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At least 1,297 records · Page 72Linked to original sources
USGS2011

Challenges of using electrical resistivity method to locate karst conduits-A field case in the Inner Bluegrass Region, Kentucky

Conduits serve as major pathways for groundwater flow in karst aquifers. Locating them from the surface, however, is one of the most challenging tasks in karst research. Geophysical methods are often deployed to help locate voids by mapping variations of physical properties of the subsurface. Conduits can cause significant contrasts of some physical properties that can be detected; other subsurface features such as water-bearing fractures often yield similar contrasts, which are difficult to distinguish from the effects of the conduits. This study used electrical resistivity method to search for an unmapped karst conduit that recharges Royal Spring in the Inner Bluegrass karst region, Kentucky, USA. Three types of resistivity techniques (surface 2D survey, quasi-3D survey, and time-lapse survey) were used to map and characterize resistivity anomalies. Some of the major anomalies were selected as drilling targets to verify the existence of the conduits. Drilling near an anomaly identified by an electrical resistivity profile resulted in successful penetration of a major water-filled conduit. The drilling results also suggest that, in this study area, low resistivity anomalies in general are associated with water-bearing features. However, differences in the anomaly signals between the water-filled conduit and other water-bearing features such as water-filled fracture zones were undistinguishable. The electrical resistivity method is useful in conduit detection by providing potential drilling targets. Knowledge of geology and hydrogeology about the site and professional judgment also played important roles in locating the major conduit. ?? 2011 Elsevier B.V.

Journal of Applied Geophysics↗
USGS2019

Three-dimensional basin and fault structure from a detailed seismic velocity model of Coachella Valley, Southern California

The Coachella Valley in the northern Salton Trough is known to produce destructive earthquakes, making it a high seismic hazard area. Knowledge of the seismic velocity structure and geometry of the sedimentary basins and fault zones is required to improve earthquake hazard estimates in this region. We simultaneously inverted first P wave travel times from the Southern California Seismic Network (39,998 local earthquakes) and explosions (251 land/sea shots) from the 2011 Salton Seismic Imaging Project to obtain a 3-D seismic velocity model. Earthquakes with focal depths ≤10 km were selected to focus on the upper crustal structure. Strong lateral velocity contrasts in the top ~3 km correlate well with the surface geology, including the low-velocity (<5 km/s) sedimentary basin and the high-velocity crystalline basement rocks outside the valley. Sediment thickness is ~4 km in the southeastern valley near the Salton Sea and decreases to <2 km at the northwestern end of the valley. Eastward thickening of sediments toward the San Andreas fault within the valley defines Coachella Valley basin asymmetry. In the Peninsular Ranges, zones of relatively high seismic velocities (~6.4 km/s) between 2 to 4 km depth may be related to Late Cretaceous mylonite rocks or older inherited basement structures. Other high-velocity domains exist in the model down to 9 km depth and help define crustal heterogeneity. We identify a potential fault zone in Lost Horse Valley unassociated with mapped faults in Southern California from the combined interpretation of surface geology, seismicity, and lateral velocity changes in the model.

California↗
USGS2012

Paleomagnetism of welded tuffs of the Yellowstone group

Two of the three ash flow tuffs of the Yellowstone Group are stably magnetized throughout their extent: the Lava Creek tuff (0.60 m.y.) in a normal direction and the Mesa Falls tuff (1.22 m.y.) in a reversed direction. In contrast, much of the Huckleberry Ridge tuff, which was erupted during a polarity transition or field excursion 1.92 m.y. ago and initially magnetized in an intermediate direction ( D = 214.5°, I = −2.2°, and α 95 = 4.1°), has been partially remagnetized in a normal field. Much of the overprint of the Huckleberry Ridge tuff is carried in low‐temperature oxidation products with low coercivities and low blocking temperatures, so that it is commonly removed in peak alternating fields less than 200 Oe or at temperatures less than 400°C. Hematite, having higher coercivities and blocking temperatures, is partly responsible for remagnetization in some specimens, but neither alternating field nor thermal demagnetization enables recovery of the original thermal remanent magnetization in these samples. The chemical overprinting is most pronounced in the devitrified tuff of the flow interior. Stable magnetization is observed in the Huckleberry Ridge tuff in the less porous densely welded portions at the base and boundaries of partial cooling units and in the tuff of the distal margins, where groundwater influences were minimal. Paleomagnetic directions of chilled margins within compound cooling units of the Lava Creek and Huckleberry Ridge tuffs support geological evidence that eruption of each ash flow sheet was rapid and that the source calderas were formed during a short period of time.

