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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 685 records · Page 38Linked to original sources
USGS2017

Links between atmosphere, ocean, and cryosphere from two decades of microseism observations on the Antarctic Peninsula

The lack of landmasses, climatological low pressure, and strong circumpolar westerly winds between the latitudes of 50°S to 65°S produce exceptional storm‐driven wave conditions in the Southern Ocean. This combination makes the Antarctic Peninsula one of Earth's most notable regions of high‐amplitude wave activity and thus, ocean‐swell‐driven microseism noise in both the primary (direct wave‐coastal region interactions) and secondary (direct ocean floor forcing due to interacting wave trains) period bands. Microseism observations are examined across 23 years (1993–2015) from Palmer Station (PMSA), on the west coast of the Antarctic Peninsula, and from East Falkland Island (EFI). These records provide a spatially integrative measure of both Southern Ocean wave amplitudes and the interactions between ocean waves and the solid Earth in the presence of sea ice, which can reduce wave coupling with the continental shelf. We utilize a spatiotemporal correlation‐based approach to illuminate how the distribution of sea ice influences seasonal microseism power. We characterize primary and secondary microseism power due to variations in sea ice and find that primary microseism energy is both more sensitive to sea ice and more capable of propagating across ocean basins than secondary microseism energy. During positive phases of the Southern Annular Mode, sea ice is reduced in the Bellingshausen Sea and overall storm activity in the Drake Passage increases, thus strongly increasing microseism power levels.

Antarctic Penninsula↗
USGS2012

Effect of crustal layering upon dislocation modeling

Slip distribution at depth on a fault may be inferred from the deformation observed on the surface. In inverting the surface deformation data to obtain the slip distribution, the Earth is generally approximated by an elastic half‐space. Slip distributions inferred from a half‐space model may contain artifacts, including zones of reversed slip, due solely to effects of layering in the real Earth. This effect is demonstrated for a vertical strike‐slip fault in an Earth consisting of an elastic layer overlying an elastic half‐space. Slip on the fault is taken to be independent of the along‐strike coordinate (i.e., antiplane strain is assumed). For a given slip distribution in this model the slip distribution on a similar fault in an elastic half‐space is found that produces the identical surface deformation. Comparison of the two slip distributions reveals structure introduced into the half‐space equivalent slip profile by crustal layering. The comparisons suggest that low‐resolution inversion schemes (e.g., single screw dislocation models) are not drastically affected by Earth structure, but attempts at detailed inversion are likely to produce profiles contaminated by artifacts of Earth structure.

Journal of Geophysical Research B: Solid Earth↗
USGS2016

Large wind ripples on Mars: A record of atmospheric evolution

Wind blowing over sand on Earth produces decimeter-wavelength ripples and hundred-meter– to kilometer-wavelength dunes: bedforms of two distinct size modes. Observations from the Mars Science Laboratory Curiosity rover and the Mars Reconnaissance Orbiter reveal that Mars hosts a third stable wind-driven bedform, with meter-scale wavelengths. These bedforms are spatially uniform in size and typically have asymmetric profiles with angle-of-repose lee slopes and sinuous crest lines, making them unlike terrestrial wind ripples. Rather, these structures resemble fluid-drag ripples, which on Earth include water-worked current ripples, but on Mars instead form by wind because of the higher kinematic viscosity of the low-density atmosphere. A reevaluation of the wind-deposited strata in the Burns formation (about 3.7 billion years old or younger) identifies potential wind-drag ripple stratification formed under a thin atmosphere.

