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USGS2020

SPEAR: The next generation GFDL modeling system for seasonal to multidecadal prediction and projection

We document the development and simulation characteristics of the next generation modeling system for seasonal to decadal prediction and projection at the Geophysical Fluid Dynamics Laboratory (GFDL). SPEAR ( S eamless System for P rediction and EA rth System R esearch) is built from component models recently developed at GFDL—the AM4 atmosphere model, MOM6 ocean code, LM4 land model, and SIS2 sea ice model. The SPEAR models are specifically designed with attributes needed for a prediction model for seasonal to decadal time scales, including the ability to run large ensembles of simulations with available computational resources. For computational speed SPEAR uses a coarse ocean resolution of approximately 1.0° (with tropical refinement). SPEAR can use differing atmospheric horizontal resolutions ranging from 1° to 0.25°. The higher atmospheric resolution facilitates improved simulation of regional climate and extremes. SPEAR is built from the same components as the GFDL CM4 and ESM4 models but with design choices geared toward seasonal to multidecadal physical climate prediction and projection. We document simulation characteristics for the time mean climate, aspects of internal variability, and the response to both idealized and realistic radiative forcing change. We describe in greater detail one focus of the model development process that was motivated by the importance of the Southern Ocean to the global climate system. We present sensitivity tests that document the influence of the Antarctic surface heat budget on Southern Ocean ventilation and deep global ocean circulation. These findings were also useful in the development processes for the GFDL CM4 and ESM4 models.

Journal of Advances in Modeling Earth Systems↗

USGS1990

Textural development of clayey and quartzofeldspathic fault gouges relative to their sliding behavior

Many of the secondary fault structures developed during triaxial friction experiments have been generally correlated with the structures of natural fault zones. Therefore, any physical differences that can be found between laboratory samples that slide stably and those that show stick-slip motion may help to identify the cause of earthquakes. We have examined petrographically the run products of many triaxial friction experiments using clayey and quartzofeldspathic gouges, which comprise the principal types of natural fault gouge material. The examined samples were tested under a wide range of temperature, confining and fluid pressure, and velocity conditions. The clayey and quartzofeldspathic gouges show some textural differences, owing to their different mineral contents and grain sizes and shapes. In the clayey gouges, for example, a clay mineral fabric and kink band sets are commonly developed, whereas in the quartzofeldspathic gouges fracturing and crushing of the predominately quartz and feldspar grains are important processes. For both types of gouge, however, and whatever the pressure-temperature-velocity conditions of the experiments, the transition from stable sliding to stick-slip motion is correlated with: (i) a change from pervasive deformation of the gouge layer to localized slip in subsidiary shears; and (ii) an increase in the angle betweem the shears that crosscut the gouge layer (Riedel shears) and ones that form along the gouge-rock cylinder boundaries (boundary shears). This suggests that the localization of shear within a fault zone combined with relatively high Riedel-shear angles are somehow connected with earthquakes. Secondary fracture sets similar to Riedel shears have been identified at various scales in major strike-slip faults such as the San Andreas of the western United States (Wallace, 1973) and the Luhuo and Fuyun earthquake faults of China (Deng and Zhang, 1984; Deng et al. , 1986). The San Andreas also contains locked and creeping sections that correspond to the stick-slip and stably sliding experimental samples, respectively. We plan to study the physical structure of the San Andreas fault, to see if the experimentally observed differences related to sliding behavior can also be distinguished in the field.

Physics and Chemistry of the Earth↗

USGS2022

Complex magmatic-tectonic interactions during the 2020 Makushin Volcano, Alaska, earthquake swarm

