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At least 451 records · Page 25Linked to original sources
USGS1977

Activity-product constants of brucite from 10 degrees to 90 degrees C

The activity-product constant of brucite, K B = [Mg 2+ ][OH - ] 2 (where the brackets denote activities), was determined experimentally at 10°, 25°, 40°, 55°, 70°, and 90°C. The values obtained for -log K B are 10.89±0.16 (10°), 10.88±0.10 (25°), 10.90±0.10 (40°), 10.90±0.10 (55°), 10.99±0.14 (70°), and 11.10±0.14 (90°). Using National Bureau of Standards Technical Note 270 data for the ions, the free energy of formation (Δ G ° t ) at 25° for brucite is 831.486 joules per mole ( 198,730 cal mol -1 ). Using data compiled by R. A. Robie and D. R. Waldbaum in 1968 for the ions, this Δ G ° t is -823,323 J mol -1 (-198,930 cal mol -1 ). Values of log KB are also calculated for the temperature range 0° to 200°C, by using thermochemical data listed by V. B. Parker, D. D. Wagman, and W. H. Evans in 1971 and E. G. King, M. J. Ferrante, and L. B. Pankratz in 1975 and the partial molal heat capacities estimated by C. M. Criss and J. W. Cobble in 1965. The experimental values are similar to the calculated values, especially at lower temperatures.

Journal of Research of the U.S. Geological Survey↗
USGS1999

Measurements of Reynolds stress profiles in unstratified tidal flow

In this paper we present a method for measuring profiles of turbulence quantities using a broadband acoustic doppler current profiler (ADCP). The method follows previous work on the continental shelf and extends the analysis to develop estimates of the errors associated with the estimation methods. ADCP data was collected in an unstratified channel and the results of the analysis are compared to theory. This comparison shows that the method provides an estimate of the Reynolds stresses, which is unbiased by Doppler noise, and an estimate of the turbulent kinetic energy (TKE) which is biased by an amount proportional to the Doppler noise. The noise in each of these quantities as well as the bias in the TKE match well with the theoretical values produced by the error analysis. The quantification of profiles of Reynolds stresses simultaneous with the measurement of mean velocity profiles allows for extensive analysis of the turbulence of the flow. In this paper, we examine the relation between the turbulence and the mean flow through the calculation of u * , the friction velocity, and C d the coefficient of drag. Finally, we calculate quantities of particular interest in turbulence modeling and analysis, the characteristic lengthscales, including a lengthscale which represents the stream-wise scale of the eddies which dominate the Reynolds stresses.

Journal of Geophysical Research C: Oceans↗
USGS2012

Uncovering the nonadiabatic response of geosynchronous electrons to geomagnetic disturbance

We describe an energy spectrum method for scaling electron integral flux, which is measured at a constant energy, to phase space density at a constant value of the first adiabatic invariant which removes much of the variation due to reversible adiabatic effects. Applying this method to nearly a solar cycle (1995 - 2006) of geosynchronous electron integral flux (E>2.0MeV) from the GOES satellites, we see that much of the diurnal variation in electron phase space density at constant energy can be removed by the transformation to phase space density at constant μ (4000 MeV/G). This allows us a clearer picture of underlying non-adiabatic electron population changes due to geomagnetic activity. Using scaled phase space density, we calculate the percentage of geomagnetic storms resulting in an increase, decrease or no change in geosynchronous electrons as 38%, 7%, and 55%, respectively. We also show examples of changes in the electron population that may be different than the unscaled fluxes alone suggest. These examples include sudden electron enhancements during storms which appear during the peak of negative Dst for μ-scaled phase space density, contrary to the slow increase seen during the recovery phase for unscaled phase space density for the same event.

