USGS Science⌕ Search

SEARCH · USGS Science

Results for “Computers and Geology”

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

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,243 records · Page 69Linked to original sources
USGS2021

Evaluation and application of the Purge Analyzer Tool (PAT) to determine in-well flow and purge criteria for sampling monitoring wells at the Stringfellow Superfund site in Jurupa Valley, California, in 2017

The U.S. Geological Survey and U.S. Environmental Protection Agency are developing analytical tools to assess the representativeness of groundwater samples from fractured-rock aquifers. As part of this effort, monitoring wells from the Stringfellow Superfund site in Jurupa Valley in Riverside County, California, approximately 50 miles east of Los Angeles, were field tested to collect information to assist in the evaluation and application of in-well flow as computed by the analytical model called the Purge Analyzer Tool, which computes in-well groundwater travel times for simple piston transport of inflowing groundwater from open intervals of a monitoring well to the pump intake and can provide insight into optimal purging parameters (duration, rate, and pump position) needed for the collection of representative groundwater samples. Field testing of wells included hydraulic, chemistry, and dye tracer analysis to investigate travel times in wells under pumping conditions. The Purge Analyzer Tool was able to replicate dye velocities (travel times) for one of three wells that had appreciable inflow from the aquifer but not the other two wells, which are screened in low-permeability sediments and rock, where flow was dominated by borehole storage. A set of criteria was established to help assess the ability to collect representative groundwater chemistry from monitoring wells; criteria included understanding the height of the static well water column and relative exchange rate between the aquifer and the well.

California↗
USGS2020

Comparison of machine learning approaches used to identify the drivers of Bakken oil well productivity

Geologists and petroleum engineers have struggled to identify the mechanisms that drive productivity in horizontal hydraulically fractured oil wells. The machine learning algorithms of Random Forest (RF), gradient boosting trees (GBT) and extreme gradient boosting (XGBoost) were applied to a dataset containing 7311 horizontal hydraulically fractured wells drilled into the middle member of the Bakken Formation from 2010 through 2017. The initial goal is to use these data‐driven machine learning algorithms to identify the most important explanatory predictors of well productivity within nine subareas and the composite area. Predictor variables representing initial gas production, the initial 180‐day water cut, and vertical depth vary spatially and are identified with geologically favorable areas. Well‐completion predictors include the well lateral length, number of fracture stages, volume of proppant per stage, and the volume of injected fluids per stage. The performance of methods is compared based on a common test sample. The analysis then examines the comparative predictive performance of the three algorithms for 1330 wells that had initiated production after the initial 7311 well sample had been producing. The computations of predictor importance identified the initial 180‐day water cut and the 30‐day initial gas production predictors as having a dominant influence in most subareas and for the composite area. The relative importance of well completion predictor variables, that is, the number of fracture stages per well, volume of injected proppant per stage, volume of injected fluids per stage, and lateral length, varied considerably across the subareas. For the common test or holdout sample, the models calibrated with the XGBoost algorithm had superior predictive power. The predictive power of all the algorithms trained on the data from the original sample suffered some loss when tested with a sample of wells that had started production after the end of that period. Implications of the empirical findings and strategies to mitigate loss of predictive power are discussed in the concluding section.

Statistical Analysis and Data Mining↗
USGS1987

Plan for the design, development, and implementation, and operation of the National Water Information System

The Water Resources Division of the U.S. Geological Survey is developing a National Water Information System (NWIS) that will integrate and replace its existing water data and information systems of the National Water Data Storage and Retrieval System, National Water Data Exchange, National Water-Use Information, and Water Resources Scientific Information Center programs. It will be a distributed data system operated as part of the Division 's Distributed Information System, which is a network of computers linked together through a national telecommunication network known as GEONET. The NWIS is being developed as a series of prototypes that will be integrated as they are completed to allow the development and implementation of the system in a phased manner. It also is being developed in a distributed manner using personnel who work under the coordination of a central NWIS Project Office. Work on the development of the NWIS began in 1983 and it is scheduled for completion in 1990. This document presents an overall plan for the design, development, implementation, and operation of the system. Detailed discussions are presented on each of these phases of the NWIS life cycle. The planning, quality assurance, and configuration management phases of the life cycle also are discussed. The plan is intended to be a working document for use by NWIS management and participants in its design and development and to assist offices of the Division in planning and preparing for installation and operation of the system. (Author 's abstract)

Open-File Report↗
USGS1999

A dynamic water-quality modeling framework for the Neuse River estuary, North Carolina

