Earth Sciences Commons^™

Using Spreadsheets In Geoscience Education: Survey And Annotated Bibliography Of Articles In The Journal Of Geoscience Education Through 2003, Beth Fratesi, H. L. Vacher

School of Geosciences Faculty and Staff Publications

Thirty-eight papers published in the Journal of Geoscience Education ( JGE) from 1989 through 2003 explicitly use or recommend the use of spreadsheets as part of classroom or field exercises, projects, or entire courses. Many of the papers include the spreadsheets, and some include the equations. The papers demonstrate how spreadsheets allow students to explore a subject through problem-oriented, interactive, and quantitative exercises. We provide an annotated bibliography and classify the 38 JGE papers by spreadsheet use, mathematics skill area, and geologic subdiscipline. Our discussion of five selected articles — abundance of elements in the Earth’s crust; directional properties of …

Seismogenic Zone Structure Of The Southern Middle America Trench, Costa Rica, H. R. Deshon, S. Y. Schwartz, S. L. Bilek, L. M. Dorman, V. Gonzalez, J. M. Protti, E. R. Flueh, Timothy H. Dixon

School of Geosciences Faculty and Staff Publications

The shallow seismogenic portion of subduction zones generates damaging large and great earthquakes. This study provides structural constraints on the seismogenic zone of the Middle America Trench offshore central Costa Rica and insights into the physical and mechanical characteristics controlling seismogenesis. We have located ∼300 events that occurred following the M_W 6.9, 20 August 1999, Quepos, Costa Rica, underthrusting earthquake using a three-dimensional velocity model and arrival time data recorded by a temporary local network of land and ocean bottom seismometers. We use aftershock locations to define the geometry and characteristics of the seismogenic zone in this region. These …

Fault Creep And Microseismicity On The Hayward Fault, California: Implications For Asperity Size, Christina R. Gans, Kevin P. Furlong, Rocco Malservisi

School of Geosciences Faculty and Staff Publications

The Hayward fault is documented to undergo significant creep, with some patches accommodating 50% or more of the long‐term fault displacement. In spite of this, the fault has also experienced moderate to large earthquakes. By comparing the patterns of microseismicity observed on the fault with models of fault zone creep, we can investigate the long‐term displacement/deformation history of the fault in terms of the relative roles of aseismic creep, fault slip accommodated through microseismicity, and strain accumulation (slip deficit). We find that microseismicity on the Hayward fault produces a negligible percentage of the seismic moment dissipated on the fault. Combining …

Self-Potential, Soil Co2 Flux, And Temperature On Masaya Volcano, Nicaragua, J. L. Lewicki, Charles B. Connor, K. St-Armand, J. Stix, W. Spinner

School of Geosciences Faculty and Staff Publications

We investigate the spatial relationship between self-potential (SP), soil CO₂ flux, and temperature and the mechanisms that produce SP anomalies on the flanks of Masaya volcano, Nicaragua. We measured SP, soil CO₂ fluxes (× 10⁴ g m⁻² d⁻¹), and temperatures (26 to 80°C) within an area surrounding a normal fault, adjacent to Comalito cinder cone (2002–2003). These variables are well spatially correlated. Wavelengths of SP anomalies are ≤100 m, and high horizontal SP gradients flank the region of elevated flux and temperature. Carbon isotopic compositions of soil CO₂ (δ¹³C = −3.3 …

Holocene Slip Rate Of The Wasatch Fault Zone, Utah, From Geodetic Data: Earthquake Cycle Effects, Rocco Malservisi, Timothy H. Dixon, Peter C. Lafemina, Kevin P. Furlong

School of Geosciences Faculty and Staff Publications

GPS data define a broad zone of present day deformation in the eastern Basin and Range province, western US. Using finite element models with elastic upper crust over viscoelastic lower crust/upper mantle and incorporating earthquake cycle effects, we show that these data are consistent with a model whereby most contemporary fault slip is focused on the Wasatch fault zone. Modeled rates of horizontal extension are 3.0–4.5 mm/yr, in agreement with Holocene geologic data. The models are non-unique, in part because much of the Wasatch fault is in the late stages of the earthquake cycle, when surface velocity gradients across the …

