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Long-term rates and the depth extent of fault creep along the San Andreas Fault system in northern California from alinement arrays and GPS data James.

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Presentation on theme: "Long-term rates and the depth extent of fault creep along the San Andreas Fault system in northern California from alinement arrays and GPS data James."— Presentation transcript:

1 Long-term rates and the depth extent of fault creep along the San Andreas Fault system in northern California from alinement arrays and GPS data James J Lienkaemper 1, Forrest S. McFarland 2, Robert W Simpson 1, S. John Caskey 2 1.U.S. Geological Survey, 2.San Francisco State University Use long-term creep record to infer locking depth of faults 2013 AGU Fall Meeting G43C-07 Thu Dec :10 p.m. Lienkaemper 2013 AGU Fall Meeting G43C-07 Thu Dec :10 p.m. Lienkaemper Fraction locked Elastic model Surface creep rates AseismicvsLocked Creep rates observed Elastic model Seismic moment rate Fraction locked

2 Long Long-term Monitoring of Creep Rate Annual measurement of angular change across ~ m aperture arrays measurements setup Corrections ALINEMENTARRAYS

3 north coast inset central coast NORTHERN SAN ANDREAS FAULT SYSTEM

4 north coast central coast Model geometry & data distribution OBSERVATION POINTS: alinement arrays, near-field GPS station pairs and short-range trilateration arrays and short-range trilateration arrays

5 Input: mean observed creep for each section Uses Okada (1992) equations Consensus loading rates and depths 29 fault sections defined by geometric discontinuities or changes in creeping behavior Find best-fitting average creep depth using boundary value dislocation solver Output: depth of creep and subsurface creep rates used to determine fraction locked Elastic deformation model north coast inset central coast

6 CREEP RATE (mm/yr) DISTANCE ALONG PLATE BOUNDARY (km) OBSERVED CREEP RATES AND MODEL FIT NORTHERN SAN ANDREAS FAULT SYSTEM

7 AVERAGE DEPTH OF CREEP (km) DISTANCE ALONG PLATE BOUNDARY (km) NORTHERN SAN ANDREAS FAULT SYSTEM

8 FRACTION LOCKED* (%) DISTANCE ALONG PLATE BOUNDARY (km) * ASSUMES HALF OF STRAIN ACCUMULATION IN CREEPING PATCHES RELEASES AS AFTERSLIP NORTHERN SAN ANDREAS FAULT SYSTEM

9 DISTANCE ALONG PLATE BOUNDARY (km) 1906 M w M w 6.8 NORTHERN SAN ANDREAS FAULT SYSTEM 1984 M w M w M w 6.0 FRACTION LOCKED* (%) * ASSUMES HALF OF STRAIN ACCUMULATION IN CREEPING PATCHES RELEASES AS AFTERSLIP

10 Coyote Ranch Array, Impact of M>5.5 earthquakes on long-term creep rate NORTHERN SAN ANDREAS FAULT SYSTEM Wright Rd array

11 ~27% aseismic moment release seismic moment rate (Nm/yr) NORTHERN SAN ANDREAS FAULT SYSTEM ~73% “locked ” ~22% ~0% ~44% ~35% ~37%  Vast majority of aseismic moment release along optimum plate boundary path

12 DISTANCE ALONG PLATE BOUNDARY (km) 1906 M w M w 6.8 NORTHERN SAN ANDREAS FAULT SYSTEM 1984 M w M w M w 6.0 FRACTION LOCKED (%) Future Big Quakes on Creeping Faults?  URBAN FAULTS without major historical events & with large locked patches: A. Rodgers Creek A. Rodgers Creek B. Northern Calaveras B. Northern Calaveras C. Green Valley C. Green Valley D. Greenville D. Greenville [not shown] [not shown]  URBAN FAULTS without major historical events & with large locked patches: A. Rodgers Creek A. Rodgers Creek B. Northern Calaveras B. Northern Calaveras C. Green Valley C. Green Valley D. Greenville D. Greenville [not shown] [not shown]  URBANIZING FAULTS: E. Maacaama, South E. Maacaama, South [Hopland, Geyserville] [Hopland, Geyserville] F. Maacama, Central F. Maacama, Central [Ukiah, Hopland] [Ukiah, Hopland]  URBANIZING FAULTS: E. Maacaama, South E. Maacaama, South [Hopland, Geyserville] [Hopland, Geyserville] F. Maacama, Central F. Maacama, Central [Ukiah, Hopland] [Ukiah, Hopland]


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