Journal of Geophysical Research↗
USGS2022

Measurements of Geologic Characteristics and Geophysical Properties of Sediments From the New England Mud Patch

The characterization of physical, geological, and geophysical properties of sediments within the New England Mud Patch (NEMP) was undertaken to provide a physical basis for acoustic inversions associated with the SeaBed Characterization EXperiment 2017 (SBCEX17). Using a suite of 89 sediment cores (piston/trigger, gravity [acoustic], and vibracore), a comprehensive database of laboratory-based sediment analyses, geophysical core logs, and the results of seismic reflection profiling, we formulate a three-layer lithostratigraphic model of the area within and immediately adjacent to the SBCEX17 focus area, referred to as the seabed experiment area (SEA). The uppermost lithostratigraphic unit, Unit 1, is relatively homogenous clayey- to sandy silt, with consistent downcore textural, mineralogical, and physical property attributes. Unit 2 is a variable-thickness transitional layer between Unit 1 and Unit 3, whose properties reflect a decrease in proximal erosion and transition to a lower energy depositional environment. Unit 3 is clean quartz sand containing abundant shells and shell fragments that was regionally deposited during Holocene sea-level rise. 210 Pb and 14 C radiocarbon geochronologies spanning the past 13 000 years are used to facilitate intercore comparison across the SEA. Analytical results and laboratory methods used in the derivation of those results are described in detail, serving as a reference for ongoing and future investigation of the SEA and entire NEMP. Although the derived lithostratigraphic model of the SEA is in good agreement with past evaluations of the regional sedimentology, comparisons of the lithostratigraphic and seismostratigraphic models highlight several significant incompatibilities that remain to be satisfactorily explained.

IEEE Journal of Ocean Engineering↗
USGS2022

Maturation study of vitrinite in carbonaceous shales and coals: Insights from hydrous pyrolysis

The presence of vitrinite in sedimentary rocks of post-Silurian age allows its reflectance to be used to estimate the thermal maturation of organic matter in petroleum systems. Increasing reflectance of vitrinite, which is primarily driven by aromaticity, depends primarily on the time and temperature attributes of its evolutionary pathway. This study evaluated carbonaceous shales proximal to coal measures and coal samples via isothermal hydrous pyrolysis (HP) to compare differences in the maturation pathways of vitrinite. Sample residues were analysed via vitrinite reflectance (VRo), geochemical screening tests (organic carbon and programmed temperature pyrolysis), and infrared spectroscopy. The study included samples from Indian and North American basins, to observe differences in vitrinite evolution with respect to enclosing mineral matrix, starting degree of aromaticity, organic matter types, stratigraphic age, and depositional environment. The organic content of HP residues shows an intuitive response to the thermal stress of HP, e.g., a general depletion of total organic carbon (TOC) content, pyrolyzate (S2), and hydrogen index with increasing HP temperature. Infrared proxies including C-factor and CH2/CH3 generally decrease with increasing thermal maturity indicating loss of O via CO2 generation and the thermal cracking of aliphatic organic matter. Tmax, production index (PI), and VRo show intuitive increasing values with respect to HP temperature. The least mature sample (0.48 ± 0.05% VRo) generally experienced the maximum change in these parameters during maturation, whereas the most mature sample (0.99 ± 0.06% VRo) generally showed the least change. This observation is consistent with higher kinetic barriers to reaction in more aromatic vitrinite which contains higher bond dissociation energies. Devolatilization of vitrinite during HP causes formation of gas evacuation vacuoles and contraction cracks in the vitrinite grains of both coal and carbonaceous shale. Similarities in vitrinite response to HP between coal and carbonaceous shale suggest that thermal evolution of the vitrinite maceral is principally controlled by inherent rate-limiting kinetic parameters related to its molecular structure. Whereas, the stratigraphic age, sedimentary environment, surrounding organic matter, lithology, and catalysis by mineral composition have less effect. To further improve our understanding of vitrinite aromatization and kinetic parameters, future studies of vitrinite reflectance thermal evolution with temperature should include coal and carbonaceous shale from the same stratigraphic section and extant woody tissue from modern vascular plants.

