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At least 343 records · Page 19Linked to original sources

USGS2007

Observations of volcanic tremor during January-February 2005 eruption of Mt. Veniaminof, Alaska

Mt. Veniaminof, Alaska Peninsula, is a stratovolcano with a summit ice-filled caldera containing a small intracaldera cone and active vent. From January 2 to February 21, 2005, Mt. Veniaminof erupted. The eruption was characterized by numerous small ash emissions (VEI 0 to 1) and accompanied by low-frequency earthquake activity and volcanic tremor. We have performed spectral analyses of the seismic signals in order to characterize them and to constrain their source. Continuous tremor has durations of minutes to hours with dominant energy in the band 0.5– 4.0 Hz, and spectra characterized by narrow peaks either irregularly (non-harmonic tremor) or regularly spaced (harmonic tremor). The spectra of non-harmonic tremor resemble those of low-frequency events recorded simultaneously with surface ash explosions, suggesting that the source mechanisms might be similar or related. We propose that non-harmonic tremor at Mt. Veniaminof results from the coalescence of gas bubbles while low-frequency events are related to the disruption of large gas pockets within the conduit. Harmonic tremor, characterized by regular and quasisinusoidal waveforms, has duration of hours. Spectra containing up to five harmonics suggest the presence of a resonating source volume that vibrates in a longitudinal acoustic mode. An interesting feature of harmonic tremor is that frequency is observed to change over time; spectral lines move towards higher or lower values while the harmonic nature of the spectra is maintained. Factors controlling the variable characteristics of harmonic tremor include changes in acoustic velocity at the source and variations of the effective size of the resonator.

Alaska↗

USGS1969

Well logging with californium-252

Californium 252 is an isotopic neutron source that has only recently become available for experimental well logging. One curie of 252Cf emits 4.4 x 109 neutrons per second by spontaneous fission, 300 times the emission rate of any other one curie radioisotopic source. California 252 has several other advantages as a high yield source for well logging: very small physical size, low gamma and heat emission, and expected low cost relative to other sources. A 50-millicurie 252Cf source fabricated at the Savannah River Laboratory was made available by the U. S. Atomic Energy Commission to the U. S. Geological Survey for a feasibility study on well logging. The nuclear and physical characteristics of this source and some of the health physics aspects of its use in the field are discussed. The source was used to make epithermal neutron logs, which are compared with logs made with plutonium beryllium and americium beryllium sources in the same well. The high neutron flux available from 252Cf permitted the use of longer than usual spacing while maintaining a high count rate and excellent sensitivity. In addition, continuous activation logs were made utilizing a spacing of 5. 5 feet from the source to detector. Aluminum 28 was identified as the chief radioisotope contributing to the log response. This new technique may provide a log more closely related to clay content than the natural gamma log. Stationary irradiation experiments were also carried out in boreholes, and sodium 24 and manganese 56 were readily produced and identified. Suggestions for additional research on logging applications and problems resulted from this feasibility study. Potential well logging applications not investigated include the activation of temporary depth markers and the use of stable tracers that can be activated at the site or in the well. The high neutron yield of californium 252 will facilitate in situ activation analysis for many elements as an aid to exploration for oil, water, and other minerals.

Conference Paper↗

USGS1991

Modes of cross-shore sediment transport on the shoreface of the Middle Atlantic Bight

The mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3-year field study. The study was conducted in the southern part of the Middle Atlantic Bight in the depth region 7–17 m using instrumented tripods supporting electromagnetic current meters, pressure sensors, suspended sediment concentration sensors, and sonar altimeters. The observations embraced fairweather, moderate energy, swell-dominated, and storm conditions. Cross-shore mean flows ranged from near zero during fairweather to > 20 cm s −1 during the storm; oscillatory flows were on the order of 10 cm s −1 during fairweather and 100 cm s −1 during the storm. Suspended sediment concentrations at about 10 cm above the bed were < 0.1 kg m −3 under fairweather conditions, 1–2 kg m −3 under moderate swell conditions, and > 5 kg m −3 during the storm. Three methods were applied to evaluate the relative importance of incident waves, long-period oscillations, mean flows and gravity in effecting shoreward or seaward sediment flux: (1) an energetics transport model was applied to instantaneous near-bottom velocity data, (2) higher moments of near-bottom flows were estimated and compared, and (3) suspended sediment fluxes were estimated directly from the instantaneous products of cross-shore velocity and suspended sediment concentration. The results show that measurable contributions were made by all four of the processes. Most significantly, mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy. Incident waves were, in all cases, the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection. Low-frequency effects involving wave groups and long-period waves made secondary contributions to cross-shore sediment flux. Contrary to expectations, low-frequency fluxes were just as often shoreward as seaward. Whereas cross-correlations between suspended sediment concentration and the instantaneous near-bottom current speed were high and in phase under storm conditions, they were weak and out of phase during fairweather conditions. This suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment.