As a result of fish kills in the Neuse River estuary in 1995, nutrient reduction strategies were developed for point and nonpoint sources in the basin. However, because of the interannual variability in the natural system and the resulting complex hydrologic-nutrient inter- actions, it is difficult to detect through a short-term observational program the effects of management activities on Neuse River estuary water quality and aquatic health. A properly constructed water-quality model can be used to evaluate some of the potential effects of manage- ment actions on estuarine water quality. Such a model can be used to predict estuarine response to present and proposed nutrient strategies under the same set of meteorological and hydrologic conditions, thus removing the vagaries of weather and streamflow from the analysis. A two-dimensional, laterally averaged hydrodynamic and water-quality modeling framework was developed for the Neuse River estuary by using previously collected data. Development of the modeling framework consisted of (1) computational grid development, (2) assembly of data for model boundary conditions and model testing, (3) selection of initial values of model parameters, and (4) limited model testing. The model domain extends from Streets Ferry to Oriental, N.C., includes seven lateral embayments that have continual exchange with the main- stem of the estuary, three point-source discharges, and three tributary streams. Thirty-five computational segments represent the mainstem of the estuary, and the entire framework contains a total of 60 computa- tional segments. Each computational cell is 0.5 meter thick; segment lengths range from 500 meters to 7,125 meters. Data that were used to develop the modeling framework were collected during March through October 1991 and represent the most comprehensive data set available prior to 1997. Most of the data were collected by the North Carolina Division of Water Quality, the University of North Carolina Institute of Marine Sciences, and the U.S. Geological Survey. Limitations in the modeling framework were clearly identified. These limitations formed the basis for a set of suggestions to refine the Neuse River estuary water-quality model.

North Carolina↗
USGS2021

Cimarron River alluvial aquifer hydrogeologic framework, water budget, and implications for future water availability in the Pawnee Nation Tribal jurisdictional area, Payne County, Oklahoma, 2016–18

The Cimarron River is a free-flowing river and is a major source of water as it flows across Oklahoma. Increased demand for water resources within the Cimarron River alluvial aquifer in north-central Oklahoma (primarily in Payne County) has led to increases in groundwater withdrawals for agriculture, public, irrigation, industrial, and domestic supply purposes. The Pawnee Nation of Oklahoma (Pawnee Nation) is particularly concerned about the sustainability of the Cimarron River alluvial aquifer and whether the aquifer will continue to be a viable water resource for future generations of Tribal members and residents. To better understand current (2021) water resources and possible future water availability in the Pawnee Nation Tribal jurisdictional area, the U.S. Geological Survey, in cooperation with the Bureau of Indian Affairs and the Pawnee Nation of Oklahoma, compiled available hydrogeologic data and developed conceptual and numerical groundwater-flow models for the Cimarron River alluvial aquifer in Payne County, north-central Oklahoma, including a focus area in the Pawnee Nation Tribal jurisdictional area for the 2016–18 study period. A conceptual water budget was created to establish estimates of groundwater fluxes into and out of the aquifer through hydrologic boundaries and groundwater withdrawals for use in the numerical groundwater-flow model. The conceptual water budget focuses on the alluvial aquifer, meaning that inflows include sources of water to the aquifer and that outflows include sources of water out of the aquifer, such as base-flow contributions to the Cimarron River. The conceptual water budget was constructed by using data from 2017 (the most complete year of record for each data type included in the model) for the Pawnee Nation subdomain of the Cimarron River alluvial aquifer model extent (Pawnee Nation subdomain). Groundwater withdrawals were estimated from groundwater-withdrawal rate information for permanent and temporary permitted wells that was obtained from the Oklahoma Water Resources Board. One-half of each annual permitted groundwater-withdrawal rate allotted was used as the estimated annual groundwater-withdrawal amount. Halving the permitted groundwater-withdrawal rate was done because permitted withdrawal rates are the maximum permitted rate and actual groundwater withdrawals are generally appreciably lower than the maximum permitted rate. Total groundwater withdrawals were estimated as 1,300 acre-feet per year for the Pawnee Nation subdomain. Various hydrogeologic data were measured to assist with model development, including depth to bedrock and water-table altitude data. In support of the model development, analyses pertaining to groundwater flow, groundwater/surface-water interactions, base flows in the Cimarron River, and lithological interpretations in the Pawnee Nation Tribal jurisdictional area were used to compute a conceptual water budget applicable to the 2016–18 study period. A numerical groundwater-flow model was developed using the hydrogeologic framework of the Cimarron River alluvial aquifer and the conceptual water budget. The numerical model consists of a single layer representing alluvium and terrace deposits within the alluvial aquifer model area. Hydraulic conductivities were estimated and modeled for the alluvium and terrace deposits in the alluvial aquifer. Base-flow values were estimated using the base-flow index from streamflow data collected at U.S. Geological Survey streamgages. Stream seepage values were derived from the mean 2017 base-flow index between certain streamgages. Hydraulic conductivities were specified an initial (before calibration) value of 120 feet per day for the alluvium deposits and 16 feet per day for the terrace deposits. The simulated inflows in the numerical groundwater-flow model of the Pawnee Nation subdomain were higher than the inflows of conceptual water budget, and the simulated outflows were lower than the outflows of the conceptual water budget. Overall, simulated base flows matched closely to observed base flows for the 2016 and 2017 stress periods. Simulated streamflow tended to match better with the observed streamflow for 2017, which was the period with the most data for the Cimarron River alluvial aquifer model. Streamflow capture analysis was applied to the steady-state simulation to identify areas of the aquifer where base flows in the Cimarron River were most sensitive to groundwater withdrawals. The initial base-flow value was assigned the value obtained from streamflow-routing software used to simulate stream outflow for the calibrated steady-state base model. Subsequent simulations were run in each active cell in the Pawnee Nation subdomain for a specified groundwater-withdrawal rate of 180,000 cubic feet per day. The study area that includes the Pawnee Nation subdomain is in the upper Arkansas River Basin. A groundwater-withdrawal rate of 180,000 cubic feet per second per day represents a 34 percent increase compared to the highest permitted groundwater-withdrawal rate for the study area, which corresponds to the estimated 34 percent increase in groundwater withdrawals predicted by 2060 for the upper Arkansas River Basin. Simulated streamflow capture was highest in the alluvium deposits adjacent to the Cimarron River; that is, base flow in the Cimarron River decreased the most for simulated groundwater withdrawals in the alluvium deposits adjacent to the Cimarron River. Streamflow capture increased as the distance of a well from the Cimarron River decreased in the simulation. The northeastern part of the Pawnee Nation subdomain showed greater streamflow capture in a broader area; streamflow in that part of the Pawnee Nation subdomain is likely more sensitive to groundwater withdrawals compared to other parts of the Pawnee Nation subdomain.

