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USGS1998

Effects of landcover, water redistribution, and temperature on ecosystem processes in the South Plate Basin

Over one-third of the land area in the South Platte Basin of Colorado, Nebraska, and Wyoming, has been converted to croplands. Irrigated cropland now comprises 8% of the basin, while dry croplands make up 31%. We used the RHESSys model to compare the changes in plant productivity and vegetation-related hydrological processes that occurred as a result of either land cover alteration or directional temperature changes (−2°C, +4°C). Land cover change exerted more control over annual plant productivity and water fluxes for converted grasslands, while the effect of temperature changes on productivity and water fluxes was stronger in the mountain vegetation. Throughout the basin, land cover change increased the annual loss of water to the atmosphere by 114 mm via evaporation and transpiration, an increase of 37%. Both irrigated and nonirrigated grains became active earlier in the year than shortgrass steppe, leading to a seasonal shift in water losses to the atmosphere. Basin-wide photosynthesis increased by 80% due to grain production. In contrast, a 4°C warming scenario caused annual transpiration to increase by only 3% and annual evaporation to increase by 28%, for a total increase of 71 mm. Warming decreased basin-wide photosynthesis by 16%. There is a large elevational range from east to west in the South Platte Basin, which encompasses the western edge of the Great Plains and the eastern front of the Rocky Mountains. This elevational gain is accompanied by great changes in topographic complexity, vegetation type, and climate. Shortgrass steppe and crops found at elevations between 850 and 1800 m give way to coniferous forests and tundra between 1800 and 4000 m. Climate is increasingly dominated by winter snow precipitation with increasing elevation, and the timing of snowmelt influences tundra and forest ecosystem productivity, soil moisture, and downstream discharge. Mean annual precipitation of <500 mm on the plains below 1800 m is far less than potential evapotranspiration of 1000–1500 mm and is insufficient for optimum plant productivity. The changes in water flux and photosynthesis from conversion of steppe to cropland are the result of redistribution of snowmelt water from the mountains and groundwater pumping through irrigation projects.

Ecological Applications↗

USGS1999

Reference conditions for giant sequoia forest restoration: structure, process, and precision

National Park Service policy directs that more natural conditions be restored to giant sequoia groves, which have been altered by a century of fire exclusion. Efforts to find a reasonable and practical definition of “natural” have helped drive scientists and land managers to use past grove conditions as reference conditions for restoration. Extensive research aimed at determining reference conditions has demonstrated that past fire regimes can be characterized with greater precision than past grove structures. Difficulty and imprecision in determining past grove structure has helped fuel a debate between “structural restorationists,” who believe that forest structure should be restored mechanically before fire is reintroduced, and “process restorationists,” who believe that simple reintroduction of fire is appropriate. I evaluate old and new studies from sequoia groves to show that some of the arguments of both groups have been flawed. Importantly, it appears that restoration of fire without a preceding mechanical restoration may restore the pre-Euro-American structure of sequoia groves, at least within the bounds of our imprecise knowledge of past grove structure. However, the same may not be true for all forest types that have experienced lengthy fire exclusion. Our ability to draw robust generalizations about fire's role in forest restoration will depend heavily on a thorough understanding of past and present interactions among climate, fire, and forest structure. Use of reference conditions will be central to developing this understanding.

Ecological Applications↗

USGS2003

A modern analogue for tectonic, eustatic, and climatic processes in cratonic basins: Gulf of Carpentaria, northern Australia

The Gulf of Carpentaria is a tropical, silled epicontinental sea and may be a modern analogue for ancient cratonic basins. For the purpose of this study, the Gulf of Carpentaria is compared to Pennsylvanian cratonic basins of the United States. During the Pennsylvanian, the North American continent moved from the Southern Hemisphere, through the Equator, into the Northern Hemisphere. Today, the Gulf of Carpentaria–New Guinea region is a few degrees south of the Equator and is moving towards it. During the Pennsylvanian, the world was subjected to major glaciations and associated sea-level changes. The island of New Guinea and the Gulf of Carpentaria have undergone similar processes during the Quaternary. A reconnaissance seismic survey of the gulf conducted by the USGS and the Australian National University (ANU), combined with oil-exploration well data, provided the first step in a systematic evaluation of a modern tropical epicontinental system. During the Cenozoic, the region was dominated by terrestrial sedimentation in a temperate climate. At the same time, carbonates were being deposited on the northern shelf edge of the Australian Plate. During the Miocene, carbonate deposition expanded southward into the gulf region. Then in the Late Miocene, carbonate sedimentation was replaced by terrigenous clastics derived from the developing Central Range of the island of New Guinea, which developed a wetter climate while moving northwards into the tropics. At least 14 basin-wide transgressive–regressive cycles are identified by channels that were eroded under subaerial conditions since about the Miocene. Comparison of the modern Gulf of Carpentaria sequences with those of the Pennsylvanian reveals many similarities.

