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At least 631 records · Page 35Linked to original sources
USGS2018

Using geologic structures to constrain constitutive laws not accessible in the laboratory

In this essay, we explore a central problem of structural geology today, and in the foreseeable future, which is the determination of constitutive laws governing rock deformation to produce geologic structures. Although laboratory experiments provide much needed data and insights about constitutive laws, these experiments cannot cover the range of conditions and compositions relevant to the formation of geologic structures. We advocate that structural geologists address this limitation by interpreting natural experiments, documented with field and microstructural data, using continuum mechanical models that enable the deduction of constitutive laws. To put this procedure into a historical context, we review the founding of structural geology by James Hutton in the late 18th century, and the seminal contributions to continuum mechanics from Newton to Cauchy that provide the tools to model geologic structures. The procedure is illustrated with two examples drawn from recent and on-going field investigations of crustal and mantle lithologies . We conclude by pointing to future research opportunities that will engage structural geologists in the pursuit of constitutive laws during the 21st century.

Journal of Structural Geology↗
USGS2011

The use of historical imagery in the remediation of an urban hazardous waste site

The information derived from the interpretation of historical aerial photographs is perhaps the most basic multitemporal application of remote-sensing data. Aerial photographs dating back to the early 20th century can be extremely valuable sources of historical landscape activity. In this application, imagery from 1918 to 1927 provided a wealth of information about chemical weapons testing, storage, handling, and disposal of these hazardous materials. When analyzed by a trained photo-analyst, the 1918 aerial photographs resulted in 42 features of potential interest. When compared with current remedial activities and known areas of contamination, 33 of 42 or 78.5% of the features were spatially correlated with areas of known contamination or other remedial hazardous waste cleanup activity.

IEEE Journal of Selected Topics in Applied Earth O↗
USGS2024

Deformation-induced graphitization and muscovite recrystallization in a ductile fault zone

A suite of slate samples collected along a 2 km transect crossing the Lishan fault in central Taiwan were evaluated to assess the role of ductile deformation in natural graphitization at lower greenschist facies metamorphic conditions. The process of natural aromatization, or graphitization, of an organic precursor is well established as a thermally driven process; however, experimental studies have shown that the energy provided by deformation can substantially reduce the activation energy required for graphitization. This study provides a natural example of deformation-induced graphitization. A strain gradient approaching the Lishan fault was established by scanning electron microscope imaging and X-ray diffraction analysis of phyllosilicates and quartz that showed an increase in the strength of slaty cleavage development via dissolution-precipitation processes. Thermal conditions were constrained to be near isothermal using calcite-dolomite geothermometry. Raman spectroscopic results from carbonaceous material, including D1-full width-at-half-maximum (FWHM), G-FWHM, Raman band separation (RBS), and a lesser-known vibrational mode B 2g -FWHM, showed robust linear trends across the same sampling transect. However, the G-FWHM parameter showed a trend opposite of that expected from thermally driven graphitization. The Raman results are interpreted to reflect a strain-driven reduction in graphite crystallite size (decrease in G-FWHM) but improvement in structural ordering in individual coherent domains. A multiple linear regression with an R 2 value of 0.92 predicts the graphite D1-FWHM values from the XRD-derived ratio of muscovite populations and muscovite microstrain, demonstrating the concomitant recrystallization of silicates and carbonaceous material across the strain gradient, despite the disparate processes accommodating the deformation. This study demonstrates the role of deformation in natural graphitization and provides a new perspective on the use of graphite as a geothermometer in strongly deformed greenschist facies rocks.

Journal of Metamorphic Geology↗
USGS2012

Compositional variations on the Moon: Recalibration of Galileo solid‐state imaging data for the Orientale region and farside