Earthscoping The Inner Workings Of Magmatic Systems, Michael Hamburger, Stephen R. Mcnutt, Daniel Dzurisin, Jonathan Fink, David P. Hill, Charles Meertens, Chris Newhall, Susan Owen, John A. Power

School of Geosciences Faculty and Staff Publications

In the shadow of one of the world's great volcanic systems, an intensive 3‐day workshop was undertaken to work toward developing a scientific plan for the magmatic systems component of the U.S. National Science Foundation's (NSF) EarthScope Initiative. This NSF‐sponsored workshop was designed to provide direction to the EarthScope planning committee and the NSF in developing scientific, technical, deployment, and management decisions related to the magmatic systems component of EarthScope. The meeting featured a mixture of oral and poster scientific sessions, breakout group and plenary discussions, and a field trip to examine one of the targets of the EarthScope magmatic …

City Of Gainesville Basin Planning Initiative: A Report With Recommendations, Jen Larson, Kelly Marrinson, Josh Muller, Keven Regan, Thomas Ankersen, Thomas Crisman, Mark Clark

School of Geosciences Faculty and Staff Publications

No abstract provided.

The Duration-Amplitude Distribution Of Volcanic Tremor, John P. Benoit, Stephen R. Mcnutt, Vilma Barboza

School of Geosciences Faculty and Staff Publications

The duration-amplitude distribution of volcanic tremor was examined in eight volcanoes and one geothermal area. An exponential model, implying a scale-bound source process, is found to be a better fit to the data than a power law (scale invariant) model. The exponential model well describes tremor associated with magmatic and phreatic eruptions, shallow and deep source regions, and geothermal sources. We tested the exponential model described by: , where d is the duration of tremor greater than or equal to a particular amplitude D_R, d_t is the total duration of tremor, and the inverse of λ is …

Seismic Cycle And Rheological Effects On Estimation Of Present-Day Slip Rates For The Agua Blanca And San Miguel-Vallecitos Faults, Northern Baja California, Mexico, Timothy H. Dixon, J. Decaix, F. Farina, K. Furlong, Rocco Malservisi

School of Geosciences Faculty and Staff Publications

Geodesy can be used to infer long‐term fault slip rates, assuming a model for crust and upper mantle rheology. We examine the sensitivity of fault slip rate estimates to assumed rheology for the Agua Blanca and San Miguel‐Vallecitos faults in northern Baja California, Mexico, part of the Pacific–North America plate boundary zone. The Agua Blanca fault is seismically quiet, but offset alluvial fans indicate young activity. Current seismicity is confined to the nearby San Miguel‐Vallecitos fault, a small offset fault better aligned with plate motion. GPS measurements between 1993 and 1998 suggest that both faults are active, with a combined …

Seismotectonics Of The Explorer Region, Jochen Braunmiller, John Nábělek

School of Geosciences Faculty and Staff Publications

The Explorer region offshore western Canada is a tectonically complex area surrounded by the Pacific, North America, and Juan de Fuca plates. Existing tectonic models for the region differ fundamentally. Proposed plate configurations range from multiple independent plate fragments to an Explorer plate now fused to North America along the continental margin and cut by Pacific–North America transform faults in the west. We present new seismological data constraining the region's current tectonics. We use three-component regional waveforms to determine the source parameters of 84 earthquakes with magnitude greater than 4. Combined with 34 Harvard centroid moment tensor solutions, they represent …

Satellite Imagery Proves Essential For Monitoring Erupting Aleutian Volcano, Kenneson Dean, Jonathan Dehn, Stephen R. Mcnutt, Christina Neal, Richard Moore, Dave Schneider

School of Geosciences Faculty and Staff Publications

Mt. Cleveland is one of more than 40 active volcanoes in Alaska that is monitored by the Alaska Volcano Observatory (AVO). It is located on the western half of Chuginadak, a remote and uninhabited island in the east central Aleutians that lies 1526 km southwest of Anchorage. The closest inhabited community, Nikolski, is 75 km to the east on Umnak Island (Figure 1). Mt. Cleveland erupted explosively on 19 February and on 11 and 19 March 2001. Because the volcano is not yet monitored with seismic, deformation, or other geophysical instruments, satellite imagery was the only effective tool for detecting …

