (still oversimplified)

..............................................................

Damage to the shallow Landersfault from the nearbyHector Mine earthquakeJohn E. Vidale* & Yong-Gang Li†

* Earth & Space Sciences Department and Institute of Geophysics & PlanetaryPhysics, University of California in Los Angeles, Los Angeles, California90095-1567, USA†Department of Earth Sciences, University of Southern California, Los Angeles,California 90089-0740, USA.............................................................................................................................................................................

Crustal faults have long been identified as sites where localizedsliding motion occurs during earthquakes1, which allows for therelative motion between adjacent crustal blocks. Although thereis a growing awareness that we must understand the evolution offault systems on many timescales to relate present-day crustalstresses and fault motions to geological structures formed in thepast, fault-zone damage and healing have been documentedquantitatively in only a few cases2,3. We have been monitoringthe healing of damage on the shallow Johnson Valley fault afterits rupture in the 1992 magnitude-7.3 Landers earthquake, andhere we report that this healing was interrupted in 1999 by themagnitude-7.1 Hector Mine earthquake rupture, which occurred20–30 km away. The Hector Mine earthquake both stronglyshook and permanently strained the Johnson Valley fault, addingdamage discernible as a temporary reversal of the healingprocess. The fault has since resumed the trend of strengthrecovery that it showed after the Landers earthquake. Theseobservations lead us to speculate that fault damage caused bystrong seismic waves may help to explain earthquake clusteringand seismicity triggering by shaking, and may be involved infriction reduction during faulting.Our field experiments (Fig. 1) were conducted in 1994, 1996,

1997, 1998, 2000 and 2001. The 1996 and 1997 experiments wereless comprehensive owing to logistical difficulties. Each experimentwas very similar: seismometers were re-buried in the same holes andthe explosions were in 35-m drill holes, which were sited within10m of the previous years’ holes. The seismic arrays line 1 and line 3had 36 and 21 seismometers, respectively. The first repetition wasused to map Landers fault-zone fine structure as a function ofdepth4. With the added iterations, we have watched the fault evolvewith time.We infer that the rupture reduced the seismic wave speeds, which

have been subsequently recovering, although data from before theLanders earthquake are lacking. Figure 2a–c shows the increase ofcompressional (P)-wave and shear (S)-wave velocity with time afterthe 1992 Landers rupture. The 1994 and 1996 observations ofhealing at Landers showed recovery of seismic velocity by about2%. The survey in 1998 showed a reduction of the healing rate by afactor of two between 1994–96 and 1996–98. The ratio of the rates ofP-wave and S-wave speed recovery is consistent with healing causedby closure of cracks that are partially fluid-filled5. A similarexperiment at HectorMine has confirmed that healing is not uniqueto Landers and shows that there is variability in healing rates amongthe fault segments that we havemeasured2. Our results are similar toan observed drop in wave speed at the time of the Loma Prietaearthquake, which recovered over subsequent years6,7 and has alsoshown damage from a smaller event3. By contrast, another studydoes not show healing 5–7 yr after the Kobe earthquake, but doessuggest damage and rapid healing on the Kobe fault zone resultingfrom the Tottori earthquake8.The velocity increase is consistent and diminishing in rate over

time across the 1994, 1996, 1997 and 1998 surveys. In the 2000

survey, however, the velocities in the fault zone decreased for bothtypes of wave and all six ray paths, although the velocities for theouter stations did not significantly change. The following year(2001), the survey showed a resumption of healing for both typesof wave on all lines. Figure 3 shows the depth dependence of theinferred healing.

The magnitude-7.1 1999 Hector Mine earthquake occurredbetween the 1998 and 2000 surveys, and provides the most likelycause for the temporary reversal in the polarity of the velocitychange. An alternative is that the water table was tens of metreshigher in 2000 than in other years, but this is unlikely because watertable changes of that magnitude would be surprising. In addition,water table changes would affect the P-wave velocity much morethan the S-wave velocity, contrary to the change observed, and 1997and 2001 are the years that had the greatest rainfall (see WesternRegional Climate Center website: http://www.wrcc.dri.edu/).

