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At least 19 recordsLinked to original sources
USGS2012

Estimation of baseline daily mean streamflows for ungaged locations on Pennsylvania streams, water years 1960-2008

Water-resource managers use daily mean streamflows to generate streamflow statistics and analyze streamflow conditions. An in-depth evaluation of flow regimes to promote instream ecological health often requires streamflow information obtainable only from a time series hydrograph. Historically, it has been difficult to estimate daily mean streamflow for an ungaged location. The U.S. Geological Survey (USGS), in cooperation with the Pennsylvania Department of Environmental Protection, Susquehanna River Basin Commission, and The Nature Conservancy, has developed the Ba seline S treamflow E stimator (BaSE) to estimate baseline streamflow at a daily time scale for ungaged streams in Pennsylvania using data collected during water years 1960–2008. Baseline streamflow is minimally altered by regulation, diversion, or mining, and other anthropogenic activities. Daily mean streamflow is estimated in BaSE using a methodology that equates streamflow as a percentile from a flow duration curve for a particular day at an ungaged location with streamflow as a percentile from the flow duration curve for the same day at a reference streamgage that is considered to be hydrologically similar to the ungaged location. An appropriate reference streamgage is selected using map correlation, in which variogram models are developed that correlate streamflow at one streamgage with streamflows at all other streamgages. The percentiles from a flow duration curve for the ungaged location are converted to streamflow through the use of regression equations. Regression equations used to predict 17 flow-duration exceedance probabilities were developed for Pennsylvania using geographic information system-derived basin characteristics. The standard error of prediction for the regression equations ranged from 11 percent to 92 percent with the mean of 31 percent. The map correlation method for estimating streamflow was tested at locations within two pilot basins, the Upper Delaware River Basin and the Lower Susquehanna River Basin, before being applied statewide. Reference streamgages within the pilot basins were used as ungaged locations for analyzing the map correlation method. Correlation using Spearman’s rho and centroid distance performed as well as, or better than, the method using the closest streamgage as a reference streamgage. Map correlation using the correlation metrics identified in the pilot basins was applied to 156 streamgages in and near Pennsylvania. BaSE uses the map correlation method and flow-duration exceedance probability regression equations to estimate baseline daily mean streamflow for an ungaged location. The output from BaSE is a Microsoft Excel® report file that summarizes the reference streamgage and ungaged location information, including basin characteristics, percent difference in basin characteristics between the two locations, any warning associated with the basin characteristics, mean and median streamflow for the ungaged location, and a daily hydrograph of streamflow for water years 1960–2008 for the ungaged location. The daily mean streamflow for the ungaged location can be exported as a text file to be used as input into other statistical software packages. BaSE estimates daily mean streamflow for baseline conditions only, and any alterations to streamflow from regulation, large water use, or substantial mining are not reflected in the estimated streamflow.

Pennsylvania↗
USGS2003

Land use and land cover change in the North Central Appalachians ecoregion

The North Central Appalachians ecoregion, spanning northern Pennsylvania and southern New York, has a long history of land use and land cover change. Turn-of-the-century logging dramatically altered the natural landscape of the ecoregion, but subsequent regeneration returned the ecoregion to a forest dominated condition. To understand contemporary land use and land cover changes, the U.S. Geological Survey with NASA and the U.S. Environmental Protection Agency used a random sample of satellite remotely sensed data for 1973, 1980, 1986, 1992, and 2000 to estimate the rates and assess the primary drivers of change in the North Central Appalachians. The overall change was 6.2%. The 1973-1980 period had the lowest rate of change (1.5%); the highest rate (2.9%) occurred during the 1992-2000 period. The primary conversions were deforestation through harvesting and natural disturbance (i.e., tornados) followed by regeneration, and conversion of forests to mining and urban lands. The primary drivers of the change included changes in access, energy and forest prices, and attitudes toward the environment.

Pennsylvania Geographer↗
USGS1998

Southeastern Pennsylvania ground water protected area

Geographical Information System data sets were developed by the U.S. Geological Survey in cooperation with the Delaware River Basin Commission (DRBC). These data are related to groundwater resources for the DRBC's Southeastern Pennsylvania Groundwater Protected Area.