Idaho, Montana, Wyoming↗
USGS2009

A comparison of phase inversion and traveltime tomography for processing near-surface refraction traveltimes

With phase inversion, one can estimate subsurface velocities using the phases of first-arriving waves, which are the frequency-domain equivalents of the traveltimes. Phase inversion is modified to make it suitable for processing traveltimes from near-surface refraction surveys. The modifications include parameterizing the model, correcting the observed phases, and selecting the complex frequency. This modified phase inversion is compared to traveltime tomography. For two comparisons using computer-simulated traveltimes, the difference between the estimated and correct models, the residual mean, and the residual standard deviation are smaller for the phase inversion than they are for the traveltime tomography. For a comparison using field data from an S-wave refraction survey, both methods estimate models that are consistent with the known geology. Nonetheless, the phase-inversion model includes small-scale features in the bedrock that are geologically plausible; the residual mean and the residual standard deviation are smaller for the phase inversion than they are for the traveltime tomography.

Geophysical Journal↗
USGS2010

Temporal patterns of apparent leg band retention in North American geese

An important assumption of mark?recapture studies is that individuals retain their marks, which has not been assessed for goose reward bands. We estimated aluminum leg band retention probabilities and modeled how band retention varied with band type (standard vs. reward band), band age (1-40 months), and goose characteristics (species and size class) for Canada (Branta canadensis), cackling (Branta hutchinsii), snow (Chen caerulescens), and Ross?s (Chen rossii) geese that field coordinators double-leg banded during a North American goose reward band study (N = 40,999 individuals from 15 populations). We conditioned all models in this analysis on geese that were encountered with >1 leg band still attached (n = 5,747 dead recoveries and live recaptures). Retention probabilities for standard aluminum leg bands were high (estimate of 0.9995, SE = 0.001) and constant over 1-40 months. In contrast, apparent retention probabilities for reward bands demonstrated an interactive relationship between 5 size and species classes (small cackling, medium Canada, large Canada, snow, and Ross?s geese). In addition, apparent retention probabilities for each of the 5 classes varied quadratically with time, being lower immediately after banding and at older age classes. The differential retention probabilities among band type (reward vs. standard) that we observed suggests that 1) models estimating reporting probability should incorporate differential band loss if it is nontrivial, 2) goose managers should consider the costs and benefits of double-banding geese on an operational basis, and 3) the United States Geological Survey Bird Banding Lab should modify protocols for receiving recovery data.

Journal of Wildlife Management↗
USGS2004

The U.S. Geological Survey Library

Established in 1879, to build and organize a collection of scientific materials in the earth sciences, the U.S. Geological Survey (USGS) Library is the largest earth sciences collection in the world. The USGS Library System is managed by the Geographic Information Office (GIO), Information Policy and Services Office, and includes four libraries in Reston, Va., Denver, Colo., Menlo Park, Calif., and Flagstaff, Ariz. The library holds over one million books and journals, 700,000 maps, 370,000 microforms, 270,000 pamphlets, and 250,000 photographs. In addition to the four libraries managed by the GIO, the USGS has smaller libraries in other locations with collections closely related to the specialized research of their local USGS scientists. The USGS Library System supports the research of USGS scientists by providing access to worldwide information resources. While continuing to build and maintain the large collections of maps, books, and periodicals, the USGS Library system is evolving from a traditional library to a more "virtual library." USGS employees, wherever they are located, have desktop access to an increasing wealth of electronic resources 24 hours a day, 7 days a week.