On June 15, 2020, at 21:16 UTC, a locally-felt earthquake of magnitude 4.2 struck Unalaska Island, Alaska, ∼15 km west of the town of Unalaska and the large fishing port of Dutch Harbor. The event was followed by a M4.1 earthquake at 00:34 UTC and several M3+ aftershocks, initiating a prolific sequence with hundreds of earthquakes recorded into late December. The earthquakes all locate about 12 km southeast of the summit of Makushin Volcano at 7 to 10 km depth. To date, no eruptive activity or other surface changes have been observed at the volcano in webcam images, GPS or InSAR. Seismic bursts close to volcanoes are often associated with the onset of unrest that can lead to eruption. However, determining whether seismicity reflects magmatic rather than tectonic stresses is often challenging, although critical for hazard assessments and risk management strategies. To investigate the triggering mechanisms of the recent Makushin seismicity, we integrate information from space-time patterns of the earthquake hypocenters with their fault-plane solutions. We relocate the swarm events using double-difference relocation techniques and a 3D velocity model and find that the earthquakes, although they seem to follow two predominant orientations (NW-SE and SW-NE), do not show clear clustering into preferred alignments. Similarly, we do not observe pronounced migration in time and space. Fault-plane solutions (FPS) for all but one M2.5+ earthquakes have P-axis orientations consistent with subhorizontal NW-SE oriented regional maximum compression, whereas many of the lower-magnitude earthquakes have P-axes perpendicular to regional maximum compression. This provides evidence for the presence of a local stress field likely induced by magma intrusion. Results from Coulomb stress modeling are also consistent with dike inflation modulated by stresses induced by the M4+ earthquakes. The seismic swarm is thus likely linked to a superposition of driving stresses from both magmatic and tectonic processes on pre-existing faults. The case of the 2020 Makushin swarm, with its unusual characteristics, challenges traditional swarm classification schemes and suggests that a reconsideration of the definition of seismic swarms as having the maximum magnitude event in the middle of the swarm is warranted.

Alaska↗

USGS2002

Cordilleran-margin quartzites in Baja California – implications for tectonic transport

One of the current controversies in Cordilleran tectonics concerns the position of Baja California prior to ∼300 km of opening of the Gulf of California. Geologic arguments, together with paleomagnetic results from Lower Cretaceous volcanic rocks, suggest that the rocks of the Baja Peninsula formed and evolved along the coast of northwestern Mexico prior to opening of the Gulf. In contrast, paleomagnetic data from Cretaceous–early Tertiary plutonic rocks and clastic strata have been interpreted by some workers to suggest that Baja was located near southern Mexico at approximately 80 Ma. The presence of similar detrital zircon ages in lower Paleozoic quartzites of northeast Baja and in lower Paleozoic strata east of the Gulf, in northwestern Mexico and southwestern US, provides strong support for the northern paleoposition, suggesting that Baja has been transported northward by only ∼300 km

Earth and Planetary Science Letters↗

USGS2004

Early Tertiary Anaconda metamorphic core complex, southwestern Montana

A sinuous zone of gently southeast-dipping low-angle Tertiary normal faults is exposed for 100 km along the eastern margins of the Anaconda and Flint Creek ranges in southwest Montana. Faults in the zone variously place Mesoproterozoic through Paleozoic sedimentary rocks on younger Tertiary granitic rocks or on sedimentary rocks older than the overlying detached rocks. Lower plate rocks are lineated and mylonitic at the main fault and, below the mylonitic front, are cut by mylonitic mesoscopic to microscopic shear zones. The upper plate consists of an imbricate stack of younger-on-older sedimentary rocks that are locally mylonitic at the main, lowermost detachment fault but are characteristically strongly brecciated or broken. Kinematic indicators in the lineated mylonite indicate tectonic transport to the east-southeast. Syntectonic sedimentary breccia and coarse conglomerate derived solely from upper plate rocks were deposited locally on top of hanging-wall rocks in low-lying areas between fault blocks and breccia zones. Muscovite occurs locally as mica fish in mylonitic quartzites at or near the main detachment. The 40Ar/39Ar age spectrum obtained from muscovite in one mylonitic quartzite yielded an age of 47.2 + 0.14 Ma, interpreted to be the age of mylonitization. The fault zone is interpreted as a detachment fault that bounds a metamorphic core complex, here termed the Anaconda metamorphic core complex, similar in age and character to the Bitterroot mylonite that bounds the Bitterroot metamorphic core complex along the Idaho-Montana state line 100 km to the west. The Bitterroot and Anaconda core complexes are likely components of a continuous, tectonically integrated system. Recognition of this core complex expands the region of known early Tertiary brittle-ductile crustal extension eastward into areas of profound Late Cretaceous contractile deformation characterized by complex structural interactions between the overthrust belt and Laramide basement uplifts, overprinted by late Tertiary Basin and Range faulting. ?? 2004 NRC Canada.