Middle Atlantic Bight↗

USGS2004

Frequency and initiation of debris flows in Grand Canyon, Arizona

Debris flows from 740 tributaries transport sediment into the Colorado River in Grand Canyon, Arizona, creating rapids that control its longitudinal profile. Debris flows mostly occur when runoff triggers failures in colluvium by a process termed “the fire hose effect.” Debris flows originate from a limited number of geologic strata, almost exclusively shales or other clay‐rich, fine‐grained formations. Observations from 1984 through 2003 provide a 20 year record of all debris flows that reached the Colorado River in Grand Canyon, and repeat photography provides a 100 year record of debris flows from 147 tributaries. Observed frequencies are 5.1 events/year from 1984 to 2003, and historic frequencies are 5.0 events/year from 1890 to 1983. Logistic regression is used to model historic frequencies based on drainage basin parameters observed to control debris flow initiation and transport. From 5 to 7 of the 16 parameters evaluated are statistically significant, including drainage area, basin relief, and the height of and gradient below debris flow source areas, variables which reflect transport distance and potential energy. The aspect of the river channel, which at least partially reflects storm movement within the canyon, is also significant. Model results are used to calculate the probability of debris flow occurrence at the river over a century for all 740 tributaries. Owing to the variability of underlying geomorphic controls, the distribution of this probability is not uniform among tributaries of the Colorado River in Grand Canyon.

Arizona↗

USGS1979

In situ determination of heat flow in unconsolidated sediments

Subsurface thermal measurements are the most effective, least ambiguous tools for identifying and delineating possible geothernml resources. Measurements of thermal gradient in the upper few tens of meters generally are sufficient to outline the major anomalies, but it is always desirable to combine these gradients with reliable estimates of thermal conductivity to provide data on the energy flux and to constrain models for the heat sources responsible for the observed, near-surface thermal anomalies. The major problems associated with heat-flow measurements in the geothermal exploration mode are concerned with the economics of casing and/or grouting holes, the repeated site visits necessary to obtain equilibrium temperature values, the possible legal liability associated with the disturbance of underground aquifers, the surface hazards presented by pipes protruding from the ground, and the security problems associated with leaving cased holes open for periods of weeks to months. We have developed a technique which provides reliable 'real-time' determinations of temperature, thermal conductivity, and hence, of heat flow during the drilling operation in unconsolidated sediments. A combined temperature, gradient, and thermal conductivity experiment can be carried out, by driving a thin probe through the bit about 1.5 meters into the formation in the time that would otherwise be required for a coring trip. Two or three such experiments over the depth range of, say, 50 to 150 meters provide a high-quality heat-flow determination at costs comparable to those associated with a standard cased 'gradient hole' to comparable depths. The hole can be backfilled and abandoned upon cessation of drilling, thereby eliminating the need for casing, grouting, or repeated site visits.

Open-File Report↗

USGS1997

One minute after: Strong-motion map, effective epicenter, and effective magnitude

This article reports the recent progress on real-time seismic monitoring in Taiwan, particularly the real-time strong-motion monitoring by the Taiwan Central Weather Bureau's telemetered seismic network ( CWBSN ), which is presently aiming at rapid reporting immediately after a large earthquake occurrence. If rapid reporting can be achieved before the arrival of the strong shaking, earthquake early warning will become possible. CWBSN has achieved the generation of the intensity map, epicenter, and magnitude within 1 min of the occurrence of a large earthquake. Both rapid reporting and early warning are principally applied to large ( M ≫ 5) events; the requirement of on-scale waveform recording prompted CWBSN in 1995 to integrate strong-motion sensors (e.g., force-balance accelerometers) into its telemetered seismic monitoring system. Time-domain recursive processing is applied to the multi-channel incoming seismic signals by a group of networked personal computers to generate the intensity map. From the isoseismal contours, an effective epicenter is immediately identified that resides in the middle of the largest (usually the 100-gal) contour curve of the intensity map. An effective magnitude is also defined that can be derived immediately from the surface area covered by the largest (usually the 100-gal) contour curve. For a large event with a finite rupture surface, the epicenter and magnitude so derived are more adequate estimates of the source location and of the strength of destruction. The effective epicenter gives the center of the damage area; it stands in contrast with the conventional epicenter location, which only gives the initial point of rupture nucleation. The effective magnitude reflects more closely the earthquake damage potential, instead of the classical magnitude definition that emphasizes the total energy release. The CWBSN has achieved in obtaining the above crucial source information well within 1 min. This time can further be reduced to better than 30 sec, as illustrated by the example in this article, showing that earthquake early warning is indeed an achievable goal. The rapid reporting and early warning information is electronically transmitted to users to allow rapid response actions, with or without further human intervention.

