Eric Kirby Penn State University Collaborators:

1. Late Pleistocene Slip Rate Along the Owens Valley Fault Eric Kirby Penn State University Collaborators: Sridhar Anadankrishnan, Fred Phillips, Shasta Marrero, Nancye Dawers, Doug Burbank SCEC Fault System History January 31, 2008

2. Geodynamics of deformation in the ECSZ • What is the significance of differences between geodetic velocities and geologic deformation rates? • Characteristic timescales of transient deformation • Postseismic relaxation • Seismic clusters • Fault switching • Role of spatial variations in fault slip • Fault growth and interaction Requires understanding the evolution of fault slip through space and time

3. Interseismic deformation in Owens Valley • Fault parallel velocities range from ~ 3 - 6 mm/yr • Savage, Dixon Malservisi et al (2001) - data from Gan, Dixon Geodetic data from Gan, Dixon Thatcher

4. Co-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

5. 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 How well do we know long-term slip rate? Dixon et al (2003)

6. Long-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 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)

7. Long-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)

8. Toward a budget of deformation…

9. Long-term slip along northern OVF Geology adapted from Bateman (1968)

10. Displacement at Crater Mountain Color orthophoto courtesy of Google Earth

11. Displacement at Crater Mountain Kirby et al., (2008 - GRL)

12. Displacement at Crater Mountain • East of OVF - abrupt transition across flow margin

13. Displacement at Crater Mountain • East of OVF - abrupt transition across flow margin • West of OVF - flow margin is buried by Qfy

14. Displacement at Crater Mountain • East of OVF - abrupt transition across flow margin • West of OVF - buried flow margin • Across fault - no evidence of buried flow

15. Displacement at Crater Mountain Buried basalt flow 235 ± 15m • Restoration of flow margin yields ~ 235m of right-lateral slip

16. ~110 ka ~130 ka Age of the Crater Mountain flow • K/Ar - 290 ± 40 ka • Turrin and Gillespie (1986) • Overlies alluvial fans ca. 130 ka • Zhefuss et al. (2001) • 3He - range from 35 - 115 ka • Stone/Gillespie (unpublished) 290±40 ka

17. Production of 36Cl by cosmic rays high energy neutrons low energy neutrons n n n spallationreactions 40Ca n 35Cl 40K absorptionreaction 36Cl n

18. 36Cl production “bulge” Gosse and Phillips (2001)

19. 36Cl exposure ages - Crater Mtn. N=6 SW flows NE flows

20. 36Cl exposure ages - Crater Mtn. N=6

21. Effect of erosion on calculated age (equivalent to 10Be or other spallation-only nuclide) F. Phillips

22. Influence of surface weathering - 1mm/kyr N=6

23. Influence of surface weathering - 2mm/kyr N=6

24. Influence of surface weathering - 3mm/kyr N=6

25. Influence of surface weathering - 4mm/kyr N=6

26. Most-likely age N=6

27. Significance of rapid Late Pleistocene slip • Owens Valley fault at Crater Mountain exhibits slip rates of 3.5 (+1.0 / -0.7) m/ka • 235 ± 15 m • 67.5 ± 12.5 ka • Possible explanations: • Paleoseismic may underestimate slip inventory

28. Significance of rapid Late Pleistocene slip • Owens Valley fault at Crater Mountain exhibits slip rates of 3.5 (+1.0 / -0.7) m/ka • 235 ± 15 m • 67.5 ± 12.5 ka • Possible explanations: • Paleoseismic may underestimate slip inventory • Spatial variations in slip rate

29. Significance of rapid Late Pleistocene slip • Owens Valley fault at Crater Mountain exhibits slip rates of 3.5 (+1.0 / -0.7) m/ka • 235 ± 15 m • 67.5 ± 12.5 ka • Possible explanations: • Paleoseismic may underestimate slip inventory • Spatial variations in slip rate • Clustered strain release sometime between 20 ka and 50-80 ka

30. Sierra pole of Dixon et al. (2000) • Velocity difference resolved parallel to OVF ~ 4.5 mm/yr • Orthogonal component ~ 1.5 mm/yr Is there a discrepancy with GPS? GPS data courtesy of P. LaFemina (unpublished)

31. Is there a discrepancy with GPS? RL Shear - 340° 2.8 - 4.5 m/kyr Kirby et al. (2008) Extension - 070° 1.1 - 1.5 m/kyr Greene et al. (in prep) Not necessarily

32. Patterns of strain release over ~ 100 ka 2.5 ± 0.4 0.5 ± 0.2 • Both major fault systems exhibit decreases in slip rate toward north • Requires… • Role for distributed deformation • Slip farther east (Frankel et al., 2007) • Temporal variations in slip (Kirby et al., 2006) 3.1 ± 0.4 3.5 ± 1.0 4.5 ± 1.5

33. Patterns of strain release over ~ 100 ka ~3 - 4 ~1.5 - 3 2.5 ± 0.4 0.5 ± 0.2 3.1 ± 0.4 • Similar variations toward Garlock? • Possible, but chronologic basis not well established • Stay tuned… 3.5 ± 1.0 4.5 ± 1.5

34. Conclusions/Implications • Slip rate at Crater Mountain is 3.5 +1.0/-0.7 m/kyr • Either previous estimates are missing slip, or slip is variable in space/time • Reduces geologic-geodetic ‘discrepancy’ across Owens Valley • But, seems to require shallow locking and/or creep • Emerging picture of systematic regional variations in slip rate along ECSZ • Are these maintained by interaction with barriers (Garlock, Mina Deflection), or do they represent nascent lengthening faults?