The Hector Mine earthquake could have caused the observedchange in seismic wave speed in two ways. These involve dynamicand static stresses, which have already been cited as possiblemechanisms for triggering distant aftershocks and inducing defor-mation on faults. Dynamic stresses during the Hector Mine earth-quake on the Johnson Valley fault were a fewmegapascals, and staticstress changes caused by the earthquake are perhaps half a mega-pascal (ref. 9).

Most probably, the dynamic stresses during the strong shakingcracked connections in the rock—as we infer the Landersmainshockdid in 1992—but to a lesser degree. This damage is healing insubsequent years, just as we observe the main shock damage tobe healing. Such shaking-induced damage has been observed inlaboratory studies10. The concept of our model is shown in Fig. 4.

Figure 1 Map of Landers and Hector Mine ruptures. Black lines indicate mapped surfacebreakage25,26, yellow lines show rupture inferred from seismic and geodetic studies27,28,

stars show the locations of shot points SP3, SP4 and SP5, and broken lines show the

extent of the seismometer profiles line 1 and line 3, which have 36 and 21 seismometers,

respectively. Fault segments are labelled as follows: CRF, Camp Rock fault; ELF, Emerson

Lake fault; HVF, Homestead Valley fault; JVF; Johnson Valley fault; KF, Kickapoo fault; LLF,

Lavic Lake fault.

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Vidale and Li (2003)

Vp and Vs decrease slightly in response to shaking during local earthquakes

inferred from fault-zone-guided waves on the scale of a few hundredmetres4.Previously we showed that fault zones heal5, and here we have

shown that the combination of shaking and static stress reduces themodulus of a recently broken fault zone. This probably indicatesthat the strength of the fault was reduced, which could triggerearthquakes. Our observation thus may provide a direct measure-ment of themissing connection between shaking and the facilitationof distant aftershocks20,21. Regional clustering of earthquakes isanother plausible result of one big earthquake weakening theregional set of faults around it, either as an anomalous activationof a region22 or as the progression of ruptures along a fault, with theshaking modulated by directivity23.Another implication of our result is that existing friction laws

may need improvement. Currently, friction is modelled simply (ornot so simply) as a function of a state variable, which is the history ofsliding, and current sliding rate of a point on a fault plane24. Ifshaking can significantly reduce strength, it may also help to explainthe puzzle of aftershock occurrence very near the mainshock faultplane, which strikes where the Earth has been strongly shaken butwhere the regional stress is reduced. Shaking-induced weakeningalso may be involved in the progression of rupture during earth-quakes, because strong shaking is likely to precede the arrival of therupture front. A

Received 22 August; accepted 29 November 2002; doi:10.1038/nature01354.

1. Reid, H. F. in The California Earthquake of April 18, 1906: Report of the State Earthquake Investigation

Commission (Carnegie Institution of Washington, Washington DC, 1910).

2. Li, Y.-G., Vidale, J. E., Day, S.M., Oglesby, D. D. & Cochran, E. Post-seismic fault healing on the rupture

zone of the 1999 M7.1 Hector Mine, California earthquake. Bull. Seismol. Soc. Am. (in the press).

3. Rubinstein, J. L., Beroza, G. C., Bokelmann, G. & Schaff, D. Near surface damage caused by the strong

ground motion of the M6.9 Loma Prieta and M5.4 Chittenden earthquakes. Eos 83, NG21B (2002).

4. Li, Y.-G., Vidale, J. E., Aki, K., Xu, F. & Burdette, T. Depth-dependence structure of the Landers fault

zone from trapped waves generated by aftershocks. J. Geophys. Res. 105, 6237–6254 (2000).

5. Li, Y.-G. & Vidale, J. E. Healing of the shallow fault zone from 1994–1998 after the M7.5 Landers,

California, earthquake. Geophys. Res. Lett. 28, 2999–3002 (2001).