Open-File Report↗
USGS2003

Late Neoproterozoic felsite (602.3 +/- 2 Ma) and associated metadiabase dikes in the Reading Prong, Pennsylvania, and rifting of Laurentia

Felsite dikes in the Rittenhouse Gap iron mine district of the Reading Prong, eastern Pennsylvania, have a close geochemical affinity with the peralkaline Battle Mountain Member of the Robertson River Igneous Suite (RRIS), northern Virginia. These newly recognized Rittenhouse Gap Felsite dikes of the Swabia Creek Igneous Suite (SCIS) of eastern Pennsylvania plot as within-plate, A-type, A1 granites on various discriminant diagrams, but are quite distinct from late Neoproterozoic Catoctin Metarhyolite of Pennsylvania which has lower Ga/Al and Nb, but higher Eu. Newly recognized metadiabase dikes, also found in the Rittenhouse Gap district and proposed as Tunnel Mine Metadiabase of the SCIS, classify as alkali within-plate or continental initial rifting alkali tholeiites. They are quite distinct chemically and mineralogically from Catoctin Metabasalt flows and equivalent metadiabase dikes in Pennsylvania, which have lower Nb. Sr and Nd isotopic data indicate that the Tunnel Mine Metadiabase and Rittenhouse Gap Felsite are of mantle origin, but that the latter also includes a crustal component. The SCIS bimodal volcanics in Pennsylvania suggest a previously unrecognized rift environment in Pennsylvania at 602 Ma, somewhat predating the recognized, latest Neoproterozoic Catoctin event in Pennsylvania. As such, they fill in both temporal and geographic gaps for the rifting of Laurentia in Pennsylvania. It is proposed that the SCIS melt developed from a remnant ember of the northeastward trace of the older Mount Rogers-RRIS hotspot as Laurentia rotated clockwise. However, release and intrusion of the SCIS may have been related to younger Catoctin event crustal thinning that slightly predated the mafic dike phase of the Catoctin as Laurentia later migrated northward over a second hotspot. Eventually, the mafic phase associated with this second hotspot sufficiently attenuated the crust to allow introduction of Catoctin volcanics.

Northeastern Geology and Environmental Sciences↗
USGS2024

Factors influencing the prevalence of hyperpigmented melanistic lesions in smallmouth bass Micropterus dolomieu in the Susquehanna River Basin, Pennsylvania

Hyperpigmented melanistic lesions (HPMLs) are a visual anomaly documented on the skin of smallmouth bass Micropterus dolomieu in the Susquehanna River Basin, Pennsylvania and in numerous other geographical locations. Currently, there is a lack of information on environmental and fish characteristics that may influence the prevalence of HPMLs associated with a recently described Adomavirus . The goal of this study was to understand potential drivers associated with HPMLs in socioeconomically and ecologically important riverine smallmouth bass populations. A total of 16,220 smallmouth bass were collected and examined for HPMLs between 2012 and 2022 in the Susquehanna River Basin. Overall, HPMLs were documented on 2.9% of fish collected. The interaction between temperature and fish size suggested differing relationships between shorter and longer fish with respect to temperature. Predicted probability of HPML prevalence ranged from 1.1% (95% CI = 0.3, 3.2) at 4°C to 0.01% (CI = 0.00, 0.04) at 26°C for an age-0 (125 mm) fish. In contrast, predicted probability of HPML prevalence ranged from 10.5% (95% CI = 5.8, 18.9) at 4°C to 0.8% (CI = 0.4, 1.5) at 26°C for an adult (322 mm) fish. Overall, HPMLs were more common in longer fish during cooler temperature periods which also corresponds to key life history periods for smallmouth bass (e.g., pre-spawn and overwintering) and could represent different exposure histories for juvenile and adult fish.

Pennsylvania↗
USGS2005

Preliminary integrated geologic map databases for the United States: Delaware, Maryland, New York, Pennsylvania, and Virginia

The growth in the use of Geographic Information Systems (GIS) has highlighted the need for regional and national digital geologic maps attributed with age and lithology information. Such maps can be conveniently used to generate derivative maps for purposes including mineral-resource assessment, metallogenic studies, tectonic studies, and environmental research. This Open-File Report is a preliminary version of part of a series of integrated state geologic map databases that cover the entire United States. The only national-scale digital geologic maps that portray most or all of the United States for the conterminous U.S. are the digital version of the King and Beikman (1974a, b) map at a scale of 1:2,500,000, as digitized by Schruben and others (1994) and the generalized digital version (Reed and Bush, 2004) of the Geologic Map of North America (Reed and others, 2005a, b) compiled at a scale of 1:5,000,000. The present series of maps is intended to provide the next step in increased detail. State geologic maps that range in scale from 1:100,000 to 1:1,000,000 are available for most of the country, and digital versions of these state maps are the basis for this product. In a few cases, new digital compilations were prepared (e.g. Ohio, South Carloina, South Dakota) or existing paper maps were digitized (e.g. Kentucky, Texas). Also as part of this series, new regional maps for Alaska and Hawaii are being compiled and ultimately new state maps will be produced. The digital geologic maps are presented in standardized formats as ARC/INFO export (.e00) files and as ArcView shape (.shp) files. Accompanying these spatial databases are a set of five supplemental attribute tables that relate the map units to detailed lithologic and age information. The maps for the CONUS have been fitted to a common set of state boundaries based on the 1:100,000 topographic map series of the United States Geological Survey (USGS). When the individual state maps are merged, the combined attribute tables can be used directly with the merged maps to make derivative maps. No attempt has been made to reconcile differences in mapped geology across state lines.