International Journal of Coal Geology↗
USGS2025

Reaction kinetics and accelerant effects of sulfides in early mature hydrocarbon generation using hydrous pyrolysis

Hydrocarbon generation in organic-rich sediments is influenced by the molecular organic composition and relative abundance of associated minerals. Certain mineral-derived elements act as catalysts and reaction intermediaries, facilitating early-stage hydrocarbon formation in potential source rocks. This study investigated the role of sulfur contributed from pyrite as an accelerant in thermal reaction, focusing on its effects on early maturation and consequent hydrocarbon generation from gilsonite (low-sulfur solid petroleum). Hydrous pyrolysis (HP) experiments were conducted on mixtures of gilsonite and pyrite in varying ratios (1:0.1, 1:0.5, 1:1, 1:2, and 1:10 w/w gilsonite:pyrite) at 320, 350, and 370 °C for 72 h. Untreated and thermally altered residues were analyzed using solid bitumen reflectance (BR o , %), total organic carbon (TOC) content, programmed temperature pyrolysis, scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD) to evaluate the potential accelerant role of pyritic sulfur in hydrocarbon formation. The results show HP residues at 320 and 350 °C with greater pyrite concentrations had higher BR o , while reflectance values were similar in the 370 °C residues, regardless of pyrite concentration, suggesting enhanced reaction at lower thermal conditions. Increasing pyrite content systematically decreased hydrogen index (HI) values while increasing the transformation ratio (TR) and production index (PI), indicating enhanced conversion of organic matter to hydrocarbons with increasing pyrite concentrations. Gas yields increased with pyrite addition, particularly at 350 °C, confirming secondary cracking effects. However, gas production stabilized or declined at higher pyrite loadings (1:10), suggesting alternative reaction pathways such as coke formation. Our data indicate the presence of pyrite lowers the activation energy for thermal cracking, shifting peak experimental hydrocarbon generation temperatures downward by 20–30 °C, with the most pronounced accelerant effects observed at moderate pyrite concentrations (1:0.5 and 1:1). The thermodynamic framework reveals that pyrite stability is influenced by experimental conditions, with pyrrhotite formation favored in the presence of gilsonite due to reduced oxygen fugacity. Pyrite transformation to pyrrhotite, as observed through XRD, SEM-EDS, and predicted by thermodynamic data, further supports the accelerant role of S, as pyrrhotite exhibits a higher hydrogen transfer potential, promoting early oil generation. These findings highlight the importance of pyrite in modulating hydrocarbon generation pathways in organic-rich systems.

Journal of Analytical and Applied Pyrolysis↗
USGS2017

Surface morphology of caldera-forming eruption deposits revealed by lidar mapping of Crater Lake National Park, Oregon- Implications for emplacement and surface modification

Large explosive eruptions of silicic magma can produce widespread pumice fall, extensive ignimbrite sheets, and collapse calderas. The surfaces of voluminous ignimbrites are rarely preserved or documented because most terrestrial examples are heavily vegetated, or severely modified by post-depositional processes. Much research addresses the internal sedimentary characteristics, flow processes, and depositional mechanisms of ignimbrites, however, surface features of ignimbrites are less well documented and understood, except for comparatively small-volume deposits of historical eruptions. The ~7,700 calendar year B.P. climactic eruption of Mount Mazama, USA vented ~50 km3 of magma, deposited first as rhyodacite pumice fall and then as a zoned rhyodacite-to-andesite ignimbrite as Crater Lake caldera collapsed. Lidar collected during summer 2010 reveals the remarkably well-preserved surface of the Mazama ignimbrite and related deposits surrounding Crater Lake caldera in unprecedented detail despite forest cover. The ±1 m lateral and ±4 cm vertical resolution lidar allows surface morphologies to be classified. Surface morphologies are created by internal depositional processes and can point to the processes at work when pyroclastic flows come to rest. We describe nine surface features including furrow-ridge sets and wedge-shaped mounds in pumice fall eroded by high-energy pyroclastic surges, flow- parallel ridges that record the passage of multiple pyroclastic flows, perched benches of marginal deposits stranded by more-mobile pyroclastic-flow cores, hummocks of dense clasts interpreted as lag deposit, transverse ridges that mark the compression and imbrication of flows as they came to rest, scarps indicating ignimbrite remobilization, fields of pit craters caused by phreatic explosions, fractures and cracks caused by extensional processes resulting from ignimbrite volume loss, and stream channels eroded in the newly formed surface. The nine morphologies presented here illustrate a dynamic depositional environment that varied spatially and with time during the eruption, and show that multiple processes modified the ignimbrite after deposition, both during and after the eruption.