6. Schaff, D. P. & Beroza, G. C. Postseismic response of repeating aftershocks. Geophys. Res. Lett. 25,

4549–4552 (1998).

7. Baisch, S. & Bokelmann, G. H. R. Seismic waveform attributes before and after the Loma Prieta

earthquake: scattering change near the earthquake and temporal recovery. J. Geophys. Res. 106,

16323–16337 (2001).

8. Ikuta, R., Yamaoka, K., Miyakawa, K., Kunitomo, T. & Kumazawa, M. Continuous monitoring of

propagation velocity of seismic wave using ACROSS. Geophys. Res. Lett. 29 5-1–5-4 (2002).

9. Fialko, Y. et al. Deformation on nearby faults induced by the 1999 Hector Mine earthquake. Science

297, 1858–1862 (2002).

10. Richardson, E. & Marone, C. Effects of normal stress vibrations on frictional healing. J. Geophys. Res.

104, 28859–28878 (1999).

11. Cochran, E. & Vidale, J. E. Seismic anisotropy of the Hector Mine fault zone. Eos 82, S41A (2001).

12. Bokelmann, G. H. R. & Harjes, H.-P. Evidence for temporal variation of seismic velocity within the

upper continental crust. J. Geophys. Res. 105, 23879–23894 (2000).

13. Ratdomopurbo, A. & Poupinet, G. Monitoring a temporal change of seismic velocity in a volcano:

Application to the 1992 eruption of Mt. Merapi (Indonesia). Geophys. Res. Lett. 22, 775–778 (1995).

14. Hill, D. P. et al. Seismicity remotely triggered by the magnitude 7.3 Landers, California, earthquake.

Science 260, 1617–1623 (1993).

15. Brodsky, E., Karakostas, V. & Kanamori, H. A new observation of dynamically triggered regional

seismicity: earthquakes in Greece following the August, 1999 Izmit, Turkey earthquake. Geophys. Res.

Lett. 27, 2741–2744 (2000).

16. Knopoff, L., Levshina, T., Keilis-Borok, V. I. & Mattoni, C. Increased long-range intermediate-

magnitude earthquake activity prior to strong earthquakes in California. J. Geophys. Res. 101,

5779–5796 (1996).

17. Bowman, D. D. & King, G. G. C. P. Accelerating seismicity and stress accumulation before large

earthquakes. Geophys. Res. Lett. 28, 4039–4042 (2001).

18. Price, E. & Sandwell, D. T. Small-scale deformations associated with the 1992 Landers, California,

earthquake mapped by synthetic aperture radar interferometry. J. Geophys. Res. 103, 27001–27016

(1998).

19. Fialko, Y., Simons, M. & Agnew, D. The complete (3-D) surface displacement field in the epicentral

region of the 1999 Mw7.1 Hector Mine earthquake, southern California, from space geodetic

observations. Geophys. Res. Lett. 28, 3063–3066 (2001).

20. Kilb, D., Gomberg, J. & Bodin, P. Triggering of earthquake aftershocks by dynamic stresses. Nature

408, 570–574 (2000).

21. Gomberg, J., Reasenberg, P. A., Bodin, P. & Harris, R. A. Earthquake triggering by seismic waves

following the Landers and Hector Mine earthquakes. Nature 411, 462–466 (2001).

22. Rockwell, T. K. et al. Paleoseismology of the Johnson Valley, Kickapoo, and Homestead Valley faults:

clustering of earthquakes in the eastern California shear zone. Bull. Seismol. Soc. Am. 90, 1200–1236

(2000).

23. Stein, R. S. Progressive failure on the North Anatolian fault since 1939 by earthquake stress triggering.

Geophys. J. Int. 128, 594–604 (1997).

24. Marone, C. Laboratory-derived friction laws and their application to seismic faulting. Annu. Rev.

Earth Planet. Sci. 26, 643–696 (1998).

25. Sieh, K. et al. Near-field investigation of the Landers earthquake sequence, April to July 1992. Science

260, 171–176 (1993).

