The Cheyenne area is on broad tablelands that form part of the High Plains aquifer. Surficial deposits, along with the Ogallala Formation and the White River Group, are included in the High Plains aquifer in the study area, and both unconfined and confined ground-water conditions exist within 100 feet of land surface. During wet years, shallow ground-water problems affect urban development. The High Plains aquifer is considered an aquifer system in the Cheyenne area. Water-yielding sandstone and conglomerate units are surrounded by sequences of clay and silt; although the water-yielding units under confined conditions may be areally extensive, they are not easily identified. Urban development has modified the High Plains aquifer system locally as indicated by the mapped potentiometric surfaces, the perched water zones, and the surface-drainage patterns. That part of the system in the shallow zones is affected by excavations and by structures that penetrate the saturated zones.
","language":"English","doi":"10.3133/wri924047","usgsCitation":"Cooley, M.E., and Crist, M.A., 1991, Geohydrology of the High Plains aquifer system, Cheyenne urban area, Wyoming: U.S. Geological Survey Water-Resources Investigations Report 92-4047, 4 Plates: 43.75 x 35.00 inches or smaller, https://doi.org/10.3133/wri924047.","productDescription":"4 Plates: 43.75 x 35.00 inches or smaller","costCenters":[{"id":5050,"text":"WY-MT Water Science Center","active":true,"usgs":true}],"links":[{"id":162783,"rank":1,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/usgs_thumb.jpg"},{"id":82015,"rank":3,"type":{"id":17,"text":"Plate"},"url":"https://pubs.usgs.gov/wri/1992/4047/plate-2.pdf","linkFileType":{"id":1,"text":"pdf"}},{"id":82017,"rank":5,"type":{"id":17,"text":"Plate"},"url":"https://pubs.usgs.gov/wri/1992/4047/plate-4.pdf","linkFileType":{"id":1,"text":"pdf"}},{"id":82016,"rank":4,"type":{"id":17,"text":"Plate"},"url":"https://pubs.usgs.gov/wri/1992/4047/plate-3.pdf","linkFileType":{"id":1,"text":"pdf"}},{"id":82014,"rank":2,"type":{"id":17,"text":"Plate"},"url":"https://pubs.usgs.gov/wri/1992/4047/plate-1.pdf","linkFileType":{"id":1,"text":"pdf"}},{"id":110258,"rank":6,"type":{"id":36,"text":"NGMDB Index Page"},"url":"https://ngmdb.usgs.gov/Prodesc/proddesc_47624.htm","linkFileType":{"id":5,"text":"html"},"description":"47624"}],"country":"United States","state":"Wyoming","city":"Cheyenne","otherGeospatial":"High Plains aquifer","geographicExtents":"{\n \"type\": \"FeatureCollection\",\n \"features\": [\n {\n \"type\": \"Feature\",\n \"properties\": {},\n \"geometry\": {\n \"coordinates\": [\n [\n [\n -104.91287316773818,\n 41.21845790398558\n ],\n [\n -104.91287316773818,\n 41.05831167067973\n ],\n [\n -104.70642356416842,\n 41.05831167067973\n ],\n [\n -104.70642356416842,\n 41.21845790398558\n ],\n [\n -104.91287316773818,\n 41.21845790398558\n ]\n ]\n ],\n \"type\": \"Polygon\"\n }\n }\n ]\n}","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"4f4e4b1be4b07f02db6a895b","contributors":{"authors":[{"text":"Cooley, Maurice E.","contributorId":8077,"corporation":false,"usgs":true,"family":"Cooley","given":"Maurice","email":"","middleInitial":"E.","affiliations":[],"preferred":false,"id":230314,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Crist, Marvin A.","contributorId":63376,"corporation":false,"usgs":true,"family":"Crist","given":"Marvin","email":"","middleInitial":"A.","affiliations":[],"preferred":false,"id":230315,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70015595,"text":"70015595 - 1991 - Brine evolution and mineral deposition in hydrologically open evaporite basins","interactions":[],"lastModifiedDate":"2019-10-03T15:32:54","indexId":"70015595","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":732,"text":"American Journal of Science","active":true,"publicationSubtype":{"id":10}},"title":"Brine evolution and mineral deposition in hydrologically open evaporite basins","docAbstract":"A lumped-parameter, solute mass-balance model is developed to define the role of water outflow from a well-mixed basin. A mass-balance model is analyzed with a geochemical model designed for waters with high ionic strengths. Two typical waters, seawater and a Na-HCO3 ground water, are analyzed to illustrate the control that the leakage ratio (or hydrologic openness of the basin) has on brine evolution and the suite and thicknesses of evaporite minerals deposited. The analysis suggests that brines evolve differently under different leakage conditions. -from Authors","language":"English","publisher":"American Journal of Science","doi":"10.2475/ajs.291.7.687","issn":"00029599","usgsCitation":"Sanford, W., and Wood, W., 1991, Brine evolution and mineral deposition in hydrologically open evaporite basins: American Journal of Science, v. 291, no. 7, p. 687-710, https://doi.org/10.2475/ajs.291.7.687.","productDescription":"24 p.","startPage":"687","endPage":"710","numberOfPages":"24","costCenters":[{"id":589,"text":"Toxic Substances Hydrology Program","active":true,"usgs":true}],"links":[{"id":480425,"rank":1,"type":{"id":40,"text":"Open Access Publisher Index Page"},"url":"https://doi.org/10.2475/ajs.291.7.687","text":"Publisher Index Page"},{"id":224106,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"291","issue":"7","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"5059f282e4b0c8380cd4b1f3","contributors":{"authors":[{"text":"Sanford, W. E. 0000-0002-6624-0280","orcid":"https://orcid.org/0000-0002-6624-0280","contributorId":102112,"corporation":false,"usgs":true,"family":"Sanford","given":"W. E.","affiliations":[],"preferred":false,"id":371325,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Wood, W.W.","contributorId":21974,"corporation":false,"usgs":true,"family":"Wood","given":"W.W.","email":"","affiliations":[],"preferred":false,"id":371324,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70014988,"text":"70014988 - 1991 - Stress magnitudes in the crust: constraints from stress orientation and relative magnitude data","interactions":[],"lastModifiedDate":"2013-03-01T10:40:41","indexId":"70014988","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":3047,"text":"Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences","active":true,"publicationSubtype":{"id":10}},"title":"Stress magnitudes in the crust: constraints from stress orientation and relative magnitude data","docAbstract":"The World Stress Map Project is a global cooperative effort to compile and interpret data on the orientation and relative magnitudes of the contemporary in situ tectonic stress field in the Earth's lithosphere. The intraplate stress field in both the