Oregon↗
USGS1999

The types of data needed for assessing the environmental and human health impacts of coal

Coal is one of the most important sources of energy. Its worldwide use will continue to expand during the next several decades, particularly in rapidly developing countries such as China and India. Unfortunately, coal use may bring with it environmental and human health costs. Many of the environmental and health problems attributed to coal combustion are due to mobilization of potentially toxic elements. Some of these problems could be minimized or even avoided if comprehensive databases containing appropriate coal quality information were available to decision makers so that informed decisions could be made regarding coal use. Among the coal quality parameters that should be included in these databases are: C, H, N, O, pyritic sulfur, organic sulfur, major, minor, and trace element concentrations, modes of occurrence of environmentally sensitive elements, cleanability, mineralogy, organic chemistry, petrography, and leachability.Coal is one of the most important sources of energy. Its worldwide use will continue to expand during the next several decades, particularly in rapidly developing countries such as China and India. Unfortunately, coal use may bring with it environmental and human health costs. Many of the environmental and health problems attributed to coal combustion are due to mobilization of potentially toxic elements. Some of these problems could be minimized or even avoided if comprehensive databases containing appropriate coal quality information were available to decision makers so that informed decisions could be made regarding coal use. Among the coal quality parameters that should be included in these databases are: C, H, N, O, pyritic sulfur, organic sulfur, major, minor, and trace element concentrations, modes of occurrence of environmentally sensitive elements, cleanability, mineralogy, organic chemistry, petrography, and leachability.

International Journal of Coal Geology↗
USGS1968

The relationship of geophysical measurements to engineering and construction parameters in the Straight Creek Tunnel pilot bore, Colorado

Seismic-refraction and electrical-resistivity measurements made along the walls of the Straight Creek Tunnel pilot bore indicate that both a low-velocity and a high-resistivity layer exist in the disturbed rock surrounding the excavation. Seismic measurements were analyzed to obtain the thickness and seismic velocity of rock in the low-velocity layer, the velocity of rock behind the layer and the amplitude of seismic energy received at the detectors. Electrical-resistivity measurements were analyzed to obtain the thickness and electrical resistivity of the high-resistivity layer and the resistivity of rock behind the layer. The electrical resistivity and the seismic velocity of rock at depth, the thickness of rock in the low-velocity layer, and the relative amplitude of seismic energy were correlated against the following parameters, all of which are important in tunnel construction: height of the tension arch, stable vertical rock load, rock quality, rate of construction and cost per foot, percentage of lagging and blocking, set spacing, and type and amount of steel support required, The correlations were statistically meaningful, having correlation coefficients ranging in absolute value from about 0·7 to nearly 1·0. This finding suggests the possibility of predicting parameters of interest in tunnel construction from geophysical measurements made in feeler holes drilled ahead of a working face. Predictions might be based on correlations established either during the early stages of construction or from geophysical surveys in other tunnels of similar design in similar geologic environments.

Colorado↗
USGS2004

Constraints of body size and swimming velocity on the ability of juvenile rainbow trout to endure periods without food

The hypothesis that body size and swimming velocity affect proximate body composition, wet mass and size-selective mortality of fasted fish was evaluated using small (107 mm mean total length, LT) and medium (168 mm mean LT) juvenile rainbow trout Oncorhynchus mykiss that were sedentary or swimming (c. 1 or 2 body lengths-1) and fasted for 147 days. The initial amount of energy reserves in the bodies of fish varied with L T. Initially having less lipid mass and relatively higher mass-specific metabolic rates caused small rainbow trout that were sedentary to die of starvation sooner and more frequently than medium-length fish that were sedentary. Swimming at 2 body length s-1 slightly increased the rate of lipid catabolism relative to 1 body length s-1, but did not increase the occurrence of mortality among medium fish. Death from starvation occurred when fish had <3.2% lipid remaining in their bodies. Juvenile rainbow trout endured long periods without food, but their ability to resist death from starvation was limited by their length and initial lipid reserves. ?? 2004 The Fisheries Society of the British Isles.