Canadian Journal of Earth Sciences↗

USGS1950

Structural geology of the Terlingua quicksilver district, Texas

Geologic mapping, supplemented by detailed investigations at the mines, has revealed new information about the geologic structure of the Terlingua quicksilver district, Texas. Attention is focused on the nature and origin of domes, grabens, and breccia pipes, structures that are unusually well developed in the area. The sedimentary rocks, of Cretaceous age, are overlain and intruded by igneous rocks of Tertiary age. Much of the structural deformation was an accompaniment of igneous intrusion. The Terlingua uplift, an irregular dome with a structural relief of several thousand feet, covers about half of the district. The southern boundary of the uplift is a steep monocline. Smaller domes, found throughout the district, were formed by igneous uplift. Evidence for this origin includes exposures of the igneous rock, the occurrence of baked rock on the domes, and theoretical consideration of the forces necessary to form a dome. Almost all the major faults are normal faults bounding depressed tracts, or grabens. Most of the major faults trend northwest; the strike varies markedly, with both sinuous curves and angular turns. The vertical displacement of the grabens below adjacent blocks varies, up to approximately 2,000 feet. Minor faults belong to two sets; one set trends northwest, parallel to the major faults, and the other northeast. Masses of breccia with a pipelike or chimneylike shape have been designated descriptively as breccia-filled pipes, or simply breccia pipes. A total of 76 breccia pipes was mapped, and four typical breccia pipes are described in detail. They range from 75 feet to 500 feet in diameter, and one has been explored vertically for more than 800 feet. The top of one breccia pipe has been found, in the Chisos mine, but the bottom of none has been found. The displacement of the fragments is downward, commonly several hundred feet, and in one instance more than 1,000 feet. The nature of the breccia and its walls indicates collapse due to undermining as the origin of the Terlingua pipes. Features, common to all the pipes, that point to this origin are the downward displacement of the fragments, the absence of drag or thrust structures, the presence of slump structures along the walls, and the vertical cylindrical form. The general structural problems of the district include the age relations, the origin of the uplift, the origin of the domes, and the origin of the grabens. The earliest structural movement involving the Cretaceous rocks was the beginning of rise of the Terlingua uplift. Before this rise ceased, the graben faulting probably began. Volcanism and widespread hypabyssal intrusion, which was accompanied by doming, was partly contemporaneous with graben faulting. The breccia pipes were formed after the beginning, and before the end, of igneous activity. Minor faulting, accompanied by mineralization, continued later than other structural movements, The Terlingua uplift was probably caused primarily by laccolithic igneous intrusion but was influenced by horizontal compression. A basic intrusion, rather than a silicic intrusion, is required to explain the exposed igneous rocks. The geometry of the large grabens indicates that they are relatively superficial accompaniments of horizontal extension. It is suggested that horizontal extension of the upper part of the earth's crust occurred during the formation of the Terlingua uplift and was accompanied by graben faulting.

Texas↗

USGS2009

Co-seismic ruptures of the 12 May 2008, M s 8.0 Wenchuan earthquake, Sichuan: East-west crustal shortening on oblique, parallel thrusts along the eastern edge of Tibet

The M s 8.0, Wenchuan earthquake, which devastated the mountainous western rim of the Sichuan basin in central China, produced a surface rupture over 200??km-long with oblique thrust/dextral slip and maximum scarp heights of ~ 10??m. It thus ranks as one of the world's largest continental mega-thrust events in the last 150??yrs. Field investigation shows clear surface breaks along two of the main branches of the NE-trending Longmen Shan thrust fault system. The principal rupture, on the NW-dipping Beichuan fault, displays nearly equal amounts of thrust and right-lateral slip. Basin-ward of this rupture, another continuous surface break is observed for over 70??km on the parallel, more shallowly NW-dipping Pengguan fault. Slip on this latter fault was pure thrusting, with a maximum scarp height of ~ 3.5??m. This is one of the very few reported instances of crustal-scale co-seismic slip partitioning on parallel thrusts. This out-of-sequence event, with distributed surface breaks on crustal mega-thrusts, highlights regional, ~ EW-directed, present day crustal shortening oblique to the Longmen Shan margin of Tibet. The long rupture and large offsets with strong horizontal shortening that characterize the Wenchuan earthquake herald a re-evaluation of tectonic models anticipating little or no active shortening of the upper crust along this edge of the plateau, and require a re-assessment of seismic hazard along potentially under-rated active faults across the densely populated western Sichuan basin and mountains. ?? 2009 Elsevier B.V.