Updated radiometric calibration and systematic processing procedures for Galileo solid‐state imaging (SSI) data from the first (1990) Earth‐Moon encounter are presented. These procedures were applied to a whole‐disk imaging sequence of the Moon centered near Mare Orientale, called Lunmap 14 (L14). Processing of L14 data included radiometric calibration, subpixel coregistration, scattered light removal, geometric control and reprojection, photometric normalization, and calibration to Earth‐based spectra. Coregistration and scattered‐light removal procedures are improvements over the initial calibration of the SSI mosaics. The effects of scattered light correction are best seen using a whole‐Moon view such as L14; resolution of the debated amounts of light scattering from within or outside the camera field of view is not necessary. Scattered light removal particularly affects the 1‐μm spectral region and has implications for interpretation of mafic mineral signatures in mare deposits of the lunar limb and farside. Recalibrated spectra indicate that mare ponds of the limb show moderately deep 1‐μm absorptions, and thus mafic mineral contents, comparable to those of other nearside basalts. Mafic mineral contents of Schiller‐Shickard cryptomaria are higher than previously thought and are similar to some low‐Ti nearside basalts. Many of the recalibrated spectra from South Pole/Aitken are similar to those of Schiller‐Schickard cryptomaria, suggesting that many of these soils represent a mixed mare/highland lithology. The hypothesis that there is an olivine enrichment in southern South Pole/Aitken basin is not supported strongly by spectra shown here.

Journal of Geophysical Research: Planets↗
USGS2012

Correlation of clayey gouge in a surface exposure of the San Andreas fault with gouge at depth from SAFOD: Implications for the role of serpentinite in fault mechanics

Magnesium-rich clayey gouge similar to that comprising the two actively creeping strands of the San Andreas Fault in drill core from the San Andreas Fault Observatory at Depth (SAFOD) has been identified in a nearby outcrop of serpentinite within the fault zone at Nelson Creek. Each occurrence of the gouge consists of porphyroclasts of serpentinite and sedimentary rocks dispersed in a fine-grained, foliated matrix of Mg-rich smectitic clays. The clay minerals in all three gouges are interpreted to be the product of fluid-assisted, shear-enhanced reactions between quartzofeldspathic wall rocks and serpentinite that was tectonically entrained in the fault from a source in the Coast Range Ophiolite. We infer that the gouge at Nelson Creek connects to one or both of the gouge zones in the SAFOD core, and that similar gouge may occur at depths in between. The special significance of the outcrop is that it preserves the early stages of mineral reactions that are greatly advanced at depth, and it confirms the involvement of serpentinite and the Mg-rich phyllosilicate minerals that replace it in promoting creep along the central San Andreas Fault.

California↗
USGS2007

Three-dimensional P wave velocity model for the San Francisco Bay region, California

[1] A new three-dimensional P wave velocity model for the greater San Francisco Bay region has been derived using the double-difference seismic tomography method, using data from about 5,500 chemical explosions or air gun blasts and approximately 6,000 earthquakes. The model region covers 140 km NE-SW by 240 km NW-SE, extending from 20 km south of Monterey to Santa Rosa and reaching from the Pacific coast to the edge of the Great Valley. Our model provides the first regional view of a number of basement highs that are imaged in the uppermost few kilometers of the model, and images a number of velocity anomaly lows associated with known Mesozoic and Cenozoic basins in the study area. High velocity ( V p > 6.5 km/s) features at ∼15-km depth beneath part of the edge of the Great Valley and along the San Francisco peninsula are interpreted as ophiolite bodies. The relocated earthquakes provide a clear picture of the geometry of the major faults in the region, illuminating fault dips that are generally consistent with previous studies. Ninety-five percent of the earthquakes have depths between 2.3 and 15.2 km, and the corresponding seismic velocities at the hypocenters range from 4.8 km/s (presumably corresponding to Franciscan basement or Mesozoic sedimentary rocks of the Great Valley Sequence) to 6.8 km/s. The top of the seismogenic zone is thus largely controlled by basement depth, but the base of the seismogenic zone is not restricted to seismic velocities of ≤6.3 km/s in this region, as had been previously proposed.