Consistency Of Geologic And Geodetic Displacements During Andean Orogenesis, David Hindle, Jonas Kley, Eryn Klosko, Seth Klosko, Timothy H. Dixon, Edmundo Norabuena

School of Geosciences Faculty and Staff Publications

Present-day displacements within the Central Andes are being measured using high precision GPS geodesy. Until now, comparison of such ground motions within deforming plate boundary zones to those on a geologic time scale has not been possible due to lack of sufficient geological data. In the Central Andes, a comparable dataset for the past 25 Ma of mountain building can be reconstructed. Here, we use new interpretations of shortening rates averaged over 25–10 Ma and 10 Ma–present and find that whilst displacement directions have remained virtually constant and parallel, an acceleration has occurred synchronously with a slowing of convergence between …

Revel: A Model For Recent Plate Velocities From Space Geodesy, Giovanni F. Sella, Timothy H. Dixon, Ailin Mao

School of Geosciences Faculty and Staff Publications

We present a new global model for Recent plate velocities, REVEL, describing the relative velocities of 19 plates and continental blocks. The model is derived from publicly available space geodetic (primarily GPS) data for the period 1993–2000. We include an independent and rigorous estimate for GPS velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates. The velocity fields for North America, Eurasia, and Antarctica clearly show the effects of glacial isostatic adjustment, and Australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field. Two thirds of tested …

Influence Of The Earthquake Cycle And Lithospheric Rheology On The Dynamics Of The Eastern California Shear Ζone, R. Malservisi, K. Furlong, Timothy H. Dixon

School of Geosciences Faculty and Staff Publications

The Eastern California Shear Zone is bounded by the high heat flow region of the Basin and Range province and the low heat flow region of the Sierra Nevada block. This difference in thermal state influences the rheology of the lower crust/upper mantle, resulting in a viscosity contrast between the two regions. We analyze the effect of such a contrast on the kinematics and dynamics of the shear zone with numerical models. This viscosity contrast drives asymmetric strain accumulation in the upper crust, producing an asymmetric surface velocity field. An additional consequence of this strain pattern is the potential for …

Refined Kinematics Of The Eastern California Shear Zone From Gps Observations, 1993-1998, M. Meghan Miller, Daniel J. Johnson, Timothy H. Dixon, Roy K. Dokka

School of Geosciences Faculty and Staff Publications

Global Positioning System (GPS) results from networks spanning the Eastern California shear zone and adjacent Sierra Nevada block, occupied annually between 1993 and 1998, constrain plate margin kinematics. We use an elastic block model to relate GPS station velocities to long-term fault slip rate estimates. The model accounts for elastic strain accumulation on the San Andreas fault, as well as faults of the Eastern California shear zone. South of the Garlock fault, 14 mm/yr of dextral shear is distributed across the Eastern California shear zone. Some of this slip penetrates eastward into the Basin and Range, and a collective budget …

Comparative Ecosystem Analysis Of Hydrologic Restoration Of Tates Hell Swamp, Chris Robert, Thomas Crisman, Loren Anderson, Carolyn Kendell

School of Geosciences Faculty and Staff Publications

No abstract provided.

Aseismic Inflation Of Westdahl Volcano, Alaska, Revealed By Satellite Radar Interferometry, Zhong Lu, Charles Wicks, Daniel Dzurisin, Wayne Thatcher, Jeffrey T. Freymuller, Stephen R. Mcnutt, Dorte Mann

School of Geosciences Faculty and Staff Publications

Westdahl volcano, located at the west end of Unimak Island in the central Aleutian volcanic arc, Alaska, is a broad shield that produced moderate-sized eruptions in 1964, 1978–79, and 1991–92. Satellite radar interferometry detected about 17 cm of volcano-wide inflation from September 1993 to October 1998. Multiple independent interferograms reveal that the deformation rate has not been steady; more inflation occurred from 1993 to 1995 than from 1995 to 1998. Numerical modeling indicates that a source located about 9 km beneath the center of the volcano inflated by about 0.05 km³ from 1993 to 1998. On the basis of the …