oceans and continents is largely compressional with one or both of the horizontal stresses greater than the vertical stress. The regionally uniform horizontal intraplate stress orientations are generally consistent with either relative or absolute plate motions indicating that plate-boundary forces dominate the stress distribution within the plates. Current models of stresses due to whole mantle flow inferred from seismic topography models predict a general compressional stress state within continents but do not match the broad-scale horizontal stress orientations. The broad regionally uniform intraplate stress orientations are best correlated with compressional plate-boundary forces and the geometry of the plate boundaries. -from Authors","largerWorkType":{"id":2,"text":"Article"},"largerWorkTitle":"Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences","largerWorkSubtype":{"id":10,"text":"Journal Article"},"language":"English","publisher":"Royal Society of London","doi":"10.1098/rsta.1991.0115","usgsCitation":"Zoback, M., and Magee, M., 1991, Stress magnitudes in the crust: constraints from stress orientation and relative magnitude data: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, v. 337, no. 1645, p. 181-194, https://doi.org/10.1098/rsta.1991.0115.","startPage":"181","endPage":"194","numberOfPages":"14","costCenters":[],"links":[{"id":224066,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"},{"id":268614,"type":{"id":10,"text":"Digital Object Identifier"},"url":"https://dx.doi.org/10.1098/rsta.1991.0115"}],"volume":"337","issue":"1645","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505b9b5ee4b08c986b31ce28","contributors":{"authors":[{"text":"Zoback, M.L.","contributorId":12982,"corporation":false,"usgs":true,"family":"Zoback","given":"M.L.","email":"","affiliations":[],"preferred":false,"id":369780,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Magee, M.","contributorId":53095,"corporation":false,"usgs":true,"family":"Magee","given":"M.","email":"","affiliations":[],"preferred":false,"id":369781,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70015088,"text":"70015088 - 1991 - Multicycle slip distribution along a laboratory fault","interactions":[],"lastModifiedDate":"2024-05-01T23:55:34.478221","indexId":"70015088","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":2312,"text":"Journal of Geophysical Research","active":true,"publicationSubtype":{"id":10}},"title":"Multicycle slip distribution along a laboratory fault","docAbstract":"Slip distribution along a laboratory fault, which consists of eight spring-connected blocks that are elastically driven to slide on a frictional surface, has been examined for a “long” sequence of slip events to test the applicability of some conceptual models proposed recently in the literature. The distributions of large slip events are found to be quite variable and do not fit the uniform slip or characteristic earthquake models. The rupture initiation points are usually not near the corresponding maximum slip points, in contrast to observations by Thatcher (1990) and by Fukao and Kikuchi (1987) that earthquake hypocenters are commonly near corresponding regions of maximum slip in the fault planes. This contrast may suggest that either the present observations or theirs are not representative or the teleseismically determined hypocenters may not always be true rupture initiation points as usually assumed. Large slip events are also found to be a stress-roughening process. They are triggered by some small events after the stresses have been adjusted by some earlier small-to-moderate events to be near the critical levels at most locations along the fault. This suggests that earthquake prediction monitoring efforts should not be limited to a small region near an asperity but should be spread out to cover the entire fault segment in a seismic gap in order to detect the condition of simultaneous strain buildup.
A small (4 km2) drainage basin in northeastern Washington contains highly uraniferous groundwater and highly uraniferous peaty sediments of Holocene age. The U is derived from granitic bedrock that underlies the entire drainage basin and that contains 9–16 ppm U. This local bedrock was studied by petrographic, chemical and isotopic methods to determine conditions of its petrogenesis and post-emplacement history that may have contributed to its present high U content and source-rock capability. The original magma was derived by anatexis of Precambrian continental crust of probable mixed metaigneous and metasedimentary character. Mineral-melt partitioning controlled the enrichment of U in chemically evolved phases of the crystallizing melt. Following emplacement in the upper crust at ∼100Ma, the pluton interacted with meteoric-hydrothermal water at ambient temperatures 300°C. Locally intense fracturing promoted alteration, and fracturing and alteration probably continued during later regional uplift in the Eocene. Regional uplift was followed by low-temperature alteration and weathering in the middle to late Tertiary. The combined result of hydrothermal alteration and low-temperature alteration and weathering was the redistribution of U from primary mineral hosts such as allanite to new sites on fracture surfaces and in secondary minerals such as hematite. Zones of highly fractured and altered rock show the most obvious evidence of this process. A model is proposed in which high-angle fractures beneath the drainage basin were the sites of Tertiary supergene enrichments of U. Recent glacio-isostatic uplift has elevated these older enriched zones to shallow levels where they are now being leached by oxidizing groundwater. The chemistry, mineralogy, texture and geological history of this U source-rock suggest criteria for locating other granitic terrane that may contain uraniferous waters and associated young surficial U deposits. The details of U distribution and mobility at this site also apply to the general topic of U mobility in granitic rocks.
Adult male mallards (Anas platyrhynchos) were banded in summer 1987 with reward bands of different dollar values (0-$400) to determine the lowest dollar value that would yield a reporting rate approaching 1.0. During the 1987-88 and 1988-89 hunting seasons, rewards of between 50 and $100 were required to yield a reporting rate near 1.0. We estimated reporting rate of standard bands to be 0.32. Reward bands with 5 and $10 values produced reporting rates that were 1.5-2.0 times as large as those of standard bands. We developed a linear-logistic model to predict reporting rate as a function of the dollar value of reward bands.