California↗
USGS2012

Hydrologic effects on water level changes associated with episodic fault creep near Parkfield, California

As part of the Parkfield, California, earthquake prediction experiment, water level is monitored in a well 460 m from the main trace of the San Andreas fault on Middle Mountain, in the preparation zone of the anticipated Parkfield earthquake. The well configuration allows water level to be monitored in two fluid reservoirs at depths of 85 and 250 m below land surface. During 1987, water level changes were recorded during 12 of the 18 episodes of accelerated fault creep detected by a creep meter spanning the fault trace 750 m northwest of the well. The creep-related water level changes in the shallow reservoir have durations of less than 1 day, whereas in the deeper reservoir the changes persist for as long as 2 months. These data suggest that the transient nature of the water level changes in the shallow interval is due to vertical flow to the water table and is not evidence that creep events propagate past the well. Phase leads of earth tidal constituents in the water level data from the shallow interval relative to the same constituents in the local volume strain tide support the interpretation of significant flow to the water table at periods of 1 day or less. The form of the water level changes in the deep interval is affected by horizontal flow to the well bore. This effect can be removed from the water level records using a theoretical response curve constrained by the phases of earth tidal constituents in the deep interval relative to the local volume strain tide. For the events where the signal in the shallow interval has been large enough to measure, the sizes of the simultaneous water level changes in the two reservoirs are consistent with the same amounts of volume strain occurring at both depths.

Journal of Geophysical Research Solid Earth↗
USGS2002

Proterozoic metamorphism and uplift history of the north-central Laramie Mountains, Wyoming, USA

The Laramie Mountains of south-eastern Wyoming contain two metamorphic domains that are separated by the 1.76 Ga. Laramie Peak shear zone (LPSZ). South of the LPSZ lies the Palmer Canyon block, where apatite U-Pb ages are c. 1745 Ma and the rocks have undergone Proterozoic kyanite-grade Barrovian metamorphism. In contrast, in the Laramie Peak block, north of the shear zone, the U-Pb apatite ages are 2.4-2.1 Ga, the granitic rocks are unmetamorphosed and supracrustal rocks record only low-T amphibolite facies metamorphism that is Archean in age. Peak mineral assemblages in the Palmer Canyon block include (a) quartz-biotite-plagioclase-garnet-staurolite-kyanite in the pelitic schists; (b) quartz-biotite-plagioclase-low-Ca amphiboles-kyanite in Mg-Al-rich schists, and locally (c) hornblende-plagioclase-garnet in amphibolites. All rock types show abundant textural evidence of decompression and retrograde re-equilibration. Notable among the texturally late minerals are cordierite and sapphirine, which occur in coronas around kyanite in Mg-Al-rich schists. Thermobarometry from texturally early and late assemblages for samples from different areas within the Palmer Canyon block define decompression from > 7 kbar to < 3 kbar. The high-pressure regional metamorphism is interpreted to be a response to thrusting associated with the Medicine Bow orogeny at c. 1.78-1.76 Ga. At this time, the north-central Laramie Range was tectonically thickened by as much as 12 km. This crustal thickening extended for more than 60 km north of the Cheyenne belt in southern Wyoming. Late in the orogenic cycle, rocks of the Palmer Canyon block were uplifted and unroofed as the result of transpression along the Laramie Peak shear zone to produce the widespread decompression textures. The Proterozoic tectonic history of the central Laramie Range is similar to exhumation that accompanied late-orogenic oblique convergence in many Phanerozoic orogenic belts.

Journal of Metamorphic Geology↗
USGS2022

One Health in action: Flea control and interpretative education at Badlands National Park

One Health involves interdisciplinary collaboration to improve, protect, and preserve the health of humans, wildlife, and ecosystems, and advocates for unified approaches to One Health challenges (Buttke et al. 2015). Here, we focus on a One Health challenge of nearly global distribution: Yersinia pestis , the flea-borne bacterial agent of plague. The bacterium poses a significant risk to humans and wildlife, causing social strife in some regions and transforming ecosystems (Eads and Biggins 2015). The conservation implications are profound in the western United States, where Y. pestis was first introduced in 1900. Considerable effort is devoted to plague mitigation, sometimes for human or wildlife health purposes separately. We present a synergy between plague mitigation for human and wildlife health.