Application Of Wave-Theoretical Seismoacoustic Models To The Interpretation Of Explosion And Eruption Tremor Signals Radiated By Pavlof Volcano, Alaska, Milton A. Garces, Stephen R. Mcnutt, Roger A. Hansen, John C. Eichelberger

School of Geosciences Faculty and Staff Publications

Tremor and explosion signals recorded on September 29 during the Fall 1996 Pavlof eruption are interpreted using video images, field observations, and seismic data. Waveform analysis of tremor and explosions provided estimates of the melt's volcano-acoustic parameters and the magma conduit dimensions. Initial mass fractions of 0.25% water and 0.025% carbon dioxide in the melt can explain the resonance characteristics of the tremor and explosion pulses inferred from seismic data. The magma conduit is modeled as a three-section rectangular crack. We infer that the tremor-radiating region consists of the lowermost two sections, both with cross-sectional areas of ∼10 m^{2 …}

Present-Day Motion Of The Sierra Nevada Block And Some Tectonic Implications For The Basin And Range Province, North American Cordillera, Timothy H. Dixon, Meghan Miller, Frederic Farina, Hongzhi Wang, Daniel Johnson

School of Geosciences Faculty and Staff Publications

Global Positioning System (GPS) data from five sites on the stable interior of the Sierra Nevada block are inverted to describe its angular velocity relative to stable North America. The velocity data for the five sites fit the rigid block model with rms misfits of 0.3 mm/yr (north) and 0.8 mm/yr (east), smaller than independently estimated data uncertainty, indicating that the rigid block model is appropriate. The new Euler vector, 17.0°N, 137.3°W, rotation rate 0.28 degrees per million years, predicts that the block is translating to the northwest, nearly parallel to the plate motion direction, at 13–14 mm/yr, faster than …

Geologic Factors Controlling Patterns Of Small‐Volume Basaltic Volcanism: Application To A Volcanic Hazards Assessment At Yucca Mountain, Nevada, Charles B. Connor, John A. Stamatakos, David A. Ferrill, Brittain E. Hill, Goodluck I. Ofoegbu, Michael Conway, Budhi Sagar, John Trapp

School of Geosciences Faculty and Staff Publications

The proposed high‐level radioactive waste repository at Yucca Mountain, Nevada, is located within an active volcanic field. Probabilistic volcanic hazard models for future eruptions through the proposed repository depend heavily on our understanding of the spatial controls on volcano distribution at a variety of scales. On regional scales, Pliocene‐Quaternary volcano clusters are located east of the Bare Mountain fault. Extension has resulted in large‐scale crustal density contrast across the fault, and vents are restricted to low‐density areas of the hanging wall. Finite element modeling indicates that this crustal density contrast can result in transient pressure changes of up to 7 …

Gps Geodetic Constraints On Caribbean-North America Plate Motion, Charles Demets, Pamela E. Jansma, Glen S. Mattioli, Timothy H. Dixon, Fred Farina, Roger Bilham, Eric Calais, Paul Mann

School of Geosciences Faculty and Staff Publications

We describe a model for Caribbean plate motion based on GPS velocities of four sites in the plate interior and two azimuths of the Swan Islands transform fault. The data are well fit by a single angular velocity, with average misfits approximately equal to the 1.5–3.0 mm yr⁻¹ velocity uncertainties. The new model predicts Caribbean-North America motion ∼65% faster than predicted by NUVEL-1A, averaging 18–20±3 mm yr⁻¹ (2σ) at various locations along the plate boundary. The data are best fit by a rotation pole that predicts obliquely convergent motion along the plate boundary east of Cuba, but are …

Neotectonics Of Puerto Rico And The Virgin Islands, Northeastern Caribbean, From Gps Geodesy, Pamela E. Jansma, Glen S. Mattioli, Alberto Lopez, Charles Demets, Timothy H. Dixon, Paul Mann, Eric Calais

School of Geosciences Faculty and Staff Publications

The boundary between the North American and Caribbean plates is characterized primarily by left-lateral motion along predominantly east-west striking faults. Seismicity and marine geophysical survey data are consistent with at least two, and possibly three, microplates in the diffuse boundary zone in the northeastern Caribbean: (1) the Gonave, (2) the Hispaniola, and (3) the Puerto Rico-northern Virgin Islands (PRVI). We discuss results from GPS geodetic measurements acquired since 1994 to test the microplate hypothesis, define PRVI translation and rotation within the boundary zone, and constrain PRVI neotectonics. GPS-derived velocities are analyzed with respect to both North American and Caribbean plate …