","language":"English","publisher":"Wiley","doi":"10.2307/3809248","usgsCitation":"Nichols, J.D., Blohm, R.J., Reynolds, R.E., Trost, R.E., Hines, J., and Bladen, J.P., 1991, Band reporting rates for mallards with reward bands of different dollar values: Journal of Wildlife Management, v. 55, no. 1, p. 119-126, https://doi.org/10.2307/3809248.","productDescription":"8 p.","startPage":"119","endPage":"126","costCenters":[{"id":531,"text":"Patuxent Wildlife Research Center","active":true,"usgs":true}],"links":[{"id":199538,"rank":1,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"country":"Canada","otherGeospatial":"Manitoba, Saskatchewan","geographicExtents":"{\n \"type\": \"FeatureCollection\",\n \"features\": [\n {\n \"type\": \"Feature\",\n \"properties\": {},\n \"geometry\": {\n \"coordinates\": [\n [\n [\n -109.8160045334979,\n 54.16079739003527\n ],\n [\n -109.8160045334979,\n 48.98422672815778\n ],\n [\n -95.1682999161388,\n 48.98422672815778\n ],\n [\n -95.1682999161388,\n 54.16079739003527\n ],\n [\n -109.8160045334979,\n 54.16079739003527\n ]\n ]\n ],\n \"type\": \"Polygon\"\n }\n }\n ]\n}","volume":"55","issue":"1","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"4f4e4a81e4b07f02db64a1f4","contributors":{"authors":[{"text":"Nichols, James D. 0000-0002-7631-2890 jnichols@usgs.gov","orcid":"https://orcid.org/0000-0002-7631-2890","contributorId":140652,"corporation":false,"usgs":true,"family":"Nichols","given":"James","email":"jnichols@usgs.gov","middleInitial":"D.","affiliations":[{"id":531,"text":"Patuxent Wildlife Research Center","active":true,"usgs":true}],"preferred":false,"id":336547,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Blohm, Robert J.","contributorId":202242,"corporation":false,"usgs":false,"family":"Blohm","given":"Robert","email":"","middleInitial":"J.","affiliations":[{"id":36385,"text":"Division of Migratory Bird Management, U.S. Fish And Wildlife Service, Retired, Bowie, MD 20715, USA","active":true,"usgs":false}],"preferred":false,"id":336552,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Reynolds, Ronald E.","contributorId":174572,"corporation":false,"usgs":false,"family":"Reynolds","given":"Ronald","email":"","middleInitial":"E.","affiliations":[],"preferred":false,"id":336548,"contributorType":{"id":1,"text":"Authors"},"rank":3},{"text":"Trost, Robert E.","contributorId":114181,"corporation":false,"usgs":true,"family":"Trost","given":"Robert","email":"","middleInitial":"E.","affiliations":[],"preferred":false,"id":336551,"contributorType":{"id":1,"text":"Authors"},"rank":4},{"text":"Hines, James E. jhines@usgs.gov","contributorId":3506,"corporation":false,"usgs":true,"family":"Hines","given":"James E.","email":"jhines@usgs.gov","affiliations":[{"id":531,"text":"Patuxent Wildlife Research Center","active":true,"usgs":true}],"preferred":false,"id":336550,"contributorType":{"id":1,"text":"Authors"},"rank":5},{"text":"Bladen, Judith P.","contributorId":26773,"corporation":false,"usgs":true,"family":"Bladen","given":"Judith","email":"","middleInitial":"P.","affiliations":[],"preferred":false,"id":336549,"contributorType":{"id":1,"text":"Authors"},"rank":6}]}} ,{"id":70016645,"text":"70016645 - 1991 - Seismic response of transamerica building. II. System identification","interactions":[],"lastModifiedDate":"2013-03-15T20:16:09","indexId":"70016645","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":2467,"text":"Journal of Structural Engineering","active":true,"publicationSubtype":{"id":10}},"title":"Seismic response of transamerica building. II. System identification","docAbstract":"A detailed analysis of the recorded seismic response of the Transamerica Building during the October 17, 1989 Loma Prieta earthquake is presented. The system identification algorithm used for the analysis is based on the discrete-time linear filtering approach with least-squares approximation, and assumes a multi-input, single-output model for the building. Fifteen modes in the north-south direction, and 18 modes in the east-west direction are identified from the records. The analysis shows that the building's response to the earthquake was dominated by a coupled mode of vibration at 0.28 Hz in the southwest-northeast direction, which is almost parallel to one of the diagonals in the building's square cross section. The reason for this behavior is the symmetry of the building's structural characteristics, as well as the strong polarization of the S-waves of the earthquake. Several higher modes of the building were excited during the strong-motion part of the earthquake. The results also show a significant amount of rocking in the building at a frequency of 2.15 Hz.","largerWorkType":{"id":2,"text":"Article"},"largerWorkTitle":"Journal of Structural Engineering","largerWorkSubtype":{"id":10,"text":"Journal Article"},"language":"English","doi":"10.1061/(ASCE)0733-9445(1991)117:8(2405)","issn":"07339445","usgsCitation":"Safak, E., and Çelebi, M., 1991, Seismic response of transamerica building. II. System identification: Journal of Structural Engineering, v. 117, no. 8, p. 2405-2425, https://doi.org/10.1061/(ASCE)0733-9445(1991)117:8(2405).","startPage":"2405","endPage":"2425","numberOfPages":"21","costCenters":[],"links":[{"id":224549,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"},{"id":269413,"type":{"id":10,"text":"Digital Object Identifier"},"url":"https://dx.doi.org/10.1061/(ASCE)0733-9445(1991)117:8(2405)"}],"volume":"117","issue":"8","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505b8b5be4b08c986b31778e","contributors":{"authors":[{"text":"Safak, E.","contributorId":104070,"corporation":false,"usgs":true,"family":"Safak","given":"E.","email":"","affiliations":[],"preferred":false,"id":374119,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Çelebi, M.","contributorId":36946,"corporation":false,"usgs":true,"family":"Çelebi","given":"M.","affiliations":[],"preferred":false,"id":374118,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70016404,"text":"70016404 - 1991 - Analysis of borehole expansion and gallery tests in anisotropic rock masses","interactions":[],"lastModifiedDate":"2013-01-18T13:16:35","indexId":"70016404","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":2071,"text":"International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts","active":true,"publicationSubtype":{"id":10}},"title":"Analysis of borehole expansion and gallery tests in anisotropic rock masses","docAbstract":"Closed-form solutions are used to show how rock anisotropy affects the variation of the modulus of deformation around the walls of a hole in which expansion tests are conducted. These tests include dilatometer and NX-jack tests in boreholes and gallery tests in tunnels. The effects of rock anisotropy on the modulus of deformation are shown for transversely isotropic and regularly jointed rock masses with planes of transverse isotropy or joint planes parallel or normal to the hole longitudinal axis for plane strain or plane stress condition. The closed-form solutions can also be used when determining the elastic properties of anisotropic rock masses (intact or regularly jointed) in situ. ?? 1991.","largerWorkType":{"id":2,"text":"Article"},"largerWorkTitle":"International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts","largerWorkSubtype":{"id":10,"text":"Journal Article"},"language":"English","publisher":"Elsevier","doi":"10.1016/0148-9062(91)90077-Y","issn":"01489062","usgsCitation":"Amadei, B., and Savage, W.Z., 1991, Analysis of borehole expansion and gallery tests in anisotropic rock masses: International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, v. 28, no. 5, p. 383-396, https://doi.org/10.1016/0148-9062(91)90077-Y.","startPage":"383","endPage":"396","numberOfPages":"14","costCenters":[],"links":[{"id":265941,"type":{"id":10,"text":"Digital Object Identifier"},"url":"https://dx.doi.org/10.1016/0148-9062(91)90077-Y"},{"id":223213,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"28","issue":"5","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"5059eb0ae4b0c8380cd48b8d","contributors":{"authors":[{"text":"Amadei, B.","contributorId":86902,"corporation":false,"usgs":true,"family":"Amadei","given":"B.","affiliations":[],"preferred":false,"id":373424,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Savage, W. Z.","contributorId":106481,"corporation":false,"usgs":true,"family":"Savage","given":"W.","email":"","middleInitial":"Z.","affiliations":[],"preferred":false,"id":373425,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70016532,"text":"70016532 - 1991 - Low intensity of the geomagnetic field in early Jurassic time","interactions":[],"lastModifiedDate":"2024-04-26T12:25:06.929138","indexId":"70016532","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":2312,"text":"Journal of Geophysical Research","active":true,"publicationSubtype":{"id":10}},"title":"Low intensity of the geomagnetic field in early Jurassic time","docAbstract":"From a large collection of Jurassic continental tholeiites cropping out in Europe and Africa, we selected 90 samples for paleointensity determinations. The samples were carefully selected to avoid any secondary magnetizations, especially viscous magnetization. Use of the Thellier method reveals that magnetic property changes due to heating begin often at quite low temperatures but fortunately without modifying noticeably their natural remanent magnetization-thermoremanent magnetization ratio. Twenty-eight well-clustered paleointensity estimates were obtained from two European dikes that were emplaced during Early Jurassic time: the Kerforne dike at Brenterc'h in Brittany (northwestern France) and the Messejana dike on the Iberian Peninsula (Spain and Portugal). Virtual dipole moments calculated from both magmatic units are similar and only about one-third of present-day values. These new data lend support to the recently postulated low dipole moment of the Mesozoic geomagnetic field.
A review of existing geophysical information and new data presented in this special section indicate that major changes in crustal properties between the Basin and Range and Colorado Plateau occur in, or directly adjacent to, the region defined as the Arizona Transition Zone. Although this region was designated on a physiographic basis, studies indicate that it is also the geophysical transition between adjoining provinces. The Transition Zone displays anomalous crustal and upper mantle seismic properties, shallow Curie isotherms, high heat flow, and steep down-to-the-plateau Bouguer gravity gradients. Seismic and gravity studies suggest that the change in crustal thickness, from thin crust in the Basin and Range to thick crust in the Colorado Plateau, may occur as a series of steps rather than a planar surface. Anomalous P wave velocities, high heat flow, shallow Curie isotherms, and results of gravity modeling suggest that the upper mantle is heterogeneous in this region. A relatively shallow asthenosphere beneath the Basin and Range and Transition Zone contrasted with a thick lithosphere beneath the Colorado Plateau would be one explanation that would satisfy these geophysical observations.
The salinity of Mono Lake has steadily increased since 1941 from 50%. to about 90%. due to diversion of tributary streams. This increase has resulted in the newly discovered precipitation of gaylussite (Na2Ca(CO3)2 · 5H2O). Chemical modeling of the lake water using Pitzer equations suggests that gaylussite has been forming year round since about 1970 when the salinity first exceeded 80%., and that it was earlier forming intermittently at lower salinities in the winter shortly after diversion began, breaking down incongruently to aragonite during summers. Lake water appears to remain at a constant 9-fold supersaturation with aragonite at all salinities, perhaps buffered by monohydrocalcite which appears to be just at saturation for all salinities. Other saline lakes also appear to be buffered by monohydrocalcite.
