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Physical properties of marine sediments

TL;DR: In this paper, it was shown that seafloor sediments that blanket the ocean floor are of widely varying thickness but seismic observations indicate that 200 to 400 meters in the Pacific and one kilometer in the Atlantic are fairly typical values for deep water.
Abstract: : The unconsolidated sediments that blanket the ocean floor are of widely varying thickness but seismic observations indicate that 200 to 400 meters in the Pacific and one kilometer in the Atlantic are fairly typical values for deep water. At present direct observation of these sediments is limited to such samples as may be recovered by dredging or coring operations, for drilling has been carried out only in the shallow waters of the coastal shelves. Knowledge of the physical properties of the great bulk of the sediments deeper than the few tens of feet reached by coring equipment is thus necessarily derived from geophysical observations.

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Journal ArticleDOI
TL;DR: In this article, it was shown that for small stresses (such as from a sound wave), water-saturated sediments respond elastically, and that the elastic equations of the Hookean model can be used to compute unmeasured elastic constants.
Abstract: This report includes discussions of elastic and viscoelastic models for water-saturated porous media, and measurements and computations of elastic constants including compressibility, incompressibility (bulk modulus), rigidity (shear modulus), Lame's constant, Poisson's ratio, density, and compressional- and shear-wave velocity. The sediments involved are from three major physiographic provinces in the North Pacific and adjacent areas: continental terrace (shelf and slope), abyssal plain (turbidite), and abyssal hill (pelagic). It is concluded that for small stresses (such as from a sound wave), water-saturated sediments respond elastically, and that the elastic equations of the Hookean model can be used to compute unmeasured elastic constants. However, to account for wave attenuation, the favored model is ‘nearly elastic,’ or linear viscoelastic. In this model the rigidity modulus μ and Lame's constant λ in the equations of elasticity, are replaced by complex Lame constants (μ + iμ′) and (λ + iλ′), which are independent of frequency; μ and λ represent elastic response (as in the Hookean model), and iμ′ and iλ′ represent damping of wave energy. This model implies that wave velocities and the specific dissipation function 1/Q are independent of frequency, and attenuation in decibels per unit length varies linearly with frequency in the range from a few hertz to the megahertz range. The components of the water-mineral system bulk modulus are porosity, the bulk modulus of pore water, an aggregate bulk modulus of mineral grains, and a bulk modulus of the structure, or frame, formed by the mineral grains. Good values of these components are available in the literature, except for the frame bulk modulus. A relationship between porosity and dynamic frame bulk modulus was established that allowed computation of a system bulk modulus that was used with measured values of density and compressional-wave velocity to compute other elastic constants. Some average laboratory values for common sediment types are given. The underlying methods of computation should apply to any water-saturated sediment. If this is so, values given in this paper predict elastic constants for the major sediment types.

332 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe version 2 of the 3D seismic velocity model of southern California developed by the Southern California Earthquake Center and designed to serve as a reference model for multidisciplinary research activities in the area.
Abstract: We describe Version 2 of the three-dimensional (3D) seismic velocity model of southern California developed by the Southern California Earthquake Center and designed to serve as a reference model for multidisciplinary research activities in the area. The model consists of detailed, rule-based representations of the major southern California basins (Los Angeles basin, Ventura basin, San Gabriel Valley, San Fernando Valley, Chino basin, San Bernardino Valley, and the Salton Trough), embedded in a 3D crust over a variable depth Moho. Outside of the basins, the model crust is based on regional tomographic results. The model Moho is represented by a surface with the depths determined by the receiver function technique. Shallow basin sediment velocities are constrained by geotechnical data. The model is implemented in a computer code that generates any specified 3D mesh of seismic velocity and density values. This parameterization is convenient to store, transfer, and update as new information and verification results become available.

296 citations


Cites methods from "Physical properties of marine sedim..."

  • ...(4) Other physical parameters are derived: density is found from VP using the relation of Nafe and Drake (1960); density is used to find Poisson’s ratio with the relation of Ludwig et al. (1970); VS is calculated from the P-wave velocity and Poisson’s ratio....

