48 Matching Results

Search Results

Advanced search parameters have been applied.

The Ecology of Stream and Riparian Habitats of the Great Basin Region

Description: "The purpose of this profile is to summarize the ecological information available for and relevant to stream and riparian habitats of the Great Basin. The Great Basin comprises the northern half of the Basin and Range physiographic province and covers most of Nevada and western Utah and portions of California, Oregon, and Idaho. The entire basin actually consists of numerous subbasins and mountain ranges which present an extremely diverse physical setting" (p. iii).
Date: September 1989
Creator: Minshall, G. Wayne; Jensen, Sherman E. & Platts, William S.
Partner: UNT Libraries Government Documents Department

Ordovician Graptolites of the Basin Ranges in California, Nevada, Utah, and Idaho

Description: From introduction: This report presents a summary of the graptolite faunas of the Basin Ranges as known from the collections of the U.S. Geological Survey and the Departments of Geology of the University of California at Los Angeles and Utah State University. The collections were made in the period 1872-1958, but only a very small number of specimens have been described or illustrated in the 80 or so years elapsed.
Date: 1963
Creator: Ross, Reuben James, Jr. & Berry, William B. N.
Partner: UNT Libraries Government Documents Department

Advances in Hydrogeochemical Indicators for the Discovery of New Geothermal Resources in the Great Basin, USA

Description: This report summarizes the results of Phase I work for a go/no go decision on Phase II funding. In the first objective, we assessed the extent to which fluid-mineral equilibria controlled deep water compositions in geothermal systems across the Great Basin. Six systems were evaluated: Beowawe; Desert Peak; Dixie Valley; Mammoth; Raft River; Roosevelt. These represent a geographic spread of geothermal resources, in different geological settings and with a wide range of fluid compositions. The results were used for calibration/reformulation of chemical geothermometers that reflect the reservoir temperatures in producing reservoirs. In the second objective, we developed a reactive -transport model of the Desert Peak hydrothermal system to evaluate the processes that affect reservoir fluid geochemistry and its effect on solute geothermometry. This included testing geothermometry on “reacted” thermal water originating from different lithologies and from near-surface locations where the temperature is known from the simulation. The integrated multi-component geothermometer (GeoT, relying on computed mineral saturation indices) was tested against the model results and also on the systems studied in the first objective.
Date: May 20, 2013
Creator: Simmons, Stuart F.; Spycher, Nicolas; Sonnenthal, Eric & Dobson, Patrick
Partner: UNT Libraries Government Documents Department

Aftershock Characteristics as a Means of Discriminating Explosions from Earthquakes

Description: The behavior of aftershock sequences around the Nevada Test Site in the southern Great Basin is characterized as a potential discriminant between explosions and earthquakes. The aftershock model designed by Reasenberg and Jones (1989, 1994) allows for a probabilistic statement of earthquake-like aftershock behavior at any time after the mainshock. We use this model to define two types of aftershock discriminants. The first defines M{sub X}, or the minimum magnitude of an aftershock expected within a given duration after the mainshock with probability X. Of the 67 earthquakes with M > 4 in the study region, 63 of them produce an aftershock greater than M{sub 99} within the first seven days after a mainshock. This is contrasted with only six of 93 explosions with M > 4 that produce an aftershock greater than M{sub 99} for the same period. If the aftershock magnitude threshold is lowered and the M{sub 90} criteria is used, then no explosions produce an aftershock greater than M{sub 90} for durations that end more than 17 days after the mainshock. The other discriminant defines N{sub X}, or the minimum cumulative number of aftershocks expected for given time after the mainshock with probability X. Similar to the aftershock magnitude discriminant, five earthquakes do not produce more aftershocks than N{sub 99} within 7 days after the mainshock. However, within the same period all but one explosion produce less aftershocks then N{sub 99}. One explosion is added if the duration is shortened to two days after than mainshock. The cumulative number aftershock discriminant is more reliable, especially at short durations, but requires a low magnitude of completeness for the given earthquake catalog. These results at NTS are quite promising and should be evaluated at other nuclear test sites to understand the effects of differences in the geologic setting and ...
Date: May 20, 2009
Creator: Ford, S R & Walter, W R
Partner: UNT Libraries Government Documents Department

