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At least 91 records · Page 5Linked to original sources
USGS2004

Marine geology and earthquake hazards of the San Pedro Shelf region, southern California

High-resolution seismic-reflection data have been com- bined with a variety of other geophysical and geological data to interpret the offshore structure and earthquake hazards of the San Pedro Shelf, near Los Angeles, California. Prominent structures investigated include the Wilmington Graben, the Palos Verdes Fault Zone, various faults below the western part of the shelf and slope, and the deep-water San Pedro Basin. The structure of the Palos Verdes Fault Zone changes mark- edly southeastward across the San Pedro Shelf and slope. Under the northern part of the shelf, this fault zone includes several strands, but the main strand dips west and is probably an oblique-slip fault. Under the slope, this fault zone con- sists of several fault strands having normal separation, most of which dip moderately east. To the southeast near Lasuen Knoll, the Palos Verdes Fault Zone locally is a low-angle fault that dips east, but elsewhere near this knoll the fault appears to dip steeply. Fresh sea-floor scarps near Lasuen Knoll indi- cate recent fault movement. The observed regional structural variation along the Palos Verdes Fault Zone is explained as the result of changes in strike and fault geometry along a master strike-slip fault at depth. The shallow summit and possible wavecut terraces on Lasuen knoll indicate subaerial exposure during the last sea-level lowstand. Modeling of aeromagnetic data indicates the presence of a large magnetic body under the western part of the San Pedro Shelf and upper slope. This is interpreted to be a thick body of basalt of Miocene(?) age. Reflective sedimentary rocks overlying the basalt are tightly folded, whereas folds in sedimentary rocks east of the basalt have longer wavelengths. This difference might mean that the basalt was more competent during folding than the encasing sedimentary rocks. West of the Palos Verdes Fault Zone, other northwest-striking faults deform the outer shelf and slope. Evidence for recent movement along these faults is equivocal, because age dates on deformed or offset sediment are lacking.

Professional Paper↗
USGS1978

U.S. Geological Survey offshore program of resource and geo-environmental studies and topical investigations, Pacific-Arctic region

The Geological Survey's marine geology investigations in the Pacific-Arctic area are presented in this report in the context of the underlying socio-economic problem of expanding the domestic production of oil and gas and other mineral and hard- and soft-rock resources while maintaining acceptable standards in the marine environment. The primary mission of the Survey 's Pacific-Arctic Branch of Marine Geology is to provide scientifically interpreted information about the (1) resource potential, (2) geo-environmental setting, and (3) overall geologic characteristics of the continental margins (that is, the continental shelf, slope and rise) and adjacent deeper water and shallower coastal areas off California, Oregon, Washington, Alaska and Hawaii and also, where it is of interest to the U.S. Government, more remote deep-sea areas of the Pacific-Arctic realm.

Open-File Report↗
USGS2018

Downhole log evidence for the coexistence of structure II gas hydrate and free gas below the bottom simulating reflector in the South China Sea

Stratigraphic layered pore-filling gas hydrates are identified above the bottom simulating reflector (BSR) using the well log and core data acquired at Sites W11 and W17 during the third gas hydrate drilling expedition conducted by China's Geological Survey/Guangzhou Marine Geological Survey (GMGS3) in the South China Sea. A seismic profile near Site W17, reveal the presence of two BSRs (i.e., double BSR), which we show to relate to zones of structure I gas hydrate (I-BSR) and structure II gas hydrate (II-BSR). Well log data from Site W17 between the “I-BSR” (projected depth of 250 mbsf) and “II-BSR” (projected depth of 330 mbsf) showed anomalous responses for gas hydrate-bearing sediments with high resistivity, high S-wave velocity, and alternating high and low P-wave velocities. Pressure core data support the interpretation that structure II gas hydrate occurs at a depth of 263 mbsf at Site W17. The cross-plot between log-derived neutron and density porosities reveals a free gas-bearing layer at a depth of 258–270 mbsf, suggesting gas hydrate coexists with free gas between the “I-BSR” and the “II-BSR.” Synthetic seismograms generated from the P-wave velocity and density logs further support the presence of free gas in this section. Based on the coexistence of hydrate, free gas and water, the simplified three-phase equation (STPE) was modified to simultaneously estimate free gas and hydrate saturations beneath the “I-BSR” from P-wave and S-wave velocity logs, assuming uniform or patchy distributions of free gas. The estimated free gas and hydrate saturations, together with gas compositions from pressure core samples, collectively indicate that structure II gas hydrate and free gas are interbedded and coexist below the “I-BSR” at Site W17. Our study of the coexistence of gas hydrate and free gas between the double BSR at Site W17 provides new insights into gas hydrate systems in nature that contain more complex gas chemistries.

South China Sea↗
USGS1978

Geophysical data from the 1975 cruise of the NOAA ship Surveyor in northern Gulf of Alaska

In April and Flay 1975, a U.S. Geological Survey marine geology field party under the leadership of Bruce F. Molnia and Paul R. Carlson collected geophysical data from the N.O.A.A. ship Surveyor. The cruise, which consisted of 3 legs, studied the area between Cross Sound and Seward (Figure 1). Maps 1, 2, and 3 (scale 1:250,000) show the location of track lines and ship positions for the 3 legs.

