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At least 163 records · Page 9Linked to original sources
USGS2009

Evidence for prolonged El Nino-like conditions in the Pacific during the Late Pleistocene: a 43 ka noble gas record from California groundwaters

Information on the ocean/atmosphere state over the period spanning the Last Glacial Maximum - from the Late Pleistocene to the Holocene - provides crucial constraints on the relationship between orbital forcing and global climate change. The Pacific Ocean is particularly important in this respect because of its dominant role in exporting heat and moisture from the tropics to higher latitudes. Through targeting groundwaters in the Mojave Desert, California, we show that noble gas derived temperatures in California averaged 4.2 ?? 1.1 ??C cooler in the Late Pleistocene (from ???43 to ???12 ka) compared to the Holocene (from ???10 to ???5 ka). Furthermore, the older groundwaters contain higher concentrations of excess air (entrained air bubbles) and have elevated oxygen-18/oxygen-16 ratios (?? 18 O) - indicators of vigorous aquifer recharge, and greater rainfall amounts and/or more intense precipitation events, respectively. Together, these paleoclimate indicators reveal that cooler and wetter conditions prevailed in the Mojave Desert from ???43 to ???12 ka. We suggest that during the Late Pleistocene, the Pacific ocean/atmosphere state was similar to present-day El Nino-like patterns, and was characterized by prolonged periods of weak trade winds, weak upwelling along the eastern Pacific margin, and increased precipitation in the southwestern U.S.

Quaternary Science Reviews↗
USGS2007

Long-term perspectives on giant earthquakes and tsunamis at subduction zones

Histories of earthquakes and tsunamis, inferred from geological evidence, aid in anticipating future catastrophes. This natural warning system now influences building codes and tsunami planning in the United States, Canada, and Japan, particularly where geology demonstrates the past occurrence of earthquakes and tsunamis larger than those known from written and instrumental records. Under favorable circumstances, paleoseismology can thus provide long-term advisories of unusually large tsunamis. The extraordinary Indian Ocean tsunami of 2004 resulted from a fault rupture more than 1000 km in length that included and dwarfed fault patches that had broken historically during lesser shocks. Such variation in rupture mode, known from written history at a few subduction zones, is also characteristic of earthquake histories inferred from geology on the Pacific Rim. Copyright ?? 2007 by Annual Reviews. All rights reserved.

Annual Review of Earth and Planetary Sciences↗
USGS2013

Working with strainmeter data

The Plate Boundary Observatory (PBO), the geodetic component of the U.S. National Science Foundation–funded Earthscope program, includes 75 borehole and 6 laser strainmeters ( http://pbo.unavco.org ). The strainmeters are installed at several locations: on the Cascadia forearc in Washington state and on Vancouver Island, Canada; in arrays of two to nine instruments along the North American–Pacific plate boundary in California; at Mount St. Helens; and in Yellowstone National Park. For deformation signals seconds to weeks in duration, strainmeters have a resolution and a signal-to-noise ratio superior to those of seismometers and GPS. However, this high sensitivity can introduce nontectonic signals into strain data, presenting data interpretation challenges, especially for borehole strainmeters.

Eos, Earth and Space Science News↗
USGS2002

Vulnerability assessment of a port and harbor community to earthquake and tsunami hazards: Integrating technical expert and stakeholder input

Research suggests that the Pacific Northwest could experience catastrophic earthquakes and tsunamis in the near future, posing a significant threat to the numerous ports and harbors along the coast. A collaborative, multiagency initiative is underway to increase the resiliency of Pacific Northwest ports and harbors to these hazards, involving Oregon Sea Grant, Washington Sea Grant, the National Oceanic and Atmospheric Administration Coastal Services Center, and the U.S. Geological Survey Center for Science Policy. One element of this research, planning, and outreach initiative is a natural hazard mitigation and emergency preparedness planning process that combines technical expertise with local stakeholder values and perceptions. This paper summarizes and examines one component of the process, the vulnerability assessment methodology, used in the pilot port and harbor community of Yaquina River, Oregon, as a case study of assessing vulnerability at the local level. In this community, stakeholders were most concerned with potential life loss and other nonstructural vulnerability issues, such as inadequate hazard awareness, communication, and response logistics, rather than structural issues, such as damage to specific buildings or infrastructure.