Bulletin of the Seismological Society of America↗

USGS2017

Partitioning evapotranspiration into green and blue water sources in the conterminous United States

In this study, we combined two 1 km actual evapotranspiration datasets (ET), one obtained from a root zone water balance model and another from an energy balance model, to partition annual ET into green (rainfall-based) and blue (surface water/groundwater) sources. Time series maps of green water ET (GWET) and blue water ET (BWET) are produced for the conterminous United States (CONUS) over 2001–2015. Our results indicate that average green and blue water for all land cover types in CONUS accounts for nearly 70% and 30% of the total ET, respectively. The ET in the eastern US arises mostly from GWET, and in the western US, it is mostly BWET. Analysis of the BWET in the 16 irrigated areas in CONUS revealed interesting results. While the magnitude of the BWET gradually showed a decline from west to east, the increase in coefficient of variation from west to east confirmed greater use of supplemental irrigation in the central and eastern US. We also established relationships between different hydro-climatology zones and their blue water requirements. This study provides insights on the relative contributions and the spatiotemporal dynamics of GWET and BWET, which could lead to improved water resources management.

Scientific Reports↗

USGS2020

Near-fault velocity spectra from laboratory failures and their relation to natural ground motion

We compared near-fault velocity spectra recorded during laboratory experiments to that of natural earthquakes. We fractured crystalline rock samples at room temperature and intermediate confining pressure (50 MPa). Subsequent slip events were generated on the fracture surfaces under higher confinement (300 MPa). Velocity spectra from rock fracture resemble the inverse frequency (1/ f ) decay of natural earthquake velocity. This spectrum can be attributed to fault creation via seismic fracturing over a wide range of spatial scales. In contrast, subsequent slips on the rough fracture surfaces are depleted in high frequency energy and falloff approximately as 1/ f 2 . The 1/ f 2 spectrum is more consistent with a slider-block model obeying static-kinetic friction than a natural earthquake. The depleted high frequency content precludes the rough fault experiments from being directly analogous to natural sources. The suppression of high frequencies may have resulted from two possible factors: (1) the presence of a well-developed shear zone and coseismic damping of the fault motion by dissipation within it or, in our favored interpretation, (2) a smaller amount of energy dissipated by shearing relative to the total energy release at elevated confining pressure. In context of the latter explanation, a unifying concept that applies to these experiments, earthquakes, ground motion, and models of complex radiated motion is that high frequency radiated energy is relatively enhanced when total energy release is nearly balanced within the source region by dissipative processes. This near-critical energy release condition can be accessed at low normal stress in laboratory experiments.

Journal of Geophysical Research↗

USGS2011

Undiscovered hydrocarbon resources in the U.S. Gulf Coast Jurassic Norphlet and Smackover Formations

The U.S. Geological Survey has completed assessments of undiscovered technically recoverable oil and gas resources in the Jurassic Norphlet and Smackover formations of the onshore coastal plain and State waters of the U.S. Gulf Coast. The Norphlet Formation consists of sandstones and interbedded shales and siltstones deposited during a marine transgression. Along its northeast margin, deposition of the Norphlet was in alluvial fans, fluvial systems, and dune and clastic sabkha environments. Mudstones of the underlying Smackover Formation act as source rocks for Norphlet reservoirs. The Norphlet was divided into the following three assessment units (AUs): the Norphlet Salt Basins and Updip AU, the Norphlet Mobile Bay Deep Gas AU, and the Norphlet South Texas Gas AU. The lower part of the Smackover consists primarily of dark carbonate mudstone and argillaceous limestone deposited in low-energy environments, and is one of the Gulf of Mexico Basin’s major source rocks. The upper part of the Smackover is comprised primarily of grain-supported carbonates deposited in high-energy environments. The Smackover was divided into the following four AUs: the Smackover Updip and Peripheral Fault Zone AU, the Smackover Salt Basin AU, the Smackover South Texas AU, and the Smackover Downdip Continuous Gas AU. Although the Norphlet and Smackover formations have been the focus of extensive exploration and production, they probably still contain significant undiscovered oil and gas resources.

