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Effective Elastic Thickness Of The Lithosphere Along The Easter Seamount Chain, Sarah E. Kruse, Zhengro J. Liu, David F. Naar, Robert A. Duncan

Geology Faculty Publications

Bathymetry and gravity data collected during Legs 5, 6, and 7 of the 1993 GLORIA Expedition and the recently released 2-min altimetry-derived global gravity grid are used to determine the effective elastic thickness of the lithosphere along the Easter Seamount Chain (ESC). Forward modeling, admittance, and coherence methods yield consistent results. With the exception of the eastern and western ends of the ESC the effective elastic thickness along the chain is ∼1–4 km. The thin elastic thickness for the majority of the ESC seamounts is compatible with a young seafloor age at the time of loading derived from new radiometric …

Evaluation Of Constructed Wetlands On Phosphate Mined Lands In Florida, G. R. Best, M. T. Brown, Thomas Crisman, Keven L. Erwin, D. A. Graetz, K. R. Reddy, H. Kale, P. Pritchard, T. M. Missimer, C. W. Walker, A. Owosina, M. J. Deuver

School of Geosciences Faculty and Staff Publications

Summarizing research conducted from June 1993 to May 1995 on hydrology, soils, water quality, and aquatic fauna on phosphate mined lands in Florida.

An Evaluation Of Plant Community Structure, Fish And Benthic Meio- And Macrofauna As Success Criteria For Reclaimed Wetlands, Thomas Crisman, William J. Streever, John H. Kiefer, David L. Evans

School of Geosciences Faculty and Staff Publications

As a result of legislative action in 1975 (Florida Administrative Code Section 16C-16, 16C-17), landscape reclamation is required on all lands mined for phosphate in the State of Florida. Between 1975 and 1991, for example, approximately 40,000 ha of land in Florida were strip mined for phosphate and thus subject to provisions of this legislation. In excess of 2,700 ha of mitigation wetlands have been constructed as part of the land reclamation effort, but the degree to which these systems mimic both the structural and functional properties of natural wetlands is poorly known.

There has been a great diversity in …

Linking Transport Infrastructure Investments And Economic Development In Sub-Saharan Africa, Ambe J. Njoh

School of Geosciences Faculty and Staff Publications

The study explores the link between investments in transportation infrastructure, operationalized in terms of road density, and economic development, defined in terms of gross domestic product per capita (GDP/Cap), in sub-Saharan Africa (SSA). The findings support the hypothesis of a positive association between the two variables. The association is stronger for paved, than for all, roads in general. Furthermore, a negative but statistically insignificant relationship is observed between unpaved roads and economic development. Thus, economic development is a function more of quality, than quantity of roads in SSA. Therefore, a more judicious use of the scarce resource of sub-Saharan African …

Relative Motion Between The Caribbean And North American Plates And Related Boundary Zone Deformation From A Decade Of Gps Observations, Timothy H. Dixon, Frederic Farina, Charles Demets, Pamela Jansma, Paul Mann, Eric Calais

School of Geosciences Faculty and Staff Publications

Global Positioning System (GPS) measurements in 1986, 1994, and 1995 at sites in Dominican Republic, Puerto Rico, Cuba, and Grand Turk define the velocity of the Caribbean plate relative to North America. The data show eastward motion of the Caribbean plate at a rate of 21 ± 1 mm/yr (1 standard error ) in the vicinity of southern Dominican Republic, a factor of 2 higher than the NUVEL-1A plate motion model prediction of 11 ± 3 mm/yr. Independent measurements on San Andres Island, and an Euler vector derived from these data, also suggest a rate that is much higher than …

Continuous Monitoring Of Surface Deformation At Long Valley Caldera, California, With Gps, Timothy H. Dixon, Ailin Mao, Marcus Bursik, Michael Heflin, John Langbein, Ross Stein, Frank Webb

School of Geosciences Faculty and Staff Publications

Continuous Global Positioning System (GPS) measurements at Long Valley Caldera, an active volcanic region in east central California, have been made on the south side of the resurgent dome since early 1993. A site on the north side of the dome was added in late 1994. Special adaptations for autonomous operation in remote regions and enhanced vertical precision were made. The data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber. Measurement precisions (1 standard error) for “absolute” position coordinates, i.e., relative to a global reference frame, are 3–4 mm (north), 5–6 …

Constraints On Present-Day Shortening Rate Across The Central Eastern Andes From Gps Data, Lisa Leffler, Seth Stein, Ailin Mao, Timothy H. Dixon, Michael A. Ellis, Leonidas Ocola, I. Selwyn Sacks

School of Geosciences Faculty and Staff Publications

Two years of continuous GPS data from several sites in South America indicate that Arequipa in the southern Peruvian Andes has a velocity of 13±3 mm/yr (two standard errors) to the northeast with respect to stable South America. We interpret these data as reflecting a combination of elastic strain accumulation associated with a locked Nazca-South America subduction zone and a small amount of crustal shortening across the fold and thrust belt on the eastern margin of the Andes. Models of elastic strain accumulation for fully locked and partly locked subduction zones constrain shortening in the eastern Andes to 0–3 mm/yr …

Kilauea Volcano Provides Hot Seismic Data For Joint Japanese-U.S. Experiment, Stephen R. Mcnutt, Y. Ida, B. A. Chouet, P. Okubo, J. Oikawa, G. Saccorotti

School of Geosciences Faculty and Staff Publications

A team of 25 researchers from the United States, Japan, and Italy joined the staff of the Hawaiian Volcano Observatory (HVO) from January 8 through February 9, 1996, to make the most detailed seismic recordings on Kilauea Volcano ever. One-hundred-sixteen portable seismographs were installed in and near Kilauea Crater in Hawaii Volcanoes National Park as a joint Japanese-U.S. research project to record volcanic earthquakes and tremor. The importance of these events has long been recognized, but their origin remains poorly understood due to inadequate network coverage and limitations of the analog instrumentation used in the past.

