Insert picture(s) here Hosgri-San Simeon Fault Zone Geologic Slip Rate Kathryn Hanson AMEC E&I Diablo Canyon SSHAC Project SSC Workshop 2 November 7, 2012
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Hosgri-San Simeon Fault Zone Geologic Slip Rate
Kathryn Hanson AMEC E&I Diablo Canyon SSHAC Project SSC Workshop 2 November 7, 2012
What insights have your geologic investigations provided on:
The slip rate on the San Simeon fault? The slip rate on the Hosgri fault? The variability of slip rate along strike on the San Gregorio-
San Simeon-Hosgri fault system?
Long-term Slip History-offset Mio-Pliocene Strata
Net Neogene right-lateral slip on SG-SS-H fault system (~156 km) since initiation in late Miocene Dickenson et al. (2005) Evidence for decrease in slip rate (Clark et al. 1999) ~25-30 mm/yr 10 - 8 Ma 16 mm/yr (8 – 3 Ma) 6 mm/yr 3 – 0 Ma
Modified from Clark et al. (1984)
San Gregorio Paleoseismic Investigations
Seal Cove Locality Simpson et al. (1998) Multiple surface rupturing events RL slip rate of 3.5 to 4.5 mm/yr (Seal
Cove trace, minimum for zone),
Aňo Nuevo Locality
Weber (1990);Weber et al. (1995); Clark et al. (1999) Late Pleistocene RL slip rate of 6 to 11 mm/yr (preferred 6-8 mm/yr)
John Caskey (person. commun., Nov.2012) Late Pleistocene RL slip rate of ≤ 5 mm/yr
Quaternary Fault and Fold Database http://earthquake.usgs.gov/hazards/qfaults/
San Simeon Fault Slip Rate Studies
San Simeon Marine Terrace Analysis- Late Pleistocene Slip Rate
–Hanson and Lettis (1994)
Offset Drainages-
Pleistocene Slip Rate –Hanson and Lettis
(1994) San Simeon Fault
Trenching Investigations- Holocene Slip Rate
–Hall et al. (1994)
Source: Hanson and Lettis
(1994, Figure 1)
Detailed Marine Terrace Mapping
Marine Terraces Southern Reach of the San Simeon Fault
Hanson et al. (1994) and Hanson and Lettis (1994)
Terraces Profiles Across San Simeon Fault
Source: Hanson et al.(1994)
Oso Terrace (210 ka) Horizontal Slip Rate (best constrained) 0.7 to 2.6mm/yr
Source: Hanson and Lettis (1994)
Source: Hanson and Lettis (1994)
Quaternary Fault and Fold Database http://earthquake.usgs.gov/hazards/qfault
s/
Source: Hanson and Lettis (1994)
Deflected Drainages (RL slip rates)
n1 Minimum 0.3-0.5 mm/yr (incision post - 330 ka)
n2a & 2b Minimum ~0.8 - 1.1 mm/yr (post - 430 and - 480 ka)
n3 Maximum ~6 mm/yr (assumes 3000 m apparent offset of
Arroyo de la Cruz channel incised into oldest marine terrace (≥ 480 ka) is due to slip on major trace of San
Simeon fault)
n6 - n8 Minimum 1.6 mm/yr (east and west strands)
Stream capture-lower Arroyo de los Chinos Minimum 1.0 - 1.6 mm/yr (500 m of post - 320 - 500 ka offset)
LTSP Trench Investigations
Airport Creek Site
Source: Hall et al. (1994)
Both walls of Airport Creek channel show RL deflection of 1.8 m; Interpreted as one or two slip events.
Trenches exposed major ~vertical N40ºW striking fault; slickenlines rake of 6˚ - 7˚ SE.
Poorly constrained offset of younger terrace margin ( )
0.9 and 3.4 mm/yr
Offset basal gravel of Airport Terrace—
16 to 28 m since ~10.8 - 13.8 ka 1.1 to 2.9 mm/yr
Geometric analysis of vertically separated soil horizons in T-1
1.0 to 3.0 mm/yr 1.0 to 1.4 mm/yr (preferred)
Are there other structures west of the San Simeon fault that are accommodating
shortening/ distributed shear that may
contribute additional slip to the Hosgri fault
zone?
