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At least 883 records · Page 49Linked to original sources
USGS2002

Interpretation of borehole geophysical logs, aquifer-isolation tests, and water quality, supply wells 1 and 2, Willow Grove Naval Air Station/Joint Reserve Base, Horsham Township, Montgomery County, Pennsylvania

Ground water pumped from supply wells 1 and 2 on the Willow Grove Naval Air Station/Joint Reserve Base (NAS/JRB) provides water for use at the base, including potable water for drinking. The supply wells have been contaminated by volatile organic compounds (VOC's), particularly trichloroethylene (TCE) and tetrachloroethylene (PCE), and the water is treated to remove the VOC's. The Willow Grove NAS/JRB and surrounding area are underlain by sedimentary rocks of the Triassic-age Stockton Formation, which form a complex, heterogeneous aquifer. The ground-water-flow system for the supply wells was characterized by use of borehole geophysical logs and heatpulse-flowmeter measurements. The heatpulse-flowmeter measurements showed upward and downward borehole flow under nonpumping conditions in both wells. The hydraulic and chemical properties of discrete water-bearing fractures in the supply wells were characterized by isolating each water-bearing fracture with straddle packers. Eight fractures in supply well 1 and five fractures in supply well 2 were selected for testing on the basis of the borehole geophysical logs and borehole television surveys. Water samples were collected from each isolated fracture and analyzed for VOC?s and inorganic constituents. Fractures at 50–59, 79–80, 196, 124–152, 182, 241, 256, and 350–354 ft btoc (feet below top of casing) were isolated in supply well 1. Specific capacities ranged from 0.26 to 5.7 (gal/min)/ft (gallons per minute per foot) of drawdown. The highest specific capacity was for the fracture isolated at 179.8–188 ft btoc. Specific capacity and depth of fracture were not related in either supply well. The highest concentrations of PCE were in water samples collected from fractures isolated at 236.8–245 and 249.8–258 ft btoc, which are hydraulically connected. The concentration of PCE generally increased with depth to a maximum of 39 mg/L (micrograms per liter) at a depth of 249.8? 258 ft btoc and then decreased to 21 mg/L at a depth of 345.3–389 ft btoc. Fractures at 68–74, 115, 162, 182, 205, and 314 ft btoc were isolated in supply well 2. Specific capacities ranged from 0.08 to less than 2.9 (gal/ min)/ft. The highest specific capacity was for the fracture isolated at 157–165.2 ft btoc. Concentrations of detected VOC's in water samples were 3.6 mg/L or less. Lithologic units penetrated by both supply wells were determined by correlating naturalgamma and single-point-resistance borehole geophysical logs. All lithologic units are not continuous water-bearing units because water-bearing fractures are not necessarily present in the same lithologic units in each well. Although the wells penetrate the same lithologic units, the lithologic location of only three water-bearing fractures are common to both wells. The same lithologic unit may have different hydraulic properties in each well. A regional ground-water divide is southeast of the supply wells. From this divide, ground water flows northwest toward Park Creek, a tributary to Little Neshaminy Creek. Potentiometric-surface maps were prepared from water levels measured in shallow and deep wells. For both depth intervals, the direction of ground-water flow is toward the northwest. For most well clusters, the vertical head gradient is downward from the shallow to the deeper part of the aquifer. Pumping of the supply wells at times can cause the vertical flow direction to reverse.

Water-Resources Investigations Report↗
USGS1984

Analysis and interpretation of data obtained in tests of the geothermal aquifer at Klamath Falls, Oregon

Water with temperatures to 130 C occurs in an extensive, heterogeneous aquifer at depths of a few hundred to nearly 2,000 feet. Chemical and isotopic analyses suggest that 190 C water mixes with cooler recharge water in a ratio of about 2 to 3 in zone within and beneath the aquifer. The water spreads from a fault zone and is tapped for space heating by more than 450 wells over a 2 square-mile area. Data obtained during a 50-day pumping and reinjection test in July and August, 1983, were fitted to theoretical double-porosity type curves. Predictions of water-level changes were made for two hypothetical pumping and reinjection schemes. It was determined that reinjection can generally offset declines due to pumping, although water levels will decline near pumped wells and will rise near injection wells. Tracer tests confirmed the double-porosity behavior of the aquifer. Discharge from thermal wells averages about 540 gallons per minute and heat discharge is about 18 x 10 to the 12th power British Thermal Units per year. Down-hole heat exchangers discharge about 13 x 10 to the 10th power British Thermal Units per year. Additional development probably is feasible. (USGS)