Oregon↗
USGS2025

Beak deformities in Buteo jamaicensis (Red-tailed Hawk) signal possible emergence of avian keratin disorder among raptors

Beginning in the late 1990s, an unusual cluster of beak deformities was observed among Buteo jamaicensis (Red-tailed Hawk) in the Pacific coastal region of North America. However, information was not available to determine the scope of this problem nor to assess a potential link between beak deformities in hawks and avian keratin disorder (AKD), an emerging disease primarily among passerines that causes overgrowth of the keratinized layer of the beak. To help address these knowledge gaps, we compiled capture records, citizen science reports, and other available data from across North America. As part of a long-term raptor monitoring program in Washington, we detected anomalously high rates of beak deformities in 29% and other keratin abnormalities in an additional 19% of B. jamaicensis between 2014 and 2021. We also identified more than 100 other AKD-like cases in B. jamaicensis , largely clustered in the Pacific coastal region, with most reports from 2000 to present. Pathologic examination of affected hawks revealed gross and microscopic features consistent with AKD in passerines, while shared epidemiological patterns, including timing of emergence, provided further evidence that this disease may impact an ecologically diverse suite of species. We detected poecivirus, a novel avian virus implicated as a likely cause of AKD in Poecile atricapillus (Black-capped Chickadee), in 1 out of 10 swabs collected from live B. jamaicensis , with gross beak deformities, suggesting the possibility of a shared viral etiology across species. However, additional work would be needed to determine the underlying cause of beak deformities in and their potential impacts on B. jamaicensis . By documenting this cluster of beak deformities, we hope to raise awareness among the ornithological community, including raptor researchers, to better track current and future outbreaks of beak deformities and related conditions.

Ornithology↗
USGS1997

Evolution of Nd and Pb isotopes in Central Pacific seawater from ferromanganese crusts

Hydrogenetic ferromanganese crusts incorporate elements from ambient seawater during their growth on seamounts. By analysing Nd, Pb and Be isotope profiles within crusts it is possible to reconstruct seawater tracer histories. Depth profiles of 10 Be/ 9 Be ratios in three Pacific ferromanganese crusts have been used to obtain growth rates which are between 1.4 and 3.8 mm/Ma. Nd and Pb isotopes provide intact records of isotopic variations in Pacific seawater over the last 20 Ma or more. There were only small changes in Pb isotope composition in the last 20 Ma. This indicates a constant Pb composition for the erosional sources and suggests further that erosional Nd inputs may have been uniform too. ε Nd values vary considerably with time and most probably reflect changes in ocean circulation. The ε Nd values of the crusts not only vary as a function of age but also as a function of water depth. From 25 to 0 Ma, crust VA13/2 from 4.8 km water depth has a similar pattern of ε Nd variation to the two shallower crusts from 1.8 and 2.3 km, but about 1.0 to 1.5 units more negative. This suggests that ε Nd stratification in Pacific seawater, as demonstrated for the present day, has been maintained for at least 20 Ma. Each crust shows a decrease in ε Nd from 3–5 Ma to the present, which is interpreted in terms of an increase in the NADW component present in the Pacific. From 10 to 3–5 Ma ago the crusts show an increase in ε Nd . This suggests a decreasing role for a deep water source with ε Nd less than circum-Pacific sources. In this regard the Panamanian gateway restriction from ∼ 10 Ma with final closure at 3–5 Ma may have played an important role in reducing access of Atlantic-derived Nd to the Pacific.