Gulf Of Carpentaria↗

USGS2014

Natural regeneration processes in big sagebrush ( Artemisia tridentata )

Big sagebrush, Artemisia tridentata Nuttall (Asteraceae), is the dominant plant species of large portions of semiarid western North America. However, much of historical big sagebrush vegetation has been removed or modified. Thus, regeneration is recognized as an important component for land management. Limited knowledge about key regeneration processes, however, represents an obstacle to identifying successful management practices and to gaining greater insight into the consequences of increasing disturbance frequency and global change. Therefore, our objective is to synthesize knowledge about natural big sagebrush regeneration. We identified and characterized the controls of big sagebrush seed production, germination, and establishment. The largest knowledge gaps and associated research needs include quiescence and dormancy of embryos and seedlings; variation in seed production and germination percentages; wet-thermal time model of germination; responses to frost events (including freezing/thawing of soils), CO 2 concentration, and nutrients in combination with water availability; suitability of microsite vs. site conditions; competitive ability as well as seedling growth responses; and differences among subspecies and ecoregions. Potential impacts of climate change on big sagebrush regeneration could include that temperature increases may not have a large direct influence on regeneration due to the broad temperature optimum for regeneration, whereas indirect effects could include selection for populations with less stringent seed dormancy. Drier conditions will have direct negative effects on germination and seedling survival and could also lead to lighter seeds, which lowers germination success further. The short seed dispersal distance of big sagebrush may limit its tracking of suitable climate; whereas, the low competitive ability of big sagebrush seedlings may limit successful competition with species that track climate. An improved understanding of the ecology of big sagebrush regeneration should benefit resource management activities and increase the ability of land managers to anticipate global change impacts.

Rangeland Ecology and Management↗

USGS2004

Process based modeling of total longshore sediment transport

Waves, currents, and longshore sand transport are calculated locally as a function of position in the nearshore region using process based numerical models. The resultant longshore sand transport is then integrated across the nearshore to provide predictions of the total longshore transport of sand due to waves and longshore currents. Model results are in close agreement with the I l –P l correlation described by Komar and Inman (1970) and the CERC (1984) formula. Model results also indicate that the proportionality constant in the I l –P l formula depends weakly upon the sediment size, the shape of the beach profile, and the particular local sediment flux formula that is employed. Model results indicate that the various effects and influences of sediment size tend to cancel out, resulting in little overall dependence on sediment size.

Journal of Coastal Research↗

USGS1992

Hydrothermal ore-forming processes in the light of studies in rock- buffered systems: II. Some general geologic applications

The experimental metal solubilities for rock-buffered hydrothermal systems, reported by Hemley et al. (1992), provide important insights into the acquisition, transport, and deposition of metals in real hydrothermal systems that produced base metal ore deposits. Water-rock reactions that determine pH, together with total chloride and changes in temperature and fluid pressure, play significant roles in controlling the solubility of metals and determining where metals are fixed to form ore deposits.Hydrothermal systems circulate fluids and heat, and the transport path of a hydrothermal fluid is likely to lie somewhere between an adiabatic (no heat loss to adjacent rocks) and a geothermal (complete thermal equilibrium with adjacent rock) path. The transport path of the hydrothermal fluids emanating from, or circulating near, deep-seated crystallizing plutons can be approximated by a quasi-adiabatic pressure-temperature path. In such a quasi-adiabatic setting, the pressure effect on rock-buffered metal solubilities is significant and allows metal transport over long distances because the trend of decreasing metal solubility with decreasing temperature is compensated by the trend of increasing metal solubility with decreasing pressure. The high-temperature portion of a quasi-adiabatic hydrothermal system will tend to leach metals from the rock and fix K and Na in feldspars. The source of the extracted metals may be late-stage magmatic melt, trace metals distributed in the lattice of silicate minerals destroyed during rock metasomatism, and/or small amounts of base metal sulfides disseminated throughout a given rock.Deposition of metals in hydrothermal systems occurs where changes such as cooling, pH increase due to rock alteration, boiling, or fluid mixing cause the aqueous metal concentration to exceed saturation. Relative metal transport concentrations, the availability of sulfur, the disposition of the saturation surfaces relative to each other, and the interplay of these variables through time are the major factors controlling the pattern of metal deposition (and nondeposition).Metal zoning results from deposition occurring at successive saturation surfaces. Zoning is not a reflection simply of relative solubility but of the manner of intersection of transport concentration paths with those surfaces. The experimental results are consistent with the typical outward zonation of Cu-Zn-Pb observed in porphyry coppers, Butte-type base metal vein deposits, skarns, and massive sulfides. Implications to mineralization patterns in Mississippi Valley-type, sedimentary Cu, and other low-temperature deposits are also of interest, with due recognition of the greater uncertainty regarding speciation and attainment of equilibrium in those environments. In such deposits, a probable outward zoning of Cu-Zn-Pb-Fe is suggested from the results.Saturation surfaces will tend to migrate outward and inward in prograde and retrograde time, respectively, controlled by either temperature or chemical variables. This, in turn, gives rise to zone migration and, where one zone encroaches on another, the appropriate apparent paragenetic relations. Such textural implications are incorrect, however, unless viewed within the context of the overall mineralization process. Additional controls bearing on metal precipitation sequence and coprecipitation, the presence or absence of zoning, reversals in zoning, sulfidation state, and timing relations between alteration and metallization are implicit in the results and are discussed.

