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D. R. Hutchinson

Publications and source records attributed to D. R. Hutchinson.

At least 37 records · Page 2Linked to original sources
USGS1996

Seismic velocities for hydrate-bearing sediments using weighted equation

A weighted equation based on the three-phase time-average and Wood equations is applied to derive a relationship between the compressional wave (P wave) velocity and the amount of hydrates filling the pore space. The proposed theory predicts accurate P wave velocities of marine sediments in the porosity range of 40-80% and provides a practical means of estimating the amount of in situ hydrate using seismic velocity. The shear (S) wave velocity is derived under the assumption that the P to S wave velocity ratio of the hydrated sediments is proportional to the weighted average of the P to S wave velocity ratios of the constituent components of the sediment. In the case that all constituent components are known, a weighted equation using multiphase time-average and Wood equations is possible. However, this study showed that a three-phase equation with modified matrix velocity, compensated for the clay content, is sufficient to accurately predict the compressional wave velocities for the marine sediments. This theory was applied to the laboratory measurements of the P and S wave velocities in permafrost samples to infer the amount of ice in the unconsolidated sediment. The results are comparable to the results obtained by repeatedly applying the two-phase wave scattering theory. The theory predicts that the Poisson's ratio of the hydrated sediments decreases as the hydrate concentration increases and the porosity decreases. In consequence, the amplitude versus offset (AVO) data for the bottom-simulating reflections may reveal positive, negative, or no AVO anomalies depending on the concentration of hydrates in the sediments.

Journal of Geophysical Research B: Solid Earth↗
USGS1996

Amplitude blanking in seismic profiles from Lake Baikal

Imaging of the deepest sedimentary section in Lake Baikal using multichannel seismic profiling was hampered by amplitude blanking that is regionally extensive, is associated with water depths greater than about 900 m and occurs at sub-bottom depths of 1-2 km in association with the first water-bottom multiple. Application of a powerful multiple suppression technique improved the quality of occasional discontinuous, dipping primary reflections, but failed to substantially alter the non-reflective character of the blanking zone. Detailed analysis of amplitudes from original data and synthetic models show that the threshold for detecting primary energy in deep water of Lake Baikal occurs when the primary is about 14-20 dB less than the multiple energy. The blanking occurs because of anomalously low reflectivities of the deep sediments coupled with this 20 dB limitation in real data processing. The blanking cuts across seismic stratal boundaries, and is therefore probably unrelated to depositional lithologies. The deepest, early rift deposits, inferred to come from a mixed fluvial and lacustrine setting, do not easily explain the widespread and uniform character of the blanked deposits. More likely, blanking occurs because of processes or phenomena that physically alter the deposits, causing them to be non-reflective and/or highly attenuating. No single process explains all the observations, but a combination of diagenesis, overpressure, and the presence of dispersed free gas at sub-bottom depths of 1-2 km, offer plausible and possible conditions that contribute to blanking. Copyright ?? 1996 Published by Elsevier Science Ltd.

Marine and Petroleum Geology↗
USGS1995

Silurian tectonic history of Penobscot Bay region, Maine

Early Paleozoic amalgamation of composite terranes was contemporaneous at widely separated regions that were later accreted to either ancestral North America or to Gondwana as those two continents approached each other. Peri-Gondwanan terranes formed from Late Cambrian and Early Ordovician rocks were amalgamated in the Late Ordovician and Early Silurian to form the Salinic orogenic belt. Salinic orogenic activity involved extensive thrust faulting and metamorphism, large strike-slip faults, and plutonism. In the Penobscot Bay region, Maine, the peri-Gondwanan St. Croix terrane was thrust northwest in the Silurian(?) upon middle amphibolite facies Ordovician and Early Silurian rocks of the Fredericton trough. The strike-slip faults are interpreted to either remain steep until they reach the sole of the thrust sheet or to become listric within the thrust sheet. -from Authors

Maine↗
USGS1994

Seismic character of gas hydrates on the Southeastern U.S. continental margin

Gas hydrates are stable at relatively low temperature and high pressure conditions; thus large amounts of hydrates can exist in sediments within the upper several hundred meters below the sea floor. The existence of gas hydrates has been recognized and mapped mostly on the basis of high amplitude Bottom Simulating Reflections (BSRs) which indicate only that an acoustic contrast exists at the lower boundary of the region of gas hydrate stability. Other factors such as amplitude blanking and change in reflection characteristics in sediments where a BSR would be expected, which have not been investigated in detail, are also associated with hydrated sediments and potentially disclose more information about the nature of hydratecemented sediments and the amount of hydrate present. Our research effort has focused on a detailed analysis of multichannel seismic profiles in terms of reflection character, inferred distribution of free gas underneath the BSR, estimation of elastic parameters, and spatial variation of blanking. This study indicates that continuous-looking BSRs in seismic profiles are highly segmented in detail and that the free gas underneath the hydrated sediment probably occurs as patches of gas-filled sediment having variable thickness. We also present an elastic model for various types of sediments based on seismic inversion results. The BSR from sediments of high ratio of shear to compressional velocity, estimated as about 0.52, encased in sediments whose ratios are less than 0.35 is consistent with the interpretation of gasfilled sediments underneath hydrated sediments. This model contrasts with recent results in which the BSR is explained by increased concentrations of hydrate near the base of the hydrate stability field and no underlying free gas is required.