Earth and Planetary Science Letters↗
USGS1986

A sublittoral population of Pleurophycus gardneri Setchell and Saunders 1900 (Phaeophyceae: Laminariaceae) in central California

Published distributional records for the stipitate kelp Pleurophycus gardneri Setchell and Saunders 1900 (Phaeophyceae: Laminariaceae) indicae a geographic range from Montague Island (59°58’N, 147°22W), Alaska to Fort Bragg (39°27’N, 123°47’W), California (Druehl 1969, 1970; Kjeldsen 1972). P. gardneri is found primarily in rocky intertidal and shallow subtidal locations (Scagel 1967; Nicholson 1976). In California, populations of P. gardneri have been reported only from the lower rocky intertidal near Fort Bragg (Kjeldsen 1972). On 7 and 8 July 1982 and 23 March 1984 we censused stipitate kelps during SCUBS dives at a site 2.3 km south southeast of Pt. Sierra Nevada (35°41’ N, 121°18’W). we counted kelps in 1 x 5-m plots along a 50-m tape laid across the bottom in an arbitrarily predetermined direction from the skiff anchor. We also measured water depth at 1-m intervals along the tape, using a SCUBA depth gauge. On 20 August 1982, we used the same tehniques to sample kelp densities at a site 2.4 km east southeast of Pt. Piedras Blancas (35°39’N, 121°15’W). The most abundant kelps at the Pt. Sierra Nevada ste were Pterygophora californica Ruprect 1852 (Phaeophyceae: Alariaceae) and a species we tentatively identified as P. gardneri (Table 1). Based on specimens we collected on 8 July 1982, our field identification was subsequently confirmed by I. A. Abbot. Voucher specimens were placed in the Gilbert M. Smith Herbarium at Hopkins Marine Station, Stanford University, Pacific Grove, California.

California↗
USGS2011

Assessment of mangrove forests in the Pacific region using Landsat imagery

The information on the mangrove forests for the Pacific region is scarce or outdated. A regional assessment based on a consistent methodology and data sources was needed to understand their true extent. Our investigation offers a regionally consistent, high resolution (30 m), and the most comprehensive mapping of mangrove forests on the islands of American Samoa, Fiji, French Polynesia, Guam, Hawaii, Kiribati, Marshall Islands, Micronesia, Nauru, New Caledonia, Northern Mariana Islands, Palau, Papua New Guinea, Samoa, Solomon Islands, Tonga, Tuvalu, Vanuatu, and Wallis and Futuna Islands for the year 2000. We employed a hybrid supervised and unsupervised image classification technique on a total of 128 Landsat scenes gathered between 1999 and 2004, and validated the results using existing geographic information science (GIS) datasets, high resolution imagery, and published literature. We also draw a comparative analysis with the mangrove forests inventory published by the Food and Agriculture Association (FAO) of the United Nations. Our estimate shows a total of 623755 hectares of mangrove forests in the Pacific region; an increase of 18% from FAO's estimates. Although mangrove forests are disproportionately distributed toward a few larger islands on the western Pacific, they are also significant in many smaller islands.

Journal of Applied Remote Sensing↗
USGS2021

Pervasive low-velocity layer atop the 410-km discontinuity beneath the northwest Pacific subduction zone: Implications for rheology and geodynamics

Regional triplication waveforms of five intermediate-depth events are modeled to simultaneously obtain the compressional (P) and shear (SH) wave velocity structure beneath northwestern Pacific subduction zone. Both the P- and SH-wave velocity models for three different sub-regions show a low-velocity layer (LVL) with a thickness of ∼55-80 km lying above the 410-km discontinuity with a ∼900 km lateral extent from the Japan Sea to the northeastern Asian continental margin. With the dihedral angle approaching to zero around 400 km, a minute amount of melt atop the 410-km discontinuity caused by the hydrous slab might completely wet olivine grain boundaries and result in a low seismic velocity layer in this specific subduction zone. This mechanism suggests that the 410-LVL is a low viscosity zone that would partially decouple the upper mantle from the transition zone. We infer that the widespread 410-LVL provides evidence for a water-bearing mantle transition zone beneath the western Pacific subduction zone.

Earth and Planetary Science Letters↗
USGS2020

The role of Northeast Pacific meltwater events in deglacial climate change

Columbia River megafloods occurred repeatedly during the last deglaciation, but the impacts of this fresh water on Pacific hydrography are largely unknown. To reconstruct changes in ocean circulation during this period, we used a numerical model to simulate the flow trajectory of Columbia River megafloods and compiled records of sea surface temperature, paleo-salinity, and deep-water radiocarbon from marine sediment cores in the Northeast Pacific. The North Pacific sea surface cooled and freshened during the early deglacial (19.0-16.5 ka) and Younger Dryas (12.9-11.7 ka) intervals, coincident with the appearance of subsurface water masses depleted in radiocarbon relative to the sea surface. We infer that Pacific meltwater fluxes contributed to net Northern Hemisphere cooling prior to North Atlantic Heinrich Events, and again during the Younger Dryas stadial. Abrupt warming in the Northeast Pacific similarly contributed to hemispheric warming during the Bølling and Holocene transitions. These findings underscore the importance of changes in North Pacific freshwater fluxes and circulation in deglacial climate events.