Alaska↗
USGS2003

High-resolution Quaternary seismic stratigraphy of the New York Bight continental shelf

A principal focus for the U.S. Geological Survey (USGS) Coastal and Marine Geology Program (marine.usgs.gov) is regional reconnaissance mapping of inner-continental shelf areas, with initial emphasis on heavily used areas of the sea floor near major population centers. The objectives are to develop a detailed regional synthesis of the sea-floor geology in order to provide information for a wide range of management decisions and to form a basis for further investigations of marine geological processes. In 1995, the USGS, in cooperation with the U.S. Army Corps of Engineers (USACOE), New York District, began to generate reconnaissance maps of the continental shelf seaward of the New York - New Jersey metropolitan area. This mapping encompassed the New York Bight inner-continental shelf, one of the most heavily trafficked and exploited coastal regions in the United States. Contiguous areas of the Hudson Shelf Valley, the largest physiographic feature on this segment of the continental shelf, also were mapped as part of a USGS study of contaminated sediments (Buchholtz ten Brink and others, 1994; 1996). The goal of the reconnaissance mapping was to provide a regional synthesis of the sea-floor geology in the New York Bight area, including: (a) a description of sea-floor morphology; (b) a map of sea-floor sedimentary lithotypes; (c) the geometry and structure of the Cretaceous strata and Quaternary deposits; and (d) the geologic history of the region. Pursuing the course of this mapping effort, we obtained sidescan-sonar images of 100 % of the sea floor in the study area. Initial interpretations of these sidescan data were presented by Schwab and others, (1997a, 1997b, 2000a). High-resolution seismic-reflection profiles collected along each sidescan-sonar line used multiple acoustic sources (e.g., watergun, CHIRP, Geopulse). Multibeam swath-bathymetry data also were obtained for a portion of the study area (Butman and others, 1998;). In this report, we present a series of structural and sediment isopach maps and interpretations of the Quaternary evolution of the inner-continental shelf off the New York - New Jersey metropolitan area based on subbottom, sidescan-sonar, and multibeam-bathymetric data.

New York↗
USGS1983

U.S. Geological Survey program of offshore resource and geoenvironmental studies, Atlantic-Gulf of Mexico region, from September 1, 1976, to December 31, 1978

Mineral and energy resources of the continental margins of the United States arc important to the Nation's commodity independence and to its balance of payments. These resources are being studied along the continental margins of the Atlantic Ocean and the Gulf of Mexico in keeping with the mission of the U.S. Geological Survey to survey the geologic structures, mineral resources, and products of the national domain.'(Organic Act of 1879). An essential corollary to these resource studies is the study of potential geologic hazards that may be associated with offshore resource exploration and exploitation. In cooperation with the U.S. Bureau of Land Management, the Geological Survey, through its Atlantic-Gulf of Mexico Marine Geology Program, carries out extensive research to evaluate hazards from sediment mobility, shallow gas, and slumping and to acquire information on the distribution and concentration of trace metals and biogenic and petroleum-derived hydrocarbons in sea-floor sediments. All these studies arc providing needed background information, including information on pollutant dispersal, on the nearshore, estuarine, and lacustrine areas that may be near pipeline and nuclear powerplant sites. Users of these data include the Congress, many Federal agencies, the coastal States, private industry, academia, and the concerned public. The results of the regional structural, stratigraphic, and resource studies carried out under the Atlantic-Gulf of Mexico Marine Geology Program have been used by the Geological Survey and the Bureau of Land Management to select areas for future leasing and to aid in the evaluation of tracts nominated for leasing. Resource studies have concentrated mostly on the Atlantic Outer Continental Shelf frontier areas. Geologic detailing of five major basins along the U.S. Atlantic margin, where sediments are as much as 14 km thick, have been revealed by 25,000 km of 24-and 48-channel common-depth-point seismic data, 187,000 km of acromagnetic data, and 39,000 km of gravity data, plus 10,000 samples and logs obtained from U.S. Geological Survey and industry drilling (for example, coreholes of the Atlantic Slope Program, Joint Oceanographic Institutions Deep Earth Sampling, Continental Offshore Stratigraphic Tests, and the Atlantic Margin Coring Program). A sedimentary section of Jurassic and Cretaceous age grades from terrigenous clastic rocks nearshore to carbonate rocks offshore; this section is part of an extensive buried bank-platform complex that could contain large reserves of natural gas and oil. The volume of sediment deposited offshore far exceeds the volume deposited onshore where extensive accumulations of oil, gas, and minerals have been found. Commercial exploratory drilling offshore thus far has been limited to the Baltimore Canyon Trough area off New Jersey, where at least two holes have found gas; leasing has taken place in the Southeast Georgia Embayment, where drilling was scheduled to begin in 1979, and is imminent in the Georges Bank area off New England. In addition, hydrogeologic and hydrochemical data obtained from the drilling studies have delineated freshwater-bearing submarine extensions of land aquifers that are important coastal ground-water resources. Hazards in the Georges Bank area include sand mobility associated with strong currents and storm-driven waves; high concentrations of suspended sediment in the water column that, when mixed with spilled oil, may sink to the bottom; and slumping along the upper slope. In the Baltimore Canyon, high sediment mobility accompanies major winter storms, and slumped material may cover as much as 20 percent of the upper slope. Potentially unstable slope areas are being studied in great detail to provide data on timing, triggering mechanisms, and rates of sediment movement. In the Southeast Georgia Embayment and Blake Plateau Basin, strong Gulf Stream flow poses a major problem to all offshore operations. In the Gulf o