Oklahoma↗
USGS2009

Analysis of vertical flow during ambient and pumped conditions in four monitoring wells at the Pantex Plant, Carson County, Texas, July-September 2008

The Pantex Plant is a U.S. Department of Energy/National Nuclear Security Administration (USDOE/NNSA)-owned, contractor-operated facility managed by Babcock & Wilcox Technical Services Pantex, LLC (B&W Pantex) in Carson County, Texas, approximately 17 miles northeast of Amarillo. The U.S. Geological Survey, in cooperation with B&W Pantex through the USDOE/NNSA, made a series of flowmeter measurements and collected other borehole geophysical logs during July–September 2008 to analyze vertical flow in screened intervals of four selected monitoring wells (PTX01–1012, PTX06–1044, PTX06–1056, and PTX06–1068) at the Pantex Plant. Hydraulic properties (transmissivity values) of the section of High Plains (Ogallala) aquifer penetrated by the wells also were computed. Geophysical data were collected under ambient and pumped flow conditions in the four monitoring wells. Unusually large drawdowns occurred at two monitoring wells (PTX06–1044 and PTX06–1056) while the wells were pumped at relatively low rates. A decision was made to redevelop those wells, and logs were run again after redevelopment in the two monitoring wells. Logs collected in monitoring well PTX01–1012 during ambient conditions indicate a dynamic environment that probably was affected by pumping of nearby irrigation or public-supply wells. During pumping, downward vertical flow of 0.2 to 2.1 gallons per minute that occurred during ambient conditions was either reversed or reduced. During pumping, a gradual trend of more positive flowmeter values (upward flow) with distance up the well was observed. Estimated total transmissivity for four production zones identified from Flow–B numerical model results taken together was calculated to be about 3,100 feet squared per day. Logs collected in monitoring well PTX06–1044 during ambient conditions before redevelopment indicate a static environment with no flow. During pumping there was upward vertical flow at rates ranging from 0.1 to about 1.5 gallons per minute. During pumping, a gradual trend of more positive flowmeter values (upward flow) with distance up the well was observed. Estimated total transmissivity before redevelopment for five production zones identified from Flow–B numerical model results, and transmissivity values for each zone, are considered to be in error because of the lack of communication between the well and the aquifer before redevelopment. After redevelopment, logs for well PTX06–1044 during ambient conditions indicate a near-static environment with minimal downward flow. During pumping there was upward vertical flow at rates ranging from 0.5 to about 4.8 gallons per minute. During pumping, a gradual trend of more positive flowmeter values with distance up the well was observed. Estimated total transmissivity after redevelopment for the same five identified production zones taken together was calculated to be about 520 feet squared per day. Logs collected in monitoring well PTX06–1056 during ambient conditions before redevelopment indicate a static environment with no flow. During pumping there was upward vertical flow at rates ranging from 0.3 to about 1.5 gallons per minute. During pumping, a gradual trend of more positive flowmeter values (upward flow) with distance up the well was observed. Estimated total transmissivity before redevelopment for four production zones identified from Flow–B numerical model results taken together was calculated to be about 450 feet squared per day. After redevelopment, logs collected in monitoring well PTX06–1056 during ambient conditions indicate a near-static environment with no flow except for a very small amount of downward flow near the bottom of the well. During pumping there was upward vertical flow at rates ranging from 0.7 to about 2.9 gallons per minute. Estimated total transmissivity after redevelopment for five production zones identified from Flow–B numerical model results taken together was calculated to be about 330 feet squared per day. Logs collected in monitoring well PTX06–1068 during ambient conditions indicate a static environment with no flow. During pumping there was upward vertical flow at rates ranging from 0.4 to 4.8 gallons per minute. During pumping, a gradual trend of more positive flowmeter values (upward flow) with distance up the well was observed. Estimated total transmissivity for four production zones identified from Flow–B numerical model results taken together was calculated to be about 200 feet squared per day.