South Dakota↗
USGS1977

Chemical variability in the Lakeview Mountains pluton, southern California batholith: A comparison of the methods of correspondence analysis and extended Q-mode factor analysis

An extended method of Q -mode factor analysis that has been described previously offers a number of important advantages over conventional Q -mode factor analysis and correspondence analysis when applied to compositional data. Among these are the ability to compute the compositions, in the original units of the data, represented by the reference axes. The only special requirement of the data is that the values for each observation sum to a constant. Mathematically derived reference axes, such as the principal-components and varimax axes, commonly represent compositions that are partly negative. Even where no negative values are present, these compositions are comparatively difficult to interpret in petrologic terms and impossible or inappropriate to include in petrogenetic models. A model has been developed for the Lakeview Mountains pluton which employs vectors representing the compositions of melanocratic schlieren, leucocratic schlieren, and inclusions as the reference axes. When the effect of the inclusions is removed, the compositional zoning in the pluton is like that found in otherwise similar plutons in the Sierra Nevada batholith. The genetic implication of the model is that the inclusions were separated from the magma at least in its marginal parts. In the central part of the pluton, the inclusions were either separated to a lesser extent than in the marginal parts, or were reincorporated into the magma.

California↗
USGS1977

Electrical soundings near Yellow Creek, Rio Blanco County, Colorado

Ten vertical electrical soundings were made in the Piceance Creek Basin in October 1974-5 along Yellow Creek, 2 in Big Duck Creek, and 1 each along Corral Gulch, on the hill in sec. 20, 1 kilometre northwest of 84 Ranch, and along the White River between the mouths of Yellow and Piceance Creeks. Interpretations of these soundings indicate that the anisotropy of the upper oil shales decreases from 2 in the basin center to 1 at a location on its flank. This decrease could result from a greater number of vertical water-filled fractures in the upper shales near the edge of the basin. On the other hand, the anisotropy coefficient for the lower shales increases from 2 to around 9 along the same section, indicating the presence of an increasing number of isolated horizontal aquifers in the lower shales on the basin flank. It is speculated that this trend for the lower shales reverses nearer the basin edge in the area of recharge of these splintered horizontal aquifers.

Colorado↗
USGS2014

Source and progression of a submarine landslide and tsunami: The 1964 Great Alaska earthquake at Valdez

Like many subduction zone earthquakes, the deadliest aspects of the 1964 M = 9.2 Alaska earthquake were the tsunamis it caused. The worst of these were generated by local submarine landslides induced by the earthquake. These caused high runups, engulfing several coastal towns in Prince William Sound. In this paper, we study one of these cases in detail, the Port Valdez submarine landslide and tsunami. We combine eyewitness reports, preserved film, and careful posttsunami surveys with new geophysical data to inform numerical models for landslide tsunami generation. We review the series of events as recorded at Valdez old town and then determine the corresponding subsurface events that led to the tsunami. We build digital elevation models of part of the pretsunami and posttsunami fjord‐head delta. Comparing them reveals a ~1500 m long region that receded 150 m to the east, which we interpret as the primary delta landslide source. Multibeam imagery and high‐resolution seismic reflection data identify a ~400 m wide chute with hummocky deposits at its terminus, which may define the primary slide path. Using these elements we run hydrodynamic models of the landslide‐driven tsunamis that match observations of current direction, maximum inundation, and wave height at Valdez old town. We speculate that failure conditions at the delta front may have been influenced by manmade changes in drainage patterns as well as the fast retreat of Valdez and other glaciers during the past century.

Alaska↗
USGS2013

Traces in the dark: sedimentary processes and facies gradients in the upper shale member of the Upper Devonian-Lower Mississippian Bakken Formation, Williston Basin, North Dakota, U.S.A.