Journal of Fish Biology↗
USGS2004

Holocene reef accretion: southwest Molokai, Hawaii, U.S.A.

Two reef systems off south Molokai, Hale O Lono and Hikauhi (separated by only 10 km), show strong and fundamental differences in modern ecosystem structure and Holocene accretion history that reflect the influence of wave-induced near-bed shear stresses on reef development in Hawaii. Both sites are exposed to similar impacts from south, Kona, and trade-wind swell. However, the Hale O Lono site is exposed to north swell and the Hikuahi site is not. As a result, the reef at Hale O Lono records no late Holocene net accretion while the reef at Hikauhi records consistent and robust accretion over late Holocene time. Analysis and dating of 24 cores from Hale O Lono and Hikauhi reveal the presence of five major lithofacies that reflect paleo-environmental conditions. In order of decreasing depositional energy they are: (1) coral-algal bindstone; (2) mixed skeletal rudstone; (3) massive coral framestone; (4) unconsolidated floatstone; and (5) branching coral framestone-bafflestone. At Hale O Lono, 10 cores document a backstepping reef ranging from ∼ 8,100 cal yr BP (offshore) to ∼ 4,800 cal yr BP (nearshore). A depauperate community of modern coral diminishes shoreward and seaward of ∼ 15 m depth due to wave energy, disrupted recruitment activities, and physical abrasion. Evidence suggests a change from conditions conducive to accretion during the early Holocene to conditions detrimental to accretion in the late Holocene. Reef structure at Hikauhi, reconstructed from 14 cores, reveals a thick, rapidly accreting and young reef (maximum age ∼ 900 cal yr BP). Living coral cover on this reef increases seaward with distance from the reef crest but terminates at a depth of ∼ 20 m where the reef ends in a large sand field. The primary limitation on vertical reef growth is accommodation space under wave base, not recruitment activities or energy conditions. Interpretations of cored lithofacies suggest that modern reef growth on the southwest corner of Molokai, and by extension across Hawaii in general, is controlled by wave-induced near-bed shear stress related to refracted North Pacific swell. Holocene accretion patterns here also reflect the long-term influence of wave-induced near-bed shear stress from north swell during late Holocene time. This finding is consistent with other studies (e.g., Grigg 1998; Cabioch et al. 1999) that reflect the dominance of swell energy and sea level in controlling modern and late Holocene accretion elsewhere in Hawaii and across the Pacific and Indian oceans. Notably, however, this result is refined and clarified for Hawaii in the hypothesis of Rooney et al. (2003) stating that enhancement of the El Niño Southern Oscillation beginning approximately 5000 years ago led to increased north swell energy and signaled the end to net accretion along exposed coastlines in Hawaii. The exposure of Hale O Lono to north swell and the age of sea floor there (ca. 4,800 cal yr BP), coupled with the lack of north swell incidence at Hikauhi and the continuous accretion that has occurred there over the last millennium, strongly supports the ENSO reef hypothesis as outlined by Rooney et al. (2003). Other factors controlling Holocene reef accretion at the study site are relative sea-level position and rate of rise, and wave sheltering by Laau Point. Habitat suitable for reef accretion on the southwest shore of Molokai has shrunk throughout the Holocene.

Hawai'i↗
USGS2014

Geographic information system (GIS)-based maps of Appalachian basin oil and gas fields