Open-File Report↗
USGS2020

Ungulate migrations of the western United States, Volume 1

Across the western United States, many ungulate herds must migrate seasonally to access resources and avoid harsh winter conditions. Because these migration paths cover vast landscapes (in other words migration distances up to 150 miles [241 kilometers]), they are increasingly threatened by roads, fencing, subdivisions, and other development. Over the last decade, many new tracking studies have been conducted on migratory herds, and analytical methods have been developed that allow for population-level corridors and stopovers to be mapped and prioritized. In 2018, the U.S. Geological Survey assembled a Corridor Mapping Team to provide technical assistance to western states working to map bison, elk, moose, mule deer, and pronghorn migrations using existing Global Positioning System data. Led by the Wyoming Cooperative Fish and Wildlife Research Unit, the team consists of federal scientists, university researchers, and biologists and analysts from participating state agencies. In its first year, the team has worked to develop standardized analytical and computational methods and a workflow applicable to datasets typically collected by state agencies. In 2019, the team completed analyses necessary to map corridors, stopovers, routes and winter ranges in Arizona, Idaho, Nevada, Utah, and Wyoming. A total of 26 corridors, 16 migration routes, 25 stopovers, and 9 winter ranges were mapped across these states and are included in this report. This report and associated data release provide the means for the habitats required for migration to be taken into account by state and federal transportation officials, land and wildlife managers, planners, and other conservationists working to maintain big-game migration in the western states.

Scientific Investigations Report↗
USGS1979

Instrumentation of urban hydrology monitoring sites in southeast Florida

An instrumentation system developed and built in laboratories of the U.S. Geological Survey, Reston, Va., has been used since 1974 to collect synchronized rainfall, runoff, and water-quality data from urban basins. A number of field modifications were made to adapt the system to local hydrologic conditions and for collection of data on about 350 rainstorms at four sites in south Florida. The instrumentation system measures rainfall at three sites, records two pressure or water-level readings for flow computations, and collects and refrigerates up to 24 water samples and rainfall-quality samples. Rainfall and runoff data are recorded every 36 seconds on a six-channel analog recorder so that all variables are time-synchronous. Flow in the storm sewer is computed from pressure measurements in a U-shaped venturi-type constriction or, when the constriction is not used, from water levels. (Kosco-USGS)

Florida↗
USGS2008

Research to More Effectively Manage Critical Ground-Water Basins

As the regional management agency for two of the most heavily used ground-water basins in California, the Water Replenishment District of Southern California (WRD) plays a vital role in sheparding the water resources of southern Los Angeles County. WRD is using the results of the U.S. Geological Survey (USGS) studies to help more effectively manage the Central and West Coast basins in the most efficient, cost-effective way. In partnership with WRD, the USGS is using the latest research tools to study the geohydrology and geochemistry of the two basins. USGS scientists are: *Drilling and collecting detailed data from over 40 multiple-well monitoring sites, *Conducting regional geohydrologic and geochemical analyses, *Developing and applying a computer simulation model of regional ground-water flow. USGS science is providing a more detailed understanding of ground-water flow and quality. This research has enabled WRD to more effectively manage the basins. It has helped the District improve the efficiency of its spreading ponds and barrier injection wells, which replenish the aquifers and control seawater intrusion into the ground-water system.