Science↗
USGS1998

On the influence of biomass burning on the seasonal CO2 signal as observed at monitoring stations

We investigated the role of biomass burning in simulating the seasonal signal in both prognostic and diagnostic analyses. The prognostic analysis involved the High-Resolution Biosphere Model, a prognostic terrestrial biosphere model, and the coupled vegetation fire module, which together produce a prognostic data set of biomass burning. The diagnostic analysis involved the Simple Diagnostic Biosphere Model (SDBM) and the Hao and Liu [1994] diagnostic data set of biomass burning, which have been scaled to global 2 and 4 Pg C yr −1 , respectively. The monthly carbon exchange fields between the atmosphere and the biosphere with a spatial resolution of 0.5° × 0.5°, the seasonal atmosphere-ocean exchange fields, and the emissions from fossil fuels have been coupled to the three-dimensional atmospheric transport model TM2. We have chosen eight monitoring stations of the National Oceanic and Atmospheric Administration network to compare the predicted seasonal atmospheric CO 2 signals with those deduced from atmosphere-biosphere carbon exchange fluxes without any contribution from biomass burning. The prognostic analysis and the diagnostic analysis with global burning emissions of 4 Pg C yr −1 agree with respect to the change in the amplitude of the seasonal CO 2 concentration introduced through biomass burning. We find that the seasonal CO 2 signal at stations in higher northern latitudes (north of 30°N) is marginally influenced by biomass burning. For stations in tropical regions an increase in the CO 2 amplitude of more than 1 ppmv (up to 50% with respect to the observed trough to peak amplitude) has been calculated. Biomass burning at stations farther south accounts for an increase in the CO 2 amplitude of up to 59% (0.6 ppmv). A change in the phase of the seasonal CO 2 signal at tropical and southern stations has been shown to be strongly influenced by the onset of biomass burning in southern tropical Africa and America. Comparing simulated and observed seasonal CO 2 signals, we find higher discrepancies at southern tropical stations if biomass burning emissions are included. This is caused by the additional increase in the amplitude in the prognostic analysis and a phase shift in a diagnostic analysis. In contrast, at the northern tropical stations biomass burning tends to improve the estimates of the seasonal CO 2 signal in the prognostic analysis because of strengthening of the amplitude. Since the SDBM predicts the seasonal CO 2 signal reasonably well for the northern hemisphere tropical stations, no general improvement of the fit occurs if biomass burning emissions are considered.

Global Biogeochemical Cycles↗
USGS2000

Quality assurance and analysis of water levels in wells on Pahute Mesa and vicinity, Nevada Test Site, Nye County, Nevada

Periodic and continual water-level data from 1963 to 1998 were compiled and quality assured for 65 observation wells on Pahute Mesa and vicinity, Nye County, Nevada. As part of the quality assurance of all water levels, ancillary data pertinent to computing hydraulic heads in wells were compiled and analyzed. Quality-assured water levels that were not necessarily in error but which did not represent static heads in the regional aquifer system, or required some other qualification, were flagged. Water levels flagged include those recovering from recent pumping or well construction, water levels affected by nuclear tests, and measurements affected by borehole deviations. A cursory examination of about 30 wells with available water-level and down-hole temperature data indicate that water levels in most wells on Pahute Mesa would not be significantly affected by temperature if corrected to 95 degrees Fahrenheit. Wells with large corrections (greater than 10 feet) are those with long water columns (greater than 1,500 feet of water above the assumed point of inflow) in combination with mean water-column temperatures exceeding 105 degrees Fahrenheit. Water-level fluctuations in wells on Pahute Mesa are caused by several factors including infiltration of precipitation, barometric pressure, Earth tides, ground-water pumpage, and seismic events caused by tectonic activity and underground nuclear testing. No observed water-level fluctuations were attributed to a naturally occurring earthquake. The magnitude and duration of changes in water levels caused by nuclear tests are affected by the test size and the distance from a well to the test. Identifying water levels that might be affected by past nuclear tests is difficult because pre-testing water-level data are sparse. Hydrologically significant trends were found in 13 of 25 wells with multiple years of water-level record. The largest change in water levels (1,029 feet in 25 years) occurred in well U-19v PS 1D as a result of the Almendro nuclear test. Likely explanations for trends in most of the wells are either changes in precipitation patterns that affect recharge rates to the ground-water system, pumping effects from water-supply well U-20 WW, or a combination of these two factors.