Earth and Planetary Science Letters↗

USGS2011

Frictional strengths of talc-serpentine and talc-quartz mixtures

Talc is a constituent of faults in a variety of settings, and it may be an effective weakening agent depending on its abundance and distribution within a fault. We conducted frictional strength experiments under hydrothermal conditions to determine the effect of talc on the strengths of synthetic gouges of lizardite and antigorite serpentinites and of quartz. Small amounts of talc weaken serpentinite gouges substantially more than predicted by simple weight averaging. In comparison, mixtures of quartz and talc show a linear trend of strength reduction at talc concentrations 15 wt % and enhanced weakening at higher concentrations. All of the strength data are fit by a modified version of the Reuss mixing law that allows for the dominance of one mineral over the other. The difference in the behavior of serpentinite-talc and quartz-talc mixtures at low talc concentrations is a reflection of their different textures. Lizardite, antigorite, and talc all have platy habits, and displacement within gouges composed of these minerals is localized to narrow shears along which the platy grains have rotated into alignment with the shear surfaces. The shears in the mixed phyllosilicate gouges maximize the proportion of the weaker mineral within them. When mixed with a strong, rounded mineral such as quartz, some minimum concentration of talc is needed to form connected pathways that enhance strength reductions. The typical development of talc by the reaction of Si-rich fluids with serpentinite or dolomite would tend to localize its occurrence in a natural fault and result in enhanced weakening.

Journal of Geophysical Research B: Solid Earth↗

USGS2016

Mapping rice-fallow cropland areas for short-season grain legumes intensification in South Asia using MODIS 250 m time-series data

The goal of this study was to map rainfed and irrigated rice-fallow cropland areas across South Asia, using MODIS 250 m time-series data and identify where the farming system may be intensified by the inclusion of a short-season crop during the fallow period. Rice-fallow cropland areas are those areas where rice is grown during the kharif growing season (June–October), followed by a fallow during the rabi season (November–February). These cropland areas are not suitable for growing rabi -season rice due to their high water needs, but are suitable for a short -season (≤3 months), low water-consuming grain legumes such as chickpea ( Cicer arietinum L.), black gram, green gram, and lentils. Intensification (double-cropping) in this manner can improve smallholder farmer’s incomes and soil health via rich nitrogen-fixation legume crops as well as address food security challenges of ballooning populations without having to expand croplands. Several grain legumes, primarily chickpea, are increasingly grown across Asia as a source of income for smallholder farmers and at the same time providing rich and cheap source of protein that can improve the nutritional quality of diets in the region. The suitability of rainfed and irrigated rice-fallow croplands for grain legume cultivation across South Asia were defined by these identifiers: (a) rice crop is grown during the primary ( kharif ) crop growing season or during the north-west monsoon season (June–October); (b) same croplands are left fallow during the second ( rabi ) season or during the south-east monsoon season (November–February); and (c) ability to support low water-consuming, short-growing season (≤3 months) grain legumes (chickpea, black gram, green gram, and lentils) during rabi season. Existing irrigated or rainfed crops such as rice or wheat that were grown during kharif were not considered suitable for growing during the rabi season, because the moisture/water demand of these crops is too high. The study established cropland classes based on the every 16-day 250 m normalized difference vegetation index (NDVI) time series for one year (June 2010–May 2011) of Moderate Resolution Imaging Spectroradiometer (MODIS) data, using spectral matching techniques (SMTs), and extensive field knowledge. Map accuracy was evaluated based on independent ground survey data as well as compared with available sub-national level statistics. The producers’ and users’ accuracies of the cropland fallow classes were between 75% and 82%. The overall accuracy and the kappa coefficient estimated for rice classes were 82% and 0.79, respectively. The analysis estimated approximately 22.3 Mha of suitable rice-fallow areas in South Asia, with 88.3% in India, 0.5% in Pakistan, 1.1% in Sri Lanka, 8.7% in Bangladesh, 1.4% in Nepal, and 0.02% in Bhutan. Decision-makers can target these areas for sustainable intensification of short-duration grain legumes.

International Journal of Digital Earth↗

USGS2008

Petrology of the 2004-2006 Mount St. Helens lava dome -- implications for magmatic plumbing and eruption triggering

