Investigation of the Hosgri fault, offshore southern California, Point Sal to Point Conception

Payne, Charles M.; Swanson, O.E.; Schell, B.A.

doi:10.3133/ofr791199

Cited by 7 publications

(6 citation statements)

References 10 publications

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“…Vertical displacements of 2.5 m across a 17,000-to 20,000-yr-old beveled surface were observed on the HFZ north of Purísima Point and lost in the area south of there (Payne et al, 1979). After not finding a shallow expression of the HFZ, it was possible to assume that "the fault probably terminates at the latitude of Purísima Point and that the regional stress is probably absorbed by folds or smaller faults with Transverse…”

Section: Overviewmentioning

confidence: 99%

“…Thus, the contributions of previous workers are necessary to regionally extend the interpretation of seismic lines shown in Figure 3. The trace of the HFZ north of Purísima Point has been mapped repeatedly and is not a point of controversy (e.g., Payne et al, 1979;McCulloch, 1980;Crouch et al, 1984). Structure west of the HFZ has been mapped by Crouch et al (1984) and McCulloch (1980) and is included in Figure 2 to describe the region between the Santa Lucia Bank fault and the HFZ.…”

Section: Seismic Reflection Data and Mappingmentioning

confidence: 99%

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Hosgri fault zone, offshore Santa Maria Basin, California

Steritz¹,

Luyendyk²

1994

Geological Society of America Special Papers

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The Hosgri fault zone (HFZ) Is the name given to the southern section of the major coastal fault in central California. The Hosgri separates Transverse Range structure from offshore Santa Maria Basin structure and is a key element for any tectonic model that includes this economically significant region. Previous published maps have not adequately defined the southern termination of the HFZ, the style of faulting on the HFZ, and the relation of the HFZ to surrounding structures. Using more than 1,500 mi of processed seismic reflection data, we have mapped upper Miocene and Pliocene structure in the region of the HFZ offshore from Point Sal in the north, to Point Conception in the south where the HFZ ends against east-west structures in the westernmost Santa Barbara Channel. In the same area, eastwest-trending structures in the western Transverse Ranges north of the channel abut against the HFZ.The HFZ is an oblique right-slip fault along most of its length, but significant changes in the style of faulting are associated with variations in fault trend. North of Point Arguello, the HFZ appears to dip at a high angle in the upper 2,000 m of section and is distinguishable from thrust and reverse faults developed to its west. Between Point Arguello and Point Conception it may be a northeast-dipping thrust. Along its mapped length, east-side-up vertical separation is typical and may be more than 400 m on a Pliocene unconformity. Older horizons show more separation; the lower Miocene is up on the east by almost 1 km off Purisima Point. However, individual en echelon segments of the fault show west-side-up vertical separation where expected in an oblique right-slip fault system. No piercing points were found to define strike separation. Pliocene drag folds indicate dextral slip in Pliocene and later time.

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Section: Overviewmentioning

confidence: 99%

Section: Seismic Reflection Data and Mappingmentioning

confidence: 99%

Hosgri fault zone, offshore Santa Maria Basin, California

Steritz¹,

Luyendyk²

1994

Geological Society of America Special Papers

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“…This surface was dated by Payne et al (1979) as 30,000 to 40,000 BP and by PS Associates (1987) as 11,000 BP. This difference in assigning age is based on different interpretations of ocean levels during the past 50,000 yr.…”

Section: Bathymetry Thickness Of Unconsolidated Sediment and A Pleimentioning

confidence: 99%

Shallow geologic structure, offshore Point Arguello to Santa Maria River; central California

Cummings

Johnson

1994

Geological Society of America Special Papers

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This work includes new interpretations of shallow offshore geologic structure between Point Arguello and the Santa Maria River within California's 3-mi coastal limit. These interpretations are based on multi-sensor high-resolution seismic reflection data collected during January and February 1986. Water depths within the survey area range from 16 m (50 ft) nearshore to 70 m (230 ft) 3 mi west of Point Arguello. The sea floor slopes between 0.3 and 0.5° southwestward. The thickness of unconsolidated Quaternary sediment in the survey area ranges from 0 (bedrock outcrop) to almost 50 m (165 ft) off Point Arguello. The survey area crosses the boundary between the northwest-trending Coast Ranges and the east-trending Transverse Ranges. The onshore faults and folds can be traced offshore in the seismic sections. From north to south, these faults include: (1) Pezzoni-Casmalia-Orcutt frontal fault, (2) Lions Head fault, (3) Santa Ynez River fault system, (4) Lompoc-Solvang fault, (5) Cañada-Honda fault, and (6) several unnamed faults offshore Point Arguello. These faults are tentatively classified as potentially active because they do not offset a Pleistocene erosion surface and the Holocene unconsolidated sediments overlying that surface do not show offset in the seismic records. Although the faults are tentatively classified as potentially active, they may be seismically active as suggested by the limited earthquake data in the area.The seismic data show that the north-northwest-striking Hosgri fault zone decreases in both vertical and right-slip displacement toward the south. In the northern and central parts of the survey area, the fault zone consists of two subparallel branches. In the south, near Purísima Point and near the boundary between the Transverse and Coast Ranges, the north-northwest strike of the fault zone changes toward the east and the fault zone shows splays. Our interpretation of the data is that this area of splays may be the terminus of the Hosgri. If that is correct, then the amount of surface rupture due to earthquakes along this segment of the Hosgri is likely to be small, if surface ruptures occur at all.

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“…Scientific interest, along with oil and gas exploration and past USAF projects, has generated detailed information on the regional and local geology of South VAFB (Dibblee 195&, USAF 1978;Payne et al 1979", Payne andRietman 1985). The following sections summarize the information available in these documents.…”

Section: Regional Environmentmentioning

confidence: 99%

“…Should it become clear that any part of that region is moving away frvm attainment of the standards, SBCAPCD will implement corrective measures to bring the region back into I attainment. These could include measures such as: (1) lowering the Net Emission Increase U U 1 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] U trigger levels, (2) more stringent air pollution control regulations for a new emission source, or (3) making regulations retroactive in certain instances and requiring existing emission sources to conform to them.…”

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confidence: 99%

Environmental Impact Analysis Process. Volume 1. Preliminary Draft Environmental Impact Statement Construction and Operation of Space Launch Complex 7, Vandenberg Air Force Base, California

WASHINGTON¹

1989

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Investigation of the Hosgri fault, offshore southern California, Point Sal to Point Conception

Cited by 7 publications

References 10 publications

Hosgri fault zone, offshore Santa Maria Basin, California

Hosgri fault zone, offshore Santa Maria Basin, California

Shallow geologic structure, offshore Point Arguello to Santa Maria River; central California

Environmental Impact Analysis Process. Volume 1. Preliminary Draft Environmental Impact Statement Construction and Operation of Space Launch Complex 7, Vandenberg Air Force Base, California

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