Nevada↗
USGS2012

Sea-level history during the Last Interglacial complex on San Nicolas Island, California: implications for glacial isostatic adjustment processes, paleozoogeography and tectonics

San Nicolas Island, California has one of the best records of fossiliferous Quaternary marine terraces in North America, with at least fourteen terraces rising to an elevation of ~270 m above present-day sea level. In our studies of the lowest terraces, we identified platforms at 38-36 m (terrace 2a), 33-28 m (terrace 2b), and 13-8 m (terrace 1). Uranium-series dating of solitary corals from these terraces yields three clusters of ages: ~120 ka on terrace 2a (marine isotope stage [MIS] 5.5), ~120 and ~100 ka on terrace 2b (MIS 5.5 and 5.3), and ~80 ka (MIS 5.1) on terrace 1. We conclude that corals on terrace 2b that date to ~120 ka were reworked from a formerly broader terrace 2a during the ~100 ka sea stand. Fossil faunas differ on the three terraces. Isolated fragments of terrace 2a have a fauna similar to that of modern waters surrounding San Nicolas Island. A mix of extralimital southern and extralimital northern species is found on terrace 2b, and extralimital northern species are on terrace 1. On terrace 2b, with its mixed faunas, extralimital southern species, indicating warmer than present waters, are interpreted to be from the ~120 ka high sea stand, reworked from terrace 2a. The extralimital northern species on terrace 2b, indicating cooler than present waters, are interpreted to be from the ~100 ka sea stand. The abundant extralimital northern species on terrace 1 indicate cooler than present waters at ~80 ka. Using the highest elevations of the ~120 ka platform of terrace 2a, and assuming a paleo-sea level of +6 m based on previous studies, San Nicolas Island has experienced late Quaternary uplift rates of ~0.25-0.27 m/ka. These uplift rates, along with shoreline angle elevations and ages of terrace 2b (~100 ka) and terrace 1 (~80 ka) yield relative (local) paleo-sea level elevations of +2 to +6 m for the ~100 ka sea stand and -11 to -12 m for the ~80 ka sea stand. These estimates are significantly higher than those reported for the ~100 ka and ~80 ka sea stands on New Guinea and Barbados. Numerical models of the glacial isostatic adjustment (GIA) process presented here demonstrate that these differences in the high stands are expected, given the variable geographic distances between the sites and the former Laurentide and Cordilleran ice sheets. Moreover, the numerical results show that the absolute and differential elevations of the observed high stands provide a potentially important constraint on ice volumes during this time interval and on Earth structure.

California↗
USGS2000

The use of earthquake rate changes as a stress meter at Kilauea volcano

Stress changes in the Earth's crust are generally estimated from model calculations that use near-surface deformation as an observational constraint. But the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues. Although this possibility has considerable appeal, because seismicity data are routinely collected and have good spatial and temporal resolution, the method has not yet proven successful, owing to the nonlinearity of earthquake rate changes with respect to both stress and time. Here, however, we present two methods for inverting earthquake rate data to infer stress changes, using a formulation for the stress- and time-dependence of earthquake rates. Application of these methods at Kilauea volcano, in Hawaii, yields good agreement with independent estimates, indicating that earthquake rates can provide a practical remote-sensing stress meter.

Nature↗
USGS2004

Pancam multispectral imaging results from the Spirit Rover at Gusev crater

Panoramic Camera images at Gusev crater reveal a rock-strewn surface interspersed with high- to moderate-albedo fine-grained deposits occurring in part as drifts or in small circular swales or hollows. Optically thick coatings of fine-grained ferric iron-rich dust dominate most bright soil and rock surfaces. Spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near-infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine. Atmospheric observations show a steady decline in dust opacity during the mission, and astronomical observations captured solar transits by the martian moons, Phobos and Deimos, as well as a view of Earth from the martian surface.