","language":"English","publisher":"Elsevier","doi":"10.1016/0016-7037(91)90144-T","issn":"00167037","usgsCitation":"Bischoff, J.L., Herbst, D., and Rosenbauer, R., 1991, Gaylussite formation at Mono Lake, California: Geochimica et Cosmochimica Acta, v. 55, no. 6, p. 1743-1747, https://doi.org/10.1016/0016-7037(91)90144-T.","productDescription":"5 p.","startPage":"1743","endPage":"1747","costCenters":[],"links":[{"id":224746,"rank":1,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"country":"United States","state":"California","otherGeospatial":"Mono Lake","geographicExtents":"{\n \"type\": \"FeatureCollection\",\n \"features\": [\n {\n \"type\": \"Feature\",\n \"properties\": {},\n \"geometry\": {\n \"coordinates\": [\n [\n [\n -119.13843775892357,\n 37.97656492875406\n ],\n [\n -119.13365913663722,\n 37.97196090697513\n ],\n [\n -119.10764219307747,\n 37.97530931508959\n ],\n [\n -119.09383728424982,\n 37.95354193228168\n ],\n [\n -119.08587291377239,\n 37.94474942941066\n ],\n [\n -119.0710060888814,\n 37.943911993306926\n ],\n [\n -119.06197980234012,\n 37.950611214907866\n ],\n [\n -119.05189159973548,\n 37.95144857465995\n ],\n [\n -119.04127243909892,\n 37.93679340110101\n ],\n [\n -119.00463633490261,\n 37.9384684260054\n ],\n [\n -118.95578819597443,\n 37.95856574718631\n ],\n [\n -118.92446167209668,\n 37.976983461868485\n ],\n [\n -118.90109951869607,\n 38.00752993241085\n ],\n [\n -118.90534718295075,\n 38.03471813776591\n ],\n [\n -118.94145232911514,\n 38.066494629884915\n ],\n [\n -118.98764567788416,\n 38.07903418456027\n ],\n [\n -119.02852944633514,\n 38.07569051351311\n ],\n [\n -119.03649381681257,\n 38.066494629884915\n ],\n [\n -119.06994417281756,\n 38.058551800070035\n ],\n [\n -119.06888225675394,\n 38.04099090639258\n ],\n [\n -119.07737758526329,\n 38.03890004321477\n ],\n [\n -119.08268716558159,\n 38.02802659238438\n ],\n [\n -119.10073973866365,\n 38.017988128232076\n ],\n [\n -119.11507560552296,\n 38.02384406611861\n ],\n [\n -119.13472105270081,\n 38.0184064250289\n ],\n [\n -119.14587117136907,\n 38.01966130109352\n ],\n [\n -119.15436649987842,\n 38.013805028957336\n ],\n [\n -119.13843775892357,\n 37.97656492875406\n ]\n ]\n ],\n \"type\": \"Polygon\"\n }\n }\n ]\n}","volume":"55","issue":"6","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a14e7e4b0c8380cd54c0b","contributors":{"authors":[{"text":"Bischoff, J. L.","contributorId":28969,"corporation":false,"usgs":true,"family":"Bischoff","given":"J.","email":"","middleInitial":"L.","affiliations":[],"preferred":false,"id":374149,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Herbst, D.B.","contributorId":69308,"corporation":false,"usgs":true,"family":"Herbst","given":"D.B.","email":"","affiliations":[],"preferred":false,"id":374151,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Rosenbauer, R.J.","contributorId":37320,"corporation":false,"usgs":true,"family":"Rosenbauer","given":"R.J.","email":"","affiliations":[],"preferred":false,"id":374150,"contributorType":{"id":1,"text":"Authors"},"rank":3}]}} ,{"id":70016708,"text":"70016708 - 1991 - Techniques and strategies for data integration in mineral resource assessment","interactions":[],"lastModifiedDate":"2012-03-12T17:18:50","indexId":"70016708","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":24,"text":"Conference Paper"},"publicationSubtype":{"id":19,"text":"Conference Paper"},"title":"Techniques and strategies for data integration in mineral resource assessment","docAbstract":"The Geologic and the National Mapping divisions of the U.S. Geological Survey have been involved formally in cooperative research and development of computer-based geographic information systems (GISs) applied to mineral-resource assessment objectives since 1982. Experience in the Conterminous United States Mineral Assessment Program (CUSMAP) projects including the Rolla, Missouri; Dillon, Montana; Butte, Montana; and Tonopah, Nevada 1?? ?? 2?? quadrangles, has resulted in the definition of processing requirements for geographically and mineral-resource data that are common to these studies. The diverse formats of data sets collected and compiled for regional mineral-resource assessments necessitate capabilities for digitally encoding and entering data into appropriate tabular, vector, and raster subsystems of the GIS. Although many of the required data sets are either available or can be provided in a digital format suitable for direct entry, their utility is largely dependent on the original intent and consequent preprocessing of the data. In this respect, special care must be taken to ensure the digital data type, encoding, and format will meet assessment objectives. Data processing within the GIS is directed primarily toward the development and application of models that can be used to describe spatially geological, geophysical, and geochemical environments either known or inferred to be associated with specific types of mineral deposits. Consequently, capabilities to analyze spatially, aggregate, and display relations between data sets are principal processing requirements. To facilitate the development of these models within the GIS, interfaces must be developed among vector-, raster-, and tabular-based processing subsystems to reformat resident data sets for comparative analyses and multivariate display of relations.","largerWorkTitle":"Proceedings of SPIE - The International Society for Optical Engineering","conferenceTitle":"Earth and Atmospheric Remote Sensing","conferenceDate":"2 April 1991 through 4 April 1991","conferenceLocation":"Orlando, FL, USA","language":"English","publisher":"Publ by Int Soc for Optical Engineering","publisherLocation":"Bellingham, WA, United States","issn":"0277786X","isbn":"0819406015","usgsCitation":"Trautwein, C.M., and Dwyer, J.L., 1991, Techniques and strategies for data integration in mineral resource assessment, in Proceedings of SPIE - The International Society for Optical Engineering, v. 1492, Orlando, FL, USA, 2 April 1991 through 4 April 1991, p. 338-338.","startPage":"338","endPage":"338","numberOfPages":"1","costCenters":[],"links":[{"id":224748,"rank":0,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"1492","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505ba415e4b08c986b3200c9","contributors":{"authors":[{"text":"Trautwein, Charles M. trautwein@usgs.gov","contributorId":2861,"corporation":false,"usgs":true,"family":"Trautwein","given":"Charles","email":"trautwein@usgs.gov","middleInitial":"M.","affiliations":[],"preferred":true,"id":374266,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Dwyer, John L. 0000-0002-8281-0896 dwyer@usgs.gov","orcid":"https://orcid.org/0000-0002-8281-0896","contributorId":3481,"corporation":false,"usgs":true,"family":"Dwyer","given":"John","email":"dwyer@usgs.gov","middleInitial":"L.","affiliations":[{"id":223,"text":"Earth Resources Observation and Science (EROS) Center (Geography)","active":false,"usgs":true},{"id":222,"text":"Earth Resources Observation and Science (EROS) Center","active":true,"usgs":true}],"preferred":true,"id":374267,"contributorType":{"id":1,"text":"Authors"},"rank":2}]}} ,{"id":70016274,"text":"70016274 - 1991 - Isotopic and chemical evidence concerning the genesis and contamination of basaltic and rhyolitic magma beneath the Yellowstone Plateau Volcanic Field","interactions":[],"lastModifiedDate":"2024-06-04T21:11:39.080814","indexId":"70016274","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":2420,"text":"Journal of Petrology","active":true,"publicationSubtype":{"id":10}},"title":"Isotopic and chemical evidence concerning the genesis and contamination of basaltic and rhyolitic magma beneath the Yellowstone Plateau Volcanic Field","docAbstract":"Since 2.2 Ma, the Yellowstone Plateau volcanic field has produced ∼6000 km3 of rhyolite tuffs and lavas in >60 separate eruptions, as well as ∼ 100 km3 of tholeiitic basalt from >50 vents peripheral to the silicic focus. Intermediate eruptive products are absent. Large calderas collapsed at 2·0, 1·3, and 0·6 Ma on eruption of ash-flow sheets representing at least 2500, 280, and 1000 km3 of zoned magma. Early postcollapse rhyolites show large shifts in Nd, Sr, Pb, and O isotopic compositions caused by assimilation of roof rocks and hydrothermal brines during collapse and resurgence. Younger intracaldera rhyolite lavas record partial isotopic recovery toward precaldera ration. Thirteen extracaldera rhyolites show none of these effects and have sources independent of the subcaldera magma system. Contributions from the Archaean crust have extreme values and wide ranges of Nd-, Sr-, and Pb-isotope ratios, but Yellowstone rhyolites have moderate values and limited ranges. This requires their deep-crustal sources to have been pervasively hybridized (and the Archaean components diluted) by distributed intrusion of Cenozoic basalt, most of which was probably contemporaneous with the Pliocene and Qualernary volcanism. In hybrid sources yielding magmas parental to the subcaldera rhyolites, half or more of the Nd and Sr may have been contributed by such young basalt. Parents for the extracaldera rhyolites, generated beyond the leading edge of the northeast-propagating focus of basaltic intrusion and deep-crustal mobilization, contained smaller fractions of mantle-derived components.