Science Advances↗
USGS2018

U.S. Department of the Interior Climate Science Centers and U.S. Geological Survey National Climate Change and Wildlife Science Center—Annual report for 2017

Introduction The year 2017 was a year of review and renewal for the Department of the Interior (DOI) Climate Science Centers (CSCs) and the U.S. Geological Survey (USGS) National Climate Change and Wildlife Science Center (NCCWSC). The Southeast, Northwest, Alaska, Southwest, and North Central CSCs’ 5-year summary review reports were released in 2017 and contain the findings of the external review teams led by the Cornell University Human Dimensions Research Unit in conjunction with the American Fisheries Society. The reports for the Pacific Islands, South Central, and Northeast CSCs are planned for release in 2018. The reviews provide an opportunity to evaluate aspects of the cooperative agreement, such as the effectiveness of the CSC in meeting project goals and assessment of the level of scientific contribution and achievement. These reviews serve as a way for the CSCs and NCCWSC to look for ways to recognize and enhance our network’s strengths and identify areas for improvement. The reviews were followed by the CSC recompetition, which led to new hosting agreements at the Northwest, Alaska, and Southeast CSCs. Learn more about the excellent science and activities conducted by the network centers in the 2017 annual report.

Open-File Report↗
USGS2015

The Holocene history of the North American Monsoon: 'known knowns' and 'known unknowns' in understanding its spatial and temporal complexity

Evidence for climatic change across the North American Monsoon (NAM) and adjacent areas is reviewed, drawing on continental and marine records and the application of climate models. Patterns of change at 12,000, 9000, 6000 and 4000 cal yr BP are presented to capture the nature of change from the Younger Dryas (YD) and through the mid-Holocene. At the YD, conditions were cooler overall, wetter in the north and drier in the south, while moving into the Holocene wetter conditions became established in the south and then spread north as the NAM strengthened. Until c. 8000 cal yr BP, the Laurentide Ice Sheet influenced precipitation in the north by pushing the Bermuda High further south. The peak extent of the NAM seems to have occurred around 6000 cal yr BP. 4000 cal yr BP marks the start of important changes across the NAM region, with drying in the north and the establishment of the clear differences between the summer-rain dominated south and central areas and the north, where winter rain is more important. This differentiation between south and north is crucial to understanding many climate responses across the NAM. This increasing variability is coincident with the declining influence of orbital forcing. 4000 cal yr BP also marks the onset of significant anthropogenic activity in many areas. For the last 2000 years, the focus is on higher temporal resolution change, with strong variations across the region. The Medieval Climate Anomaly (MCA) is characterised by centennial scale ‘megadrought’ across the southwest USA, associated with cooler tropical Pacific SSTs and persistent La Niña type conditions. Proxy data from southern Mexico, Central America and the Caribbean reveal generally wetter conditions, whereas records from the highlands of central Mexico and much of the Yucatan are typified by long -term drought. The Little Ice Age (LIA), in the north, was characterised by cooler, wetter winter conditions that have been linked with increased frequency of El Niño's. Proxy records in the central and southern regions reveal generally dry LIA conditions, consistent with cooler SSTs in the Caribbean and Gulf of Mexico. This synthesis demonstrates that in some periods, one major forcing can dominate across the whole area (e.g. insolation in the early-mid Holocene), but at other times there is strong variability in patterns of change due to the differential impact of forcings such as the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) on precipitation seasonality.