Economic Geology↗

USGS2011

Tourmaline as a recorder of ore-forming processes

Tourmaline occurs in diverse types of hydrothermal mineral deposits and can be used to constrain the nature and evolution of ore-forming fl uids. Because of its broad range in composition and retention of chemical and isotopic signatures, tourmaline may be the only robust recorder of original mineralizing processes in some deposits. Microtextures and in situ analysis of compositional and isotopic variations in ore-related tourmaline provide valuable insights into hydrothermal systems in seafl oor, sedimentary, magmatic, and metamorphic environments. Deciphering the hydrothermal record in tourmaline also holds promise for aiding exploration programs in the search for new ore deposits.

Elements↗

USGS1971

EROS — New observation vantage points and processes

The EROS Program objective is to utilize aircraft and spacecraft remote-sensing technology as complementary parts of integrated data collection, processing, and dissemination systems to support resources research and management functions of the Department of the Interior. The Program develops and coordinates research in the applications of new sensors for resources applications in cooperation with NASA. At present there are two major areas of activity: present there are two major areas of activity: The first is related to the Earth Resources Technology Satellite (ERTS). The second is a suite of projects designed to determine the applicability of new aerial and satellite sensing systems and techniques to geologic, geographic, hydrologic, and topographic mapping and for supporting natural resources management functions of the Department of the Interior. Programs with similar goals for agriculture and forestry, and for oceanography are being conducted in the Departments of Agriculture, Commerce, the Naval Oceanographic Office, and in a number of colleges and universities. The first satellite designed specifically for resources research and applications, ERTS-A, is to be launched in early 1972. It will be an unmanned satellite carrying three experimental systems: A three camera Return Beam Vidicon (RBV) system, a 4-band Multispectral Scanning (MSS) radiometer system, and a Data Collection System (DCS). The RBV cameras will photograph simultaneously and instantaneously areas of the earth 100 × 100 nautical miles - or 10,000 square nautical miles - in the blue-green (.475-.575mu m), the red (.580-.680mu m), and the near infrared (.690-.830mu m). The MSS will record three wavelength bands in the same general spectral range and the fourth band (8.0 mu m) will extend farther into the infrared...

Conference Paper↗

USGS2002

Transport and fate of nitrate in a glacial outwash aquifer in relation to ground water age, land use practices, and redox processes