Black, organic-rich rocks of the upper shale member of the Upper Devonian–Lower Mississippian Bakken Formation, a world-class petroleum source rock in the Williston Basin of the United States and Canada, contain a diverse suite of mudstone lithofacies that were deposited in distinct facies belts. The succession consists of three discrete facies associations (FAs). These comprise: 1) siliceous mudstones; 2) quartz- and carbonate-bearing, laminated mudstones; and 3) macrofossil-debris-bearing massive mudstones. These FAs were deposited in three facies belts that reflect proximal to distal relationships in this mudstone system. The macrofossil-debris-bearing massive mudstones (FA 3) occur in the proximal facies belt and contain erosion surfaces, some with overlying conodont and phosphate–lithoclast lag deposits, mudstones with abundant millimeter-scale siltstone laminae showing irregular lateral thickness changes, and shell debris. In the medial facies belt, quartz- and carbonate-bearing, laminated mudstones dominate, exhibiting sub-millimeter-thick siltstone layers with variable lateral thicknesses and localized mudstone ripples. In the distal siliceous mudstone facies belt, radiolarites, radiolarian-bearing mudstones, and quartz- and carbonate-bearing, laminated mudstones dominate. Overall, total organic carbon (TOC) contents range between about 3 and 10 wt %, with a general proximal to distal decrease in TOC content. Abundant evidence of bioturbation exists in all FAs, and the lithological and TOC variations are paralleled by changes in burrowing style and trace-fossil abundance. While two horizontal traces and two types of fecal strings are recognized in the proximal facies belt, only a single horizontal trace fossil and one type of fecal string characterize mudstones in the distal facies belt. Radiolarites intercalated into the most distal mudstones are devoid of traces and fecal strings. Bedload transport processes, likely caused by storm-induced turbidity currents, were active across all facies belts. Suspended sediment settling from near the ocean surface, however, most likely played a role in the deposition of some of the mudstones, and was probably responsible for deposition of the radiolarites. The distribution pattern of high-TOC sediments in proximal and lower-TOC deposits in some distal facies is interpreted as a function of higher accumulation rates during radiolarian depositional events leading to a decrease in suspension-derived organic carbon in radiolarite laminae. The presence of burrows in all FAs and nearly all facies in the upper Bakken shale member indicates that dysoxic conditions prevailed during its deposition. This study shows that in intracratonic high-TOC mudstone successions such as the upper Bakken shale member bed-load processes most likely dominated sedimentation, and conditions promoted a thriving infaunal benthic community. As such, deposition of the upper Bakken shale member through dynamic processes in an overall dysoxic environment represents an alternative to conventional anoxic depositional models for world-class source rocks.

North Dakota↗
USGS2017

Comparing measurement response and inverted results of electrical resistivity tomography instruments

In this investigation, we compare the results of electrical resistivity measurements made by six commercially available instruments on the same line of electrodes to determine if there are differences in the measured data or inverted results. These comparisons are important to determine whether measurements made between different instruments are consistent. We also degraded contact resistance on one quarter of the electrodes to study how each instrument responds to different electrical connection with the ground. We find that each instrument produced statistically similar apparent resistivity results, and that any conservative assessment of the final inverted resistivity models would result in a similar interpretation for each. We also note that inversions, as expected, are affected by measurement error weights. Increased measurement errors were most closely associated with degraded contact resistance in this set of experiments. In a separate test we recorded the full measured waveform for a single four-electrode array to show how poor electrode contact and instrument-specific recording settings can lead to systematic measurement errors. We find that it would be acceptable to use more than one instrument during an investigation with the expectation that the results would be comparable assuming contact resistance remained consistent.

Journal of Environmental & Engineering Geophysics↗
USGS1985

PROCEDURES FOR ACCURATE PRODUCTION OF COLOR IMAGES FROM SATELLITE OR AIRCRAFT MULTISPECTRAL DIGITAL DATA.

Because the display and interpretation of satellite and aircraft remote-sensing data make extensive use of color film products, accurate reproduction of the color images is important. To achieve accurate color reproduction, the exposure and chemical processing of the film must be monitored and controlled. By using a combination of sensitometry, densitometry, and transfer functions that control film response curves, all of the different steps in the making of film images can be monitored and controlled. Because a sensitometer produces a calibrated exposure, the resulting step wedge can be used to monitor the chemical processing of the film. Step wedges put on film by image recording machines provide a means of monitoring the film exposure and color balance of the machines.