Science↗
USGS1998

Geochemical evidence for a comet shower in the late Eocene

Analyses of pelagic limestones indicate that the flux of extraterrestrial helium-3 to Earth was increased for a 2.5-million year (My) period in the late Eocene. The enhancement began ~1 My before and ended ~1.5 My after the major impact events that produced the large Popigai and Chesapeake Bay craters ~36 million years ago. The correlation between increased concentrations of helium-3, a tracer of fine-grained interplanetary dust, and large impacts indicates that the abundance of Earth-crossing objects and dustiness in the inner solar system were simultaneously but only briefly enhanced. These observations provide evidence for a comet shower triggered by an impulsive perturbation of the Oort cloud.

Science↗
USGS1992

Diagenetic formation of bedded chert: Evidence from chemistry of the chert-shale couplet

Theories concerning the formation of bedded chert traditionally have emphasized either depositional or diagenetic processes. Major and rare earth element data from Franciscan assemblage (Mesozoic) and Claremont Formation (Miocene) bedded chert sequences, along with physical observations such as the presence of rare and highly corroded radiolarians in shale interbeds, are most consistent with a dominantly diagenetic origin of chert-shale couplets and are incompatible with many depositional theories. Chemical distributions between Franciscan and Claremont bedded chert=shale closely match chemical fractionations recorded by Monterey Formation and Deep Sea Drilling Project-sampled cherts formed by diagenetic SiO 2 dissolution, transport, and reprecipitation, suggesting that diagenetic migration of SiO 2 from proto-shale to proto-chert is also largely responsible for chert-shale couplets. Identical Ce anomalies (Ce/Ce*) found in immediately adjacent chert-shale layers indicate that turbidites or other transport mechanisms are not responsible for the alternating beds. Neither the chemistry of the chert-shale couplet nor the overall stratigraphy of the sequences is consistent with couplet formation being caused by productivity fluctuations. Chemical mass balance calculations reconstructing the total bulk sediment composition suggest that modern siliceous sequences do not contain enough labile biogenic SiO 2 to form entire stratigraphies of bedded chert.

Geology↗
USGS1994

Some observations of landslides triggered by the 29 April 1991 Racha earthquake, Republic of Georgia

On 29 April 1991 an M s 7.0 earthquake occurred in the Racha region of the Great Caucasus Mountains in north-central Republic of Georgia. The earthquake occurred on a thrust fault striking roughly east-west and dipping about 20° to 45° northward; focal depth was 17 ± 2 km. We observed no surface fault rupture, but the earthquake caused extensive structural damage to the many unreinforced stone buildings in the area, and at least 114 people were killed. Many landslides were triggered in a 2500-km 2 epicentral area, and they caused much of the structural damage and at least half the fatalities. We observed the following six types of landslides (in order of decreasing abundance): rock falls, debris slides, slumps, earth slides, rock block slides, and rock avalanches. The types of landslides triggered by the earthquake are controlled primarily by lithology and geologic structure. Enigmatic landslide processes associated with this earthquake include (1) delays of several days between earthquake shaking and significant landslide movement, probably caused by changes in groundwater conditions; (2) small co-seismic displacement of landslides active at the time of the earthquake, a possible result of viscoplastic damping of the seismic shaking; and (3) somewhat unusual failure geometries related to local topography and geologic structure.

Bulletin of the Seismological Society of America↗
USGS1974

Apollo 11 voice transcript pertaining to the geology of the landing site

On July 20, 1969, America's Eagle touched down in southwestern Mare Tranquillitatis beginning man's firsthand exploration of the moon. This document is an edited record of the conversations between astronauts Neil Armstrong and Edwin "Buzz" Aldrin, Jr., at Tranquility Base, and Bruce McCandless at Mission Control in Houston during the approximately 22 hours spent on the lunar surface. It includes additional commentary during their return to Earth. It is a condensation hopefully of all the verbal data having geological significance. All discussions and observations documenting the lunar landscape, its geologic characteristics, the rocks and soils collected, and the photographic record are retained along with supplementary remarks essential to the continuity of events during the mission. We have deleted the words of mechanical housekeeping and engineering data, attempting not to lose the personal and philosophical aspects of this intensely human experience. The sources of this verbal transcript are the complete audio tapes recorded during the mission and the Technical Air-to-Ground Voice Transcription published by NASA. The voice record is listed chronologically given in days, hours, minutes, and seconds. These are the Ground Elapsed Times (GET) after launch from Kennedy Space Center which was 9:32 a.m. EDT on July 16, 1969. Figure 1 shows the vicinity of the landing site that was described, sampled, and photographed by the Apollo 11 crewmen.