A combination of ground water modeling, chemical and dissolved gas analyses, and chlorofluorocarbon age dating of water was used to determine the relation between changes in agricultural practices, and NO − 3 concentrations in ground water of a glacial outwash aquifer in west-central Minnesota. The results revealed a redox zonation throughout the saturated zone with oxygen reduction occurring near the water table, NO − 3 reduction immediately below it, and then a large zone of ferric iron reduction, with a small area of sulfate (SO 2− 4 ) reduction and methanogenesis (CH 4 ) near the end of the transect. Analytical and NETPATH modeling results supported the hypothesis that organic carbon served as the electron donor for the redox reactions. Denitrification rates were quite small, 0.005 to 0.047 mmol NO − 3 yr −1 , and were limited by the small amounts of organic carbon, 0.01 to 1.45%. In spite of the organic carbon limitation, denitrification was virtually complete because residence time is sufficient to allow even slow processes to reach completion. Ground water sample ages showed that maximum residence times were on the order of 50 to 70 yr. Reconstructed NO − 3 concentrations, estimated from measured NO − 3 and dissolved N gas showed that NO − 3 concentrations have been increasing in the aquifer since the 1940s, and have been above the 714 μmol L −1 maximum contaminant level at most sites since the mid- to late-1960s. This increase in NO − 3 has been accompanied by a corresponding increase in agricultural use of fertilizer, identified as the major source of NO − 3 to the aquifer.

Minnesota↗

USGS2012

Soil property control of biogeochemical processes beneath two subtropical stormwater infiltration basins

Substantially different biogeochemical processes affecting nitrogen fate and transport were observed beneath two stormwater infiltration basins in north-central Florida. Differences are related to soil textural properties that deeply link hydroclimatic conditions with soil moisture variations in a humid, subtropical climate. During 2008, shallow groundwater beneath the basin with predominantly clayey soils (median, 41% silt+clay) exhibited decreases in dissolved oxygen from 3.8 to 0.1 mg L -1 and decreases in nitrate nitrogen (NO 3 - –N) from 2.7 mg L -1 to <0.016 mg L -1 , followed by manganese and iron reduction, sulfate reduction, and methanogenesis. In contrast, beneath the basin with predominantly sandy soils (median, 2% silt+clay), aerobic conditions persisted from 2007 through 2009 (dissolved oxygen, 5.0–7.8 mg L -1 ), resulting in NO 3 - –N of 1.3 to 3.3 mg L -1 in shallow groundwater. Enrichment of d15N and d18O of NO 3 - combined with water chemistry data indicates denitrification beneath the clayey basin and relatively conservative NO 3 - transport beneath the sandy basin. Soil-extractable NO 3 - –N was significantly lower and the copper-containing nitrite reductase gene density was significantly higher beneath the clayey basin. Differences in moisture retention capacity between fine- and coarse-textured soils resulted in median volumetric gas-phase contents of 0.04 beneath the clayey basin and 0.19 beneath the sandy basin, inhibiting surface/subsurface oxygen exchange beneath the clayey basin. Results can inform development of soil amendments to maintain elevated moisture content in shallow soils of stormwater infiltration basins, which can be incorporated in improved best management practices to mitigate NO 3 - impacts.

Florida↗

USGS1996

Numerical evaluation of static-chamber measurements of soil-atmospheric gas exchange--Identification of physical processes

The exchange of gases between soil and atmosphere is an important process that affects atmospheric chemistry and therefore climate. The static-chamber method is the most commonly used technique for estimating the rate of that exchange. We examined the method under hypothetical field conditions where diffusion was the only mechanism for gas transport and the atmosphere outside the chamber was maintained at a fixed concentration. Analytical and numerical solutions to the soil gas diffusion equation in one and three dimensions demonstrated that gas flux density to a static chamber deployed on the soil surface was less in magnitude than the ambient exchange rate in the absence of the chamber. This discrepancy, which increased with chamber deployment time and air-filled porosity of soil, is attributed to two physical factors: distortion of the soil gas concentration gradient (the magnitude was decreased in the vertical component and increased in the radial component) and the slow transport rate of diffusion relative to mixing within the chamber. Instantaneous flux density to a chamber decreased continuously with time; steepest decreases occurred so quickly following deployment and in response to such slight changes in mean chamber headspace concentration that they would likely go undetected by most field procedures. Adverse influences of these factors were reduced by mixing the chamber headspace, minimizing deployment time, maximizing the height and radius of the chamber, and pushing the rim of the chamber into the soil. Nonlinear models were superior to a linear regression model for estimating flux densities from mean headspace concentrations, suggesting that linearity of headspace concentration with time was not necessarily a good indicator of measurement accuracy.