26. Scientists of the USGS, SCEC, and CDMG. Preliminary report on the 16 October 1999 M7.1 Hector

Mine, California, earthquake. Seismol. Res. Lett. 71, 11–23 (2000).

27. Hauksson, E., Jones, L. M. & Hutton, K. The 1999 Mw7.1 Hector Mine, California earthquake

sequence: complex conjugate strike-slip faulting. Bull. Seismol. Soc. Am. 92, 1154–1170 (2002).

28. Ji, C., Wald, D. J. & Helmberger, D. V. Source description of the 1999 Hector Mine, California

earthquake. Part II: complexity of slip history. Bull. Seismol. Soc. Am. 92, 1208–1226 (2002).

Acknowledgements We thank E. Hauksson for supplying relocations of regional seismicity;H. Houston, P. Davis, E. Brodsky, C. Marone, R. Stein and L. Knopoff for comments; andT. Burdette, F. Xu and E. Cochran for field help.

Competing interests statement The authors declare that they have no competing financialinterests.

Correspondence and requests for materials should be addressed to J.E.V.(e-mail: vidale@ucla.edu).

..............................................................

Head and backbone of the EarlyCambrian vertebrate HaikouichthysD.-G. Shu*†, S. Conway Morris‡, J. Han*, Z.-F. Zhang*, K. Yasui§,P. Janvierk, L. Chen*, X.-L. Zhang*, J.-N. Liu*, Y. Li* & H.-Q. Liu*

* Early Life Institute and Department of Geology, Northwest University, Xi’an,710069, China† School of Earth Sciences and Resources, China University of Geosciences, Beijing,100083, China‡Department of Earth Sciences, University of Cambridge, Downing Street,Cambridge CB2 3EQ, UK§ Institute of Molecular Embryology and Genetics, Division of Development andBiohistory, Kumamoto University, 2-2-1 Honjo, Kumamoto 860-0811, JapankUMR 8569 du CNRS, Laboratoire de Paleontologie, Museum Nationald’Histoire Naturelle, 8 rue Buffon, Paris 75005, France, and Department ofPalaeontology, Natural History Museum, London SW7 5BD, UK.............................................................................................................................................................................

Agnathan fish hold a key position in vertebrate evolution,especially regarding the origin of the head and neural-crest-derived tissue1. In contrast to amphioxus2, lampreys and othervertebrates possess a complex brain and placodes that contributeto well-developed eyes, as well as auditory and olfactory systems3.

Figure 4 Model of velocity as a function of time owing to damage from the Landers

rupture, the Hector Mine shaking, and the combination of the two compared with

observations. Shown is healing as a logarithm of time10, although details just after each

event and extrapolating into the future are not well constrained. The velocity before the

Landers earthquake was not measured.

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Vs decreased by about 1-2% Vp decreased by a similar percentage (maybe a bit more)

Vidale and Li (2003)

Coseismic changes to G and , based on decreases in Vp and Vs

R=

0.7

R = 1.0 R = 0.7 R = 1.0

R =dVs/Vs

dVp/Vp

! 0.7 to 1dVp

Vp

! "0.01 to " 0.02

ν

Coseismic changes to E and ,based on changes to Vp and Vs

R=

0.7

R = 1.0 R = 1.0

Note that bulk modulus K must decrease

K =E

3(1 − 2!)

R = 0.7

ν

1 Compliant zones around faults, coseismic changes to their elastic properties

Today’s talk

4

How we would expect compliant zones to deform in response to a nearby earthquake?

How compliant zones actua!y deform and what this says about the state of stress in the upper crust and stress transfer

3 Modeling approach

2

!xy ="xy

2Gcz

x

y

due to change in isd!xy !xy

d!xy

2Gcz

•

due to change in isGczd!xy !