Alabama, Louisiana, Mississippi, Texas↗

USGS2004

The global short-period wavefield modelled with a Monte Carlo seismic phonon method

At high frequencies (∼1 Hz), much of the seismic energy arriving at teleseismic distances is not found in the main phases (e.g. P , PP , S , etc.) but is contained in the extended coda that follows these arrivals. This coda results from scattering off small-scale velocity and density perturbations within the crust and mantle and contains valuable information regarding the depth dependence and strength of this heterogeneity as well as the relative importance of intrinsic versus scattering attenuation. Most analyses of seismic coda to date have concentrated on S -wave coda generated from lithospheric scattering for events recorded at local and regional distances. Here, we examine the globally averaged vertical-component, 1-Hz wavefield (>10° range) for earthquakes recorded in the IRIS FARM archive from 1990 to 1999. We apply an envelope-function stacking technique to image the average time–distance behavior of the wavefield for both shallow (≤50 km) and deep (≥500 km) earthquakes. Unlike regional records, our images are dominated by P and P coda owing to the large effect of attenuation on PP and S at high frequencies. Modelling our results is complicated by the need to include a variety of ray paths, the likely contributions of multiple scattering and the possible importance of P -to- S and S -to- P scattering. We adopt a stochastic, particle-based approach in which millions of seismic phonons are randomly sprayed from the source and tracked through the Earth. Each phonon represents an energy packet that travels along the appropriate ray path until it is affected by a discontinuity or a scatterer. Discontinuities are modelled by treating the energy normalized reflection and transmission coefficients as probabilities. Scattering probabilities and scattering angles are computed in a similar fashion, assuming random velocity and density perturbations characterized by an exponential autocorrelation function. Intrinsic attenuation is included by reducing the energy contained in each particle as an appropriate function of traveltime. We find that most scattering occurs in the lithosphere and upper mantle, as previous results have indicated, but that some lower-mantle scattering is likely also required. A model with 3 to 4 per cent rms velocity heterogeneity at 4-km scale length in the upper mantle and 0.5 per cent rms velocity heterogeneity at 8-km scale length in the lower mantle (with intrinsic attenuation of Q α = 450 above 200 km depth and Q α = 2500 below 200 km) provides a reasonable fit to both the shallow- and deep-earthquake observations, although many trade-offs exist between the scale length, depth extent and strength of the heterogeneity.

Geophysical Journal International↗

USGS2023

Introduction to the special section on seismoacoustics and seismoacoustic data fusion

A variety of geophysical hazards (e.g., volcanic activity, earthquakes, mass movements, marine storms, bolides) and anthropogenic sources (e.g., chemical and nuclear explosions, mining blasts, rocket launches) can release energy as mechanical waves in the ground, ocean, and atmosphere (Arrowsmith et al., 2010; Campus and Christie, 2009). Due to the mechanical coupling between a planetary body, its ocean, and its atmosphere, waves can propagate across these interfaces (Ben-Menahem and Singh, 1981) and carry information about the source and the media they propagated through. The field of seismoacoustics, driven by geophysical observations of both seismic and low-frequency acoustic (infrasound) waves, has several interdisciplinary applications. Observations of both seismic and infrasonic waves can be used to discriminate between atmospheric and subsurface events, such as sonic booms and earthquakes. Moreover, seismoacoustic analyses can provide useful information for the source characterization of shallow anthropogenic events, such as underground or surface explosions, volcanic, and tectonic events (e.g., Arrowsmith et al., 2020; Assink et al., 2016; de Groot-Hedlin and Hedlin, 2019; Matoza et al., 2009). Similarly, remote observations (e.g., on regional seismic and infrasonic arrays) can help monitor natural events such as volcanic eruptions and provide additional details about eruption dynamics. Recent works additionally suggest that infrasound can be used to discriminate between different volcanic processes (Watson et al., 2022). Finally, looking outwards, the study of seismo-acoustics has been a particularly valuable tool for planetary science (e.g., Krishnamoorthy et al., 2018; Martire et al., 2018; Krishnamoorthy et al., 2019; Martire et al., 2020; Garcia et al., 2020; Brissaud et al., 2021).

