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NA-Pa Plate Boundary

NA-Pa Plate Boundary. Wilson [1960]. USGS Prof. Paper 1515. Faults: Northern California. USGS Prof. Paper 1515. Faults: Southern California. USGS Prof. Paper 1515. SCEC Clickable Fault Map. http://www.data.scec.org/faults/faultmap.html. Evolution of North American - Pacific

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NA-Pa Plate Boundary

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  1. NA-Pa Plate Boundary Wilson [1960] USGS Prof. Paper 1515

  2. Faults: Northern California USGS Prof. Paper 1515

  3. Faults: Southern California USGS Prof. Paper 1515

  4. SCEC Clickable Fault Map http://www.data.scec.org/faults/faultmap.html

  5. Evolution of North American - Pacific Plate Boundary USGS Prof. Paper 1515

  6. Evolution of North American-Pacific Plate Boundary Modern SAF (4 Ma) & opening of Gulf CA USGS Prof. Paper 1515

  7. Atwater Animation [Atwater and Stock, 1998]

  8. “Captured” North American Plate • Inactive early transform with • component of subduction • Captured part of NA plate now • moving northwesterly with • Pacific plate USGS Prof. Paper 1515

  9. Evolution of San Andreas 30-15 Ma 20-10 Ma 220 km 60 km 10-2 Ma 5-0 Ma 2-0 Ma 2-0 Ma USGS Prof. Paper 1515; Powell & Weldon [1992]

  10. Displacement of Pelona Schist Pelona Schist Orocopia Schist USGS Prof. Paper 1515; Powell & Weldon [1992]

  11. Displacement of Pelona Schist • 50 km right lateral slip by San Gabriel f. • 210 km right lateral slip by San Andreas f. USGS Prof. Paper 1515; Powell & Weldon [1992]

  12. Fault Slip Rate USGS Prof. Paper 1515

  13. Historical Faulting USGS Prof. Paper 1515

  14. Historical Faulting

  15. Seismicity (1980-86) USGS Prof. Paper 1515

  16. Probability for occurrence of major earthquake from 1988-2018 USGS Prof. Paper 1515

  17. Past and Future Earthquakes on the San Andreas Fault [Weldon et al., 2005] Wrightwood and the earthquake cycle... [Weldon et al., 2004]

  18. Exposed Trench, Pallett Creek 1857 • Fault zone intermittently • covered by debris flows • and peat layers • Samples provide approx. • event dates & offsets A.D. 800 USGS Prof. Paper 1515

  19. Wrightwood Trench fault/fissure stratigraphic contact Weldon et al. [2004]

  20. Wrightwood Event Ages Mean recurrence interval: 105 yrs (31-165 yrs) Mean slip: 3.2 m (0.7-7m) Weldon et al. [2004]

  21. Tests of Slip/Time Predictable Models Slip-predictable: length of interseismic period predicts amount of slip in next event Time-predictable: offset of the last event predicts the time length until the next event Weldon et al. [2004]

  22. Strain-Predictable Model? Weldon et al. [2004]

  23. Strain-Predictable Model? Weldon et al. [2004]

  24. Beyond Wrightwood “The current 148-year hiatus is probably not exceptional. However, no lull in the past 1600 years appears to have lasted more than ~ 200 years, and when the current hiatus ends, a substantial portion of the fault is likely to rupture, either as a single long rupture or a series of overlapping ruptures in a short time interval.” Weldon et al. [2005]

  25. Rupture Scenarios North and south ruptures w/overlap Random rupture length North 2/3’s rupture; south 1/3 rupture Long ruptures w/small additional ones 1. 3. 2. 4. Weldon et al. [2004, 2005]

  26. Conclusions Strain released in an earthquake is not simply that accumulated since the last event. It appears likely that slip occurs at a wide range of strain levels and does not always release the same amount of strain. Overlapping tails of essentially separate large ruptures may explain two small events in a short interval of time at a point, but this cannot explain the 600-900 A.D. flurry of events with large displacements, or the past 1000 years of less-frequent, smaller-than-average events. Given the rupture lengths of 1812 and 1857 events (~150, 300 km) & lack of substantial rupture in last 148 years, many doubt the possibility of frequent, small ruptures on the southern SAF.

  27. References

  28. S. California Topography USGS Prof. Paper 1515

  29. Weldon et al. [2004]

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