!xy

2Gcz

(dGcz

Gcz

)•

d!xy ="!xy

"#xy

"#xy +"!xy

"Gcz

"Gcz

Expected strain: simple shear

Strain in response to softening

is vertical

!1

!2

!3

is oriented N 20 E is oriented N 70 W

!1

!3

• for NW-oriented Mojave faults, deviatoric stress should cause right-lateral strain (some contraction)

• sense of strain depends on the orientation of the fault zone relative to the stress field

• amplitude of this component depends on stress, elastic properties, and % softening of the CZ

!2 = "gh

amplitudes: !1 !3and

•• transtensionvs. transpressionvs. pure shear

µ

What happens when bulk modulus K decreases(with no change to lithostatic stress)?

CZ deformation due to weakening: Lithostatic stress should always cause subsidence

Before earthquake. Response to coseismic weakening of CZ (unless

it’s incompressible).

1 Compliant zones around faults, coseismic changes to their elastic properties

Today’s talk

4

How we would expect compliant zones to deform in response to a nearby earthquake?

How compliant zones actua!y deform and what this says about the state of stress in the upper crust

3 Modeling approach

2

Modeling Steps

Model deformation of model with compliant zones, in response to Hector Mine or Landers earthquake stress change

!"contribution

Scale and sum to see what contribution from the total stress and coseismic weakening of compliant zones is permissible

+

=total deformationfrom both contributions

Model deformation with compliant zones with Young’s modulus = Eo, under regional stress

Model deformation with slightly softer compliant zones under regional stress (e.g. with E’ = 0.99Eo)

Difference the two results to get CZ deformation in response to softening, caused by regional stress

(softening)contribution

!E

Compute coseismic stresses with ensemble mesh and use a finer mesh to model CZ deformation.

Are coseismic stresses at the profiles sensitive to presence of the other CZ’s?

compliant zones are 50% weaker than surroundings

and extend to 15 km

Layered elastic model (modified from Jones and Helmberger 1998)Impose earthquake slip (inverted from GPS).

Model deformation of model with compliant zones, in response to Hector Mine or Landers earthquake stress change

!"contribution

!yy"yx

x

y

x

y

B

B'

B

B'

B

B'

B

B'

#!yy#"yx

+1

0

$1

Stress (MPa)

Effect of compliant zones on Hector Mine earthquake coseismic stress change

Pinto Mountain Fault

Effect of compliant zones on Hector Mine earthquake coseismic stress change

Camp Rock Fault

+1

0

!1

Stress (MPa)

"x'x'#x'y'

$"x'x'$#x'y'

x'y'

x'y'

AA'

AA'

AA'

AA'

Stress applied via: • displacing boundaries (shear and normal stress) • displacing boundaries + gravitation (lithostatic stress)

Coseismic stress from the big model (do not vary). Various estimates of tectonic stresses.

0 1 2 3 4 km

Symmetry BC0

1

2

3

4 km

Finer meshes

0 1 2 3 4 km

Symmetry BC0

1

2

3

4 km

Vary:• CZ dimensions• Background stress deviatoric (resolved shear and normal) lithostatic• CZ elastic properties and % softening

Finer meshes

Sensitivity of modeled strain to element size

0 1 2 3 4 km

Symmetry BC0

1

2

3

4 km

A B C

0

10

20

30

x d

ispla

cem

ent (

mm

)

-11 -9 -7 -5 -3 -1

-80

-40

40

80

0

Vert

ical d

ispla

cem

ent (

mm

)

x coordinate relative to CZ center (km) x coordinate relative to CZ center (km)

-11 -9 -7 -5 -3 -1

CZ mesh A, UHS

coarse mesh B, UHSCZ mesh A, layered

coarse mesh C, UHS

CZ mesh A, UHS

coarse mesh B, UHSCZ mesh A, layered

coarse mesh C, UHS

1% reduction in E= 200 MPa!xx

1 Compliant zones around faults, coseismic changes to their elastic properties

Today’s talk

4

How we would expect compliant zones to deform in response to a nearby earthquake?