Fact Sheet↗
USGS1982

Test and calibration of the Digital World-Wide Standardized Seismograph

During the past decade there has been steady progress in the modernization of the global seismograph network operated by the U.S. Geological Survey (USGS). The World-Wide Standardized Seismograph Network (WWSSN) has been augmented by new stations with advanced instrumentation, including the Seismic Research Observatories (SRO) and the modified High-Gain Long-Period (ASRO) stations. One goal in the modernization effort has been to improve signal resolution in the long-period band. A second goal has been to generate a global digital data base to support contemporary computer-based analysis and research. In 1976, a Panel on Seismograph Networks was established by the Committee on Seismology of the National Academy of Sciences to review progress in network seismology and recommend actions that would lead to an improved global data base for seismology. One recommendation in the Panel report (Engdahl, 1977) called for upgrading selected WWSSN stations by the installation of digital recorders. This was viewed as an economical way of expanding the digital network, which had proven itself to be a very promising new tool for earthquake and explosion research. Funds for the development and assembly of 15 digital recorders were provided to the USGS by the Defense Advanced Research Projects Agency and an ad Inoc panel of scientists was convened by the Committee on Seismology to advise the USGS on the selection of stations to be upgraded and on data recording requirements, A total of 19 digital World-Wide Standardized Seismograph (DWWSS) systems will be operational when all are installed. The additional systems were made available through purchase by the USGS and other organizations; for example, the University of Bergen purchased and installed a DWWSS-type recorder and agreed to furnish the USGS with the data. A list of operational and planned DWWSS network stations is given in Table 1.1. As one might expect, the digital recorder turned out to be somewhat more sophisticated than the original concept. It was decided to record three components of long-period data continuously, three components of intermediateperiod data in an event mode, and the vertical-component short-period data in and event mode (with the capability of adding short-period horizontal channels in the future). Special amplifiers were developed for use with the WWSS seismometers, and a 16-bit fixed-point analog-to-digital converter was chosen to provide increased resolution (as opposed to a 16-bit gain-ranged encoder). The microprocessor-based digital recording systems were developed and assembled at the USGS Albuquerque Seismological Laboratory (ASL) and ASL-based technicians began installation at WWSSN stations in 1980. The current and proposed locations of the DWWSSN stations, together with other stations in the Global Digital Seismograph Network (GDSN), are shown on the map in Figure 1.1. A system was operated at Albuquerque for about 18 months, serving as a test bed for evaluation studies. Although the network hardware has been available for some time, the installation of the DWWSSN has proceeded slowly. The National Science Foundation supported installation of six stations and the USGS is funding installation of most of the others; however, the network completion date is conjectural because of funding uncertainties. The DWWSSN stations are supported with supplies and technical assistance from ASL (subject to availability of funds). Data recorded on magnetic tapes are mailed to ASL where they are reviewed for quality, then merged with other GDSN station data on the network-day tapes. Hoffman (1980) provides a description of the network-day tape format. Zirbes and Buland (1981) have developed and published user software for reading and interpreting the day tapes. This report will serve several purposes. One is to provide nominal system transfer functions and calibration information that are needed in the analysis of DWWSSN data. A second purpose is to report on an evaluation of operating characteristics (calibration stability, noise levels, and linearity) that may limit the usefulness of the data and to determine if modifications may be needed to improve the data. It is not an exhaustive study in this respect. We continue to depend mostly on data user feedback to point out deficiencies and we solicit comments whenever anomalies are observed in the data.

Open-File Report↗
USGS2001

Vertical profiles of streambed hydraulic conductivity determined using slug tests in central and western Nebraska

Many issues of water-resources management rely on modeling of ground-water/surfacewater interactions, and streambed hydraulic conductivity is a key parameter controlling the water fluxes across the stream/aquifer interface. However, in central and western Nebraska, this parameter is generally undefined. The U.S. Geological Survey, in cooperation with the Nebraska Platte River Cooperative Hydrology Study Group, performed slug tests at 15 stream sites in the Platte, Republican, and Little Blue River watersheds to determine the hydraulic conductivity of streambeds in central and western Nebraska. Slug tests were completed at several discrete depth intervals using pneumatic or mechanical methods, and the water-level response was monitored on site using a pressure transducer and laptop computer. Responses were analyzed using either the Bouwer and Rice or Springer and Gelhar methods. Vertical profiles of hydraulic conductivity with depth were developed and were compared to available information on lithology. The profiles and corresponding lithology showed that different types of streambeds were tested and suggested that some streambeds display a large variability in hydraulic conductivity with depth. In some cases, hydraulic conductivity values associated with nonstreambed materials could be identified from nearby lithologic descriptions. Seven of 15 sites had streambed values that ranged over more than 3 orders of magnitude, and that variability increased significantly when the measurements considered to be from nonstreambed materials were included. Streambed profiles from the Platte and South Platte River sites generally were more homogeneous and of larger hydraulic conductivity than the other sites. No restrictive layers were detected at any of the streambed sites on the main stems or the flood plains of the main stems of their respective watersheds. Alternatively, the profiles characterized by a restrictive streambed layer at some depth below the streambed surface were all from tributary sites out of the main-stem flood plain. These profiles can be used to represent the streambed hydraulic conductivity in central and western Nebraska in various applications, including modeling ground-water/surfacewater interactions.