Journal of Imaging Technology↗
USGS2007

Structure and composition of a watershed-scale sediment information network

A 'Watershed-Scale Sediment Information Network' (WaSSIN), designed to complement UNESCO's International Sedimentation Initiative, was endorsed as an initial project by the World Association for Sedimentation and Erosion Research. WaSSIN is to address global fluvial-sediment information needs through a network approach based on consistent protocols for the collection, analysis, and storage of fluvial-sediment and ancillary information at smaller spatial scales than those of the International Sedimentation Initiative. As a second step of implementation, it is proposed herein that the WaSSIN have a general structure of two components, (1) monitoring and data acquisition and (2) research. Monitoring is to be conducted in small watersheds, each of which has an established database for discharge of water and suspended sediment and possibly for bed load, bed material, and bed topography. Ideally, documented protocols have been used for collecting, analyzing, storing, and sharing the derivative data. The research component is to continue the collection and interpretation of data, to compare those data among candidate watersheds, and to determine gradients of fluxes and processes among the selected watersheds. To define gradients and evaluate processes, the initial watersheds will have several common attributes. Watersheds of the first group will be: (1) six to ten in number, (2) less than 1000 km2 in area, (3) generally in mid-latitudes of continents, and (4) of semiarid climate. Potential candidate watersheds presently include the Weany Creek Basin, northeastern Australia, the Zhi Fanggou catchment, northern China, the Eshtemoa Watershed, southern Israel, the Metsemotlhaba River Basin, Botswana, the Aiuaba Experimental Basin, Brazil, and the Walnut Gulch Experimental Watershed, southwestern United States.

International Journal of Sediment Research↗
USGS2017

Mapping tide-water glacier dynamics in east Greenland using landsat data

Landsat multispectral scanner and thematic mapper images were co-registered For the Kangerdlugssuaq Fjord region in East Greenland and were used to map glacier drainage-basin areas, changes in the positions of tide-water glacier termini and to estimate surface velocities of the larger tide-water glaciers. Statistics were compiled to document distance and area changes to glacier termini. The methodologies developed in this study are broadly applicable to the investigation of tide-water glaciers in other areas. The number of images available for consecutive years and the accuracy with which images are co-registered are key factors that influence the degree to which regional glacier dynamics can be characterized using remotely sensed data. Three domains of glacier state were interpreted: net increase in terminus area in the southern part of the study area, net loss of terminus area for glaciers in upper Kangerdlugssuaq Fjord and a slight loss of glacier terminus area northward from Ryberg Fjord. Local increases in the concentrations of drifting icebergs in the fjords coincide with the observed extension of glacier termini positions Ice-surface velocity estimates were derived for several glaciers using automated image cross-correlation techniques The velocity determined for Kangerdlugssuaq Gletscher is approximately 5.0 km a −1 and that for Kong Christian IV Gletscher is 0.9 km a −1 . The continuous presence of icebergs and brash ice in front of these glaciers indicates sustained rates of ice-front calving.

Journal of Glaciology↗
USGS1997

The Phanerozoic impact cratering rate: Evidence from the farside of the Moon

The relatively recent (<1 b.y.) flux of asteroids and comets forming large craters on the Earth and Moon may be accurately recorded by craters with bright rays on the Moon's farside. Many previously unknown farside rayed craters are clearly distinguished in the low-phase-angle images returned by the Clementine spacecraft. Some large rayed craters on the lunar nearside are probably significantly older than 1 Ga; rays remain visible over the maria due to compositional contrasts long after soils have reached optical maturity. Most of the farside crust has a more homogeneous composition and only immature rays are visible. The size-frequency distribution of farside rayed craters is similar to that measured for Eratosthenian craters (up to 3.2 b.y.) at diameters larger than 15 km. The areal density of farside rayed craters matches that of a corrected tabulation of nearside Copernican craters. Hence the presence of bright rays due to immature soils around large craters provides a consistent time-stratigraphic basis for defining the base of the Copernican System. The density of large craters less than ∼3.2 b.y. old is ∼3.2 times higher than that of large farside rayed craters alone. This observation can be interpreted in two ways: (1) the average cratering rate has been constant over the past 3.2 b.y. and the base of the Copernican is ∼1 Ga, or (2) the cratering rate has increased in recent geologic time and the base of the Copernican is less than 1 Ga. We favor the latter interpretation because the rays of Copernicus (800–850 m.y. old) appear to be very close to optical maturity, suggesting that the average Copernican cratering rate was ∼35% higher than the average Eratosthenian rate. Other lines of evidence for an increase in the Phanerozoic (545 Ga) cratering rate are (1) the densities of small craters superimposed on Copernicus and Apollo landing sites, (2) the rates estimated from well-dated terrestrial craters (≤120 m.y.) and from present-day astronomical observations, and (3) the Proterozoic rate suggested by the crater record of Australia. The hypothesis most consistent with several key observations is that the cratering rate has increased by ∼2x during the past ∼300 m.y‥

Journal of Geophysical Research E: Planets↗