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 12 - 3:10 p.m. Lienkaemper 2013 AGU Fall Meeting G43C-07 Thu Dec 12 - 3:10 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 ~100-200 m aperture arrays http://pubs.usgs.gov/of/2009/1119/ 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 7.8 1868 M w 6.8 NORTHERN SAN ANDREAS FAULT SYSTEM 1984 M w 6.2 1979 M w 5.9 2004 M w 6.0 FRACTION LOCKED* (%) * ASSUMES HALF OF STRAIN ACCUMULATION IN CREEPING PATCHES RELEASES AS AFTERSLIP

10. Coyote Ranch Array, 1968-2013 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 7.8 1868 M w 6.8 NORTHERN SAN ANDREAS FAULT SYSTEM 1984 M w 6.2 1979 M w 5.9 2004 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]