Noise In Gps Coordinate Time Series, Ailin Mao, Christopher G.A. Harrison, Timothy H. Dixon

School of Geosciences Faculty and Staff Publications

We assess the noise characteristics in time series of daily position estimates for 23 globally distributed Global Positioning System (GPS) stations with 3 years of data, using spectral analysis and Maximum Likelihood Estimation. A combination of white noise and flicker noise appears to be the best model for the noise characteristics of all three position components. Both white and flicker noise amplitudes are smallest in the north component and largest in the vertical component. The white noise part of the vertical component is higher for tropical stations (±23° latitude) compared to midlatitude stations. Velocity error in a GPS coordinate time …

New Kinematic Models For Pacific-North America Motion From 3 Ma To Present, I: Evidence For Steady Motion And Biases In The Nuvel-1a Model, Charles Demets, Timothy H. Dixon

School of Geosciences Faculty and Staff Publications

We use velocities derived from 2–4.5 years of continuous GPS observations at 21 sites on the Pacific and North American plates along with a subset of the NUVEL-1A data to examine the steadiness of Pacific-North America motion since 3.16 Ma, the transfer of Baja California to the Pacific plate, and the magnitude of biases in the NUVEL-1A estimate of Pacific-North America motion. We find that Pacific-North America motion has remained steady since 3.16 Ma, but at rates significantly faster than predicted by NUVEL-1A. In the vicinity of Baja California, our GPS-derived model and recent seafloor spreading rates in the southern …

Decelerating Nazca-South America And Nazca-Pacific Plate Motions, Edmundo O. Norabuena, Timothy H. Dixon, Seth Stein, Christopher G. A. Harrison

School of Geosciences Faculty and Staff Publications

Space geodetic estimates of the rate of Nazca-South America convergence and Nazca-Pacific spreading averaging over several years show that present day rates are significantly slower than the 3 million year average NUVEL-1A model. The implied rates of deceleration are consistent with longer term trends extending back to at least 20 Ma, about the time of initiation of Andes growth, and may reflect consequences of ongoing subduction and construction of the Andes, e.g., increased friction and viscous drag on the subducted slab as the leading edge of South America thickens.

Gps Measurement Of Surface Deformation Around Soufriere Hills Volcano, Montserrat From October 1995 To July 1996, Glen S. Mattioli, Timothy H. Dixon, Frederic Farina, Ellen S. Howell, Pamela E. Jansma, Alan L. Smith

School of Geosciences Faculty and Staff Publications

Global Positioning System geodesy was used to measure surface deformation on Soufriere Hills volcano, Montserrat from October 6, 1995 to July 1, 1997 during initial dome growth and gravitational collapse. Our data from this period show non-axially symmetric horizontal displacements, and decreasing subsidence as a function of radial distance from the former topographic high of the volcanic edifice. Forward modeling suggests that surface deformation is caused by a shallow vertical dike (< 3 km), which expanded approximately 1 m, coupled with a deflating Mogi source at about 6 km depth. These inferred source parameters are in good agreement with independent observations of regional dike widths and preemption magma storage depth.

Gps Measurements Across The Northern Caribbean Plate Boundary Zone: Impact Of Postseismic Relaxation Following Historic Earthquakes, Fred F. Pollitz, Timothy H. Dixon

School of Geosciences Faculty and Staff Publications

GPS measurements in the northern Caribbean suggest that the rate of Caribbean plate motion relative to North America is about 10 mm/yr faster than predicted by global plate motion model NUVEL-1A. Several of the key sites used in the GPS study are located in the Dominican Republic, near the rupture zones of large earthquakes in 1946 and in the previous two centuries. Postseismic relaxation of the crust and upper mantle is a possible explanation for the plate velocity discrepancy. We explore a range of fault mechanisms and crustal and mantle rheology to place an upper bound on postseismic relaxation effects. …

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 …