Eighteen years after dome-forming eruptions ended in 1986, and with little warning, Mount St. Helens began to erupt again in October 2004. During the ensuing two years, the volcano extruded more than 80×10 6 m 3 of gas-poor, crystal-rich dacite lava. The 2004-6 dacite is remarkably uniform in bulk-rock composition and, at 65 percent SiO 2 , among the richest in silica and most depleted in incompatible elements of the magmas erupted at Mount St. Helens during the past 500 years. Since shortly after the first spine of lava appeared, samples have been collected using a steel box dredge (“Jaws”) suspended 20-35 m below a helicopter and, occasionally, by hand sampling. As of the spring of 2006, 25 age-controlled samples have been collected from the seven spines of the new lava dome. Samples were obtained from both the interiors of spines and from their carapaces, which are composed of fault gouge and cataclasite 1-2 m thick. The dacite lava is crystal rich, with 40-50 percent phenocrysts. The groundmass is extensively crystallized to a cotectic assemblage of quartz, tridymite, and Na- and K-rich feldspar microlites, raising the total crystal content to more than 80 percent on a vesicle-free basis in all but the earliest erupted samples. Early samples and those collected from near the spine margin are more glassy and vesicular that those collected later and from the interior of the spines. Oxide thermobarometer determinations for the earliest erupted samples we collected cluster at temperatures of approximately 850°C and at an oxygen fugacity one log unit above the nickel-nickel oxide (NNO) buffer curve. In contrast, samples from relatively glass-poor samples erupted in late 2004 and early 2005 have zoned oxides with apparent temperatures that range to greater than 950°C. The higher temperatures in these microlite-rich rocks are attributed to latent heat evolved during extensive and rapid groundmass crystallization. Low volatile contents of matrix glasses and presence of tridymite and quartz in the high-silica rhyolite matrix glass indicate extensive shallow (<1 km) crystallization of the matrix, driven by degassing of water and solidifying the magma below the level of the vent. The mode of eruption of the dacite as a series of fault-gouge-mantled spines is explained by this process of extensive subvent degassing and solidification. Although the dacite from this eruption is more silica rich than 1980-86 dome rocks, most major and trace element concentrations of the 1980-86 and 2004-6 magma batches are similar, and magmatic gas emissions have been low and have had similar ratios to those of the 1980s, raising the possibility that the magma might be residual from the 1980–86 reservoir. However, titanium and chromium are enriched slightly relative to the most recent 1980-86 and Goat Rocks (A.D. 1800-1857) eruptive cycles, and heavy rare-earth-element abundances are slightly depleted relative to those erupted during the past 500 years at Mount St. Helens. These data suggest either addition of new gas-poor dacite magma or tapping of a region of the preexisting reservoir that was not erupted previously. A relatively low pressure of last phenocryst growth suggests that the magma was derived from near the apex of the Mount St. Helens magma reservoir at a depth of about 5 km. Viewed in the context of seismic, deformation, and gas-emission data, the petrologic and geochemical data can be explained by ascent of a geochemically distinct batch of magma into the apex of the reservoir during the period 1987-97, followed by upward movement of magma into a new conduit beginning in late September 2004. The question of new versus residual magma has implications for the long-term eruptive behavior of Mount St. Helens, because arrival of a new batch of dacitic magma from the deep crust could herald the beginning of a new long-term cycle of eruptive activity. It is also important to our understanding of what triggered the eruption and its future course. Two hypotheses for triggering are considered: (1) top-down fracturing related to the shallow groundwater system and (2) an increase in reservoir pressure brought about by recent magmatic replenishment. With respect to the future course of the eruption, similarities between textures and character of eruption of the 2004-6 dome and the long-duration (greater than 100 years) pre-1980 summit dome, along with the low eruptive rate of the current eruption, suggest that the eruption could continue sluggishly or intermittently for years to come.