Quaternary Science Reviews↗
USGS2008

Molecular and morphological analysis of the critically endangered Fijian iguanas reveals cryptic diversity and a complex biogeographic history

The Pacific iguanas of the Fijian and Tongan archipelagos are a biogeographic enigma in that their closest relatives are found only in the New World. They currently comprise two genera and four species of extinct and extant taxa. The two extant species, Brachylophus fasciatus from Fiji, Tonga, and Vanuatu and Brachylophus vitiensis from western Fiji, are of considerable conservation concern with B. vitiensis listed as critically endangered. A recent molecular study has shown that Brachylophus comprised three evolutionarily significant units. To test these conclusions and to reevaluate the phylogenetic and biogeographic relationships within Brachylophus, we generated an mtDNA dataset consisting of 1462 base pairs for 61 individuals from 13 islands, representing both Brachylophus species. Unweighted parsimony analyses and Bayesian analyses produced a well-resolved phylogenetic hypothesis supported by high bootstrap values and posterior probabilities within Brachylophus. Our data reject the monophyly of specimens previously believed to comprise B. fasciatus. Instead, our data demonstrate that living Brachylophus comprise three robust and well-supported clades that do not correspond to current taxonomy. One of these clades comprises B. fasciatus from the Lau group of Fiji and Tonga (type locality for B. fasciatus), while a second comprises putative B. fasciatus from the central regions of Fiji, which we refer to here as B. n. sp. Animals in this clade form the sister group to B. vitiensis rather than other B. fasciatus. We herein describe this clade as a new species of Brachylophus based on molecular and morphological data. With only one exception, every island is home to one or more unique haplotypes. We discuss alternative biogeographic hypotheses to explain their distribution in the Pacific and the difficulties of distinguishing these. Together, our molecular and taxonomic results have important implications for future conservation initiatives for the Pacific iguanas. ?? 2008 The Royal Society.

Philosophical Transactions of the Royal Society B:↗
USGS2011

Proceedings of a Coastal and Marine Spatial Planning Workshop for the Western United States

Recent scientific and ocean policy assessments demonstrate that a fundamental change in our current management system is required to achieve the long-term health of our ocean, coasts, and Great Lakes in order to sustain the services and benefits they provide to society. The present (2011) species- and sector-centric way we manage these ecosystems cannot account properly for cumulative effects, sustaining multiple ecosystem services, and holistically and explicitly evaluating the tradeoffs associated with proposed alternative and multiple human uses. A transition to an ecosystem-based approach to management and conservation of coastal and marine resources is needed. Competing uses and activities such as commerce, recreation, cultural practices, energy development, conservation, and national security are increasing pressure for new and expanded resource usage in coastal marine ecosystems. Current management efforts use a sector-by-sector approach that mostly focuses on a limited range of tools and outcomes [for example, oil and gas leases, fishery management plans, and Marine Protected Areas (MPAs)]. A comprehensive, ecosystem-based, and proactive approach to planning and managing these uses and activities is needed. Further, scientific understanding and information are essential to achieve an integrated decision-making process that includes knowledge of ecosystem services, existing and possible future conditions, and potential consequences of natural and anthropogenic events. Because no single government agency has executive authority for coastal or ocean resources, conflicting objectives around competing uses abound. In recent years, regional- and state-level initiatives in Coastal and Marine Spatial Planning (CMSP) have emerged to coordinate management activities. In some respects, the components and steps of the overall CMSP process are similar to how existing ocean resources are regulated and managed. For example, the Bureau of Ocean Energy Management Regulation and Enforcement (BOEMRE) uses spatial planning exercises in State Renewable Energy Task Force meetings to identify competing and conflicting ocean uses, and to delineate areas suitable for renewable energy development. Similarly terrestrial areas such as in national parks and national wildlife refuges managed by the Department of the Interior (DOI) prepare management plans for preservation and restoration of species and habitats of concern, some of which are protected by law. The analogy to CMSP is clear - multiple users and multiple expectations, resulting in the requirement to establish spatial plans for management of different resources and different ecosystem services. A two-day workshop on December 1-2, 2010, was convened for DOI representatives and several key non-DOI participants with roles in CMSP as a step toward clarifying national perspectives and consequences of the National Ocean Policy for the West (appendix 1). Discussions helped to develop an understanding of CMSP from the federal perspective and to identify regional priorities. An overarching theme was to promote a better understanding of current and future science needs. The workshop format included briefings by key Federal agencies on their understanding of the national focus followed by discussion of regional issues, including the needs for scientific information and coordination. The workshop also explored potential science contributions by Federal agencies and others; utilizing current capabilities, data, and information systems; and provided a foundation for possible future regional workshops focusing in turn on the West Coast Region (California, Oregon, and Washington), Pacific Islands (sometimes referred to as Oceania) and Alaska. Participants were asked to share information in the following areas, recognizing that the purpose would be to learn more about the national perspective (see appendixes 2-4): Explore how the Western U.S. (Alaska, Pacific Islands, and West Coast Region) migh

