United States Geological Survey

About: United States Geological Survey is a government organization based out in Reston, Virginia, United States. It is known for research contribution in the topics: Population & Groundwater. The organization has 17899 authors who have published 51097 publications receiving 2479125 citations. The organization is also known as: USGS & US Geological Survey.

Physical properties of hydrate-bearing sediments

Abstract: [1] Methane gas hydrates, crystalline inclusion compounds formed from methane and water, are found in marine continental margin and permafrost sediments worldwide. This article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate-bearing sediments. Formation phenomena include pore-scale habit, solubility, spatial variability, and host sediment aggregate properties. Physical properties include thermal properties, permeability, electrical conductivity and permittivity, small-strain elastic P and S wave velocities, shear strength, and volume changes resulting from hydrate dissociation. The magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate-bearing sediments to changes in mechanical, thermal, or chemical boundary conditions. These predictions are vital for mitigating borehole, local, and regional slope stability hazards; optimizing recovery techniques for extracting methane from hydrate-bearing sediments or sequestering carbon dioxide in gas hydrate; and evaluating the role of gas hydrate in the global carbon cycle.

Relationships between peak ground acceleration, peak ground velocity, and Modified Mercalli Intensity in California

Abstract: We have developed regression relationships between Modified Mercalli Intensity (Imm) and peak ground acceleration (PGA) and velocity (PGV) by comparing horizontal peak ground motions to observed intensities for eight significant California earthquakes For the limited range of Modified Mercalli intensities (Imm), we find that for peak acceleration with V ≤ Imm ≤ VIII, Imm = 366 log(PGA) − 166, and for peak velocity with V ≤ Imm ≤ IX, Imm = 347 log(PGV) + 235 From comparison with observed intensity maps, we find that a combined regression based on peak velocity for intensity > VII and on peak acceleration for intensity < VII is most suitable for reproducing observed Imm patterns, consistent with high intensities being related to damage (proportional to ground velocity) and with lower intensities determined by felt accounts (most sensitive to higher‐frequency ground acceleration) These new Imm relationships are significantly different from the Trifunac and Brady (1975) correlations, which hav

Geologic map of the western equatorial region of mars

Abstract: Although the origin and composition of many units are obscure or controversial, their interpretations are based on objective descriptions of morphologic characteristics visible on Viking photomosaics and images. LOWLAND TERRAIN MATERIALS Consist of all plains-forming units between the highland-lowland boundary scarp and the north edge of the map area, exclusive of materials of the western volcanic assemblage on the Tharsis swell. Northern plains assemblage Materials deposited in widespread sheets on northern plains. Within each formation, members mapped at places on basis of crater density; these contacts are approximately located. Assemblage postdates highland-lowland boundary scarp (Scott, 1979). ARCADIA FORMATION—Forms low-lying plains in Arcadia, Amazonis, and Acidalia Planitiae. Embays highland margins and partly buries outflow channels of Kasei, Shalbatana, Simud, Tiu, and Ares Valles. Members distinguished on basis of morphology, albedo, and crater density; common boundaries of older members mapped arbitrarily at places. Flows with lobate margins and small hills with summit craters visible in many places. High-resolution pictures show that sources of some flows are small cratered cones. Interpretation: Mostly lava flows and small volcanoes Aa5 Member 5—Relatively small areal extent. Dark, fresh-appearing flows; few superposed impact craters. Type area: lat 47° N., long 30° Aa4 Member 4—In Arcadia Planitia underlies member 5 and has similar appearance; one other occurrence in channel system of Chryse Planitia. Type area: lat 45° N., long 175° Aa3 Member 3—Forms smooth plains west of Olympus Mons aureoles; embays both the aureoles and fractured terra of Acheron Fossae. Flow fronts visible in places. Type area: lat 15° N., long 155° Aa2 Member 2—Underlies members 3, 4, and 5 in Arcadia Planitia. Includes many small (<10-km-diameter) structures resembling volcanoes and cinder cones. Curved concentric ridges visible on surfaces of flows. Type area: lat 45° N., long 155° Aa1 Member l—Widespread in Chryse and Amazonis Planitiae. Mare-type (wrinkle) ridges common. Type area: lat 30° N., long 40° MEDUSAE FOSSAE FORMATION—Consists of extensive, relatively flat sheets, generally smooth to grooved and gently undulating; deposits appear to vary from soft to indurated; albedo moderate. Occurs near equator in western part of map area. Total thickness may exceed 3 km Amu Upper member—Discontinuous but widespread deposits extend from south of Olympus Mons westward across Amazonis Sulci to map boundary. Smooth, flat to rolling, light-colored surfaces; sculptured into ridges and grooves in places (as in Medusae Fossae); broadly curved margins, locally serrated. Type area: lat 0° N., long 160°. Interpretation: Nonwelded ash-flow …