Fact Sheet↗
USGS2016

Compilation of V S 30 Data for the United States

V S 30 , the time-averaged shear-wave velocity ( V S ) to a depth of 30 meters, is a key index adopted by the earthquake engineering community to account for seismic site conditions. V S 30 is typically based on geophysical measurements of V S derived from invasive and noninvasive techniques at sites of interest. Owing to cost considerations, as well as logistical and environmental concerns, V S 30 data are sparse or not readily available for most areas. Where data are available, V S 30 values are often assembled in assorted formats that are accessible from disparate and (or) impermanent Web sites. To help remedy this situation, we compiled V S 30 measurements obtained by studies funded by the U.S. Geological Survey (USGS) and other governmental agencies. Thus far, we have compiled V S 30 values for 2,997 sites in the United States, along with metadata for each measurement from government-sponsored reports, Web sites, and scientific and engineering journals. Most of the data in our V S 30 compilation originated from publications directly reporting the work of field investigators. A small subset (less than 20 percent) of V S 30 values was previously compiled by the USGS and other research institutions. Whenever possible, V S 30 originating from these earlier compilations were crosschecked against published reports. Both downhole and surface-based V S 30 estimates are represented in our V S 30 compilation. Most of the V S 30 data are for sites in the western contiguous United States (2,141 sites), whereas 786 V S 30 values are for sites in the Central and Eastern United States; 70 values are for sites in other parts of the United States, including Alaska (15 sites), Hawaii (30 sites), and Puerto Rico (25 sites). An interactive map is hosted on the primary USGS Web site for accessing V S 30 data ( https://earthquake.usgs.gov/data/vs30/us/ ).

Data Series↗
USGS2017

Predicted pH at the domestic and public supply drinking water depths, Central Valley, California

This scientific investigations map is a product of the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) project modeling and mapping team. The prediction grids depicted in this map are of continuous pH and are intended to provide an understanding of groundwater-quality conditions at the domestic and public supply drinking water zones in the groundwater of the Central Valley of California. The chemical quality of groundwater and the fate of many contaminants is often influenced by pH in all aquifers. These grids are of interest to water-resource managers, water-quality researchers, and groundwater modelers concerned with the occurrence of natural and anthropogenic contaminants related to pH. In this work, the median well depth categorized as domestic supply was 30 meters below land surface, and the median well depth categorized as public supply is 100 meters below land surface. Prediction grids were created using prediction modeling methods, specifically boosted regression trees (BRT) with a Gaussian error distribution within a statistical learning framework within the computing framework of R ( http://www.r-project.org/ ). The statistical learning framework seeks to maximize the predictive performance of machine learning methods through model tuning by cross validation. The response variable was measured pH from 1,337 wells and was compiled from two sources: USGS National Water Information System (NWIS) database (all data are publicly available from the USGS: http://waterdata.usgs.gov/ca/nwis/nwis ) and the California State Water Resources Control Board Division of Drinking Water (SWRCB-DDW) database (water quality data are publicly available from the SWRCB: http://www.waterboards.ca.gov/gama/geotracker_gama.shtml ). Only wells with measured pH and well depth data were selected, and for wells with multiple records, only the most recent sample in the period 1993–2014 was used. A total of 1,003 wells (training dataset) were used to train the BRT model, and 334 wells (hold-out dataset) were used to validate the prediction model. The training r-squared was 0.70, and the root-mean-square error (RMSE) in standard pH units was 0.26. The hold-out r-squared was 0.43, and RMSE in standard pH units was 0.37. Predictor variables consisting of more than 60 variables from 7 sources were assembled to develop a model that incorporates regional-scale soil properties, soil chemistry, land use, aquifer textures, and aquifer hydrology. Previously developed Central Valley model outputs of textures (Central Valley Textural Model, CVTM; Faunt and others, 2010) and MODFLOW-simulated vertical water fluxes and predicted depth to water table (Central Valley Hydrologic Model, CVHM; Faunt, 2009) were used to represent aquifer textures and groundwater hydraulics, respectively. In this work, wells were attributed to predictor variable values in ArcGIS using a 500-meter buffer. Faunt, C.C., ed., 2009, Groundwater availability in the Central Valley aquifer, California: U.S. Geological Survey Professional Paper 1776, 225 p., accessed at https://pubs.usgs.gov/pp/1766/ . Faunt, C.C., Belitz, K., and Hanson, R.T., 2010, Development of a three-dimensional model of sedimentary texture in valley-fill deposits of Central Valley, California, USA: Hydrogeology Journal, v. 18, no. 3, p. 625–649, https://doi.org/10.1007/s10040-009-0539-7 .