Evidence of late Quaternary wet/dry climate episodes derived from paleoclimatic proxy data recovered from the paleoenvironmental record of the Great Basin of western North America: Paleobotanical studies

Description: Through the integration of several avenues of paleoclimatic proxy data, the authors intend to arrive a definite conclusions regarding the frequency of periods of wetter climate, and to drive information regarding the magnitudes of these episodes, rates of their onset and demise, and the climatic conditions under which wetter climate can occur. These will in turn lead to rough estimates of: (1) the amounts of rainfall available for recharge during past periods of effectively wetter climate; and (2) the durations and spacing of such events that provide an indication of the amount of time that the area was subjected to these inputs. To accomplish these goals the paleobotanical record over a broad region is being examined to identify periods of greater effective precipitation. Although the project focus is on a region a of about 200 km around Yucca Mountain, they have collected data in other areas of the Great Basin in order to be able to identify large-scale climatic patterns. Once identified and described these climatic patterns can be separated from purely local climatic phenomena that might hinder the understanding of the Pliestocene climates of southern Nevada and the Yucca Mountain area in particular.
Date: July 1, 1998
Partner: UNT Libraries Government Documents Department

Ecological Monitoring and Compliance Program Fiscal Year 2000 Report

Description: The Ecological Monitoring and Compliance program, funded through the U.S. Department of Energy, Nevada Operations Office, monitors the ecosystem of he Nevada Test Site (NTS) and ensures compliance with laws and regulations pertaining to NTS biota. This report summarizes the program's activities conducted by Bechtel Nevada during fiscal year 2000. Program activities included: (1) biological surveys at proposed construction sites, (2) desert tortoise compliance,(3) ecosystem mapping, (4) sensitive species and unique habitat monitoring, and (5) biological monitoring at the HAZMAT Spill Center. Biological surveys for the presence of sensitive species were conducted for 24 NTS projects. Seventeen sites were in desert tortoise habitat, and six acres of tortoise habitat were documented as being disturbed this year. No tortoises were found in or displaced from project areas, and no tortoises were accidentally injured or killed. A topical report describing the classification of habitat types o n the NTS was completed. The report is the culmination of three years of field vegetation mapping and the analysis of vegetation data from over 1,500 ecological landform units. A long-term monitoring plan for important plant species that occur on the NTS was completed. Sitewide inventories were conducted for the western burrowing owl, bat species of concern, wild horses, raptor nests, and mule deer. Fifty-nine of 69 known owl burrows were monitored. Forty-four of the known burrows are in disturbed habitat. As in previous years, some owls were present year round on the NTS. An overall decrease in active owl burrows was observed within all three ecoregions (Mojave Desert, Transition, Great Basin Desert) from October through January. An increase in active owl burrows was observed from mid-March to early April. A total of 45 juvenile owls was detected from eight breeding pairs. One nest burrow was detected in the Mojave Desert,one in the Great Basin Desert, ...
Date: December 1, 2000
Creator: Wills, C.A.
Partner: UNT Libraries Government Documents Department

Reseeding Range Lands of the Intermountain Region

Description: "Revegetating deteriorated range lands by sowing adaptable, nutritious, and palatable grasses is vital for adequate forage production in the Intermountain region, for profitable livestock raising, and as a safeguard against flood and erosion damage. The effect of serious droughts, greatly aggravated by overstocking, has resulted in the replacement of valuable perennial grasses by annual weeds and grasses that have much less value as forage for livestock or for proper soil protection. The abandonment of unsuccessful submarginal croplands has also added greatly to the vast acreage of deteriorated but potentially productive range lands of the region in need of revegetation. Proper guides and procedure for revegetating run-down ranges and abandoned dry farms by artificial reseeding are necessary to safeguard against costly pitfalls and to insure reasonable success. The procedures herein outlined are based on the experiences and research to date and should prove helpful to those administering range lands and producing livestock in the region comprising Utah, Nevada, southern Idaho, and southwestern Wyoming, commonly referred to as the Intermountain region." -- p. i
Date: 1939
Creator: Stewart, George; Walker, R. H. (Rudger Harper), 1902- & Price, Raymond
Partner: UNT Libraries Government Documents Department

Accelerated Geothermal Resource Development in the Great Basin Through Enhanced Public Awareness and Outreach to Shareholders.