One of the more recent maps of Appalachian basin oil and gas fields (and the adjoining Black Warrior basin) is the U.S. Geological Survey (USGS) compilation by Mast and others (1998) (see Trippi and others, this volume, chap. I.1). This map is part of a larger oil and gas field map for the conterminous United States that was derived by Mast and others (1998) from the Well History Control System (WHCS) database of Petroleum Information, Inc. (now IHS Energy Group). Rather than constructing the map from the approximately 500,000 proprietary wells in the Appalachian and Black Warrior part of the WHCS database, Mast and others (1998) subdivided the region into a grid of 1-mi 2 (square mile) cells and allocated an appropriate type of hydrocarbon production (oil production, gas production, oil and gas production, or explored but no production) to each cell. Each 1-mi 2 cell contains from 0 to 5 or more exploratory and (or) development wells. For example, if the wells in the 1-mi 2 cell consisted of three oil wells, one gas well, and one dry well, then the cell would be characterized on the map as an area of oil and gas production. The map by Mast and others (1998) accurately shows the distribution and types of hydrocarbon accumulation in the Appalachian and Black Warrior basins, but it does not show the names of individual fields. To determine the locality and name of individual oil and gas fields, one must refer to State oil and gas maps (for example, Harper and others, 1982), which are generally published at scales of 1:250,000 or 1:500,000 (see References Cited), and (or) published journal articles. Other recent USGS Appalachian basin oil and gas field maps show the distribution of oil and gas production with a cell size as small as 0.25 mi 2 , such as the maps converted by Trippi and others (this volume, chap. I.1) from proprietary well-location maps used in the USGS 2002 assessment of oil and gas resources of the Appalachian basin (Milici and others, 2003). Another set of Appalachian basin oil and gas cell maps (based on a cell size of 0.25 mi 2 ) was created for the USGS 1995 National Assessment of United States Oil and Gas Resources (Gautier and others, 1995; Beeman and others, 1996). Between 1991 and 1994, R.T. Ryder (with R.E. Mattick, J.B. Roen, and J.R. San Filipo, USGS, Reston, Va.) compiled oil and gas fields on stable-base mylar greenline base maps (scale 1:500,000) for selected plays in the Appalachian basin. These map compilations included field names and field numbers where assigned by State agencies. The purpose of the maps was to provide supporting data for the USGS 1995 National Assessment of United States Oil and Gas Resources (Gautier and others, 1995). In particular, the greenline oil and gas field maps were linked, where possible, with production data from State records and (or) published literature in order to determine ultimate sizes for conventional fields and estimated ultimate recovery (EUR) values for wells in continuous accumulations (for definitions of the conventional and continuous terminology, see USGS National Oil and Gas Assessment Team, 1995; Schmoker, 1997; Schenk and Pollastro, 2002). This approach was used in the 1995 national oil and gas assessment because ultimate field size and EUR data were unavailable in the Appalachian region from Petroleum Information, Inc., and other commercial sources. In 2006 and 2007, the greenline Appalachian basin field maps were digitized under the supervision of Scott Kinney and converted to geographic information system (GIS) files for chapter I.1 (this volume). By converting these oil and gas field maps to a digital format and maintaining the field names where noted, they are now available for a variety of oil and gas and possibly carbon-dioxide sequestration projects. Having historical names assigned to known digitized conventional fields provides a convenient classification scheme into which cumulative production and ultimate field-size databases can be organized. Moreover, as exploratory and development drilling expands across the basin, many previously named fields that were originally treated as conventional fields have evolved into large, commonly unnamed continuous-type accumulations. These new digital maps will facilitate a comparison between EUR values from recently drilled, unnamed parts of continuous accumulations and EUR values from named fields discovered early during the exploration cycle of continuous accumulations.

Appalachian basin↗
USGS2018

Hydrodynamics and sediment mobility processes over a degraded senile coral reef

Coral reefs can influence hydrodynamics and morphodynamics by dissipating and refracting incident wave energy, modifying circulation patterns, and altering sediment transport pathways. In this study, the sediment and hydrodynamic response of a senile (dead) barrier reef (Crocker Reef, located in the upper portion of the Florida Reef Tract) to storms and quiescent conditions was evaluated using field observations and the Coupled Ocean-Atmosphere-Wave-Sediment Transport model. Waves, circulation, and resultant sediment mobility were modeled across different reef zones. Sediment mobility during quiescent periods and the passage of far-field storms are driven by nonbreaking waves and, to a lesser degree, regional circulation. Spatial variability in these processes produces the present-day distribution of sediment grain size at Crocker Reef, wherein finer-grain material along a shallow central ridge is frequently mobilized (43% to 62% of the time), winnowed away, and deposited along the lower-energy flanks and in the fore reef where sand mobility occurs less frequently (32% to 43% and 1% to 22% of the time, respectively). Analysis of wave conditions for the period of 2006–2014 supports that wave heights rarely exceed the threshold for breaking (0.1% and 0.3% at the reef crest and at the reef flat, respectively), predominantly during the passage of tropical storms. There is a shift to a wave-breaking regime during near-field storms, creating the potential for mobilization of larger material and enhanced reef degradation. Sediment mobility can be enhanced due to wave skewness or the generation of free infragravity waves during periods of depth-induced wave breaking.