On February 1, a …

A Gps Estimate Of Relative Motion Between North And South America, Timothy H. Dixon, Ailin Mao

School of Geosciences Faculty and Staff Publications

GPS velocity data are used to estimate the Euler vector describing rigid body motion of North America relative to South America. Assuming the boundary between the North and South American plates is located near the Fifteen Twenty fracture zone in the equatorial Atlantic, the Euler vector predicts extension across the Royal Trough up to 1 mm/yr, and convergence across the Barracuda Ridge at about 2 mm/yr, in agreement with geological estimates averaged over tens of millions of years. Further west, convergence between North and South America at rates up to 8 mm/yr may contribute to deformation of the Caribbean plate …

New Constraints On Source Processes Of Volcanic Tremor At Arenal Volcano, Costa Rica, Using Broadband Seismic Data, John P. Benoit, Stephen R. Mcnutt

School of Geosciences Faculty and Staff Publications

Broadband seismic data recorded 2.3 km from the active vent of Arenal Volcano, Costa Rica, provide new constraints on tremor source processes. Arenal's tremor contains as many as seven harmonics, whose frequencies vary temporally by up to 75 percent, from initial values of 1.9 Hz for the first peak immediately following explosive eruptions to 3.2–3.5 Hz several minutes later. We infer that gas bubble concentration is variable within the conduit and also changes as a function of time, thereby changing the acoustic velocity. We infer that the source is a shallow, 200–660 m-long, vertically oriented 1-D resonator with matched boundary …

Magnetic Surveys Help Reassess Volcanic Hazards At Yucca Mountain, Nevada, Charles B. Connor, Sammantha Lane-Magsino, John A. Stamatakos, Ronald H. Martin, Peter C. Lafemina, Brittain E. Hill, Steve Lieber

School of Geosciences Faculty and Staff Publications

Natural disasters like volcanic eruptions occur infrequently, but if they occur near nuclear power plants or high‐level radioactive waste repositories, local and global communities can be threatened. Ideally, such facilities should be constructed only where geologic risk is very low.

Estimating the probabilities of such events requires a comprehensive understanding of site geology and the geologic processes operating in the site region on timescales of 104 to 107years. In light of these requirements, geologists and geophysicists must continually improve techniques for site characterization.

Characteristics Of Street Sweepings In Florida Cities, Robert Brinkmann, Jeffrey G. Ryan, Mark Billus

Geology Faculty Publications

No abstract provided.

Timing Of Basaltic Volcanism Along The Mesa Butte Fault In The San Francisco Volcanic Field, Arizona, From 40Ar/39Ar Dates: Implications For Longevity Of Cinder Cone Alignments, F. M. Conway, David A. Ferrill, Chris M. Hall, Alan P. Morris, John A. Stamatakos, Charles B. Connor, Alex N. Halliday, Christopher Condit

School of Geosciences Faculty and Staff Publications

Using high‐precision stepwise‐heating 40Ar/39Ar methods, we dated volcanic products of at least 12 vents cropping out along the northern segment of the Mesa Butte Fault in the San Francisco Volcanic Field, Arizona, where the relationship between fault and vent alignment is unambiguous. The 40Ar/39Ar isochron dates indicate that the Mesa Butte Fault hosted five episodes of volcanism over a 1 million year interval, from 1400 to 300 ka. The first episode occurred 1 km northwest of the trace of the Mesa Butte Fault, whereas the next two episodes were centered near the intersection of the Mesa Butte and Cedar Ranch …

Variations In The Frequency-Magnitude Distribution With Depth In Two Volcanic Areas: Mount St. Helens, Washington, And Mt. Spurr, Alaska, Stefan Wiemer, Stephen R. Mcnutt

School of Geosciences Faculty and Staff Publications

The frequency-magnitude distribution of earthquakes, characterized using the b-value, is examined as a function of space beneath Mount St. Helens (1988–1996), and Mt. Spurr (1991–1995). At Mount St. Helens, two volumes of anomalously high b (b > 1.3) can be observed at depths of 2.6–3.6 km below the crater floor and below 6.4 km. These anomalies coincide with (1) the depth of vesiculation of ascending magma, and (2) the suggested location of a magma chamber at Mount St. Helens. Study of Mt. Spurr reveals an area of high b-value (b ≥ 1.3) at a depth of about 2.3–4.5 …

Observations At Costa Rican Volcano Offer Clues To Causes Of Eruptions, M. Hagerty, S. Y. Schwartz, M. Protti, Timothy H. Dixon, M. Garcés

School of Geosciences Faculty and Staff Publications

Recent measurements of ground deformation at an active volcano show great promise for elucidating the processes that lead to volcanic eruptions. A long-term effort to continuously monitor ground deformation over a very wide bandwidth using state-of-the-art geodetic, seismic, and acoustic instruments at Arenal Volcano in Costa Rica is producing high-quality recordings of harmonic tremor and explosive events and offers an exciting opportunity to explore possible lunar periodicities in volcanic eruptivity.