Water-Resources Investigations Report↗
USGS1986

Compilation and preliminary interpretation of hydrologic data for the Weldon Spring radioactive waste-disposal sites, St Charles County, Missouri — A progress report

The Weldon Spring Chemical Plant is located just north of the drainage divide separating the Mississippi River and the Missouri River in St. Charles County, Missouri. From 1957 to 1966 the plant converted uranium-ore concentrates and recycled scrap to pure uranium trioxide, uranium tetrafluoride, and uranium metal. Residues from these operations were pumped to four large pits that had been excavated near the plant. Small springs and losing streams are present in the area. Water overlying the residue in the pits has a large concentration of dissolved solids and a different chemical composition compared to the native groundwater and surface water. This difference is indicated by the concentrations of calcium, sodium, sulfate, nitrate, fluoride, uranium, radium, lithium, molybdenum, strontium, and vanadium, all of which are greater than natural or background concentrations. Water from Burgermeister Spring, located about 1.5 miles north of the chemical plant area, contains uranium and nitrate concentrations greater than background concentrations. Groundwater in the shallow bedrock aquifer moves northward from the vicinity of the chemical plant toward Dardenne Creek. An abandoned limestone quarry several miles southwest of the chemical plant also has been used for the disposal of radioactive waste and rubble. Groundwater flow from the quarry area is southward through the alluvium, away from the quarry and toward the Missouri River. The St. Charles County well field is located in the Missouri River flood plain near the quarry and the large yield wells are open to the Missouri River alluvial aquifer. Water from a well 4,000 ft southeast of the quarry was analyzed; there was no indication of contamination from the quarry. Additional water quality and water level data are needed to determine if water from the quarry moves toward the well field. Observation wells need to be installed in the area between the chemical plant, pits, and Dardenne Creek. The wells would be used to provide access for measurements of depth to ground water and for the collection of water samples from the shallow bedrock aquifer.

Missouri↗
USGS1994

Summary and interpretation of dye-tracer tests to investigate the hydraulic connection of fractures at a ridge-and-valley-wall site, near Fishtrap Lake, Pike County, Kentucky

Dye-tracer tests were done during 1985-92 to investigate the hydraulic connection between fractures in Pennsylvanian coal-bearing strata at a ridge-and-valley-wall site near Fishtrap Lake, Pike County, Ky. Fluorescent dye was injected into a core hole penetrating near-surface and mining-induced fractures near the crest of the ridge. The rate and direction of migration of dye in the subsurface were determined by measuring the relative concentration of dye in water samples collected from piezometers completed in conductive fracture zones and fractured coal beds at various stratigraphic horizons within the ridge. Dye-concentration data and water-level measurements for each piezometer were plotted as curves on dye-recovery hydrographs. The dye-recovery hydrographs were used to evaluate trends in the fluctuation of dye concentrations and hydraulic heads in order to identify geologic and hydrologic factors affecting the subsurface transport of dye. The principal factors affecting the transport of dye in the subsurface hydrologic system were determined to be (1) the distribution, interconnection, and hydraulic properties of fractures; (2) hydraulic-head conditions in the near-fracture zone at the time of dye injection; and (3) subsequent short- and long-term fluctuations in recharge to the hydrologic system. In most of the dye-tracer tests, dye-recovery hydrographs are characterized by complex, multipeaked dye-concentration curves that are indicative of a splitting of dye flow as ground water moved through fractures. Intermittent dye pulses (distinct upward spikes in dye concentration) mark the arrivals of dye-labeled water to piezometers by way of discrete fracture-controlled flow paths that vary in length, complexity, and hydraulic conductivity. Dye injections made during relatively high- or increasinghead conditions resulted in rapid transport of dye (within several days or weeks) from near-surf ace fractures to piezometers. Injections made during relatively low- or decreasing-head conditions resulted in dye being trapped in hydraulically dead zones in water-depleted fractures. Residual dye was remobilized from storage and transported (over periods ranging from several months to about 2 years) by increased recharge to the hydrologic system. Subsequent fluctuations in hydraulic gradients, resulting from increases or decreases in recharge to the hydrologic system, acted to speed or slow the transport of dye along the fracture-controlled flow paths. The dye-tracer tests also demonstrated that mining-related disturbances significantly altered the natural fracture-controlled flow paths of the hydrologic system over time. An abandoned underground mine and subsidence-related surface cracks extend to within 250 ft of the principal dye-injection core hole. Results from two of the dye-tracer tests at the site indicate that the annular seal in the core hole was breached by subsurface propagation of the mining-induced fractures. This propagation of fractures resulted in hydraulic short-circuiting between the dye-injection zone in the core hole and two lower piezometer zones, and a partial disruption of the hydraulic connection between the injection core hole and downgradient piezometers on the ridge crest and valley wall. In addition, injected dye was detected in piezometers monitoring a flooded part of the abandoned underground mine. Dye was apparently transported into the mine through a hydraulic connection between the injection core hole and subsidence-related fractures.