Washington↗

USGS2014

Porphyry copper assessment of eastern Australia

The U.S. Geological Survey (USGS) conducts national and global assessments of resources (mineral, energy, water, and biologic) to provide science in support of decision making. Mineral resource assessments provide syntheses of available information about where mineral deposits are known and suspected to occur in the Earth’s crust and which commodities may be present, together with estimates of amounts of resources that may be present in undiscovered deposits. The USGS collaborated with geologists of the Geological Survey of New South Wales and Geoscience Australia (formerly the Australian Geological Survey Organisation) on an assessment of Phanerozoic-age porphyry copper resources in Australia. Porphyry copper deposits contain about 11 percent of the identified copper resources in Australia. This study addresses resources of known porphyry copper deposits and expected resources of undiscovered porphyry copper deposits in eastern Australia. A three-part form of assessment was used for estimation of undiscovered resources. Using this method, four tracts were delineated that are permissive for porphyry copper deposits. A probabilistic estimate of the expected number of deposits in each tract was prepared on the basis of existing information about geology, geochemistry, geophysics, exploration history, and mineral occurrences. Monte Carlo simulation was used to combine the estimated number of deposits with an appropriate model of grade and tonnage for porphyry copper deposits to provide a probabilistic estimate of metal content and total tonnage for undiscovered deposits. The Delamerian permissive tract comprises igneous rocks of Cambrian age in the Delamerian Orogen, which borders the western margin of the Tasmanides. The Delamerian tract contains no known porphyry copper deposits, but the Adelaide sub-tract, one of three sub-tracts that compose the Delamerian tract, contains four porphyry copper prospects. The Adelaide sub-tract is estimated to contain 2.5±2.2 undiscovered deposits in an area of about 50,700 square kilometers. The Macquarie permissive tract comprises volcanic, volcaniclastic, and minor exposed intrusive igneous rocks of the Macquarie Arc. The nine known deposits in this tract are now estimated to contain a total of about 13.5 million metric tons of copper and 1,700 metric tons of gold. This tract is estimated to contain 6.9±3.5 undiscovered deposits for a total of about 16 deposits in an area of about 41,500 square kilometers. The Yeoval permissive tract includes subequal areas of permissive volcanic and intrusive rocks of Silurian to Devonian age exposed in and around the Cowra-Buchan Rift System, which overlaps the previously accreted Macquarie Arc. The Yeoval tract contains one porphyry copper deposit and several porphyry copper prospects. This tract is estimated to contain 1.3±0.75 undiscovered porphyry copper deposits, for a total of about 2 expected deposits in an area of about 53,200 square kilometers. The East Tasmanide permissive tract includes a semi-continuous belt of plutonic and subordinate volcanic rocks along the eastern margins of Queensland and northeastern New South Wales. The East Tasmanide tract contains 14 known porphyry copper deposits and many porphyry copper prospects, which are all in the Central sub-tract. This sub-tract is expected to contain 4.8±3.3 undiscovered porphyry copper deposits, for a total of about 19 deposits in an area of about 291,000 square kilometers. This assessment estimates that 15 undiscovered deposits contain an arithmetic mean of ~21 million metric tons or more of copper in four tracts, in addition to the 24 known porphyry copper deposits that contain identified resources of ~16 million metric tons of copper. In addition to copper, the mean expected amount of undiscovered byproduct gold predicted by the simulation is ~1,500 metric tons. The probability associated with these arithmetic means is on the order of 30 percent. Median expected amounts of metals predicted by the simulations may be ~50 percent lower than mean estimates.

Scientific Investigations Report↗

USGS2007

Recent climate trends and implications for water resources in the Catskill Mountain region, New York, USA

Climate scientists have concluded that the earth’s surface air temperature warmed by 0.6 °C during the 20th century, and that warming induced by increasing concentrations of greenhouse gases is likely to continue in the 21st century, accompanied by changes in the hydrologic cycle. Climate change has important implications in the Catskill region of southeastern New York State, because the region is a source of water supply for New York City. We used the non-parametric Mann–Kendall test to evaluate annual, monthly, and multi-month trends in air temperature, precipitation amount, stream runoff, and potential evapotranspiration (PET) in the region during 1952–2005 based on data from 9 temperature sites, 12 precipitation sites, and 8 stream gages. A general pattern of warming temperatures and increased precipitation, runoff, and PET is evident in the region. Regional annual mean air temperature increased significantly by 0.6 °C per 50 years during the period; the greatest increases and largest number of significant upward trends were in daily minimum air temperature. Daily maximum air temperature showed the greatest increase during February through April, whereas minimum air temperature showed the greatest increase during May through September. Regional mean precipitation increased significantly by 136 mm per 50 years, nearly double that of the regional mean increase in runoff, which was not significant. Regional mean PET increased significantly by 19 mm per 50 years, about one-seventh that of the increase in precipitation amount, and broadly consistent with increased runoff during 1952–2005, despite the lack of significance in the mean regional runoff trend. Peak snowmelt as approximated by the winter–spring center of volume of stream runoff generally shifted from early April at the beginning of the record to late March at the end of the record, consistent with a decreasing trend in April runoff and an increasing trend in maximum March air temperature. This change indicates an increased supply of water to reservoirs earlier in the year. Additionally, the supply of water to reservoirs at the beginning of winter is greater as indicated by the timing of the greatest increases in precipitation and runoff—both occurred during summer and fall. The future balance between changes in air temperature and changes in the timing and amount of precipitation in the region will have important implications for the available water supply in the region.