Florida↗
USGS2016

Reaction softening by dissolution–precipitation creep in a retrograde greenschist facies ductile shear zone, New Hampshire, USA

We describe strain localization by a mixed process of reaction and microstructural softening in a lower greenschist facies ductile fault zone that transposes and replaces middle to upper amphibolite facies fabrics and mineral assemblages in the host schist of the Littleton Formation near Claremont, New Hampshire. Here, Na-poor muscovite and chlorite progressively replace first staurolite, then garnet, and finally biotite porphyroblasts as the core of the fault zone is approached. Across the transect, higher grade fabric-forming Na-rich muscovite is also progressively replaced by fabric-forming Na-poor muscovite. The mineralogy of the new phyllonitic fault-rock produced is dominated by Na-poor muscovite and chlorite together with late albite porphyroblasts. The replacement of the amphibolite facies porphyroblasts by muscovite and chlorite is pseudomorphic in some samples and shows that the chemical metastability of the porphyroblasts is sufficient to drive replacement. In contrast, element mapping shows that fabric-forming Na-rich muscovite is selectively replaced at high-strain microstructural sites, indicating that strain energy played an important role in activating the dissolution of the compositionally metastable muscovite. The replacement of strong, high-grade porphyroblasts by weaker Na-poor muscovite and chlorite constitutes reaction softening. The crystallization of parallel and contiguous mica in the retrograde foliation at the expense of the earlier and locally crenulated Na-rich muscovite-defined foliation destroys not only the metastable high-grade mineralogy, but also its stronger geometry. This process constitutes both reaction and microstructural softening. The deformation mechanism here was thus one of dissolution–precipitation creep, activated at considerably lower stresses than might be predicted in quartzofeldspathic rocks at the same lower greenschist facies conditions.

New Hampshire↗
USGS2006

Tectonic stressing in California modeled from GPS observations

What happens in the crust as a result of geodetically observed secular motions? In this paper we find out by distorting a finite element model of California using GPS-derived displacements. A complex model was constructed using spatially varying crustal thickness, geothermal gradient, topography, and creeping faults. GPS velocity observations were interpolated and extrapolated across the model and boundary condition areas, and the model was loaded according to 5-year displacements. Results map highest differential stressing rates in a 200-km-wide band along the Pacific-North American plate boundary, coinciding with regions of greatest seismic energy release. Away from the plate boundary, GPS-derived crustal strain reduces modeled differential stress in some places, suggesting that some crustal motions are related to topographic collapse. Calculated stressing rates can be resolved onto fault planes: useful for addressing fault interactions and necessary for calculating earthquake advances or delays. As an example, I examine seismic quiescence on the Garlock fault despite a calculated minimum 0.1-0.4 MPa static stress increase from the 1857 M???7.8 Fort Tejon earthquake. Results from finite element modeling show very low to negative secular Coulomb stress growth on the Garlock fault, suggesting that the stress state may have been too low for large earthquake triggering. Thus the Garlock fault may only be stressed by San Andreas fault slip, a loading pattern that could explain its erratic rupture history.