Kentucky↗
USGS1970

Study and interpretation of the chemical characteristics of natural water

The chemical composition of natural water is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from activities of man. Some of the processes of solution or precipitation of minerals can be closely evaluated by means of principles of chemical equilibrium including the law of mass action and the Nernst equation. Other processes are irreversible and require consideration of reaction mechanisms and rates. The chemical composition of the crustal rocks of the earth and the composition of the ocean and the atmosphere are significant in evaluating sources of solutes in natural fresh water. The ways in which solutes are taken up or precipitated and the amounts present in solution are influenced by many environmental factors, especially climate, structure and position: of rock strata, and biochemical effects associated with life cycles of plants and animals, both microscopic and macroscopic. Taken all together and in application with the further influence of the general circulation of all water in the hydrologic cycle, the chemical principles and environmental factors form a basis for the developing science of natural-water chemistry. Fundamental data used in the determination of water quality are obtained by the chemical analysis of water samples in the laboratory or onsite sensing of chemical properties in the field. Sampling is complicated by changes in composition of moving water and the effects of particulate suspended material. Most of the constituents determined are reported in gravimetric units, usually milligrams per liter or milliequivalents per liter. More than 60 constituents and properties are included in water analyses frequently enough to provide a basis for consideration of the sources from which each is generally derived, most probable forms of elements and ions in solution, solubility controls, expected concentration ranges and other chemical factors. Concentrations of elements that are commonly present in amounts less than a few tens of micrograms per liter cannot always be easily explained, but present information suggests many are controlled by solubility of hydroxide or carbonate or by sorption on solid particles. Chemical analyses may be grouped and statistically evaluated by averages, frequency distributions, or ion correlations to summarize large volumes of data. Graphing of analyses or of groups of analyses aids in showing chemical relationships among waters, probable sources of solutes, areal water-quality regimen, and water-resources evaluation. Graphs may show water type based on chemical composition, relationships among ions, or groups of ions in individual waters or many waters considered simultaneously. The relationships of water quality to hydrologic parameters, such as stream discharge rate or ground-water flow patterns, can be shown by mathematical equations, graphs, and maps. About 75 water analyses selected from the literature are tabulated to illustrate the relationships described, and some of these, along with many others that are not tabulated, are also utilized in demonstrating graphing and mapping techniques. Relationships of water composition to source rock type are illustrated by graphs of some of the tabulated analyses. Activities of man may modify water composition extensively through direct effects of pollution and indirect results of water development, such as intrusion of sea water in ground-water aquifiers. Water-quality standards for domestic, agricultural, and industrial use have been published by various agencies. Irrigation project requirements for water quality are particularly intricate. Fundamental knowledge of processes that control natural water composition is required for rational management of water quality.