Delaware, Maryland, New York, Pennsylvania, Virgin↗
USGS2011

Data compilation and assessment for water resources in Pennsylvania state forest and park lands

As a result of a cooperative study between the U.S. Geological Survey and the Pennsylvania Department of Conservation and Natural Resources (PaDCNR), available electronic data were compiled for Pennsylvania state lands (state forests and parks) to allow PaDCNR to initially determine if data exist to make an objective evaluation of water resources for specific basins. The data compiled included water-quantity and water-quality data and sample locations for benthic macroinvertebrates within state-owned lands (including a 100-meter buffer around each land parcel) in Pennsylvania. In addition, internet links or contacts for geographic information system coverages pertinent to water-resources studies also were compiled. Water-quantity and water-quality data primarily available through January 2007 were compiled and summarized for site types that included streams, lakes, ground-water wells, springs, and precipitation. Data were categorized relative to 35 watershed boundaries defined by the Pennsylvania Department of Environmental Protection for resource-management purposes. The primary sources of continuous water-quantity data for Pennsylvania state lands were the U.S. Geological Survey (USGS) and the National Weather Service (NWS). The USGS has streamflow data for 93 surface-water sites located in state lands; 38 of these sites have continuous-recording data available. As of January 2007, 22 of these 38 streamflow-gaging stations were active; the majority of active gaging stations have over 40 years of continuous record. The USGS database also contains continuous ground-water elevation data for 32 wells in Pennsylvania state lands, 18 of which were active as of January 2007. Sixty-eight active precipitation stations (primarily from the NWS network) are located in state lands. The four sources of available water-quality data for Pennsylvania state lands were the USGS, U.S. Environmental Protection Agency, Pennsylvania Department of Environmental Protection (PaDEP), and the Susquehanna River Basin Commission. The water-quality data, which were primarily collected after 1970, were summarized by categorizing the analytical data for each site into major groups (for example, trace metals, pesticides, major ions, etc.) for each type (streams, lakes, ground-water wells, and springs) of data compiled. The number of samples and number of detections for each analyte within each group also were summarized. A total of 410 stream sites and 205 ground-water wells in state lands had water-quality data from the available data sets, and these sites were well-distributed across the state. A total of 107 lakes and 47 springs in state lands had water-quality data from the available data sets, but these data types were not well-distributed across the state; the majority of water-quality data for lakes was in the western or eastern sections of the state and water-quality data for springs was primarily located in the central part of the Lower Susquehanna River Valley. The most common types of water-quality data collected were major ions, trace elements, and nutrients. Physical parameters, such as water temperature, stream discharge, or water level, typically were collected for most water-quality samples. Given the large database available from PaDEP for benthic macroinvertebrates, along with some data from other agencies, there is very good distribution of benthic-macroinvertebrate data for state lands. Benthic macroinvertebrate samples were collected at 1,077 locations in state lands from 1973 to 2006. Most (980 samples) of the benthic-macroinvertebrate samples were collected by PaDEP as part of the state assessment of stream conditions required by the Clean Water Act. Data compiled in this report can be used for various water-resource issues, such as basin-wide water-budget analysis, studies of ecological or instream flow, or water-quality assessments. The determination of an annual water budget in selected basins is best supported by the availab

Pennsylvania↗
USGS2011

Fish species composition two second-order headwater streams the North Central Appalachians ecoregion