Description: The Great Basin Center for Geothermal Energy conducted work encompassing two main tasks. We (1) produced a web-based, stakeholder geothermal information system for Nevada geothermal data relevant to assessing and developing geothermal resources, and (2) we held informational stakeholder workshops (both as part of GeoPowering the West Initiative). The objective of this grant was to conduct workshops and fund database and web development activities. This grant funds salaries for web and database developers and part of the administrative assistant who helps to coordinate and organize workshops, and maintain selected databases.
Date: April 10, 2002
Creator: Taranik, James V.; Oppliger, Gary & Sawatsky, Don
Partner: UNT Libraries Government Documents Department

Measurement of the Parameter Kappa, and Reevaluation of Kappa for Small to Moderate Earthquakes at Seismic Stations in the Vicinity of Yucca Mountain, Nevada

Description: The parameter kappa was defined by Anderson and Hough (1984) to describe the high-frequency spectral roll-off of the strong motion seismic spectrum. In the work of Su et al., (1996) the numerical value of kappa estimated for sites near Yucca Mountain was small (~20 ms). The estimate obtained from these events has been applied through a rigorous methodology to develop design earthquake spectra with magnitude over 5.0. Smaller values of kappa lead to higher estimated ground motions in the methodology used by the Probabilistic Seismic Hazard Analysis (PSHA) for Yucca Mountain. An increase of 10 ms in kappa could result in a substantial decrease in the high frequency level of the predicted ground motions. Any parameter that plays such a critical role deserves close examination. Here, we study kappa and its associated uncertainties. The data set used by Su et al (1996) consisted of 12 M 2.8 to 4.5 earthquakes recorded at temporary stations deployed after the June 1992 Little Skull Mountain earthquake. The kappa elements of that study were revisited by Anderson and Su (MOL.20071203.0134) and substantially confirmed. One weakness of those studies is the limited data used. Few of these stations were on tuff or on Yucca Mountain itself. A decade of Southern Great Basin Digital Seismic Network (SGBDSN) recording has now yielded a larger body of on-scale, well calibrated digital ground motion records suitable for investigating kappa. We use the SGBDSN data to check some of the original assumptions, improve the statistical confidence of the conclusions, and determine values of kappa for stations on or near Yucca Mountain. The outstanding issues in kappa analysis, as they apply to Yucca Mountain, include: 1. The number itself. The kappa estimate near 20 msec from Su et al. (1996) and Anderson and Su (MOL.20071203.0134) is markedly smaller than is considered ...
Date: December 5, 2007
Creator: Biasi, Glenn & Anderson, John G.
Partner: UNT Libraries Government Documents Department

How to Get the Biggest Bang for Your Buck: Wildlife Monitoring on Shrublands of the Nevada Test Site

Description: The Nevada Test Site (NTS) covers 1,375 square miles and extends over portions of both the Mojave and Great Basin Deserts. The resulting diverse and complex flora and fauna exhibit elements of both deserts. There are 20 vegetation associations, composed primarily of shrubs, nested within 10 vegetation alliances. Of the more than 1,200 invertebrates and 339 vertebrates found in these shrubland habitats, 267 are considered sensitive or protected/regulated by federal or state laws. Wildlife and wildlife habitat monitoring ensures NTS activities comply with all federal and state laws enacted for the protection of these valuable biological resources. This paper describes the monitoring approach used at this large site. Monitoring techniques include conducting preactivity surveys, repeated sampling of permanent plots, proactively monitoring sensitive species, and collaborating with other agencies and biologists. Ways to make monitoring more efficient and examples of successful monitoring and collaborations are discussed.
Date: March 1, 2008
Creator: Derek Hall, Paul D. Greger
Partner: UNT Libraries Government Documents Department

