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Articles 331 - 355 of 355
Full-Text Articles in Earth Sciences
Gps Measurements Of Regional Deformation In Southern California: Some Constraints On Performance, Timothy H. Dixon, G. Blewitt, K. Larson, D. Agnew, B. Hager, P. Kroger, L. Krumega, W. Strange
Gps Measurements Of Regional Deformation In Southern California: Some Constraints On Performance, Timothy H. Dixon, G. Blewitt, K. Larson, D. Agnew, B. Hager, P. Kroger, L. Krumega, W. Strange
School of Geosciences Faculty and Staff Publications
Geodetic measurements are an important tool for understanding plate boundary zone deformation. They provide data on fault motion rates and indirectly provide constraints on crustal rheology, earthquake processes, and evolution of geologic structures. In southern California the pattern of strain resulting from interaction of the Pacific and North American plates is very complex, and a robust geodetic experiment requires dense spatial sampling. In addition, the signals of interest may have strain rates smaller than 10−7/yr. Taken together, these conditions imply the need for geodetic techniques that are both economical, enabling large numbers of measurements, and highly accurate. Conventional …
A Final Feasibility Report Submitted To Sylvan Lake Improvement Association, Inc, Thomas Crisman
A Final Feasibility Report Submitted To Sylvan Lake Improvement Association, Inc, Thomas Crisman
School of Geosciences Faculty and Staff Publications
No abstract provided.
A Study For The Improvement, Restoration, And Protection Of Lake Bruce, Fulton And Pulaski Counties Indiana, William B. Eviston, Thomas Crisman, Eric P. Ellingson
A Study For The Improvement, Restoration, And Protection Of Lake Bruce, Fulton And Pulaski Counties Indiana, William B. Eviston, Thomas Crisman, Eric P. Ellingson
School of Geosciences Faculty and Staff Publications
No abstract provided.
Comment On “Timing Of Mantle Upwelling: Evidence For A Passive Origin For The Red Sea Rift” By A. V. Mcguire And R. G. Bohannon, Timothy H. Dixon
Comment On “Timing Of Mantle Upwelling: Evidence For A Passive Origin For The Red Sea Rift” By A. V. Mcguire And R. G. Bohannon, Timothy H. Dixon
School of Geosciences Faculty and Staff Publications
No abstract provided.
The Effect Of Tracking Network Configuration On Gps Baseline Estimates For The Casa Uno Experiment, S. Kornreich Wolf, Timothy H. Dixon, J. T. Freymuller
The Effect Of Tracking Network Configuration On Gps Baseline Estimates For The Casa Uno Experiment, S. Kornreich Wolf, Timothy H. Dixon, J. T. Freymuller
School of Geosciences Faculty and Staff Publications
Geodetic monitoring of subduction of the Nazca and Cocos plates is a goal of the CASA (Central and South America) Global Positioning System (GPS) experiments, and requires measurement of intersite distances (baselines) in excess of 500 km. The major error source in these measurements is the uncertainty in the position of the GPS satellites at the time of observation. A key aspect of the first CASA experiment, CASA Uno, was the initiation of a global network of tracking stations to minimize these errors. We studied the effect of using various subsets of this global tracking network on long (>100 …
First Gps Baseline Results From The North Andes, James N. Knellogg, Jeffrey T. Freymuller, Timothy H. Dixon, Ruth E. Neilan, Ropain U. Clemente, M. Camargo Sergio, Fernandez Ch. Benjamin, James L. Stowell, Anibal Salazai, Mora V. Jaime, Luis Espin, Vernon Perdue, Leonard Leos
First Gps Baseline Results From The North Andes, James N. Knellogg, Jeffrey T. Freymuller, Timothy H. Dixon, Ruth E. Neilan, Ropain U. Clemente, M. Camargo Sergio, Fernandez Ch. Benjamin, James L. Stowell, Anibal Salazai, Mora V. Jaime, Luis Espin, Vernon Perdue, Leonard Leos
School of Geosciences Faculty and Staff Publications
The CASA UNO GPS (Global Positioning System) experiment (January-February 1988) has provided the first epoch baseline measurements for the study of plate motions and crustal deformation in and around the North Andes. Two dimensional horizontal baseline repeatabilities are as good as 5 parts in 108 for short baselines (100–1000 km), and better than 3 parts in 108 for long baselines (>1000 km). Vertical repeatabilities are typically 4–6 cm, with a weak dependence on baseline length. The expected rate of plate convergence across the Colombia Trench is 6–8 cm/yr, which should be detectable by the repeat experiment planned …
Central And South America Gps Geodesy - Casa Uno, James N. Kellog, Tim Dixon
Central And South America Gps Geodesy - Casa Uno, James N. Kellog, Tim Dixon
School of Geosciences Faculty and Staff Publications