Fish species composition was determined for two second-order headwater streams within the North Central Appalachians ecoregion in northern Pennsylvania. The two streams were widely spaced geographically (over 193 km apart) and occurred in different drainage systems. Streams were sampled in the spring and fall over two years (1996–98) yielding similar fish assemblages. A total of five species was collected. Mottled sculpin ( Cottus bairdli ), slimy sculpin ( Cottus cognatus ), brook trout ( Salvetinus fontinalis ), and brown trout ( Salmo trutta ) were the dominant adult fishes. Two creek chubs ( Semotilus atromaculatus ) were also collected. No significant differences were found in sculpin weight, sculpin length, salmonid length, or brook trout length between streams. Paired t-tests detected eight significant seasonal differences within sites. Brook trout and mottled sculpin lengths were significantly greater in fall versus spring, while the reverse was found with slimy sculpins. Catches per unit effort were similar between the two streams, yielding 8.46 and 8.07 fish per minute of electrofishing. Both streams were very similar in faunal assemblages attributed to small, coldwater, high quality headwater streams in other regions.

Pennsylvanaia↗
USGS2007

A Roundtable on a National Framework for Natural Hazard Risk Reduction and Management: Developing a Research AgendaSummary Report

Introduction This report summarizes discussion at the Roundtable on a National Framework for Risk Reduction and Management held on November 15, 2006, at the Cosmos Club in Washington, D.C. The Roundtable was cosponsored by the U.S. Geological Survey (USGS), the Association of American Geographers (AAG), and The Wharton School, University of Pennsylvania. Comments made by speakers not affiliated with the USGS do not necessarily reflect the positions of the USGS.

Open-File Report↗
USGS2013

Statistical classification of hydrogeologic regions in the fractured rock area of Maryland and parts of the District of Columbia, Virginia, West Virginia, Pennsylvania, and Delaware

Hydrogeologic regions in the fractured rock area of Maryland were classified using geographic information system tools with principal components and cluster analyses. A study area consisting of the 8-digit Hydrologic Unit Code (HUC) watersheds with rivers that flow through the fractured rock area of Maryland and bounded by the Fall Line was further subdivided into 21,431 catchments from the National Hydrography Dataset Plus. The catchments were then used as a common hydrologic unit to compile relevant climatic, topographic, and geologic variables. A principal components analysis was performed on 10 input variables, and 4 principal components that accounted for 83 percent of the variability in the original data were identified. A subsequent cluster analysis grouped the catchments based on four principal component scores into six hydrogeologic regions. Two crystalline rock hydrogeologic regions, including large parts of the Washington, D.C. and Baltimore metropolitan regions that represent over 50 percent of the fractured rock area of Maryland, are distinguished by differences in recharge, Precipitation minus Potential Evapotranspiration, sand content in soils, and groundwater contributions to streams. This classification system will provide a georeferenced digital hydrogeologic framework for future investigations of groundwater availability in the fractured rock area of Maryland.

Delaware;District of Columbia;Maryl;Pennsylvania;V↗
USGS2015

Organic and inorganic composition and microbiology of produced waters from Pennsylvania shale gas wells

Hydraulically fractured shales are becoming an increasingly important source of natural gas production in the United States. This process has been known to create up to 420 gallons of produced water (PW) per day, but the volume varies depending on the formation, and the characteristics of individual hydraulic fracture. PW from hydraulic fracturing of shales are comprised of injected fracturing fluids and natural formation waters in proportions that change over time. Across the state of Pennsylvania, shale gas production is booming; therefore, it is important to assess the variability in PW chemistry and microbiology across this geographical span. We quantified the inorganic and organic chemical composition and microbial communities in PW samples from 13 shale gas wells in north central Pennsylvania. Microbial abundance was generally low (66–9400 cells/mL). Non-volatile dissolved organic carbon (NVDOC) was high (7–31 mg/L) relative to typical shallow groundwater, and the presence of organic acid anions (e.g., acetate, formate, and pyruvate) indicated microbial activity. Volatile organic compounds (VOCs) were detected in four samples (∼1 to 11.7 μg/L): benzene and toluene in the Burket sample, toluene in two Marcellus samples, and tetrachloroethylene (PCE) in one Marcellus sample. VOCs can be either naturally occurring or from industrial activity, making the source of VOCs unclear. Despite the addition of biocides during hydraulic fracturing, H 2 S-producing, fermenting, and methanogenic bacteria were cultured from PW samples. The presence of culturable bacteria was not associated with salinity or location; although organic compound concentrations and time in production were correlated with microbial activity. Interestingly, we found that unlike the inorganic chemistry, PW organic chemistry and microbial viability were highly variable across the 13 wells sampled, which can have important implications for the reuse and handling of these fluids

Pennsylvania↗
USGS2010

Pennsylvania StreamStats: A web-based application for obtaining water-resource-related information

StreamStats is a national web-based Geographic Information System (GIS) application, developed by the U.S. Geological Survey (USGS), in cooperation with Environmental Systems Research Institute, Inc., to provide a variety of water-resource-related information. Users can easily obtain descriptive information, basin characteristics, and streamflow statistics for USGS streamgages and ungaged stream locations throughout Pennsylvania. StreamStats also allows users to search upstream and (or) downstream from user-selected points to identify locations of and obtain information for water-resource-related activities, such as dams and streamgages.