Response to"Analysis of the Treatment, by the U.S. Department of Energy, of the FEP Hydrothermal Activity in the Yucca Mountain Performance Assessment" by Yuri Dublyansky

Description: This paper presents a rebuttal to Dublyansky (2007), which misrepresents technical issues associated with hydrothermal activity at the proposed Yucca Mountain nuclear waste repository and their importance to the long-term performance of the repository. In this paper, questions associated with hydrothermal activity are reviewed and the justification for exclusion of hydrothermal activity from performance assessment is presented. The hypothesis that hydrothermal upwelling into the present-day unsaturated zone has occurred at Yucca Mountain is refuted by the unambiguous evidence that secondary minerals and fluid inclusions in the unsaturated zone formed in an unsaturated environment from downward percolating meteoric waters. The thermal history at Yucca Mountain, inferred from fluid inclusion and isotopic data, is explained in terms of the tectonic extensional environment and associated silicic magmatism. The waning of tectonic extension over millions of years has led to the present-day heat flux in the Yucca Mountain region that is below average for the Great Basin. The long time scales of tectonic processes are such that any effects of a resumption of extension or silicic magmatism on hydrothermal activity at Yucca Mountain over the 10,000-year regulatory period would be negligible. The conclusion that hydrothermal activity was incorrectly excluded from performance assessment as asserted in Dublyansky (2007) is contradicted by the available technical and regulatory information.
Date: November 17, 2008
Creator: Houseworth, J.E. & Hardin, E.
Partner: UNT Libraries Government Documents Department

Annual report on paleoclimate studies for the Yucca Mountain project site characterization conducted by the Desert Research Institute

Description: The prospect that Yucca Mountain may become a repository for high-level radionuclides with especially long half-lives means that the intended waste containment area must be well beyond the reach of the hydrologic system for at least ten millennia. Through the integration of several avenues of paleoclimatic proxy data, the authors intend to arrive at definite conclusions regarding rates of change, and extremes and stabilities of past climate regimes. These will in turn lead to rough estimates of: the amounts of rainfall available for recharge during past periods of effectively wetter climate, and the durations and frequencies of recharge periods. The paper gives summaries of the following studies: Late Quaternary and Holocene climate derived from vegetation history and plant cellulose stable isotope records from the Great basin of western North America; Accomplishments of paleofaunal studies, 1993--1994; Geomorphology studies in the Great Basin; Alluvial fan response to climatic change, Buena Vista Valley, central Nevada; Sedimentology, stratigraphy, and chronology of lacustrine deposition in the Fernley Basin, west-central Nevada; Tree-rings, lake chronologies, alluvial sequences and climate--Implications for Great Basin paleoenvironmental studies; Stable isotopic validation studies--Fossil snails; and Late Pleistocene and Holocene eolian activity in the Mojave Desert.
Date: December 31, 1994
Partner: UNT Libraries Government Documents Department

Hunter-gatherer adaptations and environmental change in the southern Great Basin: The evidence from Pahute and Rainier mesas

Description: This paper reviews the evidence for fluctuations in past environments in the southern Great Basin and examines how these changes may have affected the strategies followed by past hunter and gatherers in their utilization of the resources available on a highland in this region. The evidence used to reconstruct past environments for the region include botanical remains from packrat middens, pollen spectra from lake and spring deposits, faunal remains recovered from archaeological and geologic contexts, tree-ring indices from trees located in sensitive (tree-line) environments, and eolian, alluvial and fluvial sediments deposited in a variety of contexts. Interpretations of past hunter and gatherer adaptive strategies are based on a sample of 1,311 archaeological sites recorded during preconstruction surveys on Pahute and Rainier mesas in advance of the US Department of Energy`s nuclear weapons testing program. Projectile point chronologies and available tree-ring, radiocarbon, thermoluminescence and obsidian hydration dates were used to assign these archaeological sites to specific periods of use.
Date: June 1, 1998
Creator: Pippin, L. C.
Partner: UNT Libraries Government Documents Department