California↗
USGS2004

Application of deterministic deconvolution of ground-penetrating radar data in a study of carbonate strata

We successfully applied deterministic deconvolution to real ground-penetrating radar (GPR) data by using the source wavelet that was generated in and transmitted through air as the operator. The GPR data were collected with 400-MHz antennas on a bench adjacent to a cleanly exposed quarry face. The quarry site is characterized by horizontally bedded carbonate strata with shale partings. In order to provide groundtruth for this deconvolution approach, 23 conductive rods were drilled into the quarry face at key locations. The steel rods provided critical information for: (1) correlation between reflections on GPR data and geologic features exposed in the quarry face, (2) GPR resolution limits, (3) accuracy of velocities calculated from common midpoint data and (4) identifying any multiples. Comparing the results of deconvolved data with non-deconvolved data demonstrates the effectiveness of deterministic deconvolution in low dielectric-loss media for increased accuracy of velocity models (improved at least 10-15% in our study after deterministic deconvolution), increased vertical and horizontal resolution of specific geologic features and more accurate representation of geologic features as confirmed from detailed study of the adjacent quarry wall. ?? 2004 Elsevier B.V. All rights reserved.

Journal of Applied Geophysics↗
USGS2005

Direct measurement of methane hydrate composition along the hydrate equilibrium boundary

The composition of methane hydrate, namely n w for CH 4 · n w H 2 O, was directly measured along the hydrate equilibrium boundary under conditions of excess methane gas. Pressure and temperature conditions ranged from 1.9 to 9.7 MPa and 263 to 285 K. Within experimental error, there is no change in hydrate composition with increasing pressure along the equilibrium boundary, but n w may show a slight systematic decrease away from this boundary. A hydrate stoichiometry of n w = 5.81−6.10 H 2 O describes the entire range of measured values, with an average composition of CH 4 ·5.99(±0.07)H 2 O along the equilibrium boundary. These results, consistent with previously measured values, are discussed with respect to the widely ranging values obtained by thermodynamic analysis. The relatively constant composition of methane hydrate over the geologically relevant pressure and temperature range investigated suggests that in situ methane hydrate compositions may be estimated with some confidence.

Journal of Physical Chemistry B↗
USGS2012

Galileo observations of Post-Imbrium lunar craters during the first Earth-Moon flyby

Copernican‐age craters are among the most conspicuous features seen on the far side and western limb of the Moon in the Galileo multispectral images acquired in December 1990. Among the new morphologic observations of far‐side craters are bright rays, continuous ejecta deposits, and dark rings associated with probable impact‐melt veneers. These observations suggest that the mapped age assignments of several large far‐side craters (Ohm, Robertson, and possibly Lowell and Lenz) need revision. New crater size‐frequency measurements on Lunar Orbiter images suggest the following age reassignments: Hausen (170 km diameter), Pythagoras (120 km), and Bullialdus (61 km) from Eratosthenian to Upper Imbrian, and Carpenter (60 km) and Harpalus (39 km) from Copernican to Eratosthenian. Colors and albedos of craters (away from impact‐melt veneers) are correlated with their geologic emplacement ages as determined from counts of superposed craters; these age‐color relations are used to estimate the emplacement age (time since impact event) for other Copernican‐age craters. These age‐color relations indicate a probable Copernican age for 27 far‐side or western limb craters larger than 10 km diameter that were not previously mapped as Copernican. The apparent deficiency of Copernican craters on the far side compared with the near side in published geologic maps is not present in our data. Age‐color trends differ between mare and highland regions and between the interiors and continuous ejecta of the craters. Similar trends are established for color and albedo versus soil‐maturity indices for the returned lunar samples, with distinct trends for mare and highland soils. However, the mare versus highland offsets are reversed in the two comparisons. These relations can be explained by variations in regolith thicknesses and rates of mixing with relatively fresh, crystalline ejecta. Therefore, the soil‐maturity trends represent longer geologic time periods in regions with thinner regoliths, such as the maria.

