Hosgri-San Simeon Fault Zone Geologic Slip Rate

Transcription

1 Hosgri-San Simeon Fault Zone Geologic Slip Rate Insert picture(s) here Kathryn Hanson AMEC E&I Diablo Canyon SSHAC Project SSC Workshop 2 November 7, 2012

2 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?

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4 Long-term Slip Historyoffset Mio-Pliocene Strata Modified from Clark et al. (1984) 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

5 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

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8 San Simeon Fault Slip Rate Studies San Simeon Marine Terrace Analysis- Late Pleistocene Slip Rate Hanson and Lettis (1994) Source: Hanson and Lettis (1994, Figure 1) Offset Drainages- Pleistocene Slip Rate Hanson and Lettis (1994) Detailed Marine Terrace Mapping San Simeon Fault Trenching Investigations- Holocene Slip Rate Hall et al. (1994)

9 Marine Terraces Southern Reach of the San Simeon Fault Hanson et al. (1994) and Hanson and Lettis (1994)

10 Terraces Profiles Across San Simeon Fault Source: Hanson et al.(1994)

11 Oso Terrace (210 ka) Horizontal Slip Rate (best constrained) 0.7 to 2.6mm/yr Source: Hanson and Lettis (1994)

12 Source: Hanson and Lettis (1994)

13 Quaternary Fault and Fold Database s/

14 Deflected Drainages (RL slip rates) n 1 Minimum mm/yr (incision post ka) n 2a & 2b Minimum ~ mm/yr (post and ka) n 3 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) n 6 - n 8 Minimum 1.6 mm/yr (east and west strands) Stream capture-lower Arroyo de los Chinos Minimum mm/yr (500 m of post ka offset) Source: Hanson and Lettis (1994)

15 LTSP Trench Investigations

16 Airport Creek Site 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 ~ ka 1.1 to 2.9 mm/yr Geometric analysis of vertically separated soil horizons in T to 3.0 mm/yr 1.0 to 1.4 mm/yr (preferred) Source: Hall et al. (1994)

17 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)

18 Source: Response to Question GSG Q13-2 (PG&E, 1990)

19 Source: Response to Question GSG Q13-2 (PG&E, 1990)

20 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 1-3 mm/yr 1-3 mm/yr Source: Hanson et al. (2004)

21 6-8 mm/yr ( 5 mm/yr) Modified from Lettis et al.(2009 ) mm/yr 0-2 mm/yr Tectonic Setting Right-lateral shear couple 34 Wrench-style deformation pattern

22 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 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 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 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.

23 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 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 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..