Soil Science Society of America Journal↗

USGS2008

Modeling soil moisture processes and recharge under a melting snowpack

Recharge into granitic bedrock under a melting snowpack is being investigated as part of a study designed to understand hydrologic processes involving snow at Yosemite National Park in the Sierra Nevada Mountains of California. Snowpack measurements, accompanied by water content and matric potential measurements of the soil under the snowpack, allowed for estimates of infiltration into the soil during snowmelt and percolation into the bedrock. During portions of the snowmelt period, infiltration rates into the soil exceeded the permeability of the bedrock and caused ponding to be sustained at the soil-bedrock interface. During a 5-d period with little measured snowmelt, drainage of the ponded water into the underlying fractured granitic bedrock was estimated to be 1.6 cm d?1, which is used as an estimate of bedrock permeability. The numerical simulator TOUGH2 was used to reproduce the field data and evaluate the potential for vertical flow into the fractured bedrock or lateral flow at the bedrock-soil interface. During most of the snowmelt season, the snowmelt rates were near or below the bedrock permeability. The field data and model results support the notion that snowmelt on the shallow soil overlying low permeability bedrock becomes direct infiltration unless the snowmelt rate greatly exceeds the bedrock permeability. Late in the season, melt rates are double that of the bedrock permeability (although only for a few days) and may tend to move laterally at the soil-bedrock interface downgradient and contribute directly to streamflow. ?? Soil Science Society of America.

Conference Paper↗

USGS2001

Stable isotopes in seafloor hydrothermal systems: Vent fluids, hydrothermal deposits, hydrothermal alteration, and microbial processes

The recognition of abundant and widespread hydrothermal activity and associated unique life-forms on the ocean floor is one of the great scientific discoveries of the latter half of the twentieth century. Studies of seafloor hydrothermal processes have led to revolutions in understanding fluid convection and the cooling of the ocean crust, the chemical and isotopic mass balance of the oceans, the origin of stratiform and statabound massive-sulfide ore-deposits, the origin of greenstones and serpentinites, and the potential importance of the subseafloor biosphere. Stable isotope geochemistry has been a critical and definitive tool from the very beginning of the modern era of seafloor exploration.

Reviews in Mineralogy and Geochemistry↗

USGS2023

Lunar mare basaltic volcanism: Volcanic features and emplacement processes

Volcanism is a fundamental process in the geological evolution of the Moon, providing clues to the composition and structure of the mantle, the location and duration of interior melting, the nature of convection and lunar thermal evolution. Progress in understanding volcanism has been remarkable in the short 60-year span of the Space Age. Before Sputnik 1 in 1957, the lunar farside was unknown, the origin of the dark lunar maria was debated (sedimentary or volcanic), and significant controversy surrounded the question of how the multitude of craters on the surface formed. Was the Moon formed hot or cold, was the lunar surface young or old, were the craters of impact or volcanic origin? A lunar farside deficient in the darker maria was revealed by Luna 3 in 1959 ( Lipsky 1965a , b ). The Ranger, Lunar Orbiter, Surveyor, Luna and Zond missions significantly augmented pre-Sputnik telescopic observations and began to reveal the diversity of lunar geologic landforms. Return of lunar soil and rock samples from the lunar surface by Apollo (11–12, 14–17) ( Compton 1989 ) and Luna (16, 20, 24) missions ( Harvey 2007a , b ; Huntress and Marov 2011 ) changed the debates overnight ( Hinners 1971 ; Taylor 1975 ). The lunar rocks were igneous and extremely ancient, all from the first half of Solar System history; the oldest, highland anorthosites, were overlain by relatively younger, but still extremely old, extrusive basalts forming the maria.

Reviews in Mineralogy and Geochemistry↗

USGS2004

Effects of elk herbivory on vegetation and nitrogen processes

We used 35-year and 4-year ungulate exclosures to determine the effects of elk ( Cervus elaphus ) herbivory on above-ground and below-ground production and soil fertility on the elk winter range in Rocky Mountain National Park (RMNP), Colorado, USA. We used paired grazed and ungrazed plots to evaluate ungulate herbivory effects in short and tall willow ( Salix spp.), aspen ( Populus spp.), and upland grass/shrub vegetation associations. We measured nitrogen (N) fluxes (litter deposition, fecal and urinary deposition from elk, movements of N by elk, N mineralization, soil N availability, elk consumption rates) within the elk winter, above-ground and below-ground N pools (herbaceous, shrub and root biomass, %N in plants, roots, and soil), and N fluxes on and off the elk winter range (seasonal movement of N by elk). Nitrogen mineralization and soil nitrate (NO 3 ) pools were reduced in the short willow community ( P = 0.07 and 0.10, respectively; n = 4 sites) in grazed plots, but not in the upland grass/shrub community or tall willow sites ( P >0.10). Annual growth of willows was reduced by 98% in grazed plots, relative to 35-year exclosures, and 66% relative to 4-year exclosures. Thus, height, canopy size, and litter biomass of willows were reduced, and N yield of willows was 64% less in grazed plots. We evaluated movement of N by elk among 6 major vegetation associations and found that elk grazed more and bedded less in willow vegetation association compared to mixed conifer, mesic meadow, and grassland/shrub associations ( P = 0.014, 0.001, and 0.026, respectively), suggesting that elk herbivory and movement led to a net loss of N in the willow vegetation association. Elk spent less total time in willows than mesic meadow association, yet they consumed large amounts of willow plant biomass. We recommend management of elk numbers and elk herbivory that takes into consideration impacts to N process function, as negative effects from current levels of herbivory were observed in ≥1 of 3 vegetation associations studied.