National Emission Standards for Hazardous Air Pollutants Submittal - 1998

Description: The Nevada Test Site (NTS) is operated by the U.S. Department of Energy Nevada Operations Office (DOE/NV) as the site for nuclear weapons testing, now limited to readiness activities and experiments in support of the national Stockpile Stewardship Management Program. It is located in Nye County, Nevada, with the southeast corner about 105 km (65 mi) northwest of Las Vegas, Nevada. The NTS covers about 3,500 km2 (1,350 mi2), an area larger than Rhode Island. Its size is about 46 to 56 km (28 to 35 mi) east to west and from 64 to 88 km (40 to 55 mi)north to south. The NTS is surrounded, except on the south side, by public exclusion areas (Nellis Air Force Range) that provide another 24 to 104 km (15 to 65 mi) between the NTS and public lands. The NTS is characterized by desert valley and Great Basin mountain topography, with a climate, flora, and fauna typical of the southwest deserts. Surface waters are scarce on the NTS and there is great depth to slow-moving groundwater.
Date: June 1, 1999
Creator: Black, Stuart & Townsend, Yvonne
Partner: UNT Libraries Government Documents Department

Isotopic investigation of recharge to a regional groundwater flow system, Great Basin, NV

Description: Groundwater recharge processes were investigated in central Nevada by examining the relationships between the stable isotope ({delta}D and {delta}{sup 18}O) compositions of snowfall, snowmelt, alpine spring waters, and regional groundwaters. Snowmelt infiltration is inferred to he the dominant source of groundwater recharge in this region. Bulk snow cores collected throughout central Nevada near the time of maximum accumulation have {delta}D and {delta}{sup 18}O pairs that plot subparallel to the global meteoric water line (GMWL), but have negative d-values, implying kinetic isotope enrichments. Heavy isotope enrichments occur at the base of snowpacks due to fractionation during snow metamorphism, sometimes resulting in remarkably systematic isotopic variations. Ice crystals in the soil immediately beneath the snowpack can be strongly depleted in heavy isotopes relative to the overlying snow, implying fractionation or exchange with the snowpack. Late season ablation processes tend to homogenize isotopic variations between snowpack layers, and cause the bulk isotopic composition of the snowpack to become enriched in {sup 18}O by 2-3{per_thousand} relative to the composition during peak accumulation. The dynamic evolution of the snowpack and snowmelt isotopic compositions over time makes it difficult to directly ascertain groundwater recharge compositions without careful mass balance measurements. Preliminary evidence suggests that small local springs may be reasonable indicators of the integrated isotopic value of the snowmelt recharge in a particular area. Springs and snowmelt runoff samples collected throughout central Nevada during the peak runoff plot along a least squares regression line with the equation {delta}D = 7.3{delta}{sup 18}O - 7, which is similar to the line obtained for 28 metamorphosed snow cores collected during peak accumulation ({delta}D = 7.5{delta}{sup 18}O - 3). These results suggest that kinetic fractionation processes during snow metamorphism and ablation may largely account for the low d-values that are widely observed in groundwaters from both local and regional flow ...
Date: May 4, 1999
Creator: Criss, R E; Davisson, M L; Rose, T & Smith, D K
Partner: UNT Libraries Government Documents Department

Erosion Potential of a Burn Site in the Mojave-Great Basin Transition Zone: Interim Summary of One Year of Measurements