The character of high-frequency strong ground motion

Abstract: Analysis of more than 300 horizontal components of ground acceleration written by the San Fernando earthquake, eight other moderate-to-large California earthquakes, and seven Oroville aftershocks reveal that these acceleration time histories are, to a very good approximation, band-limited white Gaussian noise within the S -wave arrival window; the band limitation is defined by the spectral corner frequency f 0 and f max , the highest frequency passed by the accelerograph or the Earth9s attenuation, and the S -wave arrival window is (0 ≦ t − R/β ≦ T d ), where R is distance, β is shear-wave velocity, and T d is the faulting duration. An examination of the root-mean-square acceleration ( a rms ) characteristics of these records for 0 ≦ t − R/β ≦ T d in terms of the relation a rms = 0.85 ( 2 π ) 106 2 Δ σ ϕ R f max f o where Δ σ is the earthquake stress drop, yields the surprising result that all 16 earthquakes have stress drops, as determined by record values of a rms , very nearly equal to 100 bars (within a factor of 2). The source dependence of a rms thus depends solely on the parameter 1 / f o , which increases only as the one-sixth power of seismic moment for constant stress drop earthquakes. Put another way, model and record a rms are in agreement within a factor of 2 approximately 85 per cent of the time for Δσ = 100 bars and knowledge of 1 / f o . On the basis that acceleration time histories are finite-duration, band-limited, white Gaussian noise, for any of which a rms is fixed by Δσ = 100 bars and 1 / f o , we can estimate the peak accelerations ( a max ) for all of these records with considerable accuracy (50 per cent or less). The relation is a max = a rms 2 In ( 2 f max f o ) , where a rms is defined above. With less accuracy, this relation fits the peak acceleration set of Hanks and Johnson (1976) as well, again with Δσ = 100 bars. At a fixed, close distance, we determine the magnitude dependence of a max to be log a max ∝ 0.30 M for 4 ≲ M = M L ≲ 6 1 2 , close to that recently determined empirically by Joyner and Boore (1981) for 5.0 ≦ M ≦ 7.7, their coefficient on M (moment magnitude) being 0.25 ± 0.04. In the model presented here, the magnitude dependence of peak acceleration is a function of faulting duration alone; larger earthquakes have larger peak accelerations because they last longer, not because they are intrinsically more powerful at the high frequencies controlling peak acceleration. These well-behaved characteristics of high-frequency strong ground motion also suggest that the stress differences which develop in the course of crustal faulting are comparably well behaved, both in the average stress release across the characteristic source dimension and in the spectral composition and distribution of stress differences that develop across smaller dimensions.

Endocrine control of osmoregulation in teleost fish

Abstract: As the primary link between environmental change and physiological response, the neuroendocrine system is a critical part of osmoregulatory adaptations. Cortisol has been viewed as ‘the’ seawater-adapting hormone in fish and prolactin as ‘the’ fresh water adapting hormone. Recent evidence indicates that the growth hormone/insulin-like growth factor I axis is also important in seawater adaptation in several teleosts of widely differing evolutionary lineages. In salmonids, growth hormone acts in synergy with cortisol to increase seawater tolerance, at least partly through the upregulation of gill cortisol receptors. Cortisol under some conditions may promote ion uptake and interacts with prolactin during acclimation to fresh water. The osmoregulatory actions of growth hormone and prolactin are antagonistic. In some species, thyroid hormones support the action of growth hormone and cortisol in promoting seawater acclimation. Although a broad generalization that holds for all teleosts is unlikely, our current understanding indicates that growth hormone promotes acclimation to seawater, prolactin promotes acclimation to fresh water, and cortisol interacts with both of these hormones thus having a dual osmoregulatory function.