Nebraska↗
USGS2009

Littoral transport rates in the Santa Barbara Littoral Cell: a process-based model analysis

Identification of the sediment transport patterns and pathways is essential for sustainable coastal zone management of the heavily modified coastline of Santa Barbara and Ventura County (California, USA). A process-based model application, based on Delft3D Online Morphology, is used to investigate the littoral transport potential along the Santa Barbara Littoral Cell (between Point Conception and Mugu Canyon). An advanced optimalization procedure is applied to enable annual sediment transport computations by reducing the ocean wave climate in 10 wave height - direction classes. Modeled littoral transport rates compare well with observed dredging volumes, and erosion or sedimentation hotspots coincide with the modeled divergence and convergence of the transport gradients. Sediment transport rates are strongly dependent on the alongshore variation in wave height due to wave sheltering, diffraction and focusing by the Northern Channel Islands, and the local orientation of the geologically-controlled coastline. Local transport gradients exceed the net eastward littoral transport, and are considered a primary driver for hot-spot erosion.

California↗
USGS2009

Description and evaluation of numerical groundwater flow models for the Edwards Aquifer, south-central Texas

A substantial number of public water system wells in south-central Texas withdraw groundwater from the karstic, highly productive Edwards aquifer. However, the use of numerical groundwater flow models to aid in the delineation of contributing areas for public water system wells in the Edwards aquifer is problematic because of the complex hydrogeologic framework and the presence of conduit-dominated flow paths in the aquifer. The U.S. Geological Survey, in cooperation with the Texas Commission on Environmental Quality, evaluated six published numerical groundwater flow models (all deterministic) that have been developed for the Edwards aquifer San Antonio segment or Barton Springs segment, or both. This report describes the models developed and evaluates each with respect to accessibility and ease of use, range of conditions simulated, accuracy of simulations, agreement with dye-tracer tests, and limitations of the models. These models are (1) GWSIM model of the San Antonio segment, a FORTRAN computer-model code that pre-dates the development of MODFLOW; (2) MODFLOW conduit-flow model of San Antonio and Barton Springs segments; (3) MODFLOW diffuse-flow model of San Antonio and Barton Springs segments; (4) MODFLOW Groundwater Availability Modeling [GAM] model of the Barton Springs segment; (5) MODFLOW recalibrated GAM model of the Barton Springs segment; and (6) MODFLOW–DCM (dual conductivity model) conduit model of the Barton Springs segment. The GWSIM model code is not commercially available, is limited in its application to the San Antonio segment of the Edwards aquifer, and lacks the ability of MODFLOW to easily incorporate newly developed processes and packages to better simulate hydrologic processes. MODFLOW is a widely used and tested code for numerical modeling of groundwater flow, is well documented, and is in the public domain. These attributes make MODFLOW a preferred code with regard to accessibility and ease of use. The MODFLOW conduit-flow model incorporates improvements over previous models by using (1) a user-friendly interface, (2) updated computer codes (MODFLOW–96 and MODFLOW–2000), (3) a finer grid resolution, (4) less-restrictive boundary conditions, (5) an improved discretization of hydraulic conductivity, (6) more accurate estimates of pumping stresses, (7) a long transient simulation period (54 years, 1947–2000), and (8) a refined representation of high-permeability zones or conduits. All of the models except the MODFLOW–DCM conduit model have limitations resulting from the use of Darcy’s law to simulate groundwater flow in a karst aquifer system where non-Darcian, turbulent flow might actually dominate. The MODFLOW–DCM conduit model is an improvement in the ability to simulate karst-like flow conditions in conjunction with porous-media-type matrix flow. However, the MODFLOW–DCM conduit model has had limited application and testing and currently (2008) lacks commercially available pre- and post-processors. The MODFLOW conduit-flow and diffuse-flow Edwards aquifer models are limited by the lack of calibration for the northern part of the Barton Springs segment (Travis County) and their reliance on the use of the calibrated hydraulic conductivity and storativity values from the calibrated Barton Springs segment GAM model. The major limitation of the Barton Springs segment GAM and recalibrated GAM models is that they were calibrated to match measured water levels and springflows for a restrictive range of hydrologic conditions, with each model having different hydraulic conductivity and storativity values appropriate to the hydrologic conditions that were simulated. The need for two different sets of hydraulic conductivity and storativity values increases the uncertainty associated with the accuracy of either set of values, illustrates the non-uniqueness of the model solution, and probably most importantly demonstrates the limitations of using a one-layer model to represent the heterogeneous hydrostratigraphic units composing the Edwards aquifer. In general, the best matches or agreement between groundwater flow directions inferred by numerical model simulation, and by dye-tracer tests, are observed where model outputs accurately reproduce the configuration of the potentiometric surface with regard to the positions of major and minor groundwater troughs and divides. None of the models, with the possible exception of the MODFLOW–DCM conduit model, has a documented capability to accurately simulate travel times for conduit-dominated velocities in the Edwards aquifer. Public water system assessments of wells in the Barton Springs segment of the Edwards aquifer, and elsewhere where conduit-flow conditions are thought to dominate aquifer hydraulic behavior, might be enhanced by use of either the MODFLOW–DCM model or the newly developed U.S. Geological Survey MODFLOW Conduit-Flow Process module for MODFLOW–2005, because each incorporates a type of dual or triple hydraulic conductivity approach and has the capability to explicitly simulate turbulent flow and conduit hydraulic characteristics.