Bulletin of the Seismological Society of America↗

USGS2020

Relative toxicity and sublethal effects of NaCl and energy-related saline wastewaters on prairie amphibians

Increasing salinity in freshwater environments is a growing problem due both to the negative influences of salts on ecosystems and their accumulation and persistence in environments. Two major sources of increased salinity from sodium chloride salts (NaCl) are saline wastewaters co-produced during energy production (herein, wastewaters) and road salts. Effects of road salts have received more attention, but legacy contamination from wastewaters is widespread in some regions and spills still occur. Amphibians are sensitive to contaminants, including NaCl, because of their porous skin and osmoregulatory adaptations to freshwater. However, similarities and differences between effects of wastewaters and road salts have not been investigated. Therefore, we investigated the relative influence of wastewaters and NaCl at equivalent concentrations of chloride on three larval amphibian species that occur in areas with increased salinity. We determined acute toxicity and growth effects on Boreal Chorus Frogs ( Pseudacris maculata ), Northern Leopard Frogs ( Rana pipiens ), and Barred Tiger Salamanders ( Ambystoma mavortium ). We posited that wastewaters would have additive effects on amphibians compared to NaCl because wastewaters often have additional toxic heavy metals and other contaminants. For NaCl, toxicity was higher for frogs than the salamander. Toxicity of wastewaters was also similar between chorus and leopard frogs. Only chorus frog survival was lower when exposed to wastewater compared to NaCl. Mass and length of leopard and chorus frog larvae decreased with increasing salinity after only 96 hours of exposure but did not for tiger salamanders. Size of leopard frogs was lower when exposed to NaCl compared to wastewater. However, growth effects were similar between wastewater and NaCl for chorus frogs. Taken together, our results suggest that previous studies on effects of road salt could inform future studies and management of wastewater-contaminated ecosystems, and vice versa. Nevertheless, effects of road salts and wastewaters may be context-, species-, and trait-specific and require further investigations. The negative influence of salts on imperiled amphibians underscores the need to restore landscapes with increased salinity and reduce future salinization of freshwater ecosystems.

Aquatic Toxicology↗

USGS2015

Earthquake hypocenters and focal mechanisms in central Oklahoma reveal a complex system of reactivated subsurface strike-slip faulting

The sharp increase in seismicity over a broad region of central Oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure. Since early 2010, numerous organizations have deployed temporary portable seismic stations in central Oklahoma in order to record the evolving seismicity. In this study, we apply a multiple-event relocation method to produce a catalog of 3,639 central Oklahoma earthquakes from late 2009 through 2014. RMT source parameters were determined for 195 of the largest and best-recorded earthquakes. Combining RMT results with relocated seismicity enabled us to determine the length, depth and style-of-faulting occurring on reactivated subsurface fault systems. Results show that the majority of earthquakes occur on near vertical, optimally oriented (NE-SW and NW-SE), strike-slip faults in the shallow crystalline basement. These are necessary first order observations required to assess the potential hazards of individual faults in Oklahoma.

Oklahoma↗

USGS2019

Evidence of age-related improvement in the foraging efficiency of Adélie penguins

Age variation in reproductive performance is well-documented but the mechanisms underlying this variation remain unclear. Foraging efficiency is likely to be a key source of demographic variation as it determines the amount of energy that can be invested in fitness-related activities. Evidence of age-related changes in the foraging efficiency of adult seabirds is scarce and inconsistent. We investigated the effects of age on the foraging efficiency of breeding Adélie penguins, a relatively short-lived seabird species, in order to gain a broader perspective on the processes driving variation in ageing rates. We found support for a positive effect of age, either linear or levelling off at old ages, on both our proxies for daily catch rate and catch per unit effort. Across all age classes, males were more performant foragers than females. We found no strong evidence for differing ageing patterns between sexes or individual quality levels, and no evidence for senescence. We infer that continuous individual improvement could be responsible for a larger amount of the variation in foraging efficiency with age at our study site, compared with selective disappearance of underperforming phenotypes. The different results reported by other studies highlight the need to conduct longitudinal studies across a range of species in different environments.