Journal of Geophysical Research B: Solid Earth↗
USGS2009

Evaluation of airborne lidar data to predict vegetation Presence/Absence

This study evaluates the capabilities of the Experimental Advanced Airborne Research Lidar (EAARL) in delineating vegetation assemblages in Jean Lafitte National Park, Louisiana. Five-meter-resolution grids of bare earth, canopy height, canopy-reflection ratio, and height of median energy were derived from EAARL data acquired in September 2006. Ground-truth data were collected along transects to assess species composition, canopy cover, and ground cover. To decide which model is more accurate, comparisons of general linear models and generalized additive models were conducted using conventional evaluation methods (i.e., sensitivity, specificity, Kappa statistics, and area under the curve) and two new indexes, net reclassification improvement and integrated discrimination improvement. Generalized additive models were superior to general linear models in modeling presence/absence in training vegetation categories, but no statistically significant differences between the two models were achieved in determining the classification accuracy at validation locations using conventional evaluation methods, although statistically significant improvements in net reclassifications were observed. ?? 2009 Coastal Education and Research Foundation.

Journal of Coastal Research↗
USGS2000

Bottom currents and sediment transport in Long Island Sound: A modeling study

A high resolution (300-400 m grid spacing), process oriented modeling study was undertaken to elucidate the physical processes affecting the characteristics and distribution of sea-floor sedimentary environments in Long Island Sound. Simulations using idealized forcing and high-resolution bathymetry were performed using a three-dimensional circulation model ECOM (Blumberg and Mellor, 1987) and a stationary shallow water wave model HISWA (Holthuijsen et al., 1989). The relative contributions of tide-, density-, wind- and wave-driven bottom currents are assessed and related to observed characteristics of the sea-floor environments, and simple bedload sediment transport simulations are performed. The fine grid spacing allows features with scales of several kilometers to be resolved. The simulations clearly show physical processes that affect the observed sea-floor characteristics at both regional and local scales. Simulations of near-bottom tidal currents reveal a strong gradient in the funnel-shaped eastern part of the Sound, which parallels an observed gradient in sedimentary environments from erosion or nondeposition, through bedload transport and sediment sorting, to fine-grained deposition. A simulation of estuarine flow driven by the along-axis gradient in salinity shows generally westward bottom currents of 2-4 cm/s that are locally enhanced to 6-8 cm/s along the axial depression of the Sound. Bottom wind-driven currents flow downwind along the shallow margins of the basin, but flow against the wind in the deeper regions. These bottom flows (in opposition to the wind) are strongest in the axial depression and add to the estuarine flow when winds are from the west. The combination of enhanced bottom currents due to both estuarine circulation and the prevailing westerly winds provide an explanation for the relatively coarse sediments found along parts of the axial depression. Climatological simulations of wave-driven bottom currents show that frequent high-energy events occur along the shallow margins of the Sound, explaining the occurrence of relatively coarse sediments in these regions. Bedload sediment transport calculations show that the estuarine circulation coupled with the oscillatory tidal currents result in a net westward transport of sand in much of the eastern Sound. Local departures from this regional westward trend occur around topographic and shoreline irregularities, and there is strong predicted convergence of bedload transport over most of the large, linear sand ridges in the eastern Sound, providing a mechanism which prevents their decay. The strong correlation between the near-bottom current intensity based on the model results and the sediment response, as indicated by the distribution of sedimentary environments, provides a framework for predicting the long-term effects of anthropogenic activities.

New York↗
USGS2012

Refinements to the method of epicentral location based on surface waves from ambient seismic noise: introducing Love waves

The purpose of this study is to develop and test a modification to a previous method of regional seismic event location based on Empirical Green’s Functions (EGFs) produced from ambient seismic noise. Elastic EGFs between pairs of seismic stations are determined by cross-correlating long ambient noise time-series recorded at the two stations. The EGFs principally contain Rayleigh- and Love-wave energy on the vertical and transverse components, respectively, and we utilize these signals between about 5 and 12 s period. The previous method, based exclusively on Rayleigh waves, may yield biased epicentral locations for certain event types with hypocentral depths between 2 and 5 km. Here we present theoretical arguments that show how Love waves can be introduced to reduce or potentially eliminate the bias. We also present applications of Rayleigh- and Love-wave EGFs to locate 10 reference events in the western United States. The separate Rayleigh and Love epicentral locations and the joint locations using a combination of the two waves agree to within 1 km distance, on average, but confidence ellipses are smallest when both types of waves are used.

Geophysical Journal International↗