Texas↗
USGS2018

Rayleigh wave ellipticity measurement uncertainty across the IRIS/USGS and New China Digital Seismograph Networks

Long-period Rayleigh wave horizontal to vertical amplitude (H/V) ratios at a station provide information about local earth structure that is complementary to phase velocity. However, a number of studies have observed that significant scatter appears in these measurements making it difficult to use H/V ratio measurements to resolve earth structure. Some of the scatter in these measurements has been attributed to local geological structure while some has remained unaccounted for. Most Global Seismographic Network (GSN) stations contain two nearby high-quality broad-band seismometers (e.g. in the same vault, but on different piers or in different boreholes). For each broad-band sensor in the IRIS/USGS component of the GSN, we estimate H/V ratios of fundamental mode Rayleigh waves using M > 6.5 earthquakes from 2001 to 2018 (around 19 000 measurements). We compute these ratios at a number of discrete periods (25, 50, 75, 100 and 150 s) and find that for well-isolated Rayleigh waves (windows where the correlation coefficients between radial and the phase-shifted vertical components are greater than 0.9) significant scatter in H/V ratios occurs between colocated sensors (greater than 25 per cent at 100 s period). This suggests the scatter in H/V ratio measurements can be at least partially attributed to extremely local phenomena such as sensor emplacement in the vault. We also find that H/V ratios can vary as a function of event backazimuth, indicating that care must be taken when computing average ratios for a station, as a large number of events from a given region could bias H/V ratio measurements at a station.

Geophysical Journal International↗
USGS1988

Elastic-wave propagation and site amplification in the Salt Lake Valley, Utah, from simulated normal faulting earthquakes

The two-dimensional seismic response of the Salt Lake valley to near- and far-field earthquakes has been investigated from simulations of vertically incident plane waves and from normal-faulting earthquakes generated on the basin-bounding Wasatch fault. The response to normal faulting earthquakes was simulated using a two-dimensional finite-element method and the plane-wave response was calculated from two-dimensional finite-difference simulations. The plane-wave simulations were then compared with observed site amplifications in the Salt Lake valley, based on seismic recordings from nuclear explosions in southern Nevada, that show 10 times greater amplification within the basin than measured values on hard-rock sites. While previous studies attribute this increased site amplification to the near-surface unconsolidated/consolidated alluvial fill contact, our synthetic seismograms suggest that in the frequency band 0.3 to 1.5 Hz at least one-half the site amplification can be attributed to the impedance contrast between the basin sediments and higher velocity basement rocks. Synthetic seismograms from vertically incident plane-wave sources and buried double-couple sources predict large amplitude Rayleigh-wave propagation from the edges of the basin and, in general, uniform site amplification. In contrast, near-field simulations of basin-bounding, normal-faulting earthquakes predict large-amplitude Rayleigh waves propagating westward from the fault across the basin. Spectra of synthetic accelerograms computed from the normal-faulting earthquakes shows that spectral amplification within the basin is primarily due to source directivity with a maxima near the surface projection of the fault that decays rapidly away from the fault. Importantly, the synthetic modeling of near-field earthquake sources show that near-field directivity effects are important and should be considered in an earthquake hazard assessment of the Salt Lake valley and similar geologic settings along the Wasatch Front.