Journal of Geophysical Research E: Planets↗
USGS2012

Basal slip and mechanical anisotropy of biotite

The basal slip systems of biotite and their mechanical expressions have been investigated by shortening single crystals oriented to maximize and minimize shear stresses on (001). Samples loaded at 45° to (001) exhibit gentle external rotations associated with dislocation glide. High‐angle kink bands in these samples, unlike those developed in micas loaded parallel to (001), are limited to sample corners. Samples shortened perpendicular to (001) show no evidence of nonbasal slip and fail by fracture over all conditions tested. The mechanical response of biotite shortened at 45° to (001) is nearly perfectly elastic‐plastic; stress‐strain curves are characterized by a steep elastic slope, a sharply defined yield point, and continued deformation at low (mostly 1%. Stresses measured beyond the yield point are insensitive to confining pressure over the range 200 to 500 MPa and exhibit weak dependencies upon strain rate and temperature. Assuming an exponential relationship between differential stress σ and strain rate of the form , the data collected over strain rates and temperatures of 10−7 to 10−4 s−1 and 20° to 400°C, respectively, are best fit by an exponential constant α of 0.41±0.08 MPa‐1 and an activation energy of 82±13 kJ/mol. A power law fits the data equally well with = 18±4 and = 51±9 kJ/mol. Samples oriented favorably for slip in directions [100] and [110] are measurably weaker than those shortened at 45° to [010] and [310], consistent with the reported Burgers vectors 〈100〉, 1/2 〈110〉, and 1/2 〈110〉. The anisotropy of biotite is further revealed by contrasting these plastic strengths with results of samples deformed parallel and perpendicular to (001). Previous studies have shown that biotite loaded in the (001) plane is strong prior to the nucleation of kink bands. The strength of biotite shortened perpendicular to (001) exceeds that measured parallel to (001) and is pressure dependent. Application of the results to deformation within the continental crust suggests that biotite oriented favorably for slip is much weaker than most other silicates over a wide range of geologic conditions. Its presence within foliated rocks and shear zones may limit locally the stresses that can be supported.

Journal of Geophysical Research B: Solid Earth↗
USGS2025

A crustal thermal model of the conterminous U.S. constrained by multiple data sets: A Monte-Carlo approach

The thermal structure of the continental crust plays a critical role in understanding its elastic and rheologic properties as well as its dynamic processes. Thermal parameter data sets on continental scales have been used to constrain the crustal thermal structure, including both the direct (e.g. temperature, heat flux and heat conductivity measured at the surface) and indirect (e.g. seismically derived Mohorovičić discontinuity (Moho) temperature, geomagnetically derived Curie depth) observations. In this study, we present a new continental scale crustal heat generation model with additional information from seismologically inferred crustal composition. Together with previous direct and indirect thermal parameter data sets in the conterminous United States, we use the new crustal heat generation model to construct a 3-D crustal temperature model under a newly developed Bayesian framework. Specifically, we first derive profiles of crustal heat generation based on an empirical geochemical relationship at 1683 locations where seismologically derived crustal composition information is available. Then for each of these locations, the average heat generation values in the upper, middle and lower crust are combined with other thermal parameters through a Markov Chain Monte-Carlo inversion for a conductive, vertically smooth temperature profile. The results, posterior distributions of temperature profiles, are used to generate a 3-D crustal thermal model with the uncertainties systematically assessed. The new temperature model overall exhibits similar patterns to that from the U.S. Geological Survey National Crustal Model, but also reduces possible biases and the model's dependence on a single thermal parameter.