","language":"English","publisher":"Oxford Academic","doi":"10.1093/petrology/32.1.63","issn":"00223530","usgsCitation":"Hildreth, W., Halliday, A.N., and Christiansen, R., 1991, Isotopic and chemical evidence concerning the genesis and contamination of basaltic and rhyolitic magma beneath the Yellowstone Plateau Volcanic Field: Journal of Petrology, v. 32, no. 1, p. 63-138, https://doi.org/10.1093/petrology/32.1.63.","productDescription":"76 p.","startPage":"63","endPage":"138","numberOfPages":"76","costCenters":[],"links":[{"id":223509,"rank":1,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"volume":"32","issue":"1","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a3f96e4b0c8380cd64634","contributors":{"authors":[{"text":"Hildreth, W. 0000-0002-7925-4251","orcid":"https://orcid.org/0000-0002-7925-4251","contributorId":100487,"corporation":false,"usgs":true,"family":"Hildreth","given":"W.","affiliations":[],"preferred":false,"id":373041,"contributorType":{"id":1,"text":"Authors"},"rank":1},{"text":"Halliday, A. N.","contributorId":87663,"corporation":false,"usgs":true,"family":"Halliday","given":"A.","email":"","middleInitial":"N.","affiliations":[],"preferred":false,"id":373040,"contributorType":{"id":1,"text":"Authors"},"rank":2},{"text":"Christiansen, R.L. 0000-0002-8017-3918","orcid":"https://orcid.org/0000-0002-8017-3918","contributorId":25565,"corporation":false,"usgs":true,"family":"Christiansen","given":"R.L.","affiliations":[],"preferred":false,"id":373039,"contributorType":{"id":1,"text":"Authors"},"rank":3}]}} ,{"id":70016516,"text":"70016516 - 1991 - Implications for organic maturation studies of evidence of a geologically rapid increase and stabilization of vitrinite reflectance at peak temperature: Cerro Prieto geothermal system, Mexico","interactions":[],"lastModifiedDate":"2023-01-19T15:35:41.392266","indexId":"70016516","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":701,"text":"American Association of Petroleum Geologists Bulletin","active":true,"publicationSubtype":{"id":10}},"title":"Implications for organic maturation studies of evidence of a geologically rapid increase and stabilization of vitrinite reflectance at peak temperature: Cerro Prieto geothermal system, Mexico","docAbstract":"A short-term rapid heating and cooling of the rock in well M-94 below 1300 m was caused by a pulse of hot water passing through the edge of the Cerro Prieto, Mexico, geothermal system. Below 1300 m, the peak paleotemperatures were about 225-250 degrees C, but equilibrium well log temperatures indicate a decrease to 150-210 degrees C at present. This hot water pulse sharply increased vitrinite reflectance to levels comparable to those measured in the central part of the system, even though studies of apatite fission-track annealing indicate that the duration of heating was only 10{0}-10{1} yr in M-94, in contrast to 10{3}-10{4} yr in the central part of the system.
These data indicate that sedimentary organic matter chemically reacts quickly to temperature increases of about 125 degrees C above ambient, even when the higher temperature existed for only 10{0}-10{1} yr. The quick change of the vitrinite reflectance geothermometer indicates that thermal maturation reactions can stabilize, after a geologically short period of heating, to a level consistent with peak temperature under moderate to high-temperature diagenesis in open, fluid-rich, geothermal systems.
Cerro Prieto is one of the most intensively studied and well-known geothermal systems in the world. Thus, data from Cerro Prieto are a benchmark to compare with the predictions of published thermal maturation models such as those formulated by J. Karweil, N. V. Lopatin, and A. K. Burnham and J. J. Sweeney. These thermal maturation models inaccurately predict duration of heating at Cerro Prieto. The kinetic equations used in these models explicitly allow thermal maturation to continue indefinitely at peak temperature, which does not seem to be the case at Cerro Prieto.