Water Supply Paper↗
USGS1959

Study and interpretation of the chemical characteristics of natural water

The chemical composition of natural water is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from activities of man. Some of the processes of solution or precipitation of minerals can be closely evaluated by means of principles of chemical equilibrium including the law of mass action and the Nernst equation. Other processes are irreversible and require consideration of reaction mechanisms and rates. The chemical composition of the crustal rocks of the earth and the composition of the ocean and the atmosphere are significant in evaluating sources of solutes in natural fresh water. The ways in which solutes are taken up or precipitated and the amounts present in solution are influenced by many environmental factors, especially climate, structure and position: of rock strata, and biochemical effects associated with life cycles of plants and animals, both microscopic and macroscopic. Taken all together and in application with the further influence of the general circulation of all water in the hydrologic cycle, the chemical principles and environmental factors form a basis for the developing science of natural-water chemistry. Fundamental data used in the determination of water quality are obtained by the chemical analysis of water samples in the laboratory or onsite sensing of chemical properties in the field. Sampling is complicated by changes in composition of moving water and the effects of particulate suspended material. Most of the constituents determined are reported in gravimetric units, usually milligrams per liter or milliequivalents per liter. More than 60 constituents and properties are included in water analyses frequently enough to provide a basis for consideration of the sources from which each is generally derived, most probable forms of elements and ions in solution, solubility controls, expected concentration ranges and other chemical factors. Concentrations of elements that are commonly present in amounts less than a few tens of micrograms per liter cannot always be easily explained, but present information suggests many are controlled by solubility of hydroxide or carbonate or by sorption on solid particles. Chemical analyses may be grouped and statistically evaluated by averages, frequency distributions, or ion correlations to summarize large volumes of data. Graphing of analyses or of groups of analyses aids in showing chemical relationships among waters, probable sources of solutes, areal water-quality regimen, and water-resources evaluation. Graphs may show water type based on chemical composition, relationships among ions, or groups of ions in individual waters or many waters considered simultaneously. The relationships of water quality to hydrologic parameters, such as stream discharge rate or ground-water flow patterns, can be shown by mathematical equations, graphs, and maps. About 75 water analyses selected from the literature are tabulated to illustrate the relationships described, and some of these, along with many others that are not tabulated, are also utilized in demonstrating graphing and mapping techniques. Relationships of water composition to source rock type are illustrated by graphs of some of the tabulated analyses. Activities of man may modify water composition extensively through direct effects of pollution and indirect results of water development, such as intrusion of sea water in ground-water aquifiers. Water-quality standards for domestic, agricultural, and industrial use have been published by various agencies. Irrigation project requirements for water quality are particularly intricate. Fundamental knowledge of processes that control natural water composition is required for rational management of water quality.

Water Supply Paper↗
USGS1972

Hydrologic interpretations based on infrared imagery of Long Island, New York

Six remote-sensing flights over Long Island's north and south shores were made during the period July 13, 1967, to February 25, 1970. Infrared imagery in the 8- to 14-micrometer range was obtained; results varied from poor to excellent in quality. The ability of the RS 7 and Reconofax IV imagers to discern thermal contrasts of as little .as 1 ? to 2?C (Celsius) permitted identification of areas of heavy ground-water discharge. These areas were concentrated primarily along the eroded headlands of the north shore and in the lower reaches of watercourses draining into Great South Bay. Only a few highly localized examples of direct ground-water discharge into the embankments ,along Long Island's south shore were detected in the imagery. Thermal loading emanating from a powerplant near Oceanside is shown to be quickly dissipated in Middle Bay. Specific examples show that infrared imagery may ,also be used to identify circulation patterns, ice cover, changes in stream-temperature regimen, and the location of sewer outfalls. Optimal time for the collection of infrared imagery for hydrologic studies on Long Island is in summer and in winter, when surface-water thermal differences are relatively large.