Open-File Report↗
USGS1993

Map showing sediment isopachs in the deep-sea basins of the Pacific continental margin, Cape Mendocino to Point Conception

The U.S. Geological Survey conducted a series of cruises, EEZSCAN 84 (EEZ-SCAN 84 Scientific Staff, 1986), to collect reconnaissance data on the newly proclaimed Exclusive Economic Zone (EEZ), the area out to 200 nautical miles from the coastline of the United States. The cruises systematically surveyed the entire conterminous United States west coast EEZ using the Geological Long-Range Inclined Asdic (GLORIA) side-scan sonar, a 160-in 3 airgun seismic-reflection profiler, a 3.5-kHz high-resolution seismic-reflection profiler, a 10-kHz echo sounder, and a proton-precession magnetometer. The nominal trackline spacing throughout the survey was 30 km. Derivative maps of sediment thickness (I-2089-A, I-2090-A, I-2091-A) and depth to basement (I-2089-B, I-2090-B, I-2091-B) in the basins of the west coast EEZ were compiled from both the sonar-image dala and the deep-penetration seismic data obtained on these cruises. Only EEZ-SCAN 84 data were used for the map compilations because available data from other cruises in this region are sparsely located, have poor navigational control, or were obtained with seismic systems that were not powerful enough to resolve oceanic basement. For this map series, sediment thickness and depth to basement were determined only in the deep-ocean basin regions because the seismic system used on the EEZ-SCAN 84 cruises could not resolve oceanic basement beneath the thick sediments of the continental slope. All the data used to compile the maps are presented in the "Atlas of the Exclusive Economic Zone, Western Conterminous United States" (EEZ-SCAN 84 Scientific Staff, 1986). Basement Outcrops GLORIA imagery was used to locate areas of basement outcrop throughout the region. Where possible, sediment thickness on and immediately adjacent to basement outcrops was measured from seismic data. Where there was no bathymetric or seismic control, a seamount peak was assumed to have no sediment cover. A pattern is used on the map to indicate all basement outcrops. Data Reduction Acoustic basement in the basins, invariably oceanic Layer 2, was observed on all of the seismic records. One-way traveltime was measured from the sea floor to acoustic basement. Because the trackline spacing of about 30 km is relatively large compared to the data density along track, we chose to measure the sediment thickness every 0.5 hour or at an interval of approximately 7.5 km. Water depth was measured with a 10-kHz profiler. Depth to basement was calculated using the sea surface as the zero datum and adding the corrected water depth (Carter, 1980) to the sediment thickness. Acoustic travel times were converted to depths by first calculating a regression equation from the interval velocity versus depth data of Connard and others (1984). Their data base comprises a compilation of all available Deep Sea Drilling Project data plus wide-angle refraction data, which were collected in Cascadia Basin west of Oregon and represents the best data set available for the United States west coast