conterminous United States↗
USGS2015

Literature review of the potential effects of formalin on nitrogen oxidation efficiency of the biofilters of recirculating aquaculture systems (RAS) for freshwater finfish

A comprehensive literature review was done for the effects of formalin on biofilter function in recirculating aquaculture systems (RAS) using these databases: ISI/Web of Knowledge, Scopus, and Pubmed. Inclusion and exclusion criteria were developed as the literature review was conducted. The initial search produced 5,682 potential citations. Once the literature search was complete, these 5,682 titles were screened for applicable papers using the inclusion and exclusion criteria. If the title contained any of the inclusion terms, it was retained. Titles of the remaining papers were then screened for exclusion terms. If the title contained one or more of the exclusion terms, it was eliminated from further consideration. This refined search produced 1,287 papers. After the initial screening, the remaining 1,287 papers underwent a second screening. Titles and abstracts (when available) were again read to verify that the topic of the paper was related to RAS. During the second screening, a second person verified that the papers proposed for elimination were not related to RAS. A combined reference list of the 443 remaining papers was created and submitted to the U.S. Geological Survey (USGS) Upper Midwest Environmental Sciences Center (UMESC) librarian to obtain the actual papers; electronic copies of those citations were obtained and reviewed. The UMESC librarian also would receive weekly updates from Scopus (a bibliographic database containing abstracts and citations for academic journal articles) using the search terms. Any resulting papers from those updates also were screened using the inclusion criteria, and any relevant papers were requested. From those, 82 were cited in the literature review. An additional 10 references were obtained from weekly updates or reference mining other sources and were incorporated into the final literature review.

Open-File Report↗
USGS2018

Combining sediment fingerprinting with age-dating sediment using fallout radionuclides for an agricultural stream, Walnut Creek, Iowa, USA

Purpose The main purpose of this study was to demonstrate the utility of the sediment fingerprinting approach to apportion surface-derived sediment, and then age date that portion using short-lived fallout radionuclides. In systems where a large mass of mobile sediment is in channel storage, age dating provides an understanding of the transfer of sediment through the watershed and the time scales over which management actions to reduce sediment loadings may be effective. Materials and methods In the agricultural Walnut Creek watershed, Iowa, the sediment-fingerprinting approach with elemental analysis was used to apportion the sources of fine-grained sediment (croplands, prairie, unpaved roads, and channel banks). Fallout radionuclides ( 7 Be, 210 Pb ex ) were used to age the portion of suspended sediment that was derived from agricultural topsoil. Age dating was performed at two different scales: 210 Pb ex which can date sediment to ~ 85 years and 7 Be to ~ 1 year. Results and discussion Sediment fingerprinting results indicated that the majority of suspended sediment is derived from cropland (62%) with streambanks contributing 36%, and prairie, pasture, and unpaved roads each contributing ≤ 1%. The topsoil–derived portion of sediment (primarily agriculture) dated using 210 Pb ex has ages ranging from 1 to 58 years, and using 7 Be, a component of much younger sediment that yields ages ranging from 44 to 205 days. The occurrence of 7 Be indicates that some portion of the sediment is young, on the order of months, whereas the dating based on 210 Pb ex indicates that some of the surface-derived sediment has been in channel storage for decades. Published studies in Walnut Creek indicate that a large component of sediment is stored in the channel bed. Conclusions We conclude that the 210 Pb ex -based ages are a reasonable estimate for the mean age of the surface-derived fraction and that 7 Be activities are evidence that there is a smaller fraction of very young sediment in the stream. We propose a geomorphic model where agricultural soil is delivered to the channel and conveyed to the watershed outlet at three time scales: a geologic-millennial time scale, decades, and a young time scale (< 1 year).