In January 1988, scientists from over 25 organizations in 13 countries and territories cooperated in the largest Global Positioning System (GPS) campaign in the world to date (Table 1). 43 GPS receivers collected approximately 590 station-days of data in American Samoa, Australia, Canada, Colombia, Costa Rica, Ecuador, New Zealand, Norway, Panama, Sweden, United States, West Germany, and Venezuela. The experiment was entitled CASA UNO, an acronym for Central and South America – and uno is the Spanish word for one, designating first epoch measurements. The CASA UNO experiment was the first civilian effort implementing a global GPS satellite tracking network. …
Some Tests Of Wet Tropospheric Calibration For The Casa Uno Global Positioning System Experiment, Timothy H. Dixon, S. Kornreich Wolf
Some Tests Of Wet Tropospheric Calibration For The Casa Uno Global Positioning System Experiment, Timothy H. Dixon, S. Kornreich Wolf
School of Geosciences Faculty and Staff Publications
Wet tropospheric path delay can be a major error source for Global Positioning System (GPS) geodetic experiments. We investigate strategies for minimizing this error using data from CASA Uno, the first major GPS experiment in Central and South America, where wet path delays may be both high and variable. We compared wet path delay calibration using water vapor radiometers (WVRs) and residual delay estimation, with strategies where the entire wet path delay is estimated stochastically without prior calibration, using data from a 270 km test baseline in Costa Rica. Both approaches yield centimeter-level baseline repeatability and similar tropospheric estimates, suggesting …
A Study For The Improvement, Restoration, And Protection Of Mill Pond, William B. Eviston, Thomas Crisman, Eric P. Ellingson
A Study For The Improvement, Restoration, And Protection Of Mill Pond, William B. Eviston, Thomas Crisman, Eric P. Ellingson
School of Geosciences Faculty and Staff Publications
No abstract provided.
Rupture Process Of The Macquarie Ridge Earthquake Of May 23, 1989, Jochen Braunmiller, John Nábělek
Rupture Process Of The Macquarie Ridge Earthquake Of May 23, 1989, Jochen Braunmiller, John Nábělek
School of Geosciences Faculty and Staff Publications
Broadband body waves recorded at 15 digital seismic stations worldwide are used to study the rupture process of the May 23, 1989 Macquarie Ridge earthquake. The centroidal solution (strike 211°, dip 86°, rake 180°, and depth of 10 km below the seafloor) indicates shallow rupture with pure right-lateral strike-slip motion along the Pacific-Australia plate boundary, in agreement with motion predicted by plate tectonic models. The total seismic moment is 13.4×1020 Nm, 80% of which was released in the first 24 s of the rupture process. Modeling favors a bilaterally propagating rupture with slightly different dip and rake for the …
Topographic And Volcanic Asymmetry Around The Red Sea: Constraints On Rift Models, Timothy H. Dixon, Erik R. Ivins, Brenda J. Franklin
Topographic And Volcanic Asymmetry Around The Red Sea: Constraints On Rift Models, Timothy H. Dixon, Erik R. Ivins, Brenda J. Franklin
School of Geosciences Faculty and Staff Publications
The Red Sea rift is asymmetric, with the locus of uplift and Tertiary volcanism in Saudi Arabia, 200–400 km east of the present rift axis. One model for this asymmetry involves simple shear extension on an east dipping, low-angle master fault that penetrates the lithosphere. Uplift and volcanism would mark the location where the fault enters the asthenosphere. However, observed seismicity, regional heat flow, and sedimentation are not in accord with this model's predictions. An alternate model involves interaction of upwelling asthenosphere in the early rifting stage with a nearby crustal weak zone such as a suture that controls rift …
Casa Central And South America Gps Geodesy, James Kellogg, Timothy H. Dixon, R. Neilan
Casa Central And South America Gps Geodesy, James Kellogg, Timothy H. Dixon, R. Neilan
School of Geosciences Faculty and Staff Publications
In January 1988, scientists from over 25 organizations in 13 countries and territories cooperated in the largest Global Positioning System (GPS) campaign in the world to date (Table 1) [Neilan et al., 1988]. From January 18 to February 5, 1988, 43 GPS receivers collected about 590 station-days of data in American Samoa, Australia, Canada, Colombia, Costa Rica, Ecuador, New Zealand, Norway, Panama, Sweden, United States, West Germany, and Venezuela. The experiment was entitled CASA UNO, an acronym for Central and South America—and “uno” is Spanish for “one,” designating first-epoch measurements. The CASA UNO experiment was the first civilian …
The Cultural Eutrophication Of Koontz Lake, Indiana: Causes, Consequences, Correction, Willaim B. Eviston, Thomas Crisman
The Cultural Eutrophication Of Koontz Lake, Indiana: Causes, Consequences, Correction, Willaim B. Eviston, Thomas Crisman
School of Geosciences Faculty and Staff Publications
No abstract provided.