Pennsylvania↗
USGS2017

Evaluation of the streamgage network for estimating streamflow statistics at ungaged sites in Pennsylvania and the Susquehanna River Basin in Pennsylvania and New York

The current (2015) streamgage network in Pennsylvania and the Susquehanna River Basin in Pennsylvania and New York was evaluated in order to design a network that would meet the hydrologic needs of many partners and serve a variety of purposes and interests, including estimation of streamflow statistics at ungaged sites. This study was done by the U.S. Geological Survey, in cooperation with the Pennsylvania Department of Environmental Protection and the Susquehanna River Basin Commission. The study area includes the Commonwealth of Pennsylvania and the Susquehanna River Basin in Pennsylvania and New York. For this study, 229 streamgages were identified as reference streamgages that could be used to represent ungaged watersheds. Criteria for a reference streamgage are a minimum of 10 years of continuous record, minimally altered streamflow, and a drainage area less than 1,500 square miles. Some of the reference streamgages have been discontinued but provide historical hydrologic information valuable in the determination of streamflow characteristics of ungaged watersheds. Watersheds in the study area not adequately represented by a reference streamgage were identified by examining a range of basin characteristics, the extent of geographic coverage, and the strength of estimated streamflow correlations between gaged and ungaged sites. Basin characteristics were determined for the reference streamgage watersheds and the 1,662 12-digit hydrologic unit code (HUC12) subwatersheds in Pennsylvania and the Susquehanna River Basin using a geographic information system (GIS) spatial analysis and nationally available GIS datasets. Basin characteristics selected for this study include drainage area, mean basin elevation, mean basin slope, percentage of urbanized area, percentage of forested area, percentage of carbonate bedrock, mean annual precipitation, and soil thickness. A GIS spatial analysis was used to identify HUC12 subwatersheds outside the range of basin characteristics of the reference streamgages. There were 320 HUC12 subwatersheds, or 19 percent of the study area, with basin characteristics outside the range represented by the reference streamgage watersheds. A GIS spatial analysis was used to identify geographic gaps in the streamgage network. For each streamgage, a watershed area, called the gage statistical area (GSA), was delineated. The GSA shows the drainage area within a specific drainage-area ratio of the streamgage for transfer of streamflow statistics from that streamgage to ungaged sites on the valid statistical reach of the GSA for a streamgage. In Pennsylvania, a drainage-area ratio of 0.33–3 times the drainage area of the ungaged site was found to perform as well as, if not better than, more traditional ratios such as 0.5–1.5 (or 2) for transfer of selected streamflow statistics. A total of 1,102 HUC12 subwatersheds, or 66 percent of the study area, are outside the GSA for a reference streamgage. The USGS Baseline Streamflow Estimator (BaSE) program was used to determine how well HUC12 subwatersheds outside the streamgage GSAs are represented by the reference streamgage network in Pennsylvania, based on estimated streamflow correlation. The centroid of each HUC12 subwatershed was run through the BaSE program to determine the reference streamgage with the highest estimated streamflow correlation. There were 929 HUC12 subwatersheds in Pennsylvania, or 56 percent of the State, with an estimated correlation coefficient less than 0.96. The results from the basin characteristic, geographic, and streamflow correlation analyses were combined to identify 1,405 HUC12 subwatersheds in Pennsylvania and the Susquehanna River Basin in Pennsylvania and New York that lack a representative reference, based on at least one identified gap. Of the 1,405 HUC12 subwatersheds, 139 exhibited all three gaps, indicating a 8-percent gap in the reference streamgage network. Streamgages in areas with similar hydrologic characteristics and in close proximity to one another can potentially provide similar information (termed streamgages with high substitution potential). Streamgages were considered to have a high substitution potential with a nearby streamgage(s) if (1) the streamflow correlation coefficient was equal to or greater than 0.96, (2) the streamgages had 10 years of concurrent record, and (3) the streamgages are in the same watershed within the GSA of the streamgage. Seventy-four current (2015) streamgages with high substitution potential with at least one other streamgage were identified in the study area. Although these identified streamgages have a high substitution potential, they provide valuable streamflow information to a stakeholder. Selected primary uses of these streamgages were identified to determine the overall need for an individual streamgage.