EEZ. The regression equation was integrated to determine sediment thickness as a function of one-way traveltime . The resulting equation is z = 1400t + 0 .5t 2 where z is sediment thickness in meters, and t is one-way traveltime in seconds. Sediment thicknesses calculated using this equation were compared to values calculated from the general equation of Carlson and others (1986). Values for sediment thickness calculated by the two equations differed by no greater than 10 percent throughout the range of travel times. Bathymetry The bathymetry is from Chase and others (1981). The bathymetric data were compiled from a variety of sources, and data quality is inconsistent. Because of differences in navigational precision and density of coverage, the bathymetric contours of a feature may be at a different location than the corresponding isopleths derived from the EEZ-SCAN 84 data, or a feature may not be indicated on the bathymetry at all. These situations occur because either the feature is poorly located in the bathymetric data set or, especially in the outer EEZ, the bathymetric data are too sparse to have defined the existence of a feature. Acknowledgments Topographic digital data bases were corrected and verified by Christina Lief. Gerald Evenden developed the computer software system MAPGEN, used to compose this map. Reviews, suggestions, and technical contributions from Edward C. Escowitz and Florence Wong and advice about cartographic design from Will Stettner substantially improved the quality of this map. References Cited Carlson, R.L., Gangi, A.F., and Snow, K.R., 1986, Empirical reflection-traveltime/ depth and velocity/depth functions for the deep-sea sediment column: Journal of Geophysical Research, v. 91, no. B8, p. 8249-8266. Carter, D.J.T., 1980, Echo-sounding correction tables: Taunton, United Kingdom, Hydrographic Department, Ministry of Defence, 150 p. Chase, T.E., Wilde, Pat, Normark, W.R, Miller, C.P., Seekins, B.A., and Young, J.D., 1981, Offshore topography of the Western United States between 32° and 49° North latitudes: U.S. Geological Survey Open-File Report 81-443, scale 1:864,518 at 38° latitude, 2 sheets. Connard, G., Couch, R., Keeling , K., Roy, J., and Troseth, S., 1984, Abyssal plain and continental net-objective sedimentary thicknesses, in Kulm, L.D., and others, eds., Western North America continental margin and adjacent ocean floor off Oregon and Washington, Atlas 1 of Regional Atlas Series, Ocean Margin Drilling Program: Woods Hole, Mass., Marine Science International, sheet 7. EEZ-SCAN 84 Scientific Staff, 1986, Atlas of the Exclusive Economic Zone, Western Conterminous United States: U.S. Geological Survey Miscellaneous Investigations Series I-1792, scale 1:500,000, 152 p. See Also "U.S. Pacific West Coast Field Activities" (Paskevich and others, 2011; http://pubs.usgs.gov/of/2010/1332/htmldocs/pc/pc_overview.html). Paskevich, V.F., Wong, F.L., O?Malley, J.J., Stevenson, A.J., and Gutmacher, C.E., 2011, GLORIA sidescan-sonar imagery for parts of the U.S. Exclusive Economic Zone and adjacent areas: U.S. Geological Survey Open-File Report 2010?1332, available at http://pubs.usgs.gov/of/2010/1332/.

