Distributed Deformation Adjacent to Active Strike Slip Faults - Examples from the Eastern California...
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Distributed Deformation Adjacent to Active Strike Slip Faults - Examples from the Eastern California Shear Zone. Acknowledgments: Dr. Mike Oskin, Dr. Jonathan Lees, Dr. Allen Glazner, Dr. Elizabeth Cochran, Dr. Yuri Fialko, Dr. Joe Kirschvink, Dr.Brad Singer, Dr. Xifan Zhang, Dr. Jim Casidy,

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Distributed Deformation Adjacent to Active Strike Slip Faults - Examples from the Eastern California Shear Zone

Acknowledgments:

Dr. Mike Oskin, Dr. Jonathan Lees, Dr. Allen Glazner, Dr. Elizabeth Cochran, Dr. Yuri Fialko, Dr. Joe Kirschvink, Dr.Brad Singer, Dr. Xifan Zhang, Dr. Jim Casidy,

Neta Bar,Richard Lease, Dolev Shelef, Mariana Vale, Mike Strane, Tomer Ben-David,

Kim Le, Scott Bennet, Jacob Selander, Sabrina Belknap, Emily Gurney.

SCEC, NSF, Martin Fund.


  • Motivation – Faults - Examples from the Eastern California Shear Zonetransient strain accumulation across the Mojave

Geodetic: 10 - 14 mm/yr

Geologic: faults + distributed displacement


Real offset Faults - Examples from the Eastern California Shear Zone

Is that all ?

  • Questions –

  • how much?

  • how wide?

  • How distributed?

  • how active?

  • How (mechanism)?


How Faults - Examples from the Eastern California Shear Zone

(After Nelson and Jones, 1987)


Study sites Faults - Examples from the Eastern California Shear Zone


Mylonitic lineation direction- Faults - Examples from the Eastern California Shear Zone

Predates strike slip faulting

(Fletcher et al., 1995)


  • Block rotation Faults - Examples from the Eastern California Shear Zone

  • Width of rotation zone

  • ~20% of total displacement

  • Block size as function of distance from the fault

  • Ratio of secondary faults to the main fault

2σ = ~20°.


Block dimensions Faults - Examples from the Eastern California Shear Zone

Distance from fault (m)

Distance from fault (m)


Y=16+0.7x Faults - Examples from the Eastern California Shear Zone

R2=0.87

Block size decrease towards fault

Radius of largest possible block (m)


Secondary faults length Faults - Examples from the Eastern California Shear Zone

≅12

main fault length

  • Order of magnitude greater length than main fault

  • Accommodates up to 20% of displacement

  • Active? – seismic energy sink


  • paleomagnetism Faults - Examples from the Eastern California Shear Zone

  • Pre/post faulting

  • Faults of different displacement


  • How come? Faults - Examples from the Eastern California Shear Zone

  • Different mechanisms

  • Spatial changes in magnitude

No significant rotation


Spatial and mechanical changes Faults - Examples from the Eastern California Shear Zone


Is it active? Faults - Examples from the Eastern California Shear Zone


752 Faults - Examples from the Eastern California Shear Zone110 ka

725  85m

2000m

2000m

16329 ka

~100m

Distributed faulting cutting lava flows of different age, Pisgah fault


  • Summary : Faults - Examples from the Eastern California Shear Zone

  • Mechanisms: block rotation and offset along secondary faults

  • Width: 0-2 km

  • Activity: probably active

  • Magnitude: up to 20%

  • 5. All may change along fault strike.


Acknowledgments: Faults - Examples from the Eastern California Shear Zone

Dr. Mike Oskin, Dr. Jonathan Lees, Dr. Allen Glazner, Dr. Elizabeth Cochran, Dr. Yuri Fialko, Dr. Joe Kirschvink, Dr.Brad Singer, Dr. Xifan Zhang, Dr. Jim Casidy,

Neta Bar,Richard Lease, Dolev Shelef, Mariana Vale, Mike Strane, Tomer Ben-David,

Kim Le, Scott Bennet, Jacob Selander, Sabrina Belknap, Emily Gurney.

SCEC, NSF, Martin Fund.

The end


  • Questions Faults - Examples from the Eastern California Shear Zone

  • What may determine rotation vs. displacement along secondary faults

  • Relations to fault geometry

  • What happens at depth?

  • What determines where OFD occurs and where not

  • Scaling: ECSZ vs. Harper Lake

  • Difference between dike and Harper Lake in terms of faults density

  • Too beautiful trend of block size

  • Affects on geomorphology – ideas:which geomorphic indicators will suggest active OFD zone.


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