Water Supply Paper↗
USGS1985

Study and interpretation of the chemical characteristics of natural water

The chemical composition of natural water is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from human activities. Broad interrelationships among these processes and their effects can be discerned by application of principles of chemical thermodynamics. Some of the processes of solution or precipitation of minerals can be closely evaluated by means of principles of chemical equilibrium, including the law of mass action and the Nernst equation. Other processes are irreversible and require consideration of reaction mechanisms and rates. The chemical composition of the crustal rocks of the Earth and the composition of the ocean and the atmosphere are significant in evaluating sources of solutes in natural freshwater. The ways in which solutes are taken up or precipitated and the amounts present in solution are influenced by many environmental factors, especially climate, structure and position of rock strata, and biochemical effects associated with life cycles of plants and animals, both microscopic and macroscopic. Taken together and in application with the further influence of the general circulation of all water in the hydrologic cycle, the chemical principles and environmental factors form a basis for the developing science of natural-water chemistry. Fundamental data used in the determination of water quality are obtained by the chemical analysis of water samples in the laboratory or onsite sensing of chemical properties in the field. Sampling is complicated by changes in the composition of moving water and by the effects of particulate suspended material. Some constituents are unstable and require onsite determination or sample preservation. Most of the constituents determined are reported in gravimetric units, usually milligrams per liter or milliequivalents per liter. More than 60 constituents and properties are included in water analyses frequently enough to provide a basis for consideration of the sources from which each is generally derived, the most probable forms of elements and ions in solution, solubilitycontrols, expected concentration ranges, and other chemical factors. Mechanisms that control concentrations of elements commonly present in amounts less than a few tens of micrograms per liter cannot always be easily ascertained, but present information suggests that many are controlled by solubility of their hydroxides or carbonates or by sorption on solid particles. Many dissolved organic compounds can now be specifically determined. Chemical analyses may be grouped and statistically evaluated by means, medians, frequency distributions, or ion correlations to summarize large volumes of data. Graphing of analyses or of groups of analyses aids in showing chemical relationships among water, probable sources of solutes, areal water-quality regimen, temporal and spatial variation, and water-resources evaluation. Graphs may show water type based on chemical composition, relationships among ions, or groups of ions in individual waters or many waters considered simultaneously. The relationships of water quality to hydrogeologic characteristics, such as stream discharge rate or ground-water flow patterns, can be shown by mathematical equations, graphs, and maps. About 80 water analyses selected from the literature are tabulated to illustrate the relationships described, and some of these, along with many others that are not tabulated, are also used in demonstrating graphing and mapping techniques. Relationships of water composition to source rock type are illustrated by graphs of some of the tabulated analyses. Human activities may modify water composition extensively through direct effects of pollution and indirect results of water development, such as intrusion of seawater in groundwater aquifers. Water-quality standards for domestic, agricultural, and industrial use have been published by various agencies. Irrigation project requirements for water quality are particularly intricate. Fundamental knowledge of processes that control natural-water composition is required for rational management of water quality.

Water Supply Paper↗
USGS1987

Analysis and interpretation of water-quality trends in major U.S. rivers, 1974-81

Water-quality records from two nationwide sampling networks are now of sufficient length to permit nationally consistent analysis of long-term water-quality trends at more than 300 locations on major U.S. rivers. Observed trends in 24 water-quality measures for the period 1974--81 provide evidence of both improvement and deterioration in stream quality during a time of major changes in atmospheric and terrestrial influences on surface waters. Particularly noteworthy are widespread decreases in lead and fecal bacteria concentrations and widespread increases in nitrate, arsenic, and cadmium concentrations. Changes in municipal waste treatment, leaded-gasoline consumption, highway-salt use, and nitrogen-fertilizer application, and regionally variable trends in coal production and combustion during the period, appear to be reflected in water-quality changes. There is evidence that atmospheric deposition of a variety of substances has played a surprisingly large role in water-quality changes.

Water Supply Paper↗
USGS2017

The significance of pre-existing, deeply weathered crystalline rock in interpreting the effects of glaciation in the Minnesota River valley, U.S.A.

Minnesota is largely underlain by Precambrian crystalline bedrock that was weathered to an average depth of 30 m prior to Late Cretaceous time. The fresh-rock-weathered-rock interface is irregular, with as much as 45 m of relief. Weathering exploited joints, locally isolating meter-sized volumes of rock known as corestones. Variable amounts of residuum were removed through glaciation to leave (1) saprolite overlain by an in-situ Late Cretaceous soil profile; (2) partially eroded saprolite; and (3) undulating fresh rock surfaces (commonly mantled by rounded boulders) that display striae and glacial or fluvial polish. Significant subglacial erosion of fresh bedrock is not required to form smoothly undulating bedrock surfaces with closed depressions; they may also form through removal of weathered bedrock and exposure of the weathering front. Large rounded boulders are not always shaped during transport; they may represent chemically rounded corestones resting at or near the bedrock source. Unambiguous evidence for glacial erosion includes striae and streamlining of bedrock parallel to striae. Polish on rock can be created fluvially, and smoothed grooves and ridges in the rock may be chemically produced. Many rounded boulders found in glacial till and strewn on bedrock surfaces probably originated as corestones.