New York↗

USGS2000

Surveys of water velocities in the vicinity of the discharge-release gates of Salamonie Lake Dam, northeastern Indiana, spring and winter 1998

Two water-velocity surveys in the vicinity of the discharge-release gates were performed at the Salamonie Lake flood-control reservoir in northeastern Indiana during periods of high-discharge release. One survey was done in the spring when the reservoir pool was at high elevation; the other survey was in the winter when the reservoir pool was low. The maximum measured velocity was 2.4 feet per second for the spring survey and 1.9 feet per second for the winter survey. The maximum measured velocities occurred in the immediate vicinity of the spillway tower containing the discharge-release gates. Velocity-field magnitudes diminished rapidly with distance from the tower. Beyond an estimated 40 feet from the tower, velocity magnitudes were below 0.5 feet per second. For the spring and winter surveys, data were collected along four transects that were parallel to the face of the spillway tower. The transects were at the following approximate distances from the spillway tower: 900, 600, and 300 feet and as close to the tower as practical. For the spring and winter surveys, velocity-contour plots were produced for the transects closest to the tower. Plots were not made for the transects at 900-, 600-, and 300-foot intervals because velocities were negligible at these distances. An acoustic Doppler current profiler (ADCP) mounted on a boat was used to collect velocity and depth data and to compute positions of the velocity and depth data relative to the boat track. A global positioning system (GPS) was used to collect earth-referenced position data, and a GPS base station receiver was used to improve the accuracy of the earth-referenced position data. The earth-referenced position data were used to transform the ADCP-computed positions (which were relative to boat tracks) to positions referenced to a point on the spillway tower.

Indiana↗

USGS2024

A two-dimensional, reach-scale implementation of space-time image velocimetry (STIV) and comparison to particle image velocimetry (PIV)

Image-based algorithms have become a powerful tool for estimating flow velocities in rivers. In this study, we generalize the space-time image velocimetry (STIV) framework for reach-scale application rather than along a cross section. The new algorithm provides information on both the magnitude and orientation of velocity vectors, and we refer to the algorithm as two-dimensional STIV, or 2D-STIV. The workflow involves setting up a grid, using centreline tangent vectors as initial estimates of flow direction, and then extracting space-time images (STIs) along search lines radiating from each grid node. The autocorrelation function is used to infer the inclination of streak lines present in STIs, which represents the advection of water surface features. Information on flow direction is obtained by evaluating various candidate search lines and identifying that which yields the highest velocity. This search can be performed exhaustively or via optimization. We applied the new 2D-STIV algorithm to three test cases, one simulated data set and two natural channels, and compared image-derived velocities to modelled or measured values. We also applied two established particle image velocimetry (PIV) algorithms to the same data sets. 2D-STIV performed as well as the two PIV algorithms for simulated images. For a natural river with distinct water surface features, 2D-STIV was effective for much of the channel but also led to a more patchy, irregular velocity field than the two PIV algorithms. For a site lacking obvious surface features, exhaustive 2D-STIV led to velocity estimates uncorrelated with field data while the optimization-based version produced erratic flow directions. 2D-STIV also required greater image sequence durations, higher frame rates, and generally longer computational run times. Overall, ensemble PIV was the most reliable algorithm.

Earth Surface Processes and Landforms↗

USGS2026

Carbon sequestration along a gradient of tidal marsh degradation in response to sea level rise

Tidal marshes are considered one of the world's most efficient ecosystems for belowground organic carbon sequestration and hence climate mitigation. Marsh systems are however also vulnerable to degradation due to climate-induced sea level rise, whereby marsh vegetation conversion to open water often follows distinct spatial patterns: levees (i.e. marsh zones < 10 m from tidal creeks) show lower vulnerability of vegetation conversion to open water than basins (i.e. interior marsh zones > 30 m from creeks). Here, we use sediment cores to investigate spatial variations in organic carbon accumulation rates (OCAR) in a microtidal system (Blackwater marshes, Maryland, USA): (1) across a gradient of marsh zones with increasing marsh degradation, assessed as increasing ratio of unvegetated versus vegetated marsh area and (2) by comparing levees versus basins. We show that OCAR is up to four times higher on marsh levees than in adjacent basins. The data suggest that this is caused by spatial variation in three processes: sediment accretion rate, vegetation productivity, and sediment compaction, which are all higher on levees. Additionally, OCAR was observed to increase with increasing degree of marsh degradation in response to sea level rise. We hypothesize this may be due to more soil waterlogging in more degraded marsh zones, which may decrease carbon decomposition. Our results highlight that tidal marsh levees, in a microtidal system, are among the fastest soil organic carbon sequestration systems on Earth, and that both levees and basins sustain their carbon accumulation rate along gradients of increasing marsh degradation in response to sea level rise.