New York, Pennsylvania↗
USGS2004

Intestinal helminths in mourning doves (Zenaida macroura) from Arizona, Pennsylvania, South Carolina, and Tennessee, U.S.A.

We examined 115 hunter-killed mourning doves ( Zenaida macroura ) from 4 states (Arizona, Pennsylvania, South Carolina, and Tennessee, U.S.A.) in 1998 and 1999 to investigate geographical variation in the prevalence and intensity of intestinal helminth infections. Four intestinal helminth species were identified: Killigrewia delafondi , Ornithostrongylus crami , Ascaridia columbae , and Capillaria obsignata . The number of worms (all helminth species combined) per infected bird ranged from 1 to 166 (mean ± SE = 12.7 ± 7.45, median = 2.0). Filarids, Aproctella stoddardi , were found in 2 birds but were probably adhering to the outside of the intestine. Overall, 18% of the doves were infected with 1 or more species of helminths. The percentage of doves infected with at least 1 helminth species varied from 4% in Arizona to 27% in South Carolina. Mixed infections occurred in only 3 individuals (14% of infected birds). We found no significant differences in prevalence of infection among any of the 4 helminths by host age or sex, and prevalences were too low to test for differences among states. The intensity of O. crami was higher in males than in females but did not differ significantly among states. Intensities of the other 3 helminths did not differ by sex or state, and we found no differences in helminth intensity by age. Intestinal length was significantly greater in infected than in uninfected birds.

Arizona, Pennsylvania, South Carolina, Tennessee↗
USGS2018

Geoelectric hazard maps for the Mid-Atlantic United States: 100 year extreme values and the 1989 magnetic storm

Maps of extreme value geoelectric field amplitude are constructed for the Mid‐Atlantic United States, a region with high population density and critically important power grid infrastructure. Geoelectric field time series for the years 1983–2014 are estimated by convolving Earth surface impedances obtained from 61 magnetotelluric survey sites across the Mid‐Atlantic with historical 1 min (2 min Nyquist) measurements of geomagnetic variation obtained from a nearby observatory. Statistical models are fitted to the maximum geoelectric amplitudes occurring during magnetic storms, and extrapolations made to estimate threshold amplitudes only exceeded, on average, once per century. For the Mid‐Atlantic region, 100 year geoelectric exceedance amplitudes have a range of almost 3 orders of magnitude (from 0.04 V/km at a site in southern Pennsylvania to 24.29 V/km at a site in central Virginia), and they have significant geographic granularity, all of which is due to site‐to‐site differences in magnetotelluric impedance. Maps of these 100 year exceedance amplitudes resemble those of the estimated geoelectric amplitudes attained during the March 1989 magnetic storm, and, in that sense, the March 1989 storm resembles what might be loosely called a “100 year” event. The geoelectric hazard maps reported here stand in stark contrast with the 100 year geoelectric benchmarks developed for the North American Electric Reliability Corporation.

Geophysical Research Letters↗
USGS2019

Empirical estimation of natural geoelectric hazards

Geoelectric field time series can be estimated by convolving estimates of Earth‐surface impedance, such as those obtained from magnetotelluric survey measurements, with historical records of geomagnetic variation obtained at magnetic observatories. This straightforward procedure permits the mapping of geoelectric field variation during magnetic storms. Statistical analysis of the time series allows extrapolation to extreme‐value amplitudes, such as might be realized during an intense magnetic storm in the future. The development of these products is illustrated for the Mid‐Atlantic United States, using impedances obtained from EarthScope survey data and geomagnetic variation records obtained at the Fredericksburg observatory operated by the U.S. Geological Survey. For this region, 100‐year geoelectric exceedance amplitudes have a range of almost three orders of magnitude (from 0.04 V/km at a site in southern Pennsylvania to 24.29 V/km at a site in central Virginia), and they have significant geographic granularity, which is due to site‐to‐site differences in surface impedance (and subsurface electrical conductivity structure). Maps of 100‐year exceedance amplitudes resemble those of geoelectric amplitudes for the March 1989 magnetic storm, and, in that sense, the March 1989 storm resembles what might be loosely called a “100‐year” event.

Book chapter↗