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AN understanding of the nature of seismic discontinuities in the Earth's upper mantle is important for understanding mantle processes: in particular, the amplitude and sharpness of these discontinuities are critical for assessing models of upper-mantle phase changes and chemical layering. So far, seismic studies aimed at determining the thickness and...

Possible effects of climate change on the Apalachicola-Chattahoochee-Flint (ACF) River basin is simulated with a computer model. Model inputs are monthly temperature and precipitation that simulate several possible climate change scenarios. Preliminary results for climate scenarios based on output for three popular general circulation models indicate that lower flows will...

Most Alabama Gulf and estuarine shoreline is undergoing long-term erosion; threatened shorelines will need programs of replenishment and maintenance if they are to be even temporarily stabilized. Highest priority beach replenishment areas include eastern Dauphin Island; west of Perdido Pass; and west of the inlet at Little Lagoon. There are...

Nitrate-nitrogen (NO3-N) concentrations at public water supply intakes on the Des Moines and Raccoon Rivers in Iowa exceeded the maximum contaminant level (MCL) of 10 mg L-1 for public water supplies established by the USEPA for extended periods of time from March through early August 1990. The excessive NO3-N levels...

A finite-difference model is used to compare long wave amplitudes arising from two-group forced generation mechanisms in the nearshore: long waves generated at a time-varying breakpoint and the shallow-water extension of the bound long wave. Plane beach results demonstrate that the strong frequency selection in the outgoing wave predicted by...

Investigations of earthquakes world wide show that rock falls are the most abundant type of landslide that is triggered by earthquakes. An engineering classification originally used in tunnel design, known as the rock mass quality designation (Q), was modified for use in rating the susceptibility of rock slopes to seismically-induced...

Coastal lake ice includes a belt of mobile crash and slush ice and a stable nearshore-ice complex (NIC). Sediment concentrations indicate that the NIC and the belt of brash and slush contains 180 to 280 t (113 to 175m3) of sand per kilometer of coast. This static sediment load is...

The development of faults and shear fracture systems over a broad range of temperature and pressure and for a variety of rock types involves the growth and interaction of microcracks. Acoustic emission (AE), which is produced by rapid microcrack growth, is a ubiquitous phenomenon associated with brittle fracture and has...

We present a tightly controlled and comprehensive set of analytical data for the 250-Ma Siberian flood-basalt province. Consideration of major- and trace-element compositions, along with strontium, lead and neodymium isotopic compositions, strongly supports earlier Russian subdivision of this magmatism into three magmatic cycles, giving rise to three assemblages of eleven...

Numerous petroleum-geochemical analyses of deeply buried, high-rank, fine-grained rocks from ultra-deep wellbores by different investigators demonstrate that C15+ hydrocarbons (HCs) persist in moderate to high concentrations at vitrinite reflectance (R0) values of 2.0–5.0% and persist in measurable concentrations up to R0 = 7.0–8.0%, at...

Acceleration response records obtained during the October 17, 1989 Loma Prieta earthquake [Ms = 7.1] from the 47-story, eccentrically braced Embarcadero Building (No. 4) [EMB], located in San Francisco, California, are studied. The predominant response modes of the building and the associated dynamic characteristics are determined by spectral analyses and...

Diatom assemblages across estuarine marshes show a three-part vertical ecologic zonation of the intertidal zone similar to zonations of foraminiferal and vascular plant assemblages. Gradual changes in the compositions of all three types of assemblages reflect gradational zone boundaries, 5-40m wide. Modern mudflat, low marsh, and high marsh zones can...

We developed a statistical method to distinguish the large demersal eggs of American shad from those of white sucker in riverine samples using egg morphometric analysis. Eggs were first screened by total diameter in deionized water according to ranges reported in the published literature. Differences in relative yolk...

Macroscopic frictional slip in water-saturated granular media occurs commonly during landsliding, surface faulting, and intense bedload transport. A mathematical model of dynamic pore-pressure fluctuations that accompany and influence such sliding is derived here by both inductive and deductive methods. The inductive derivation shows how the governing differential equations represent the...

The mechanism for U(VI) reduction by Desulfovibrio vulgaris (Hildenborough) was investigated. The H2-dependent U(VI) reductase activity in the soluble fraction of the cells was lost when the soluble fraction was passed over a cationic exchange column which extracted cytochrome c3. Addition of cytochrome c3 back to the soluble fraction that...

The 25 April 1992 magnitude 7.1 Cape Mendocino thrust earthquake demonstrated that the North America—Gorda plate boundary is seismogenic and illustrated hazards that could result from much larger earthquakes forecast for the Cascadia region. The shock occurred just north of the Mendocino Triple Junction and caused strong ground motion and...

Manifestations of a major thermal anomaly in the Geysers-Clear Lake area of northern California include the late Pliocene to Holocene Clear Lake Volcanics, The Geysers geothermal field, abundant thermal springs, and epithermal mercury and gold mineralization. The epithermal mineralization and thermal springs typically occur along high-angle faults within the broad...

Tourmaline-rich rocks are widespread minor lithologies within the Early Proterozoic Willyama Supergroup in the Broken Hill district, Australia. Tourmaline concentrations occur in strata-bound and local stratiform tourmalinites, clastic metasedimentary rocks, quartz-gahnite lode rocks, stratiform Pb-Zn-Ag sulfide ores, garnet quartzites, strata-bound scheelite deposits, quartz-tourmaline nodules, discordant quartz veins, and granitic pegmatites....

No abstract available ...

A new method is developed to efficiently compute exact Scheffé-type confidence intervals for output (or other function of parameters) g(β) derived from a groundwater flow model. The method is general in that parameter uncertainty can be specified by any statistical distribution having a log probability density function (log pdf) that can...

Heavy mineral assemblages in rivers in the Apure River drainage basin of Venezuela and Colombia closely reflect the nature of the source regions, which lie in the Andean orogenic terranes to the west and northwest. The Caribbean Mountains, largely composed of greenschist-facies pelites, phyllites, carbonates, and metavolcanics, supply assemblages dominated...

No abstract available at this time...

Epiguruk, a prominent bluff along the Kobuk River in northwestern Alaska, exposes a rich depositional record of Quaternary eolian and fluvial sand, with associated loess, paleosols, and periglacial features. Three major complexes of alluvial and eolian deposits are separated by two conspicuous organic-rich paleosols which formed during cool-moist interstadial intervals....

We have developed a program for performing Monte Carlo simulation of oil-field discovery histories. A synthetic parent population of fields is generated as a finite sample from a distribution of specified form. The discovery sequence then is simulated by sampling without replacement from this parent population in accordance with a...