Variation In Sulfur Dioxide Emissions Related To Earth Tides, Halemaumau Crater, Kilauea Volcano, Hawaii, Charles B. Connor, Richard E. Stoiber, Lawrence L. Malinconico Jr.
Variation In Sulfur Dioxide Emissions Related To Earth Tides, Halemaumau Crater, Kilauea Volcano, Hawaii, Charles B. Connor, Richard E. Stoiber, Lawrence L. Malinconico Jr.
School of Geosciences Faculty and Staff Publications
Variation in SO2 emissions from Halemaumau crater, Kilauea volcano, Hawaii is analyzed using a set of techniques known as exploratory data analysis. SO2 flux was monitored using a correlation spectrometer. A total of 302 measurements were made on 73 days over a 90‐day period. The mean flux was 171 t/d with a standard deviation of 52 t/d. A significant increase in flux occurs during increased seismic activity beneath the caldera. SO2 flux prior to the this change varies in a systematic way and may be related to variation in the tidal modulation envelope.
Effect Of Wet Tropospheric Path Delays On Estimation Of Geodetic Baselines In The Gulf Of California Using The Global Positioning System, David M. Tralli, Timothy H. Dixon, Scott A. Stephens
Effect Of Wet Tropospheric Path Delays On Estimation Of Geodetic Baselines In The Gulf Of California Using The Global Positioning System, David M. Tralli, Timothy H. Dixon, Scott A. Stephens
School of Geosciences Faculty and Staff Publications
Geodetic baseline measurements using the Global Positioning System (GPS) were acquired in the Gulf of California between Loreto and Cabo San Lucas in Baja California and Mazatlan on the mainland of Mexico. Tropospheric water vapor content was high during the experiment, typically yielding wet path delays in excess of 20 cm at zenith. Surface meteorological (SM) and water vapor radiometer (WVR) measurements were recorded at each site, providing independent means of calibrating the GPS signal for the wet tropospheric path delay. Residual wet delays at zenith are estimated as constants and also as first-order exponentially correlated stochastic processes. In addition, …
Lake Apopka Trophic Structure Manipulation, Thomas Crisman, John R. Beaver
Lake Apopka Trophic Structure Manipulation, Thomas Crisman, John R. Beaver
School of Geosciences Faculty and Staff Publications
No abstract provided.
A Few Parts In 108 Geodetic Baseline Repeatability In The Gulf Of California Using The Global Positioning System, David M. Tralli, Timothy H. Dixon
A Few Parts In 108 Geodetic Baseline Repeatability In The Gulf Of California Using The Global Positioning System, David M. Tralli, Timothy H. Dixon
School of Geosciences Faculty and Staff Publications
Global Positioning System (GPS) geodetic measurements of 350–650 km baselines across the Pacific-North America plate boundary in the Gulf of California are presented. The analysis employs a four-station U.S. fiducial network and combined carrier phase and pseudorange data. Water vapor radiometer (WVR) data at the Gulf sites are used to calibrate the GPS signal for wet tropospheric path delays. Residual tropospheric delays are modeled as first-order exponentially correlated stochastic processes. The measurement precision for horizontal components is a few parts in 108 or better. Comparison of the Gulf data with other geodetic techniques is not yet possible, however the …
Eruptions Of Pavlof Volcano And Their Possible Modulation By Ocean Load And Tectonic Stresses, Stephen R. Mcnutt, R. J. Beavan
Eruptions Of Pavlof Volcano And Their Possible Modulation By Ocean Load And Tectonic Stresses, Stephen R. Mcnutt, R. J. Beavan
School of Geosciences Faculty and Staff Publications
All nine magmatic eruptions at Pavlof Volcano in six of the years from 1973 to 1984 have occurred between September 9 and November 20. Volumes of erupted material range from 0.1 to 15.9 × 106 m3 (dense rock equivalent) at an average rate of ∼3 × 106 m3 yr−1. The volumes are estimated from eyewitness reports for two eruptions; the others are estimated from a relationship that we derive between eruption volume and harmonic tremor duration and amplitude. The volume of lava erupted is approximately time predictable. A significant correlation exists between the eruptions …
Lake Weir Eutrophication Study: Final Report For Phases I And Ii, Thomas Crisman, Anne E. Keller, Jeffrey K. Jones, Henry Meier, John R. Beaver
Lake Weir Eutrophication Study: Final Report For Phases I And Ii, Thomas Crisman, Anne E. Keller, Jeffrey K. Jones, Henry Meier, John R. Beaver
School of Geosciences Faculty and Staff Publications
No abstract provided.