IMAP↗
USGS1993

Map showing depth to basement in the deep-sea basins of the Pacific continental margin, Cape Mendocino to Point Conception

The U.S. Geological Survey conducted a series of cruises, EEZSCAN 84 (EEZ-SCAN 84 Scientific Staff, 1986), to collect reconnaissance data on the newly proclaimed Exclusive Economic Zone (EEZ), the area out to 200 nautical miles from the coastline of the United States. The cruises systematically surveyed the entire conterminous United States west coast EEZ using the Geological Long-Range Inclined Asdic (GLORIA) side-scan sonar, a 160-in 3 airgun seismic-reflection profiler, a 3.5-kHz high-resolution seismic-reflection profiler, a 10-kHz echo sounder, and a proton-precession magnetometer. The nominal trackline spacing throughout the survey was 30 km. Derivative maps of sediment thickness (I-2089-A, I-2090-A, I-2091-A) and depth to basement (I-2089-B, I-2090-B, I-2091-B) in the basins of the west coast EEZ were compiled from both the sonar-image dala and the deep-penetration seismic data obtained on these cruises. Only EEZ-SCAN 84 data were used for the map compilations because available data from other cruises in this region are sparsely located, have poor navigational control, or were obtained with seismic systems that were not powerful enough to resolve oceanic basement. For this map series, sediment thickness and depth to basement were determined only in the deep-ocean basin regions because the seismic system used on the EEZ-SCAN 84 cruises could not resolve oceanic basement beneath the thick sediments of the continental slope. All the data used to compile the maps are presented in the "Atlas of the Exclusive Economic Zone, Western Conterminous United States" (EEZ-SCAN 84 Scientific Staff, 1986). Basement Outcrops GLORIA imagery was used to locate areas of basement outcrop throughout the region. Where possible, sediment thickness on and immediately adjacent to basement outcrops was measured from seismic data. Where there was no bathymetric or seismic control, a seamount peak was assumed to have no sediment cover. A pattern is used on the map to indicate all basement outcrops. Data Reduction Acoustic basement in the basins, invariably oceanic Layer 2, was observed on all of the seismic records. One-way traveltime was measured from the sea floor to acoustic basement. Because the trackline spacing of about 30 km is relatively large compared to the data density along track, we chose to measure the sediment thickness every 0.5 hour or at an interval of approximately 7.5 km. Water depth was measured with a 10-kHz profiler. Depth to basement was calculated using the sea surface as the zero datum and adding the corrected water depth (Carter, 1980) to the sediment thickness. Acoustic travel times were converted to depths by first calculating a regression equation from the interval velocity versus depth data of Connard and others (1984). Their data base comprises a compilation of all available Deep Sea Drilling Project data plus wide-angle refraction data, which were collected in Cascadia Basin west of Oregon and represents the best data set available for the United States west coast EEZ. The regression equation was integrated to determine sediment thickness as a function of one-way traveltime . The resulting equation is z = 1400t + 0 .5t 2 where z is sediment thickness in meters, and t is one-way traveltime in seconds. Sediment thicknesses calculated using this equation were compared to values calculated from the general equation of Carlson and others (1986). Values for sediment thickness calculated by the two equations differed by no greater than 10 percent throughout the range of travel times. Bathymetry The bathymetry is from Chase and others (1981). The bathymetric data were compiled from a variety of sources, and data quality is inconsistent. Because of differences in navigational precision and density of coverage, the bathymetric contours of a feature may be at a different location than the corresponding isopleths derived from the EEZ-SCAN 84 data, or a feature may not be indicated on the bathymetry at all. These situations occur because either the feature is poorly located in the bathymetric data set or, especially in the outer EEZ, the bathymetric data are too sparse to have defined the existence of a feature. Acknowledgments Topographic digital data bases were corrected and verified by Christina Lief. Gerald Evenden developed the computer software system MAPGEN, used to compose this map. Reviews, suggestions, and technical contributions from Edward C. Escowitz and Florence Wong and advice about cartographic design from Will Stettner substantially improved the quality of this map. References Cited Carlson, R.L., Gangi, A.F., and Snow, K.R., 1986, Empirical reflection-traveltime/ depth and velocity/depth functions for the deep-sea sediment column: Journal of Geophysical Research, v. 91, no. B8, p. 8249-8266. Carter, D.J.T., 1980, Echo-sounding correction tables: Taunton, United Kingdom, Hydrographic Department, Ministry of Defence, 150 p. Chase, T.E., Wilde, Pat, Normark, W.R, Miller, C.P., Seekins, B.A., and Young, J.D., 1981, Offshore topography of the Western United States between 32° and 49° North latitudes: U.S. Geological Survey Open-File Report 81-443, scale 1:864,518 at 38° latitude, 2 sheets. Connard, G., Couch, R., Keeling , K., Roy, J., and Troseth, S., 1984, Abyssal plain and continental net-objective sedimentary thicknesses, in Kulm, L.D., and others, eds., Western North America continental margin and adjacent ocean floor off Oregon and Washington, Atlas 1 of Regional Atlas Series, Ocean Margin Drilling Program: Woods Hole, Mass., Marine Science International, sheet 7. EEZ-SCAN 84 Scientific Staff, 1986, Atlas of the Exclusive Economic Zone, Western Conterminous United States: U.S. Geological Survey Miscellaneous Investigations Series I-1792, scale 1:500,000, 152 p. See Also "U.S. Pacific West Coast Field Activities" (Paskevich and others, 2011; http://pubs.usgs.gov/of/2010/1332/htmldocs/pc/pc_overview.html). Paskevich, V.F., Wong, F.L., O?Malley, J.J., Stevenson, A.J., and Gutmacher, C.E., 2011, GLORIA sidescan-sonar imagery for parts of the U.S. Exclusive Economic Zone and adjacent areas: U.S. Geological Survey Open-File Report 2010?1332, available at http://pubs.usgs.gov/of/2010/1332/.

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