SCEC Fault System SCEC Fault System History History

January 31, 2008January 31, 2008

Eric KirbyEric KirbyPenn State UniversityPenn State University

Collaborators:Collaborators:Sridhar Anadankrishnan, Fred Sridhar Anadankrishnan, Fred Phillips, Shasta Marrero, Nancye Phillips, Shasta Marrero, Nancye Dawers, Doug BurbankDawers, Doug Burbank

Late Pleistocene Slip Rate Along the Late Pleistocene Slip Rate Along the Owens Valley FaultOwens Valley Fault

Geodynamics of deformation in the ECSZGeodynamics of deformation in the ECSZ

What is the significance of differences between geodetic velocities and geologic deformation rates?

– Characteristic timescales of Characteristic timescales of transient deformationtransient deformation

Postseismic relaxationPostseismic relaxation Seismic clustersSeismic clusters Fault switchingFault switching

– Role of spatial variations in Role of spatial variations in fault slipfault slip

Fault growth and interactionFault growth and interaction

Requires understanding the evolution of fault slip through space and timeRequires understanding the evolution of fault slip through space and time

Interseismic deformation in Owens ValleyInterseismic deformation in Owens Valley

Malservisi et al (2001) - data from Gan, Dixon

Fault parallel velocities range from Fault parallel velocities range from ~ 3 - 6 mm/yr~ 3 - 6 mm/yr

Savage, DixonSavage, Dixon

Geodetic data from Gan, Dixon Thatcher

Co-seismic deformation in Owens ValleyCo-seismic deformation in Owens Valley

1872 rupture ~ 100km– Mw 7.5-7.8

– 6 ± 2 m dextral slip– 1 ± 0.5 m vertical

Long-term slip rates ~1 - 2 mm/yr

Looking north along the Lone Pine fault scarp

How to reconcile? How to reconcile?

Elastic dislocation models require 4 - 7 mm/yr slip at depth

Viscoelastic models suggest high velocity could be legacy of 1872 event

Dixon et al (2003)

How well do we How well do we know long-term slip know long-term slip

rate?rate?

Long-term slip rate along OVFLong-term slip rate along OVF

What do we know?– Beanland and Clark (1994)– Lubetkin and Clark (1985; 1988)– Bierman et al. (1995)– Lee et al. (2001)– Bacon and Pezzopane (2007)

Records restricted to Late Records restricted to Late Pleistocene - Holocene:Pleistocene - Holocene:– Lone Pine faultLone Pine fault

0.8 ± 0.4 m/kyr0.8 ± 0.4 m/kyr– Owens Valley faultOwens Valley fault

South - 1.0 ± 0.5 m/kyrSouth - 1.0 ± 0.5 m/kyr Central - 1.8 ± 0.3 m/kyrCentral - 1.8 ± 0.3 m/kyr

Bacon and Pezzopane (2007)

Long-term slip rate along OVFLong-term slip rate along OVF

Sources of uncertainty– Multiple fault strands– Restricted to 10 - 15 ka

2 - 3 events

– Assumptions of uniform recurrence, characteristic slip

Late Pleistocene - Holocene:– Lone Pine fault

0.8 ± 0.4 m/kyr

– Owens Valley fault South - 1.0 ± 0.5 m/kyr Central - 1.8 ± 0.3 m/kyr

Bacon and Pezzopane (2007)

Toward a budget of deformation…Toward a budget of deformation…

Long-term slip along northern OVFLong-term slip along northern OVF

Geology adapted from Bateman (1968)

Displacement at Crater MountainDisplacement at Crater Mountain

Color orthophoto courtesy of Google Earth

Displacement at Crater MountainDisplacement at Crater Mountain

Kirby et al., (2008 - GRL)

Displacement at Crater MountainDisplacement at Crater Mountain

East of OVF - abrupt transition East of OVF - abrupt transition across flow marginacross flow margin

Displacement at Crater MountainDisplacement at Crater Mountain

East of OVF - abrupt transition across flow margin

West of OVF - flow margin is West of OVF - flow margin is buried by Qfyburied by Qfy

Displacement at Crater MountainDisplacement at Crater Mountain

East of OVF - abrupt transition across flow margin

West of OVF - buried flow margin

Across fault - no evidence of Across fault - no evidence of buried flowburied flow

Displacement at Crater MountainDisplacement at Crater Mountain

Buried basalt flow235 ± 15m

Restoration of flow margin Restoration of flow margin yields ~ 235m of right-lateral yields ~ 235m of right-lateral slipslip

Age of the Crater Mountain flowAge of the Crater Mountain flow

K/Ar - 290 ± 40 kaK/Ar - 290 ± 40 ka– Turrin and Gillespie (1986)Turrin and Gillespie (1986)

Overlies alluvial fans ca. 130 kaOverlies alluvial fans ca. 130 ka– Zhefuss et al. (2001)Zhefuss et al. (2001)

33He - range from 35 - 115 kaHe - range from 35 - 115 ka– Stone/Gillespie (unpublished)Stone/Gillespie (unpublished)

290±40 ka

~110 ka

~130 ka

Production of Production of 3636Cl by cosmic raysCl by cosmic rays

35Cl40K

40Ca

high energy neutrons

36Cln

low energy neutrons

n

n

nn

spallation reactions

absorption reaction

3636Cl production “bulge”Cl production “bulge”

Gosse and Phillips (2001)

3636Cl exposure ages - Crater Mtn.Cl exposure ages - Crater Mtn.