","language":"English","publisher":"American Association of Petroleum Geologists","doi":"10.1306/0C9B2A51-1710-11D7-8645000102C1865D","usgsCitation":"Barker, C., 1991, Implications for organic maturation studies of evidence of a geologically rapid increase and stabilization of vitrinite reflectance at peak temperature: Cerro Prieto geothermal system, Mexico: American Association of Petroleum Geologists Bulletin, v. 75, no. 12, p. 1852-1863, https://doi.org/10.1306/0C9B2A51-1710-11D7-8645000102C1865D.","productDescription":"12 p.","startPage":"1852","endPage":"1863","numberOfPages":"12","costCenters":[],"links":[{"id":223474,"rank":1,"type":{"id":24,"text":"Thumbnail"},"url":"https://pubs.usgs.gov/thumbnails/outside_thumb.jpg"}],"country":"Mexico, United States","otherGeospatial":"Cerro Prieto fault","geographicExtents":"{\n \"type\": \"FeatureCollection\",\n \"features\": [\n {\n \"type\": \"Feature\",\n \"properties\": {},\n \"geometry\": {\n \"coordinates\": [\n [\n [\n -115.93369314042859,\n 33.27841604648326\n ],\n [\n -115.93369314042859,\n 31.617852838278367\n ],\n [\n -114.37067035754815,\n 31.617852838278367\n ],\n [\n -114.37067035754815,\n 33.27841604648326\n ],\n [\n -115.93369314042859,\n 33.27841604648326\n ]\n ]\n ],\n \"type\": \"Polygon\"\n }\n }\n ]\n}","volume":"75","issue":"12","noUsgsAuthors":false,"publicationStatus":"PW","scienceBaseUri":"505a3919e4b0c8380cd617d3","contributors":{"authors":[{"text":"Barker, C.E.","contributorId":69991,"corporation":false,"usgs":true,"family":"Barker","given":"C.E.","affiliations":[],"preferred":false,"id":373787,"contributorType":{"id":1,"text":"Authors"},"rank":1}]}} ,{"id":70016468,"text":"70016468 - 1991 - Use of a single-bowl continuous-flow centrifuge for dewatering suspended sediments: effect on sediment physical and chemical characteristics","interactions":[],"lastModifiedDate":"2024-03-28T00:14:53.430863","indexId":"70016468","displayToPublicDate":"1991-01-01T00:00:00","publicationYear":"1991","noYear":false,"publicationType":{"id":2,"text":"Article"},"publicationSubtype":{"id":10,"text":"Journal Article"},"seriesTitle":{"id":1924,"text":"Hydrological Processes","active":true,"publicationSubtype":{"id":10}},"title":"Use of a single-bowl continuous-flow centrifuge for dewatering suspended sediments: effect on sediment physical and chemical characteristics","docAbstract":"The use of a single-bowl continuous-flow centrifuge (CFC, Sharples-Pennwalt Model AS-12) for dewatering suspended sediment from large volumes of river water is evaluated. Sediment-recovery efficiency of 86-91 per cent is comparable to that of other types of CFC units. The recovery efficiency is limited by the particle-size distribution of the feed water and by the limiting particle diameter that is retained in the centrifuge bowl. The limiting particle diameter, using the parameters for this study (bowl radius = 10.5cm; bowl length = 71.1 cm; rotational velocity = 16000 r min−1; flow rate = 2 L min−1, and an assumed hydrated particle density = 1.7 gm cm−3), is 370 nm. There seems to be no particle-size fractionation within the centrifuge bowl—the median particle size was the same at the top as at the bottom. Particle electrophoretic mobility plays some role in fractionation of particles within the centrifuge. The mobility ranged from −1.19 to −2.01 × 10−8 m2 V−1 s−1, which is typical of clays coated with organic matter, the charge of which is partially neutralized by divalent cations and iron. Contamination by trace metals and organics is minimized by coating all surfaces that come in contact with the sample with either FEP or PFA Teflon and using a removable FEP Teflon liner in the centrifuge bowl. Because of the physical and chemical factors affecting particle fractionation within the centrifuge, care must be exercised in interpreting the environmental consequences of particles collected by continuous-flow centrifugation.
We present a new compilation of the structural and stratigraphic evolution of the Tharsis region of Mars that incorporates recent advances in understanding its stratigraphy, and we introduce a lithospheric deformation model that can account for the observations. The first period in the formation of Tharsis occurred in Late Noachian/Early Hesperian time with the deposition of volcanic plains materials throughout the surrounding highlands (e.g., Lunae Planum) and on the Tharsis rise (which includes the giant volcanoes and surrounding, elevated lava fields). Extensive radial normal faulting occurred on the rise, locally extending outward at Valles Marineris and Tempe Terra, and concentric wrinkle ridges formed along the edge of the rise. This regional deformation appears to have been modulated by a global compressional stress field due to rapid planetary cooling and contraction. The second period occurred during the Late Hesperian/Amazonian with Tharsis volcanism centered on the rise and radial extensional deformation that extended from the center of the rise for thousands of kilometers. We propose a model in which the lithosphere beneath Tharsis consists of a thin elastic crustal cap on the rise that is mechanically detached from the strong upper mantle by a volcanically thickened, hot, weak lower crust. These layers merge into a single cooler, strong lithospheric layer around the edges of the rise. This model is capable of generating large extensional hoop stresses throughout much of the western hemisphere, in agreement with observations. The tectonic interpretation of the stresses predicted by this model requires the reconciliation of extensional strain within narrow grabens and compressional strain within wrinkle ridges with (1) processes in the deeper lithosphere, (2) the sparsity of strike-slip faults, and (3) other global or locally important stress fields. Stresses predicted by global models affect the entire thickness of the lithosphere, and they can be reconciled with narrow, closely spaced grabens that accommodate large amounts of extensional strain in the upper few kilometers of the lithosphere if the grabens are underlain and kinematically linked with dikes or other tension cracks, such as hydrofractures. Deeper levels of the lithosphere can accommodate this strain by elastic expansion if grabens are spaced far apart (many tens to hundreds of kilometers). Mechanical considerations suggest that deformation on faults beneath wrinkle ridges could extend through a significant thickness of the brittle crust. A number of factors, including stresses generated by the addition of overburden, intrusion of dikes, weakness of geologic materials under extension, and the laterally constrained nature of a single lithospheric plate, may have inhibited the formation of strike-slip faults on Mars. Stresses generated from the removal of overburden could have augmented planetwide wrinkle ridge formation during the Late Noachian/Early Hesperian and in Kasei Valles and western Chryse Planitia during the Early Amazonian. The nonuniform distribution of tectonic features around Tharsis can be understood in terms of the concentration of regional stresses and strain near weaker volcanotectonic centers.