Final Report↗
USGS2024

Empirical ground-motion basin response in the California Great Valley, Reno, Nevada, and Portland, Oregon

We assess how well the Next-Generation Attenuation-West 2 (NGA-West2) ground-motion models (GMMs), which are used in the US Geological Survey’s (USGS) National Seismic Hazard Model (NSHM) for crustal faults in the western United States, predict the observed basin response in the Great Valley of California, the Reno basin in Nevada, and Portland and Tualatin basins in Oregon. These GMMs rely on site parameters such as the time-averaged shear-wave velocity ( V S ) in the upper 30 m of Earth’s crust ( V S30 ) and depths to 1.0 and 2.5 km/s shear-wave isosurfaces ( Z 1.0 and Z 2.5 ) to capture basin effects and were developed using observations and simulations primarily from the Los Angeles region in southern California. Using ground-motion records from mostly small-to-moderate earthquakes and mixed-effects regression analysis, we find that the GMMs perform well with our local basin-depth models for the California Great Valley. With our local basin-depth models for Reno, the GMMs do not perform as well for this relatively shallow basin and exhibit little sensitivity to the basin parameters used in the NGA-West2 GMMs. We also find good performance for the local Z 1.0 model across the Portland region, whereas the local Z 2.5 model provides little predictive power except at sites in the deepest part of the Tualatin basin. Additional work could improve the performance of the site and basin terms in the NGA-West2 GMMs for regions with geologic structure different than the deep basins in southern California and the Great Valley. In addition, we find significant discrepancies among the GMMs in how the uncertainty in the ground motion varies with basin depth and pseudospectral period. Our results can help guide seismic hazard analyses on whether to include these local basin-depth models.

Earthquake Spectra↗
USGS2013

U–Pb, Rb–Sr, and U-series isotope geochemistry of rocks and fracture minerals from the Chalk River Laboratories site, Grenville Province, Ontario, Canada

As part of the Geologic Waste Management Facility feasibility study, Atomic Energy of Canada Ltd. (AECL) is evaluating the suitability of the Chalk River Laboratories (CRL) site in Ontario, situated in crystalline rock of the southwestern Grenville Province, for the possible development of an underground repository for low- and intermediate-level nuclear waste. This paper presents petrographic and trace element analyses, U–Pb zircon dating results, and Rb–Sr, U–Pb and U-series isotopic analyses of gneissic drill core samples from the deep CRG-series characterization boreholes at the CRL site. The main rock types intersected in the boreholes include hornblende–biotite (±pyroxene) gneisses of granitic to granodioritic composition, leucocratic granitic gneisses with sparse mafic minerals, and garnet-bearing gneisses with variable amounts of biotite and/or hornblende. The trace element data for whole-rock samples plot in the fields of within-plate, syn-collision, and volcanic arc-type granites in discrimination diagrams used for the tectonic interpretation of granitic rocks. Zircons separated from biotite gneiss and metagranite samples yielded SHRIMP-RG U–Pb ages of 1472 ± 14 (2 σ ) and 1045 ± 6 Ma, respectively, in very good agreement with widespread Early Mesoproterozoic plutonic ages and Ottawan orogeny ages in the Central Gneiss Belt. The Rb–Sr, U–Pb, and Pb–Pb whole-rock errorchron apparent ages of most of the CRL gneiss samples are consistent with zircon U–Pb age and do not indicate substantial large-scale preferential element mobility during superimposed metamorphic and water/rock interaction processes. This may confirm the integrity of the rock mass, which is a positive attribute for a potential nuclear waste repository. Most 234 U/ 238 U activity ratios (AR) in whole rock samples are within errors of the secular equilibrium value of one, indicating that the rocks have not experienced any appreciable U loss or gain within the past 1 Ma. However, 234 U/ 238 U AR in fracture mineral samples collected down to borehole lengths of about 740 m deviate from the secular equilibrium value and 234 U/ 238 U model ages calculated for fracture mineral samples showing excess 234 U range from 593 to 1415 ka, thus providing evidence of fracture flow in the associated bedrock during the past 1.5 Ma. Rare earth element patterns are variable in fracture-filling calcites and Fe oxides/hydroxides but are similar to those observed in associated whole-rock samples. The observed Ce anomalies are very small ( Ce N / Ce N ∗ ≈ 1 "> CeN/CeN∗≈1 ), do not vary with depth, and, therefore, do not contain evidence that the studied fracture minerals precipitated from oxidizing waters at the conceptual depth of a repository.