N=6

NE flows

SW flows

3636Cl exposure ages - Crater Mtn.Cl exposure ages - Crater Mtn.

N=6

Effect of erosion on calculated ageEffect of erosion on calculated age

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 100 200 300 400 500 600

Apparent Exposure Age (kyr)

Spallation Only

70% Spallation15%Spallation

54% Spallation(actual value)

(equivalent to 10Be or otherspallation-only nuclide)

F. Phillips

Influence of surface weathering - 1mm/kyrInfluence of surface weathering - 1mm/kyr

N=6

Influence of surface weathering - 2mm/kyrInfluence of surface weathering - 2mm/kyr

N=6

Influence of surface weathering - 3mm/kyrInfluence of surface weathering - 3mm/kyr

N=6

Influence of surface weathering - 4mm/kyrInfluence of surface weathering - 4mm/kyr

N=6

Most-likely ageMost-likely age

N=6

Significance of rapid Late Pleistocene slipSignificance of rapid Late Pleistocene slip

Owens Valley fault at Crater Owens Valley fault at Crater Mountain exhibits slip rates of Mountain exhibits slip rates of 3.5 (+1.0 / -0.7) m/ka3.5 (+1.0 / -0.7) m/ka – 235 ± 15 m235 ± 15 m– 67.5 ± 12.5 ka67.5 ± 12.5 ka

Possible explanations:Possible explanations:

Paleoseismic may Paleoseismic may underestimate slip inventoryunderestimate slip inventory

Significance of rapid Late Pleistocene slipSignificance of rapid Late Pleistocene slip

Owens Valley fault at Crater Owens Valley fault at Crater Mountain exhibits slip rates of Mountain exhibits slip rates of 3.5 (+1.0 / -0.7) m/ka3.5 (+1.0 / -0.7) m/ka – 235 ± 15 m235 ± 15 m– 67.5 ± 12.5 ka67.5 ± 12.5 ka

Possible explanations:Possible explanations:

Paleoseismic may underestimate slip inventory

Spatial variations in slip rateSpatial variations in slip rate

Significance of rapid Late Pleistocene slipSignificance of rapid Late Pleistocene slip

Owens Valley fault at Crater Owens Valley fault at Crater Mountain exhibits slip rates of Mountain exhibits slip rates of 3.5 (+1.0 / -0.7) m/ka3.5 (+1.0 / -0.7) m/ka – 235 ± 15 m235 ± 15 m– 67.5 ± 12.5 ka67.5 ± 12.5 ka

Possible explanations:Possible explanations:

Paleoseismic may underestimate slip inventory

Spatial variations in slip rate

Clustered strain release Clustered strain release sometime between 20 ka and sometime between 20 ka and 50-80 ka50-80 ka

Is there a discrepancy with GPS?Is there a discrepancy with GPS?

GPS data courtesy of P. LaFemina (unpublished)

Sierra pole of Dixon et al. (2000)

Velocity difference resolved Velocity difference resolved parallel to OVF ~ 4.5 mm/yrparallel to OVF ~ 4.5 mm/yr

Orthogonal component ~ 1.5 Orthogonal component ~ 1.5 mm/yrmm/yr

Is there a discrepancy with GPS?Is there a discrepancy with GPS?

Not necessarilyNot necessarily

Extension - 070°1.1 - 1.5 m/kyrGreene et al. (in prep)

RL Shear - 340°2.8 - 4.5 m/kyrKirby et al. (2008)

Patterns of strain release over ~ 100 kaPatterns of strain release over ~ 100 ka

Both major fault systems Both major fault systems exhibit decreases in slip exhibit decreases in slip rate toward northrate toward north

Requires…Requires…– Role for distributed Role for distributed

deformationdeformation– Slip farther east Slip farther east (Frankel (Frankel

et al., 2007)et al., 2007)– Temporal variations in Temporal variations in

slip slip (Kirby et al., 2006)(Kirby et al., 2006)

3.1 ± 0.4

2.5 ± 0.4

4.5 ± 1.53.5 ± 1.0

0.5 ± 0.2

Patterns of strain release over ~ 100 kaPatterns of strain release over ~ 100 ka

Similar variations toward Similar variations toward Garlock?Garlock?

– Possible, but Possible, but chronologic basis not chronologic basis not well establishedwell established

– Stay tuned…Stay tuned…

3.1 ± 0.4

2.5 ± 0.4

4.5 ± 1.53.5 ± 1.0

0.5 ± 0.2

~1.5 - 3

~3 - 4

Conclusions/ImplicationsConclusions/Implications Slip rate at Crater Mountain is 3.5 +1.0/-0.7 m/kyrSlip rate at Crater Mountain is 3.5 +1.0/-0.7 m/kyr

– Either previous estimates are missing slip, or slip is variable in Either previous estimates are missing slip, or slip is variable in space/timespace/time

Reduces geologic-geodetic ‘discrepancy’ across Owens ValleyReduces geologic-geodetic ‘discrepancy’ across Owens Valley– But, seems to require shallow locking and/or creepBut, seems to require shallow locking and/or creep

Emerging picture of systematic regional variations in slip rate Emerging picture of systematic regional variations in slip rate along ECSZalong ECSZ– Are these maintained by interaction with barriers (Garlock, Mina Are these maintained by interaction with barriers (Garlock, Mina

Deflection), or do they represent nascent lengthening faults?Deflection), or do they represent nascent lengthening faults?