How compliant zones actua!y deform and what this says about the state of stress in the upper crust

3 Modeling approach

2

Pinto Mountain Fault LOS displacement profiles

Hect

or M

ine

B’B

(MPa)

!yy

(MPa)

Land

ers

B’B

!yy

UP and a bit of LEFT-LATERAL DOWN

B B’ B B’

Hect

or M

ine

B’B

(MPa)

!yy

(MPa)

Land

ers

B’B

!yy

shear sense is backward for Landersinsufficient uplift (Ecz = .5Ehost)

Pinto Mountain Fault LOS displacement profiles

B B’ B B’

Adding the softening contribution• assume a 1% decrease in E• vary CZ width (400m to 2 km) and depth (1 to 15 km)

-40

-30

-20

-10

0

Model DModel C

Model E

Model A

Model F

Distance from center of CZ (km)

0 2 4 6-2-4-6

LO

S d

isp

lace

me

nt

(mm

)

Model B

0

4

8

12

16

20

24

Model DModel C

Model E

Model A

Model F

0 2 4 6-2-4-6

Model B

Distance from center of CZ (km)

LO

S d

ispla

cem

ent (m

m)

Yikes.

Hector Mine Landers

What works?

• 2 km wide near the surface• may taper at depth• incompressible or anisotropic? (to prevent subsidence)• background stress: pure shear, high friction

If we restrict softening to a few % and CZ is half as rigid as the host rock:

-8

-6

-4

-2

0

2

-12

-10

Distance from center of CZ (km)

0 2 4 6-2-4-6

Model DModel F

"Funnel"

2 4 6 8-2-4

-5

0

5

10

15

20

25

0

Distance from center of CZ (km)

Model DModel F

"Funnel"

LO

S d

isp

lace

me

nt

(mm

) c.

Camp Rock Fault LOS displacement profile

LOS displacements:UP and a bit of RIGHT-LATERAL

15

LO

S D

ispla

ce

me

nt

(m

m)

20

0

5

Distance along Profile (km)

0 2 4 6-2-4-6

10

-5

15

LO

S D

ispla

cem

ent (

mm

)

20

0

5

Distance from center of profile (km)

0 2 4 6-2-4-6

10

-5

deformation fromcoseismic stress:(Ecz = .5Ehost)UP and a bit of LEFT-LATERAL

+1!1 Stress (MPa)

"x'x'

#x'y'

AA'

AA'

x'y'

A A’

Distance from center of CZ (km)

! -30

! -25

! -20

! -15

! -10

! -5

0

5

0 2 4 6-2-4-6

LO

S D

ispla

cem

ent (

mm

)

10

Data

Models

Yikes again.

Adding the softening contribution

• assume a 1% decrease in E• vary CZ width (400m to 2 km) and depth (1 to 15 km)

What works for the Camp Rock Fault CZ?

15

LO

S D

isp

lacem

en

t (

mm

)

20

0

5

Distance along Profile (km)

0 2 4 6-2-4-6

Model D

"Funnel"

Model F

Model F,

rotated

-5

10

• 2 km wide near the surface• may taper at depth• incompressible or anisotropic? (to prevent subsidence)• background stress: pure shear, high friction

Must soften 4-9 % and CZ is >80% as rigid as the host rock

Best PMF and CRF models

Similarities:

Differences:

• 2 km wide near the surface• may taper at depth• incompressible or anisotropic? (or shallow?) to prevent subsidence• background stress: pure shear, high friction coefficient

• Different strength contrast with host rock• Different % softening in response to earthquake

Given• compliant zone geometry and strength contrast

• % change in elastic properties

• coseismic stress perturbation

we should be able to place constraints on background stress on the uppermost crust using models of compliant zone strain based on LOS displacements.

(targeted seismic, geodetic, and modeling studies)

(trapped wave and other seismic studies)

(dense GPS and seismic networks, elastic model)

Also• Compliant zones probably do not influence static stress transfer significantly at distances of exceeding tens of km.

Main conclusion

+1!1 Stress (MPa)

"x'x'

#x'y'

AA'

AA'

x'y'

Future directions:

• Model spatial variations in elastic moduli• Model more extreme tapering with depth (to 100 m)• Why no subsidence?

A

A’ up!

up!up!