Annals of Glaciology↗
USGS2021

The Yorktown Formation: Improved stratigraphy, chronology and paleoclimate interpretations from the U.S. mid-Atlantic Coastal Plain

The Yorktown Formation records paleoclimate conditions along the mid-Atlantic Coastal Plain during the mid-Piacenzian Warm Period (3.264 to 3.025 Ma), a climate interval of the Pliocene in some ways analogous to near future climate projections. To gain insight into potential near future changes, we investigated Yorktown Formation outcrops and cores in southeastern Virginia, refining the stratigraphic framework. We analyzed 485 samples for alkenone-based sea surface temperature (SST) and productivity estimates from the Holland and Dory cores, an outcrop at Morgarts Beach, Virginia, and the lectostratotype of the Yorktown Formation at Rushmere, Virginia, and analyzed planktonic foraminferal assemblage data from the type section. Using the structure of the SST record, we improved the chronology of the Yorktown Formation by establishing the maximum age ranges of the Rushmere (3.3–3.2 Ma) and Morgarts Beach (3.2–3.15 Ma) Members. SST values for these members average ~26 °C, corroborating existing sclerochronological data. Increasing planktonic foraminifer abundance, productivity, and species diversity parallel increasing SST over the MIS M2/M1 transition. These records constitute the greatest temporal concentration of paleoecological estimates within the Yorktown Formation, aiding our understanding of western North Atlantic temperature patterns, seasonality and ocean circulation during this interval. We provide a chronologic framework for future studies analyzing ecological responses to profound climate change.

Virginia↗
USGS2014

Interpreting the paleozoogeography and sea level history of thermally anomalous marine terrace faunas: A case study from the the last interglacial complex of San Clemente Island, California

Marine invertebrate faunas with mixtures of extralimital southern and extralimital northern faunal elements, called thermally anomalous faunas, have been recognized for more than a century in the Quaternary marine terrace record of the Pacific Coast of North America. Although many mechanisms have been proposed to explain this phenomenon, no single explanation seems to be applicable to all localities where thermally anomalous faunas have been observed. Here, we describe one such thermally anomalous fossil fauna that was studied on the second emergent marine terrace at Eel Point on San Clemente Island. The Eel Point terrace complex is a composite feature, consisting of a narrow upper bench (terrace 2a) and a broader lower bench (terrace 2b). Terrace 2b, previously dated from ∼128 ka to ∼114 ka, was thought to date solely to marine isotope stage (MIS) 5.5, representing the peak of the last interglacial period. Nevertheless, the fauna contains an extralimital northern species and several northward-ranging species, as well as an extralimital southern species and several southward-ranging species. Similar faunas with thermally anomalous elements have also been reported from San Nicolas Island, Point Loma (San Diego County), and Cayucos (San Luis Obispo County), California. U-series dating of corals at those localities shows that the thermally anomalous faunas may be the result of mixing of fossils from both the ∼100-ka (cool-water) and the ∼120-ka (warm-water) sea level high stands. Submergence, erosion, and fossil mixing of the ∼120-ka terraces by the ∼100-ka high-sea stand may have been possible due to glacial isostatic adjustment (GIA) effects on North America, which could have resulted in a higher-than-present local sea level stand at ∼100 ka. The terrace elevation spacing on San Clemente Island is very similar to that on San Nicolas Island, and we hypothesize that a similar mixing took place on San Clemente Island. Existing fossil records from older terraces elsewhere in California also show thermally anomalous elements, indicating that the scenario presented here for the last interglacial complex may have applicability to much of the marine Quaternary record for the Pacific Coast.

California↗
USGS2021

Horizontal-to-vertical spectral ratios from California sites: Open-source database and data interpretation to establish site parameters

Frequency-dependent horizontal-to-vertical spectral ratios (HVSR) of Fourier amplitudes from three-component recordings can provide information on one or more site resonant frequencies and relative levels of amplification at those frequencies. Such information is potentially useful for predicting site amplification but is not present in site databases that have been developed over the last 15–20 years for the Next-Generation Attenuation (NGA) projects, which instead use the time-averaged shear-wave velocity (VS) in the upper 30 m of the site (VS30) as the primary site parameter and are supplemented with basin depth terms where available. As a consequence, HVSR parameters are also not used in NGA ground motion models. In order for HVSR-based parameters to be used in future versions of site databases, a publicly accessible repository of this information is needed. We adapt a relational database developed to archive and disseminate VS data to also include HVSR. The database provides relevant microtremor-based HVSR data (mHVSR) and supporting metadata. We consider the most relevant data to be the frequency-dependent mHVSR, where the horizontal is taken as the median component and also as a function of horizontal azimuth (referred to as polar plots). Relevant metadata includes site location information, details about the equipment used to make the measurements, and processing details related to windowing, anti-trigger routines, and filtering. We describe the database schema developed to organize and present this information.

California↗