History Of Cultural Eutrophication At Lake Manitou, Indiana And Prospects For Its Management, Thomas Crisman
History Of Cultural Eutrophication At Lake Manitou, Indiana And Prospects For Its Management, Thomas Crisman
School of Geosciences Faculty and Staff Publications
No abstract provided.
Determination Of Large-Scale Velocity Structure Of The Crust And Upper Mantle In The Vicinity Of Pavlof Volcano, Alaska, Stephen R. Mcnutt, K. H. Jacob
Determination Of Large-Scale Velocity Structure Of The Crust And Upper Mantle In The Vicinity Of Pavlof Volcano, Alaska, Stephen R. Mcnutt, K. H. Jacob
School of Geosciences Faculty and Staff Publications
Pavlof Volcano is a 2715-m-high stratovolcano located at latitude 55.4°N and longitude 161.9°W, near the western end of the Alaska Peninsula. In this study the large-scale lateral perturbations to a vertical reference velocity structure in the vicinity of Pavlof Volcano are determined using modified versions of standard three-dimensional inversion techniques. We use as the primary data set P wave arrival times and residuals from shallow (deep) regional earthquakes located by the Shumagin Islands seismic network. Relative residuals mainly from refracted (e.g., Pn) arrivals allow us to constrain models for a laterally varying crustal velocity structure. Several strong ray path dependent …
Historical Analysis Of The Cultural Eutrophication Of Lake Maxinkuckee, Indiana, Thomas Crisman
Historical Analysis Of The Cultural Eutrophication Of Lake Maxinkuckee, Indiana, Thomas Crisman
School of Geosciences Faculty and Staff Publications
No abstract provided.
Patterns Of Earthquakes And The Effect Of Solid Earth And Ocean Load Tides At Mount St. Helens Prior To The May 18, 1980, Eruption, Stephen R. Mcnutt, R. J. Beavan
Patterns Of Earthquakes And The Effect Of Solid Earth And Ocean Load Tides At Mount St. Helens Prior To The May 18, 1980, Eruption, Stephen R. Mcnutt, R. J. Beavan
School of Geosciences Faculty and Staff Publications
Seismographs near Mount St. Helens Volcano recorded an earthquake swarm lasting nearly 2 months prior to the catastrophic May 18, 1980, eruption. The earthquakes are divided into four classes based on station CPW (Δ = 116 km) seismogram characteristics: (1) events with Sv:P amplitude ratio >3 and dominant frequency >3 Hz; (2) events with Sv:P ratio between 1 and 3 and dominant frequency >2 Hz; (3) events similar to characteristic 2 but with a strong (probably surface wave) phase just after the S phase; and (4) events with frequencies between 1 and 2 Hz lacking a clear S phase. The …
Bathymetric Prediction From Seasat Altimeter Data, Timothy H. Dixon, M. Naraghi, M. K. Mcnutt, S. M. Smith
Bathymetric Prediction From Seasat Altimeter Data, Timothy H. Dixon, M. Naraghi, M. K. Mcnutt, S. M. Smith
School of Geosciences Faculty and Staff Publications
The linear response function technique is used to analyze two 1300-km tracks of SEASAT altimeter data and corresponding bathymetry in the Musician Seamounts region north of Hawaii. Bathymetry and geoid height are highly correlated in the 50- to 300-km wavelength range. A predictive filter is developed which can operate on SEASAT altimetry in poorly surveyed oceanic regions to indicate the presence of major bathymétrie anomalies. Modeling of the bathymetry-geoid correlation in the Musician region is attempted using the elastic plate model. The flexural rigidity D of the plate is not well constrained by our data but appears to lie in …
Large-Scale Operations Management Test Of Use Of The White Amur For Control Of Problem Aquatic Plants. Report 2. First Year Poststocking Results. Volume Iii. The Plankton And Benthos Of Lake Conway, Florida, Thomas Crisman, Floor M. Kooijam, University Of Florida, Department Of Enviromental Engineering Sciences
Large-Scale Operations Management Test Of Use Of The White Amur For Control Of Problem Aquatic Plants. Report 2. First Year Poststocking Results. Volume Iii. The Plankton And Benthos Of Lake Conway, Florida, Thomas Crisman, Floor M. Kooijam, University Of Florida, Department Of Enviromental Engineering Sciences
School of Geosciences Faculty and Staff Publications
No abstract provided.