Marine Geophysical Research↗
USGS1993

Method of estimating the amount of in situ gas hydrates in deep marine sediments

The bulk volume of gas hydrates in marine sediments can be estimated by measuring interval velocities and amplitude blanking of hydrated zones from true amplitude processed multichannel seismic reflection data. In general, neither velocity nor amplitude information is adequate to independently estimate hydrate concentration. A method is proposed that uses amplitude blanking calibrated by interval velocity information to quantify hydrate concentrations in the Blake Ridge area of the US Atlantic continental margin. On the Blake Ridge, blanking occurs in conjunction with relatively low interval velocities. The model that best explains this relation linearly mixes two end-member sediments: hydrated and unhydrated sediment. Hydrate concentration in the hydrate end-member can be calculated from a weighted equation that uses velocity estimated from the seismic data, known properties of the pure hydrate, and porosity inferred from a velocity-porosity relationship. Amplitude blanking can be predicted as the proportions of hydrated and unhydrated sediment change across a reflection boundary. Our analysis of a small area near DSDP 533 indicates that the amount of gas hydrates is about 6% in total volume when the interval velocity is used as a criterion and about 9.5% when amplitude information is used. This compares with a calculated value of about 8% derived from the only available measurement in DSDP 533.

North Carolina, South Carolina↗
USGS1992

Depositional and tectonic framework of the rift basins of Lake Baikal from multichannel seismic data

Recent multichannel seismic reflection data from Lake Baikal, located in a large, active, continental rift in central Asia, image three major stratigraphic units totalling 3.5 to 7.5 km thick in four subbasins. A major change in rift deposition and faulting between the oldest and middle-rift units probably corresponds to the change from slow to fast rifting. A brief comparison of the basins of Lake Baikal with those of the East African rift system highlights differences in structural style that can be explained by differences in age and evolution of the surrounding basement rocks. -from Authors

Lake Baikal↗
USGS1992

A method of estimating the amount of in-situ gas hydrates in deep marine sediments

The bulk volume of gas hydrate in marine sediment can be estimated by measuring interval velocities and amplitude blanking of hydrated zones from true-amplitude processed multichannel seismic reflection data. In general, neither velocity nor amplitude information is adequate to independently estimate hydrate concentration. We propose a method that uses amplitude blanking calibrated by interval-velocity information to quantify hydrate concentrations in the Blake Ridge area of the U.S. Atlantic continental margin. On the Blake Ridge, blanking occurs in conjunction with relatively low interval velocities. The model that best explains this relation linearly mixes two end-member sediments, hydrated and unhydrated sediment. Hydrate concentration in the hydrate end-member can be calculated from a weighted equation that uses velocity estimated from the seismic data, known properties of pure hydrate, and porosity inferred from a velocity/porosity relationship. Amplitude blanking can be predicted as the proportions of hydrated and unhydrated sediment change across a reflection boundary. Our analysis of a small area near DSDP 533 indicates that the amount of gas hydrates is about 6% in total volume when interval velocity is used as a criterion and about 9.5% when amplitude information is used. This compares with a calculated value of about 8% derived from the only available measurement in DSDP 533.

Open-File Report↗
USGS1990

GLIMPCE Seismic reflection evidence of deep-crustal and upper-mantle intrusions and magmatic underplating associated with the Midcontinent Rift system of North America

Deep-crustal and Moho reflections, recorded on vertical incidence and wide angle ocean bottom Seismometer (OBS) data in the 1986 GLIMPCE (Great Lakes International Multidisciplinary Program on Crustal Evolution) experiment, provide evidence for magmatic underplating and intrusions within the lower crust and upper mantle contemporaneous with crustal extension in the Midcontinent Rift system at 1100 Ma. The rift fill consists of 20-30 km (7-10 s) of basalt flows, secondary syn-rift volcaniclastic and post-basalt sedimentary rock. Moho reflections recorded in Lake Superior over the Midcontinent Rift system have times from 14-18 s (about 46 km to as great as 58 km) in contrast to times of about 11-13 s (about 36-42 km crustal thickness) beneath the surrounding Great Lakes. The Seismically complex deep-crust to mantle transition zone (30-60 km) in north-central Lake Superior, which is 100 km wider than the rift half-graben, reflects the complicated products of tectonic and magmatic interaction of lower-crustal and mantle components during evolution or shutdown of the aborted Midcontinent Rift. In effect, mantle was changed into crust by lowering Seismic velocity (through intrusion of lower density magmatic rocks) and increasing Moho (about 8.1 km s-1 depth.

Great Lakes↗
USGS1989

Processing and attenuation of noise in deep seismic-reflection data from the Gulf of Maine

The U.S. Geological Survey deep crustal studies reflection profile across the Gulf of Maine off southeastern New England was affected by three sources of noise: side-scattered noise, multiples, and 20-Hz whale sounds. The special processing most effective in minimizing this noise consisted of a combination of frequency-wavenumber (F-K) filtering, predictive deconvolution, and spectral whitening, each applied in the shot domain (prestack). Application of the F-K filter to remove side-scatter noise in the poststack domain resulted in a much poorer quality profile. The prestack noise suppression processing techniques resulted in a reflection profile with good signal-to-noise ratios and reliable strong reflections, especially at depths equivalent to the lower crust (24-34 km). Certain geologic features, such as a buried rift basin and a crustal fault are resolved much better within the upper crust after this processing. Finite difference migration of these data using realistic velocities produced excellent results. Migration was essential to distinguish between abundant dipping and subhorizontal reflections in the lower crust as well as to show an essentially transparent upper mantle. ?? 1989 Kluwer Academic Publishers.

Marine Geophysical Research↗