Description: A historic return interval of 100 years for large fires in deserts in the Southwest U.S. is being replaced by one where fires may reoccur as frequently as every 20 to 30 years. This increase in fires has implications for management of Soil Sub-Project Corrective Action Units (CAUs) for which the Department of Energy, National Nuclear Security Administration Nevada Site office (NNSA/NSO) has responsibility. A series of studies has been initiated at uncontaminated analog sites to better understand the possible impacts of erosion and transport by wind and water should contaminated soil sites burn over to understand technical and perceived risk they might pose to site workers and public receptors in communities around the NTS, TTR, and NTTR; and to develop recommendations for stabilization and restoration after a fire. The first of these studies was undertaken at the Jacob fire, a lightning-caused fire approximately 12 kilometers north of Hiko, Nevada, that burned approximately 200 ha between August 6-8, 2008, and is representative of a transition zone on the NTS between the Mojave and Great Basin Deserts, where the largest number of Soil Sub-Project CAUs/CASs are located.
Date: May 18, 2010
Creator: V. Etyemezian, D. Shafer, J. Miller, I. Kavouras, S. Campbell, D. DuBois, J. King, G. Nikolich, and S. Zitzer
Partner: UNT Libraries Government Documents Department

Constructing a large-scale 3D Geologic Model for Analysis of the Non-Proliferation Experiment

Description: We have constructed a regional 3D geologic model of the southern Great Basin, in support of a seismic wave propagation investigation of the 1993 Nonproliferation Experiment (NPE) at the Nevada Test Site (NTS). The model is centered on the NPE and spans longitude -119.5{sup o} to -112.6{sup o} and latitude 34.5{sup o} to 39.8{sup o}; the depth ranges from the topographic surface to 150 km below sea level. The model includes the southern half of Nevada, as well as parts of eastern California, western Utah, and a portion of northwestern Arizona. The upper crust is constrained by both geologic and geophysical studies, while the lower crust and upper mantle are constrained by geophysical studies. The mapped upper crustal geologic units are Quaternary basin fill, Tertiary deposits, pre-Tertiary deposits, intrusive rocks of all ages, and calderas. The lower crust and upper mantle are parameterized with 5 layers, including the Moho. Detailed geologic data, including surface maps, borehole data, and geophysical surveys, were used to define the geology at the NTS. Digital geologic outcrop data were available for both Nevada and Arizona, whereas geologic maps for California and Utah were scanned and hand-digitized. Published gravity data (2km spacing) were used to determine the thickness of the Cenozoic deposits and thus estimate the depth of the basins. The free surface is based on a 10m lateral resolution DEM at the NTS and a 90m lateral resolution DEM elsewhere. Variations in crustal thickness are based on receiver function analysis and a framework compilation of reflection/refraction studies. We used Earthvision (Dynamic Graphics, Inc.) to integrate the geologic and geophysical information into a model of x,y,z,p nodes, where p is a unique integer index value representing the geologic unit. For seismic studies, the geologic units are mapped to specific seismic velocities. The gross geophysical structure of ...
Date: April 9, 2008
Creator: Wagoner, J & Myers, S
Partner: UNT Libraries Government Documents Department


Description: The objective of this study was to evaluate archaeological materials from underground openings or shallow burial in arid environments relevant to Yucca Mountain and to draw conclusions about how their state and their environment of preservation could be of relevance to design and operational aspects of the high-level waste repository. The study has evaluated materials from cultures in the arid regions of the ancient Middle East and compared them with the preservation of ancient materials in dry cave sites in the Great Basin desert area of Nevada. The emphasis has been on materials found in undisturbed underground openings such as caves and un-backfilled tombs. Long-term preservation of such materials in underground openings and the stability of the openings themselves provide useful analogue information that serves as a reference point for considering the operation and evolution of the Yucca Mountain repository. Being able to shed light, by close physical and environmental analogy, on what happens in underground openings over many thousands of years provides valuable underpinning to illustrations of expected system performance and offers pointers towards optimizing repository system and operational design.
Date: February 24, 2006
Creator: N. Chapman, A. Dansie, C. McCombie
Partner: UNT Libraries Government Documents Department

Seismicity in the Vicinity of Yucca Mountain, Nevada, for the Period October 1, 2002, to September 30, 2003