Circular↗
USGS1977

The United States Geological Survey in Alaska: Organization and status of programs in 1977

United States Geological Survey projects in Alaska include a wide range of topics of economic and scientific interest. Studies in 1976 include economic geology, regional geology, stratigraphy, environmental geology, engineering geology, hydrology, and marine geology. Discussions of the findings or, in some instances, narratives of the course of the investigations are grouped in eight subdivisions corresponding to the six major onshore geographic regions, the offshore projects, and projects that are statewide in scope. Locations of the study areas are shown. In addition, many reports and maps covering various aspects of the geology and mineral and water resources of the State were published. These publications are listed. (Woodard-USGS)

Circular↗
USGS1977

The United States Geological Survey in Alaska: Accomplishments during 1976

United States Geological Survey projects in Alaska include a wide range of topics of economic and scientific interest. Studies in 1976 include economic geology, regional geology, stratigraphy, environmental geology, engineering geology, hydrology, and marine geology. Discussions of the findings or, in some instances, narratives of the course of the investigations are grouped in eight subdivisions corresponding to the six major onshore geographic regions, the offshore projects, and projects that are statewide in scope. Locations of the study areas are shown. In addition, many reports and maps covering various aspects of the geology and mineral and water resources of the State were published. These publications are listed. (Woodard-USGS)

Circular↗
USGS1978

The United States Geological Survey in Alaska; organization and status of programs in 1978

United States Geological Survey projects in Alaska study a wide range of topics of economic and scientific interest. Work done in 1977 includes contributions to economic geology, regional geology, stratigraphy, engineering geology, hydrology, and marine geology. Many maps and reports covering various aspects of the geology and mineral and water resources of the State were published. In addition, the published 1:1,000,000-scale map of the State has been revised in two areas. A bibliography containing 263 reports on Alaska published in 1977 is included. (Woodard-USGS)

Circular↗
USGS1978

The United States Geological Survey in Alaska: Accomplishments during 1977

United States Geological Survey projects in Alaska study a wide range of topics of economic and scientific interest. Work done in 1977 includes contributions to economic geology, regional geology, stratigraphy, engineering geology, hydrology, and marine geology. Many maps and reports covering various aspects of the geology and mineral and water resources of the State were published. In addition, the published 1:1,000,000-scale map of the State has been revised in two areas. A bibliography containing 263 reports on Alaska published in 1977 is included.

Alaska↗
USGS1999

Archive of 15 cubic inch water gun data collected during USGS Cruise ALPH98013, New York Bight, 10-22, September, 1998

Background This CD-ROM contains copies of the navigation and field water gun subbottom data collected aboard the F/V Alpha & Omega II. The USGS Cruise ALPH98013 was conducted from 10-22 September, 1998, and is a collaborative involving the U.S Army Corps of Engineers, New York District and the United States Geological SurveyCoastal and Marine Geology Program, Woods Hole Field Center. In 1995, the USGS, in cooperation with the U.S Army Corps of Engineers (USACOE), New York District, began a program to generate reconnaissance maps of the sea floor offshore of the New York-New Jersey metropolitan area, one of the most populated coastal regions of the United States. The goal of this mapping program is to provide a regional synthesis of the sea-floor environment, including a description of sedimentary environments, sediment texture, sea-floor morphology, and geologic history to aid in understanding the impacts of anthropogenic activities, such as ocean dumping. This mapping effort differs from previous studies of this area by obtaining digital, sidescan sonar images that cover 100 percent of the sea floor. This investigation was motivated by the need to develop an environmentally acceptable solution for the disposal of dredged material from the New York - New Jersey Port, by the need to identify potential sources of sand for renourishment of the southern shore of Long island, and by the opportunity to develop a better understanding of the transport and long-term fate of contaminants by investigations of the present distribution of materials discharged into the New York Bight over the last 100+ years (Schwab and others, 1997). Sidescan-sonar data collected during USGS Cruises Seax95007 and Seax96004 (May 1995 and May 1996, respectively) were digitally mosaicked to provide a base suitable for use in Geographic Information Systems of the New York Bight Apex region. During USGS Cruise Alph98013, supplemental sidescan sonar and seismic reflection data were collected within the New York Bight Apex region, primarily to augment the seismic reflection portion of the mapping project. Additional sidescan sonar and seismic reflection data were collected east of the Seax95007 and Seax96004 survey areas. These data abut sidescan sonar and seismic reflection data collected off the Southern Long Island shoreline during USGS Cruises Dian96040, Dian97011, and Dian97032 (September 1996, May 1997, October 1997, respectively).

Open-File Report↗