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Journal ArticleDOI
TL;DR: In this article, a 3D simulation of the Los Angeles basin was used to estimate the 3D response of the basin to nine different earthquake scenarios, including the 1994 Northridge earthquake.
Abstract: It is well established that sedimentary basins can significantly amplify earthquake ground motion. However, the amplification at any given site can vary with earthquake location. To account for basin response in probabilistic seismic hazard analysis, therefore, we need to know the average amplification and intrinsic variability (standard deviation) at each site, given all earthquakes of concern in the region. Due to a dearth of empirical ground-motion observations, theoretical simu- lations constitute our best hope of addressing this issue. Here, 0-0.5 Hz finite- difference, finite-fault simulations are used to estimate the three-dimensional (3D) response of the Los Angeles basin to nine different earthquake scenarios. Amplifi- cation is quantified as the peak velocity obtained from the 3D simulation divided by that predicted using a regional one-dimensional (1D) crustal model. Average ampli- fication factors are up to a factor of 4, with the values from individual scenarios typically differing by as much as a factor of 2.5. The average amplification correlates with basin depth, with values near unity at sites above sediments with thickness less than 2 km, and up to factors near 6 above the deepest (! 9 km) and steepest-dipping parts of the basin. There is also some indication that amplification factors are greater for events located farther from the basin edge. If the 3D amplification factors are divided by the 1D vertical SH-wave amplification below each site, they are lowered by up to a factor of 1.7. The duration of shaking in the 3D model is found to be longer, by up to more than 60 seconds, relative to the 1D basin response. The simu- lation of the 1994 Northridge earthquake reproduces recorded 0-0.5 Hz particle velocities relatively well, in particular at near-source stations. The synthetic and observed peak velocities agree within a factor of two and the log standard deviation of the residuals is 0.36. This is a reduction of 54% and 51% compared to the values obtained for the regional 1D model and a 1D model defined by the velocity and density profile below a site in the middle of the basin (DOW), respectively. This result suggests that long-period ground-motion estimation can be improved consid- erably by including the 3D basin structure. However, there are uncertainties con- cerning accuracy of the basin model, model resolution, the omission of material with shear velocities lower than 1 km/s, and the fact that only nine scenarios have been considered. Therefore, the amplification factors reported here should be used with caution until they can be further tested against observations. However, the results do serve as a guide to what should be expected, particularly with respect to increased amplification factors at sites located above the deeper parts of the basin.

267 citations


Cites methods from "Physical properties of marine sedim..."

  • ...The density is estimated from the P-wave velocity using the Nafe-Drake relation (Nafe and Drake, 1960)....

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Journal ArticleDOI
TL;DR: In this article, sound velocity, elasticity, and related properties of marine sediments from sedimentary environments associated with three major physiographic provinces in the North Pacific and adjacent areas: the continental terrace (shelf and slope), the deepwater abyssal plain (turbidite), and the abyssal hill (pelagic).
Abstract: This is the first of a series of reports on sound velocity, elasticity, and related properties of marine sediments from sedimentary environments associated with three major physiographic provinces in the North Pacific and adjacent areas: the continental terrace (shelf and slope), the deep-water abyssal plain (turbidite), and the abyssal hill (pelagic). The following properties are listed in tables and illustrated in diagrams that interrelate various properties: grain size (mean diameter, percentages of sand, silt, and clay), bulk density, density of mineral grains, porosity, sound velocity, velocity ratio (velocity in sediment/velocity in sea water), impedance, and density × (velocity)2. Values are given for each sediment type within each environment. Significant differences in the density and porosity of the environments studied are caused by mineralogy, size and shape of grains, and sediment structure; presence of diatoms and clay mineralogy are particularly important. General equations and diagrams relating density and porosity to velocity should be abandoned in favor of entry into diagrams or equations for a single environment; velocity is then predictable within 1 to 2 per cent in most environments. Mean grain size has one of the best empirical relationships with velocity, which permits derivation of useful data from size analyses of dried cores. Porosity and density are excellent indices by which to determine values of impedance and density × (velocity)2. There is no usable, empirical relationship between sound velocity and shear strength (cohesion) as measured in soil mechanics tests. No anisotropic velocity relationships were measured in surficial sediments, and none is predicted for the upper few hundred meters in sea-floor sediments.

237 citations

Journal ArticleDOI
TL;DR: A comprehensive review of ASC science was undertaken by an international group of scientists under the auspices of ICES, prompted by the growing need to classify and map marine ecosystems across a range of spatial scales in support of ecosystem-based science for ocean management.
Abstract: Anderson, J T, Holliday, D V, Kloser, R, Reid, D G, and Simard, Y 2008 Acoustic seabed classification: current practice and future directions - ICES Journal of Marine Science, 65: 1004-1011Acoustic remote sensing of the seabed using single-beam echosounders, multibeam echosounders, and sidescan sonars combined and individually are providing technological solutions to marine-habitat mapping initiatives We believe the science of acoustic seabed classification (ASC) is at its nascence A comprehensive review of ASC science was undertaken by an international group of scientists under the auspices of ICES The review was prompted by the growing need to classify and map marine ecosystems across a range of spatial scales in support of ecosystem-based science for ocean management A review of the theory of sound-scattering from seabeds emphasizes the variety of theoretical models currently in use and the ongoing evolution of our understanding Acoustic-signal conditioning and data quality assurance before classification using objective, repeatable procedures are important technical considerations where standardization of methods is only just beginning The issue of temporal and spatial scales is reviewed, with emphasis on matching observational scales to those of the natural world It is emphasized throughout that the seabed is not static but changes over multiple time-scales as a consequence of natural physical and biological processes A summary of existing commercial ASC systems provides an introduction to existing capabilities Verification (ground-truthing) methods are reviewed, emphasizing the difficulties of matching observational scales with acoustic-backscatter data Survey designs for ASC explore methods that extend beyond traditional oceanographic and fisheries survey techniques Finally, future directions for acoustic seabed classification science were identified in the key areas requiring immediate attention by the international scientific community

227 citations


Cites background from "Physical properties of marine sedim..."

  • ...The science of correlating acoustic properties to marine surficial sediments dates from the early use of marine acoustics (Nafe and Drake, 1964; Morris et al., 1978)....

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