Description: Earthquake activity in the Yucca Mountain from October 1, 2002 through September 30, 2003 (FY03) is assessed and compared with previous activity in the region. FY03 is the first reporting year since the 1992 M 5.6 Little Skull Mountain earthquake with no earthquakes greater than M 3.0 within 65 km of Yucca Mountain. In addition, FY03 includes the fewest number of earthquakes greater than M 2.0 in any reporting year since the LSM event. With 3075 earthquakes in the catalog, FY03 represents the second largest number of earthquakes (second to FY02) since FY96 when digital seismic network operations began. The largest event during FY03 was M 2.78 in eastern NTS and there were only 8 earthquakes greater than M 2.0.
Date: December 4, 2007
Creator: Smith, Ken & von Seggern, David
Partner: UNT Libraries Government Documents Department

Preliminary evaluation of the radioactive waste isolation potential of the alluvium-filled valleys of the Great Basin

Description: The occurrences, geologic features, hydrology, and thermal, mechanical, and mineralogical properties of the alluvium-filled valleys are compared with those of other media within the Great Basin. Computer modeling of heat conduction indicates that heat generated by the radioactive waste can be dissipated through the alluvium in a manner that will not threaten the integrity of the repository, although waste emplacement densities will be lower than for other media available. This investigation has not revealed any failure mechanism by which one can rule out alluvium as a primary waste isolation medium. However, the alluvium appears to rank behind one or more other possible media in all properties examined except, perhaps, in sorption properties. It is therefore recommended that alluvium be considered as a secondary isolation medium unless primary sites in other rock types in the Great Basin are eliminated from consideration on grounds other than those considered here.
Date: August 1, 1979
Creator: Smyth, J.R.; Crowe, B.M.; Halleck, P.M. & Reed, A.W.
Partner: UNT Libraries Government Documents Department

Great Basin paleoenvironmental studies project; Technical progress report: First quarter (January--August 1993)

Description: Project goals, project tasks, progress on tasks, and problems encountered are described and discussed for each of the studies that make up the Great Basin Paleoenvironmental Studies Project for Yucca Mountain. These studies are: Paleobotany, Paleofauna, Geomorphology, and Transportation. Budget summaries are also given for each of the studies and for the overall project.
Date: December 31, 1993
Partner: UNT Libraries Government Documents Department


Description: It is well accepted that the 1992 M 5.6 Little Skull Mountain earthquake, the largest historical event to have occurred within 25 km of Yucca Mountain, Nevada, was triggered by the M 7.2 Landers earthquake that occurred the day before. On the premise that earthquakes can be triggered by applied stresses, we have examined the earthquake catalog from the Southern Great Basin Digital Seismic Network (SGBDSN) for other evidence of triggering by external and internal stresses. This catalog now comprises over 12,000 events, encompassing five years of consistent monitoring, and has a low threshold of completeness, varying from M 0 in the center of the network to M 1 at the fringes. We examined the SGBDSN catalog response to external stresses such as large signals propagating from teleseismic and regional earthquakes, microseismic storms, and earth tides. Results are generally negative. We also examined the interplay of earthquakes within the SGBDSN. The number of ''foreshocks'', as judged by most criteria, is significantly higher than the background seismicity rate. In order to establish this, we first removed aftershocks from the catalog with widely used methodology. The existence of SGBDSN foreshocks is supported by comparing actual statistics to those of a simulated catalog with uniform-distributed locations and Poisson-distributed times of occurrence. The probabilities of a given SGBDSN earthquake being followed by one having a higher magnitude within a short time frame and within a close distance are at least as high as those found with regional catalogs. These catalogs have completeness thresholds two to three units higher in magnitude than the SGBDSN catalog used here. The largest earthquake in the SGBDSN catalog, the M 4.7 event in Frenchman Flat on 01/27/1999, was preceded by a definite foreshock sequence. The largest event within 75 km of Yucca Mountain in historical time, the M 5.7 ...
Date: February 8, 2001
Creator: na
Partner: UNT Libraries Government Documents Department