The inception of the Rio Grande rift in northern New Mexico and southern Colorado was accompanied by voluminous mafic volcanism preserved in part as erosional remnants on an intrarift horst within the current axial rift graben of the San Luis Valley. Oligocene (∼26 Ma) volcanic rocks of the Hinsdale Formation at San Luis Hills range from 49 to 57 wt % SiO2 and include nepheline and hypersthene normative lavas. A mildly alkalic series consisting of trachybasalt, basaltic trachyandesite, and trachyandesite is volumetrically dominant, olivine tholeiites are subordinate, and xenocrystic trachyandesites containing abundant quartz and plagioclase xenocrysts occur only locally. Relative to the San Luis Hills olivine tholeiites which have La/Smn ∼ 2, the more alkaline series are enriched in light rare earth elements (LREE) and have La/Sm ratios that increase in the trachybasalt-basaltic trachyandesite suite (La/Smn ∼ 3) to xenocrystic trachyandesites that are the most LREE enriched (La/Smn ∼ 4). Chondrite-normalized, trace element patterns for the lavas in the San Luis Hills are similar in shape within the mildly alkaline to transitional series; they have characteristic Nb and Ta depletions and high K and Th relative to Ta, Nb, and LREE. Major and trace element constraints support a petrogenetic model of fractionation plus lower crustal assimilation for petrologic suites within the San Luis Hills rocks, although the model cannot relate lavas for the entire series to a common parent. Most mafic lavas of the San Luis Hills were evolved (Mg # <60) and contaminated by LREE-enriched silicic partial melts of granulitic lower crust depleted in Rb, Th, and U. Pb isotopes are the most sensitive indicators of crustal contamination, whereas shifts in Nd and Sr isotope ratios are associated with large amounts of assimilation. However, relatively noncontaminated lavas can be identified and indicate at least two mantle source regions were involved.
This study examines the relationship between the distribution of small earthquakes (ML≤4.3) and mechanisms of strain accumulation and relaxation in an area with long repeat times between large events, the Southern Great Basin Seismic Network (SGBSN) region. The Great Basin is a unique continental extensional province characterized by normal and strike-slip faulting, high heat flow, crust of thin to normal thickness, and high elevations. The SGBSN is operated to provide data to address suitability issues pertaining to Yucca Mountain, Nevada which is being evaluated as a potential site for a national mined geologic nuclear waste repository. Suitability issues include estimation of the probability of occurrence of future damaging earthquakes, the characterization of the mechanisms that drive hydrologic flow, and the identification of fractures (faults) that might act as flow conduits or barriers. This study attempts to explain the distribution of small earthquakes in terms of spatial variations in the shear strain field; where strain concentrates there should be a greater number of small earthquakes. Strain field models are constructed under the assumption that long term fault behavior perturbs an otherwise uniform strain field. These strain field models are then interpreted with regard to the regional tectonics and site suitability issues. Modeling results provide one possible explanation of why earthquake clusters cover regions much larger than the surface projections of any of mapped major faults; clusters in a wide band along and extending northeast of the northern half of the Furnace Creek fault may correspond to elevated shear strains along the fault and a broad cluster in the Pahranagat Shear Zone may be associated with shear strain arising from a distribution of smaller localized faults. The relatively large number of small earthquakes in the southern and eastern portions of the Nevada Test Site is consistent with the strain field models. A minimum in shear strain at Yucca Mountain is predicted by all models consistent with an almost total lack of earthquakes observed there. The region to the west of the Death Valley/Furnace Creek fault system, the portion of the study area with the most active deformation but few small earthquakes, is an area of low shear strain. A possible reason for this is that the fault configuration in the area is optimal for accommodating regional deformation via large earthquakes or creep. While there is also a relative lack of earthquakes at Yucca Mountain, this may be indicative of a lack of accumulating strain energy and thus, a lower potential for a large earthquake.
This paper describes the recovery of stable bank form and development of vegetated depositional surfaces along the banks of channelized West Tennessee streams. Most perennial streams in West Tennessee were straightened and dredged since the turn of the century. Patterns of fluvial ecological responses to channelization have previously been described by a six-stage model. Dendrogeomorphic (tree-ring) techniques allowed the determination of location, timing, amount, and rate of bank-sediment deposition. Channel cross sections and ecological analyses made at 101 locations along 12 streams, encompassing bends and straight reaches, show that channel and bank processes initially react vertically to channelization through downcutting. A depositional surface forms on banks once bed-degradation and heightened bank mass wasting processes have eased or slowed. The formation of this depositional surface marks the beginning of bank recovery from channelization. Dominating lateral processes, characteristic of stable or natural channels, return during the formation and expansion of the depositional surface, suggesting a relation with thalweg deflection, point-bar development, and meanderloop extension. Characteristic woody riparian vegetation begins to grow as this depositional surface develops and becomes part of the process and form of restabilizing banks. The depositional surface initially forms low on the bank and tends to maintain a slope of about 24°. Mean accretion rates ranges from 5.9 cm/yr on inside bends to 0 cm/yr on most outside bends; straight reaches have a mean-accretion rate of 4.2 cm/yr. The relatively stable, convex upward, depositional surface expands and ultimately attaches to the flood plain. The time required for the recovery process to reach equilibrium averaged about 50 years. Indicative pioneer speccies of woody riparian vegetation include black willow, river birch, silver maple, and boxelder. Stem densities generally decrease with time after and initial flush of about 160 stems per 100 m2. Together bank accretion and vegetative regrowth appear to be the most important environmental processes involved in channel bank recovery from channelization or rejuvenation.
Precise measurements of local magnetic fields have been obtained with a differentially connected array of three proton magnetometers in the Long Valley caldera region since 1984. Two magnetometers are located inside the caldera with a third reference magnetometer located 26km southeast of the caldera. After correction for secular variation, it is apparent that an anomalous 2 nT decrease in the magnetic field occurred from mid-1989 to mid-1990 at the magnetometer located closest to the center of the resurgent dome inside the caldera. During this period a significant increase in geodetic strain rate of 8.5 ppm/a was observed on the two-color geodimeter network within the caldera from October, 1989, to mid-1990 and a dramatic increase in seismic activity occurred from December, 1989 to July, 1990. A simple dilatational point-source model with pressure increasing by 52 Mpa from October 1989 to August 1990 at a depth of about 7km beneath the center of the resurgent dome can be fit to the strain data. If this same model is used to calculate piezomagnetic fields in the caldera, the results obtained agree with the observed local magnetic field data provided the Curie point isotherm is at a depth of ≤5km. Taken together, these magnetic, seismic and geodetic data suggest that an episode of active magmatic intrusion occurred from late 1989 to mid-1990 at a depth of about 7–8km beneath the resurgent dome within the Long Valley caldera. Other indications of this intrusion should be evident in measurements of leveling, local gravity, and seismic imaging data.