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  1. 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.

  2. Motivation – transient strain accumulation across the Mojave Geodetic: 10 - 14 mm/yr Geologic: faults + distributed displacement

  3. Real offset Is that all ? • Questions – • how much? • how wide? • How distributed? • how active? • How (mechanism)?

  4. How (After Nelson and Jones, 1987)

  5. Study sites

  6. Mylonitic lineation direction- Predates strike slip faulting (Fletcher et al., 1995)

  7. Block rotation • 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°.

  8. Block dimensions Distance from fault (m) Distance from fault (m)

  9. Y=16+0.7x R2=0.87 Block size decrease towards fault Radius of largest possible block (m)

  10. Secondary faults length ≅12 main fault length • Order of magnitude greater length than main fault • Accommodates up to 20% of displacement • Active? – seismic energy sink

  11. paleomagnetism • Pre/post faulting • Faults of different displacement

  12. How come? • Different mechanisms • Spatial changes in magnitude No significant rotation

  13. Spatial and mechanical changes

  14. Is it active?

  15. 752110 ka 725  85m 2000m 2000m 16329 ka ~100m Distributed faulting cutting lava flows of different age, Pisgah fault

  16. Summary : • 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.

  17. 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. The end

  18. Questions • 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.