Ontario↗
USGS2019

Stormquakes

Seismic signals from ocean-solid Earth interactions are ubiquitously recorded on our planet. However, these wavefields are typically incoherent in most frequency bands limiting their utilization for understanding ocean dynamics or solid Earth properties. In contrast, we find that during large storms such as hurricanes and Nor’easters the interaction of long-period ocean waves with shallow seafloor features located near the edge of continental shelfs, known as ocean banks, excites coherent transcontinental Rayleigh wave packets in the 20 to 50 s period band. These “stormquakes” migrate coincident with the storms, but are spatiotemporally focused seismic point sources with equivalent earthquake magnitudes that can be greater than 3.5. Stormquakes thus provide new coherent sources to investigate Earth structure in locations that typically lack both seismic instrumentation and earthquakes. Moreover, they provide a new geophysical observable with high spatial and temporal resolution with which to investigate ocean wave dynamics during large storms.

Geophysical Research Letters↗
USGS2006

Comment on “222Rn Premonitory signals for earthquakes?”

Radon and other terrestrial gases in groundwater and soil air have been studied in recent years in seismically active areas, especially in China, Japan, the former Soviet Union, and the United States, in search of changes that may be useful for earthquake prediction. Concentrations of radon, helim, hydrogen, mercury vapor, carbon dioxide, and several other gases have been found to be high along active faults. Faults may thus be paths of least resistance along which terrestrial gases generated or stored in the Earth can escape into the atmosphere. Gas-concentration changes with durations of hours to months have been observed before and after earthquakes at relatively few favorably situated sites, and their patterns have not always been repeated. Some of these sites are located as far as several hundred kilometers away from earthquake epicenters. These “sensitive” sites are generally situated along active faults, whether the seismogenic ones or not, especially at their intersections or bends, or at other structurally weak zones, possibly because of concentration of tectonic strain and abundance of pore fluids at such places (see review papers by King , 1986, 1990). Due to this selectivity and for two other important reasons, studies of terrestrial gases for earthquake prediction have not been viewed favorably by most geophysicists, especially those in the United States.

Eos Science News↗
USGS2017

A land data assimilation system for sub-Saharan Africa food and water security applications

Seasonal agricultural drought monitoring systems, which rely on satellite remote sensing and land surface models (LSMs), are important for disaster risk reduction and famine early warning. These systems require the best available weather inputs, as well as a long-term historical record to contextualize current observations. This article introduces the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (FLDAS), a custom instance of the NASA Land Information System (LIS) framework. The FLDAS is routinely used to produce multi-model and multi-forcing estimates of hydro-climate states and fluxes over semi-arid, food insecure regions of Africa. These modeled data and derived products, like soil moisture percentiles and water availability, were designed and are currently used to complement FEWS NET’s operational remotely sensed rainfall, evapotranspiration, and vegetation observations. The 30+ years of monthly outputs from the FLDAS simulations are publicly available from the NASA Goddard Earth Science Data and Information Services Center (GES DISC) and recommended for use in hydroclimate studies, early warning applications, and by agro-meteorological scientists in Eastern, Southern, and Western Africa.

Scientific Data↗