Scientific Reports↗

USGS2020

The 1933 Long Beach Earthquake (California, USA): Ground motions and rupture scenario

We present a synoptic analysis of the ground motions from the 11 March 1933 Mw 6.4 Long Beach, California, earthquake, the largest known earthquake within the central Los Angeles Basin region. Our inferred shaking intensity pattern supports the association of the earthquake with the Newport-Inglewood fault; it further illuminates the concentration of severe damage in the town of Compton, where accounts suggest vertical ground motions exceeding 1 g . We use a broadband simulation approach to develop a rupture scenario for this earthquake, informed by the damage distribution. The predicted shaking for a 25-km-long fault matches the intensity distribution, with an indication that non-linear site response on soft sediments in some near-field regions was stronger than predicted using a simple model to account for non-linearity. Our results suggest that the concentration of damage near Compton can be explained by a combination of local site amplification, source-controlled directivity, and three-dimensional basin effects whereby energy was channeled towards the deepest part of the Los Angeles Basin.

California↗

USGS1998

Maps showing geology, oil and gas fields and geological provinces of Africa

The CD-ROM was compiled according to the methodology developed by the U.S. Geological Survey's World Energy Project . The goal of the project was to assess the undiscovered, technically recoverable oil and gas resources of the world and report these results by the year 2000. A worldwide series of geologic maps, published on CD-ROMs, was released by the U.S. Geological Survey's World Energy Project during 1997-2000. Specific details of the data sources and map compilation are given in the metadata files on this CD-ROM. These maps were compiled using Environmental Systems Research Institute Inc. (ESRI) ARC/INFO software. Political boundaries and cartographic representations on this map are shown (with permission) from ESRI's ArcWorld 1:3M digital coverage: they have no political significance and are displayed as general reference only. Portions of this database covering the coastline and country boundaries contain proprietary property of ESRI. (Copyright 1992 and 1996, Environmental Systems Research Institute Inc. All rights reserved.)

Open-File Report↗

USGS2002

Digital geologic and geophysical data of Bangladesh

This CD-ROM was compiled according to the methodology developed by the U.S. Geological Survey's World Energy Project . The goal of the project was to assess the undiscovered, technically recoverable oil and gas resources of the world and report these results by the year 2000. A worldwide series of geologic maps, published on CD-ROMs, was released by the U.S. Geological Survey's World Energy Project during 1997 - 2000. Specific details of the data sources and map compilation are given in the metadata files on this CD-ROM. These maps were compiled using Environmental Systems Research Institute Inc. (ESRI) ARC/INFO software. Political boundaries and cartographic representations on this map are with permission from ESRI's ArcWorld 1:3M digital coverage: they have no political significance and are displayed as general reference only. Portions of this database covering the coastline and country boundaries contain proprietary property of ESRI. (© 1992 and 1996, Environmental Systems Research Institute Inc. All rights reserved.)

Open-File Report↗

USGS1978

The Aleutian Basin, Bering Sea a frontier area for hydrocarbon exploration

The Aleutian Basin is the deep water (>3000 m) basin that lies north of the Aleutian Islands adjacent to the Bering Sea continental shelf. The basin, about the size of the state of Texas, is underlain by a 2-9 km-thick flat-lying sequence of mostly Cenozoic sediment and rock that includes diatomaceous silty clay interbedded with turbidities in the upper 1 km. Before 1974, geologic and geophysical investigations in the Aleutian Basin were directed at determining its geologic history; more recently, investigations have also been aimed at assessing the basin's hydrocarbon potential. The four major requirements for hydrocarbon accumulation may be present, namely, structural and stratigraphic traps, source rocks, reservoir beds, and an adequate thermal and sedimentation history. Energy resource investigations by the US Geological Survey indicate that: (1) numerous structural features (gentle folds, diapirs, basement ridges) are present in the central and eastern parts of the basin, (2) acoustic features (VAMP's _ Velocity AMPlitude features) that may be due to trapped gases within the sedimentary section are common (over 350 identified) in the central basin, (3) concentrations of organic gases, primarily methane, in the upper 1-3 m beneath the seafloor are very small, they increase with depth, and they are highest in areas near VAMP's, and (4) both the thermal gradient and the sediment thickness are sufficiently great to allow hydrocarbon maturation at depth, if source rocks are present. Adverse conditions in the Aleutian Basin such as excessive water depths and severe weather pose difficult technical problems for the recovery of hydrocarbons that may be present. The data nevertheless suggest the basin is a promising site for hydrocarbon accumulations and therefore warrants further exploration.

Conference Paper↗