Colorado↗

USGS1989

Retention and transport of nutrients in a third-order stream: Channel processes

Chloride was injected as a conservative tracer with nitrate to examine nitrate retention (storage plus biotic uptake) and transport in a 327—m reach of a third—order stream draining a forested basin in northwestern California. Prior to injections, diel patterns of nutrient concentrations were measured under background conditions. Nitrate concentration of stream water increased downstream, indicating that the reach was a source of dissolved inorganic nitrogen to downstream communities under background, low—flow conditions, despite uptake by photoautotrophs. At the onset of continuous solute injection over a 10—d period, timing the passage of the solute front indicated that storage dominated nitrate retention. Instantaneous concentration differences at the base of the reach at hour 24 indicated that biotic uptake accounted for 13% of the nitrate amendment while hydrologic storage constituted 29%. Corrected for groundwater dilution (11.7%), saturation of the stream's channel and hyporheic zones was not complete until 6.8 d of continuous injection. By day 3 nitrate retention was dominated by biotic processes. Biotic uptake was greatest during daylight hours indicating retention by photoautotrophs, but also occurred during darkness. After 10 d of continuous injection, mass balance calculations indicated that 29% of N (339 g) was retained from the total injected (1155 g), while the balance of injected nitrate was transported downstream. Storage of NO 3 — N was 117 g or 10% while biotic uptake was 222 g or 19%. Periphyton biomass on slides, chlorophyll a both on slides and on natural cobbles, and net community primary production all indicated a lag in periphyton response to nitrate amendment. Earliest indicators of a biotic response to nutrient amendment were decreases in both tissue C/N and epilithic respiration.

Ecology↗

USGS2025

Catastrophic lava flow levee failure: Precursors, processes, and implications

During an effusive eruption crisis the initial advance of a lava flow is typically the primary focus of model forecasts and hazard management efforts. Flow branching and lateral expansion of lava flows can pose significant dangers within evolving flow fields throughout the duration of an eruption and are an underappreciated hazard. We use field monitoring, infrasound, time lapse imagery, and lidar data collected during the 2018 lower East Rift Zone eruption of Kīlauea (Hawai‘i) to track the origins, progression, and implications of a flow branching event caused by catastrophic levee failure. Our analyses show that surges in effusion rate, rheologic transitions between pāhoehoe and ‘a‘ā flow regimes, slope-breaks, pre-existing topographic highs, and the structure of perched levee walls all played a role in the failure of the levee and subsequent re-routing of the lava flow. Failure of perched lava structures leads to an acutely hazardous situation because lava impounded by the structure can rapidly inundate the landscape. This is the first time a levee failure event has been observed in such detail with numerous monitoring techniques; this unprecedented level of observation provides quantifiable insights into levee failure processes that have important implications for hazard mitigation and an improved understanding of lava flow emplacement dynamics.

Hawaii↗

USGS1962

Digital processing of array seismic recordings

This technical letter contains a brief review of the operations which are involved in digital processing of array seismic recordings by the methods of velocity filtering, summation, cross-multiplication and integration, and by combinations of these operations (the "UK Method" and multiple correlation). Examples are presented of analyses by the several techniques on array recordings which were obtained by the U.S. Geological Survey during chemical and nuclear explosions in the western United States. Seismograms are synthesized using actual noise and P n -signal recordings, such that the signal-to-noise ratio, onset time and velocity of the signal are predetermined for the synthetic record. These records are then analyzed by summation, cross-multiplication, multiple correlation and the UK technique, and the results are compared. For all of the examples presented, analysis by the non-linear techniques of multiple correlation and cross-multiplication of the traces on an array recording are preferred to analyses by the linear operations involved in summation and the UK Method.

Crustal Studies Technical Letter↗