Utah↗
USGS1997

Use of remote-sensing techniques to survey the physical habitat of large rivers

Remote-sensing techniques that can be used to quantitatively characterize the physical habitat in large rivers in the United States where traditional survey approaches typically used in small- and medium-sized streams and rivers would be ineffective or impossible to apply. The state-of-the-art remote-sensing technologies that we discuss here include side-scan sonar, RoxAnn, acoustic Doppler current profiler, remotely operated vehicles and camera systems, global positioning systems, and laser level survey systems. The use of these technologies will permit the collection of information needed to create computer visualizations and hard copy maps and generate quantitative databases that can be used in real-time mode in the field to characterize the physical habitat at a study location of interest and to guide the distribution of sampling effort needed to address other habitat-related study objectives. This report augments habitat sampling and characterization guidance provided by Meador et al. (1993) and is intended for use primarily by U.S. Geological Survey National Water Quality Assessment program managers and scientists who are documenting water quality in streams and rivers of the United States.

Report↗
USGS2002

Rationale and operational plan to upgrade the U.S. gravity database

A concerted effort is underway to prepare a substantially upgraded digital gravity anomaly database for the United States and to make this data set and associated usage tools available on the internet. This joint effort, spearheaded by the geophysics groups at the National Imagery and Mapping Agency (NIMA), University of Texas at El Paso (UTEP), U.S. Geological Survey (USGS), and National Oceanic and Atmospheric Administration (NOAA), is an outgrowth of the new geoscientific community initiative called Geoinformatics (www.geoinformaticsnetwork.org). This dominantly geospatial initiative reflects the realization by Earth scientists that existing information systems and techniques are inadequate to address the many complex scientific and societal issues. Currently, inadequate standardization and chaotic distribution of geoscience data, inadequate accompanying documentation, and the lack of easy-to-use access tools and computer codes for analysis are major obstacles for scientists, government agencies, and educators. An example of the type of activities envisioned, within the context of Geoinformatics, is the construction, maintenance, and growth of a public domain gravity database and development of the software tools needed to access, implement, and expand it. This product is far more than a high quality database; it is a complete data system for a specific type of geophysical measurement that includes, for example, tools to manipulate the data and tutorials to understand and properly utilize the data. On August 9, 2002, twenty-one scientists from the federal, private and academic sectors met at a workshop to discuss the rationale for upgrading both the United States and North American gravity databases (including offshore regions) and, more importantly, to begin developing an operational plan to effectively create a new gravity data system. We encourage anyone interested in contributing data or participating in this effort to contact G.R. Keller or T.G. Hildenbrand. This workshop was the first step in building a web-based data system for sharing quality gravity data and methodology, and it builds on existing collaborative efforts. This compilation effort will result in significant additions to and major refinement of the U.S. database that is currently released publicly by NOAA’s National Geophysical Data Center and will also include an additional objective to substantially upgrade the North American database, released over 15 years ago (Committee for the Gravity Anomaly Map of North America, 1987).

Open-File Report↗
USGS2010

Preliminary slope-stability analysis of Augustine Volcano: Chapter 14 in The 2006 eruption of Augustine Volcano, Alaska

Augustine Volcano has been a prolific producer of large debris avalanches during the Holocene. Originating as landslides from the steep upper edifice, these avalanches typically slide into the surrounding ocean. At least one debris avalanche that occurred in 1883 during an eruption initiated a far-traveled tsunami. The possible occurrence of another edifice collapse and ensuing tsunami was a concern during the 2006 eruption of Augustine. To aid in hazard assessments, we have evaluated the slope stability of Augustine's edifice, using a quasi-three-dimensional, geotechnically based slope-stability model implemented in the computer program SCOOPS. We analyzed the effects of topography, variations in rock strength, and earthquake-induced strong ground motion on the relative stability of millions of potential large (>0.1 km 3 volume) slope failures throughout the edifice. Preliminary results from pre-2006 topography provide three insights. First, the predicted stability of all parts of the upper edifice is approximately the same, suggesting an equal likelihood of slope failure, in agreement with geologic observations that debris avalanches have swept all sectors of the volcano. Second, the least stable (by a small amount) sector is on the east flank where a debris avalanche would flow into deeper ocean water and a resulting tsunami would be directed toward the southwestern part of the Kenai Peninsula. Third, most model scenarios predict stable edifice slopes, and only scenarios assuming extensive weak rocks and moderate to strong ground shaking predict potential large collapses. Because other transient triggering mechanisms, such as shallow magma intrusion, may be needed to instigate slope instability, monitoring ground deformation and seismicity could

Alaska↗