Source: Response to Question GSG Q13-2 (PG&E, 1990)
Source: Response to Question GSG Q13-2 (PG&E, 1990)
Source: Response to Question GSG Q13-2 (PG&E, 1990)
San Simeon-Hosgri Stepover Basin (PG&E, 1988; Hanson et al. 2005)
1-3 mm/yr RL San Simeon fault slip rate transferred to northern Hosgri fault zone
Source: Hanson et al. (2004)
1-3 mm/yr
1-3 mm/yr
122° 120°
36°
34°
Tectonic Setting • Right-lateral shear couple
• Wrench-style deformation pattern
1-3 mm/yr
6-8 mm/yr (≤ 5 mm/yr)
0-2 mm/yr
Modified from Lettis et al.(2009 )
References
Clark, J.C, Brabb, E.E., Greene, H.G, and Ross, D.C, 1984, Geology of Point Reyes Peninsula and implications for San Gregorio fault history, in Crouch, J .K., and Bachman, S.B., eds., Tectonics and Sedimentation along the California Margin: Pacific Section S.E.P.M., vol. 38, p. 67-86
Clark , J.C., Weber, G.E., Rosenberg, L.I., and Burnham, K., 1999, Neotectonics of the San Gregorio fault zone, Central Coastal California: Pacific Section AAPG Field Trip Guide, April 28, 1999, p. 119-144.
Hall, N.T., Hunt, T.D., and Vaughan, P.R., 1994, Holocene behavior of the San Simeon fault zone, south-central coastal California in Alterman, I.B., McMullen, R.B., Cluff, L.S., and Slemmons, D.B., eds., Seismotectonics of the Central California Coast Ranges: Geological Society of America Special Paper 292.
Hanson, K.L., and Lettis, W.R., 1994, Estimated Pleistocene slip rate for the San Simeon fault zone, south-central coastal California: in Alterman, I.B., McMullen, R.B., Cluff, L.S., and Slemmons, D.B. (eds.), Seismotectonics of the Central California Coast Ranges: Geological Society of America Special Paper 292, p. 133-150.
Hanson, K. L., Lettis, W. R, McLaren, M. Savage, W.U. and Hall, N.T., 2004, Style and Rate of Quaternary Deformation of the Hosgri Fault Zone, Off-Shore South-Central California: Santa Maria Province Project: U.S. Geological Survey Bulletin, 1995-AA. M.A. Keller,( ed.) .
Lettis, W. R., Unruh, J., and Hanson, K.L., 2009, Tectonic setting of South Central Coastal California, SSA presentation slides.
PG &E, 1990, Response to RAI GSG Q13-2 –Piedras Blancas antiform, assessment of orientation, rates, and sense of vergence.
References
Weber, G. E., 1990, Late Pleistocene slip rates on the San Gregorio fault zone at Point Ano Nuevo, San Mateo County, California, in Griggs, G. B. and Weber, G. E., eds., Coastal Geologic Hazards and Coastal Tectonics, Northern Monterey Bay and Santa Cruz/San Mateo County Coastlines, Field Trip Guide: Association of Engineering Geologists, March 3, 1990, p. 64-79.
Weber, G. E., 1990, Late Pleistocene slip rates on the San Gregorio fault zone at Point Ano Nuevo, San Mateo County, California, in Geology and tectonics of the Central California coast region, San Francisco to Monterey, Volume and Guidebook, Garrison, R. E., and others (eds.), Pacific Section, Am. Assoc. Pet. Geol., p. 193-204.
Weber, G. E.,Nolan, J.M>, and Zinn, E.K., 1995, Determination of Late Pleistocene-Holocene
slip rates along the San Gregorio fault zone, San Mateo Co., CA: U.S. Geological Survey Final Technical Report, National Earthquake Hazard Reduction Program, 52 p..
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