Iowa↗
USGS2011

Characterization of the Cretaceous aquifer structure of the Meskala region of the Essaouira Basin, Morocco

The aquifer of early Cretaceous age in the Meskala region of the Essaouira Basin is defined by interpretation of geological drilling data of oil and hydrogeological wells, field measurement and analysis of in situ fracture orientations, and the application of a morphostructural method to identify lineaments. These analyzes are used to develop a stratigraphic–structural model of the aquifer delimited by fault zones of two principal orientations: NNE and WNW. These fault zones define fault blocks that range in area from 4 to 150 km 2 . These blocks correspond either to elevated zones (horsts) or depressed zones (grabens). This structural setting with faults blocks of Meskala region is in accordance with the structure of the whole Essaouira Basin. Fault zones disrupt the continuity of the aquifer throughout the study area, create recharge and discharge zones, and create dip to the units from approximately 10° to near vertical in various orientations. Fracture measurements and morphometric-lineament analyzes help to identify unmapped faults, and represent features important to groundwater hydraulics and water quality within fault blocks. The above geologic features will enable a better understanding of the behaviour and hydro-geo-chemical and hydrodynamics of groundwater in the Meskala aquifer.

Essaouira Basin↗
USGS2003

An empirical approach to inversion of an unconventional helicopter electromagnetic dataset

A helicopter electromagnetic (HEM) survey acquired at the U.S. Idaho National Engineering and Environmental Laboratory (INEEL) used a modification of a traditional mining airborne method flown at low levels for detailed characterization of shallow waste sites. The low sensor height, used to increase resolution, invalidates standard assumptions used in processing HEM data. Although the survey design strategy was sound, traditional interpretation techniques, routinely used in industry, proved ineffective. Processed data and apparent resistivity maps were severely distorted, and hence unusable, due to low flight height effects, high magnetic permeability of the basalt host, and the conductive, three-dimensional nature of the waste site targets.To accommodate these interpretation challenges, we modified a one-dimensional inversion routine to include a linear term in the objective function that allows for the magnetic and three-dimensional electromagnetic responses in the in-phase data. Although somewhat ad hoc, the use of this term in the inverse routine, referred to as the shift factor, was successful in defining the waste sites and reducing noise due to the low flight height and magnetic characteristics of the host rock. Many inversion scenarios were applied to the data and careful analysis was necessary to determine the parameters appropriate for interpretation, hence the approach was empirical. Data from three areas were processed with this scheme to highlight different interpretational aspects of the method. Wastes sites were delineated with the shift terms in two of the areas, allowing for separation of the anthropomorphic targets from the natural one-dimensional host. In the third area, the estimated resistivity and the shift factor were used for geological mapping. The high magnetic content of the native soil enabled the mapping of disturbed soil with the shift term. Published by Elsevier Science B.V.

Journal of Applied Geophysics↗
USGS2001

Observation of the geology and geomorphology of the 1999 Marsokhod test site

The Marsokhod rover returned data from six stations that were used to decipher the geomorphology and geology of a region not previously visited by members of the geomorphology field team. Satellite images and simulated descent images provided information about the regional setting. The landing zone was on an alluvial apron flanking a mountain block to the west and a playa surface to the east. Rover color images, infrared spectra analysis of the mountains, and the apron surface provided insight into the rock composition of the nearby mountains. From the return data the geomorphology team interpreted the region to consist of compressionally deformed, ancient marine sediments and igneous rocks exposed by more recent extensional tectonics. Unconsolidated alluvial materials blanket the lower flanks of the mountains. An ancient shoreline cut into alluvial material marks a high stand of water during a past, wetter climate period. Playa sediments floor a present-day, seasonally, dry lake. Observations made by the rover using panoramic and close-up (hand specimens-scale) image data and color scene data confirmed the presence of boulders, cobbles, and fines of various provinces. Rover traverses to sites identified as geologically distinct, such as fan, channel, shoreline, and playa, provided useful clues to the geologic interpretations. Analysis of local rocks was given context only through comparison with distant geologic features. These results demonstrated the importance of a multifaceted approach to site interpretation through comparison of interpretations derived by differing geologic techniques.

California↗