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At least 1,531 records · Page 85Linked to original sources
USGS2008

Spatial Distribution of Ground-Water Recharge Estimated with a Water-Budget Method for the Jordan Creek Watershed, Lehigh County, Pennsylvania

This report presents the results of a study by the U.S. Geological Survey, in cooperation with the Pennsylvania Geological Survey, to illustrate a water-budget method for mapping the spatial distribution of ground-water recharge for a 76-square-mile part of the Jordan Creek watershed, northwest of Allentown, in Lehigh County, Pennsylvania. Recharge was estimated by using the Hydrological Evaluation of Landfill Performance (HELP) water-budget model for 577 landscape units in Jordan Creek watershed, delineated on the basis of their soils, land use/land cover, and mean annual precipitation during 1951-2000. The water-budget model routes precipitation falling on each landscape unit to components of evapotranspiration, surface runoff, storage, and vertical percolation (recharge) for a five-layer soil column on a daily basis. The spatial distribution of mean annual recharge during 1951-2000 for each landscape unit was mapped by the use of a geographic information system. Recharge simulated by the water-budget model in Jordan Creek watershed during 1951-2000 averaged 12.3 inches per year and ranged by landscape unit from 0.11 to 17.05 inches per year. Mean annual recharge during 1951-2000 simulated by the water-budget model was most sensitive to changes to input values for precipitation and runoff-curve number. Mean annual recharge values for the crop, forest, pasture, and low-density urban land-use/land-cover classes were similar (11.2 to 12.2 inches per year) but were substantially less for high-density urban (6.8 inches per year), herbaceous wetlands (2.5 inches per year), and forested wetlands (1.3 inches per year). Recharge rates simulated for the crop, forest, pasture, and low-density urban land-cover classes were similar because those land-use/land-cover classes are represented in the model with parameter values that either did not significantly affect simulated recharge or tended to have offsetting effects on recharge. For example, for landscapes with forest land cover, values of runoff-curve number assigned to the model were smaller than for other land-use/land-cover classes (causing more recharge and less runoff), but the maximum depth of evapotranspiration was larger than for other land-use/ land-cover classes because of deeper root penetration in forests (causing more evapotranspiration and less recharge). The smaller simulated recharge for high-density urban and wetland land-use/land-cover classes was caused by the large values of runoff-curve number (greater than 90) assigned to those classes. The large runoff-curve number, however, certainly is not realistic for all wetlands; some wetlands act as areas of ground-water discharge and some as areas of recharge. Simulated mean annual recharge computed by the water-budget model for the 53-square-mile part of the watershed upstream from the streamflow-gaging station near Schnecksville was compared to estimates of recharge and base flow determined by analysis of streamflow records from 1967 to 2000. The mean annual recharge of 12.4 inches per year simulated by the water-budget method for 1967-2000 was less than estimates of mean annual recharge of 19.3 inches per year computed from the RORA computer program and base flow computed by the PART computer program (15.1 inches per year). In theory, the water-budget method provides a practical tool for estimating differences in recharge at local scales of interest, and the watershed- average recharge rate of 12.4 inches per year computed by the method is reasonable. However, the mean annual surface runoff of 4.5 inches per year simulated by the model is unrealistically small. The sum of surface runoff and recharge simulated by the water-budget model (16.9 inches per year) is 7 inches per year less than the streamflow measured at the gaging station near Schnecksville (23.9 inches per year) during 1967-2000, indicating that evapotranspiration is overestimated by the water-budget model by that amount. This discrepancy ca

Scientific Investigations Report↗
USGS1998

Global teleseismic earthquake relocation with improved travel times and procedures for depth determination

We relocate nearly 100,000 events that occurred during the period 1964 to 1995 and are well-constrained teleseismically by arrival-time data reported to the International Seismological Centre ( ISC ) and to the U.S. Geological Survey's National Earthquake Information Center ( NEIC ). Hypocenter determination is significantly improved by using, in addition to regional and teleseismic P and S phases, the arrival times of PKiKP, PKPdf , and the teleseismic depth phases pP, pwP , and sP in the relocation procedure. A global probability model developed for later-arriving phases is used to independently identify the depth phases. The relocations are compared to hypocenters reported in the ISC and NEIC catalogs and by other sources. Differences in our epicenters with respect to ISC and NEIC estimates are generally small and regionally systematic due to the combined effects of the observing station network and plate geometry regionally, differences in upper mantle travel times between the reference earth models used, and the use of later-arriving phases. Focal depths are improved substantially over most other independent estimates, demonstrating (for example) how regional structures such as downgoing slabs can severely bias depth estimation when only regional and teleseismic P arrivals are used to determine the hypocenter. The new data base, which is complete to about Mw 5.2 and includes all events for which moment-tensor solutions are available, has immediate application to high-resolution definition of Wadati-Benioff Zones ( WBZ s) worldwide, regional and global tomographic imaging, and other studies of earth structure.

Bulletin of the Seismological Society of America↗
USGS2025

Statistical approaches for modeling correlated grade and tonnage distributions and applications for mineral resource assessments

Correlations between grade and tonnage exist in mineral resource data compiled from published reports, but they are not always addressed during quantitative assessment of undiscovered mineral resources. Failure to account for correlated grade and tonnage distributions can result in geologically unrealistic assessment results. Current software tools simulate univariate ore tonnage and multivariate resource grades of undiscovered deposits independently. As a result, analysts are forced to rely on ad-hoc solutions to minimize the correlation issues by: 1) creating subsets of data with restricted criteria; 2) truncating grade and tonnage distributions; and 3) testing model robustness using exploratory data analysis. While these methods represent pragmatic solutions, the statistical solutions presented here provide additional options to address real correlations in grade and tonnage data used for mineral resource assessments. We present a modified version of the MapMark4 package in R that introduces two alternatives for modeling grade and tonnage distributions, consisting of a multivariate solution that accounts for correlations between ore tonnage and metal grades and an empirical solution that utilizes simple random sampling with replacement to reproduce coupled grades and tonnages from the input data. We present simulations for contained ore and metal for three case studies representing tungsten skarn, komatiite-hosted nickel, and sediment-hosted carbonate amagmatic zinc-lead (Mississippi Valley-type) deposits. Employing the methods presented here yields quantitative mineral resource assessment results that more closely reflect the empirical distributions of grades and tonnages observed in nature and expands the applicability of these tools for ongoing critical mineral resource assessments.

Applied Computing and Geosciences↗
USGS2006

Quantitative x-ray diffraction mineralogy of Los Angeles basin core samples

This report contains X-ray diffraction (XRD) analysis of mineralogy for 81 sediment samples from cores taken from three drill holes in the Los Angeles Basin in 2000-2001. We analyzed 26 samples from Pier F core, 29 from Pier C core, and 26 from the Webster core. These three sites provide an offshore-onshore record across the Southern California coastal zone. This report is designed to be a data repository; these data will be used in further studies, including geochemical modeling as part of the CABRILLO project. Summary tables quantify the major mineral groups, whereas detailed mineralogy is presented in three appendices. The rationale, methodology, and techniques are described in the following paper.

Open-File Report↗