Maryland↗

USGS1988

An improved dark-object subtraction technique for atmospheric scattering correction of multispectral data

Digital analysis of remotely sensed data has become an important component of many earth-science studies. These data are often processed through a set of preprocessing or “clean-up” routines that includes a correction for atmospheric scattering, often called haze. Various methods to correct or remove the additive haze component have been developed, including the widely used dark-object subtraction technique. A problem with most of these methods is that the haze values for each spectral band are selected independently. This can create problems because atmospheric scattering is highly wavelength-dependent in the visible part of the electromagnetic spectrum and the scattering values are correlated with each other. Therefore, multispectral data such as from the Landsat Thematic Mapper and Multispectral Scanner must be corrected with haze values that are spectral band dependent. An improved dark-object subtraction technique is demonstrated that allows the user to select a relative atmospheric scattering model to predict the haze values for all the spectral bands from a selected starting band haze value. The improved method normalizes the predicted haze values for the different gain and offset parameters used by the imaging system. Examples of haze value differences between the old and improved methods for Thematic Mapper Bands 1, 2, 3, 4, 5, and 7 are 40.0, 13.0, 12.0, 8.0, 5.0, and 2.0 vs. 40.0, 13.2, 8.9, 4.9, 16.7, and 3.3, respectively, using a relative scattering model of a clear atmosphere. In one Landsat multispectral scanner image the haze value differences for Bands 4, 5, 6, and 7 were 30.0, 50.0, 50.0, and 40.0 for the old method vs. 30.0, 34.4, 43.6, and 6.4 for the new method using a relative scattering model of a hazy atmosphere.

Arizona↗

USGS2023

Dense geophysical observations reveal a triggered, concurrent multi-fault rupture at the Mendocino Triple Junction

A central question of earthquake science is how far ruptures can jump from one fault to another, because cascading ruptures can increase the shaking of a seismic event. Earthquake science relies on earthquake catalogs and therefore how complex ruptures get documented and cataloged has important implications. Recent investments in geophysical instrumentation allow us to resolve increasingly complex, multi-fault ruptures for even moderate-sized earthquakes. We combine dense seismic and geodetic measurements to reveal an enigmatic rupture in late 2021 at the Mendocino Triple Junction in northern California. We show that rupture was dynamically triggered, yet concurrent, on two distinct faults roughly 30 km apart. Thus, this rupture combines features of complex ruptures usually considered to be single earthquakes, and triggered ruptures considered as multiple earthquakes. This event illustrates that moderate-sized earthquakes can exhibit similar complexity to that more commonly documented for large earthquakes.

California↗

USGS2015

GEAR1: A Global Earthquake Activity Rate model constructed from geodetic strain rates and smoothed seismicity

Global earthquake activity rate model 1 (GEAR1) estimates the rate of shallow earthquakes with magnitudes 6–9 everywhere on Earth. It was designed to be reproducible and testable. Our preferred hybrid forecast is a log–linear blend of two parent forecasts based on the Global Centroid Moment Tensor (CMT) catalog (smoothing 4602 m≥5.767 shallow earthquakes, 1977–2004) and the Global Strain Rate Map version 2.1 (smoothing 22,415 Global Positioning System velocities), optimized to best forecast the 2005–2012 Global CMT catalog. Strain rate is a proxy for fault stress accumulation, and earthquakes indicate stress release, so a multiplicative blend is desirable, capturing the strengths of both approaches. This preferred hybrid forecast outperforms its seismicity and strain‐rate parents; the chance that this improvement stems from random seismicity fluctuations is less than 1%. The preferred hybrid is also tested against the independent parts of the International Seismological Centre‐Global Earthquake Model catalog (m≥6.8 during 1918–1976) with similar success. GEAR1 is an update of this preferred hybrid. Comparing GEAR1 to the Uniform California Earthquake Rupture Forecast Version 3 (UCERF3), net earthquake rates agree within 4% at m≥5.8 and at m≥7.0. The spatial distribution of UCERF3 epicentroids most resembles GEAR1 after UCERF3 is smoothed with a 30 km kernel. Because UCERF3 has been constructed to derive useful information from fault geometry, slip rates, paleoseismic data, and enhanced seismic catalogs (not used in our model), this is encouraging. To build parametric catastrophe bonds from GEAR1, one could calculate the magnitude for which there is a 1% (or any) annual probability of occurrence in local regions.

Bulletin of the Seismological Society of America↗