The northern Walker Lane refraction experiment: Pn arrivals and the northern Sierra Nevada root     

John N. Louie  Weston Thelen  Shane B. Smith  James B. Scott  Matthew Clark  Satish Pullammanappallil   《Tectonophysics》2004,388(1-4):253

In May 2002, we collected a new crustal refraction profile from Battle Mountain, Nevada across western Nevada, the Reno area, Lake Tahoe, and the northern Sierra Nevada Mountains to Auburn, CA. Mine blasts and earthquakes were recorded by 199 Texan instruments extending across this more than 450-km-long transect. The use of large mine blasts and the ultra-portable Texan recorders kept the field costs of this profile to less than US$10,000. The seismic sources at the eastern end were mining blasts at Barrick's GoldStrike mine. The GoldStrike mine produced several ripple-fired blasts using 8000–44,000 kg of ANFO each, a daily occurrence. First arrivals from the larger GoldStrike blasts are obvious to distances of 300 km in the raw records. First arrivals from a quarry blast west of the survey near Watsonville, CA, located by the Northern California Seismic Network with a magnitude of 2.2, can be picked across the recording array to distances of 600 km. The Watsonville blast provides a western source, nearly reversing the GoldStrike blasts. A small earthquake near Bridgeport, CA. also produced pickable P-wave arrivals across the transect, providing fan-shot data. Arrivals from M5 events in the Mariana and Kuril Islands also appear in the records. This refraction survey observes an unexpectedly deep crustal root under the northern Sierra Nevada range, over 50 km in thickness and possibly centered west of the topographic crest. Pn delays of 4–6 s support this interpretation. At Battle Mountain, Nevada, we observe anomalously thin crust over a limited region perhaps only 150 km wide, with a Moho depth of 19–23 km. Pn crossover distances of less than 80 km support this anomaly, which is surrounded by observations of more normal, 30-km-thick crust. A 10-km-thick and high-velocity lower-crustal “pillow” is an alternative hypothesis, but unlikely due to the lack of volcanics west of Battle Mountain. Large mine and quarry blasts prove very effective crustal refraction sources when recorded with a dense receiver array, even over distances exceeding 600 km. New elastic synthetic seismogram modeling suggests that Pn can be strong as a first arrival, easing the modeling and interpretation of crustal refraction data. Fast eikonal computations of first-arrival time can match pickable Pn arrival times.  相似文献   

The H.T. Odum synthesis essay, a new section in estuaries     

Carlos M. Duarte  Scott Nixon  Stephen Threlkeld 《Estuaries and Coasts》2005,28(1):1-1

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Geotechnical analysis of paleoseismic shaking using liquefaction features: a major updating   总被引：1，自引：0，他引：1  

Scott M. Olson  Russell A. Green  Stephen F. Obermeier   《Engineering Geology》2005,76(3-4):235-261

A new methodology is proposed for the geotechnical analysis of strength of paleoseismic shaking using liquefaction effects. The proposed method provides recommendations for selection of both individual and regionally located test sites, provides techniques for validation of field data for use in back-analysis, and presents a recently developed energy-based solution to back-calculate paleoearthquake magnitude and strength of shaking. The proposed method allows investigators to qualitatively assess the influence of post-earthquake density change and aging. The proposed method also describes how the back-calculations from individual sites should be integrated into a regional assessment of paleoseismic parameters.  相似文献   

Reduction of U(VI) to U(IV) on the surface of magnetite     

T.B. Scott  G.C. Allen  M.G. Randell 《Geochimica et cosmochimica acta》2005,69(24):5639-5646

To increase the understanding of uranium transport in the environment and in the presence of steel corrosion products, the interaction of U(VI) with natural magnetite has been studied. Sorption studies have been carried out using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The XPS results clearly indicate the reduction of U(VI) to U(IV) on the surface of magnetite facilitated by electron transfer between the Fe and U, leading to a coupled oxidation of Fe(II) to Fe(III).  相似文献   

The validity and precision of spotlighting for surveying desert mammal communities     

D.M. Scott  S. Waite  T.M. Maddox  R.A. Freer  N. Dunstone 《Journal of Arid Environments》2005,61(4):589

We investigated the validity of spotlighting techniques for surveying and monitoring desert mammal populations by determining the effect of repeating spotlight transects on the relative precision of density estimates. Precision was modelled by calculating cumulative mean density and associated coefficient of variation. The effect of moonlight at the time of surveying was also investigated. The results show that spotlighting is a valid technique for monitoring some species, however the number of transects required to obtain pre-defined adequate levels of precision is species-dependent. Reasons for these findings are discussed and recommendations for future spotlight surveys for monitoring desert mammal populations are given.  相似文献   

Geology of the Gahcho Kué kimberlite pipes, NWT, Canada: root to diatreme magmatic transition zones     

C.M. Hetman  B.H. Scott Smith  J.L. Paul  F. Winter 《Lithos》2004,76(1-4):51-74

The Cambrian Gahcho Kué kimberlite cluster includes four main pipes that have been emplaced into the Archaean basement granitoids of the Slave Craton. Each of the steep-sided pipes were formed by the intrusion of several distinct phases of kimberlite in which the textures vary from hypabyssal kimberlite (HK) to diatreme-facies tuffisitic kimberlite breccia (TKB). The TKB displays many diagnostic features including abundant unaltered country rock xenoliths, pelletal lapilli, serpentinised olivines and a matrix composed of microlitic phlogopite and serpentine without carbonate. The HK contains common fresh olivine set in a groundmass composed of monticellite, phlogopite, perovskite, serpentine and carbonate. A number of separate phases of kimberlite display a magmatic textural gradation from TKB to HK, which is characterised by a decrease in the proportion of pelletal lapilli and country rock xenoliths and an increase in groundmass crystallinity, proportion of fresh olivine and the degree of xenolith digestion.

The pipe shapes and infills of the Gahcho Kué kimberlites are similar to those of the classic South African pipes, particularly those of the Kimberley area. Similar intrusive magmatic emplacement processes are proposed in which the diatreme-zone results from the degassing, after breakthrough, of the intruding magma column. The transition zones represent ‘frozen’ degassing fronts. The style of emplacement of the Gahcho Kué kimberlites is very different from that of many other pipes in Canada such as at Lac de Gras, Fort à la Corne or Attawapiskat.  相似文献   

Editorial: A Land Between Us     

Robin Kearns  Scott Nichol 《New Zealand geographer》2004,60(2):1-1

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Spatial and temporal variations in the grain-size characteristics of historical flood plain deposits, Blue River, Wisconsin, USA     

Scott A. Lecce  Robert T. Pavlowsky 《Geomorphology》2004,61(3-4):361-371

This study examined vertical, lateral, and downstream variations in the grain-size characteristics of historical (post-1830) overbank deposits in a watershed that has experienced high rates of accelerated flood plain sedimentation. More than 800 samples were collected from 53 cores along nine flood plain transects. Overbank deposits exhibit a coarsening-upward sequence attributed to historical changes in the sand content of source materials. The erosion of loess-capped soils increased the exposure, erosion, and transport of sandy parent materials. The average sand content of near-channel cores increases moderately downstream along two of the reaches because sandy source materials are increasingly exposed in larger main valleys in the northern part of the watershed. The two northernmost reaches are coarser overall, but do not display significant downstream trends. The sand content of surface and early historical overbank deposits generally decreases laterally as an exponential function of distance from the channel, suggesting transport by turbulent diffusion. The presence of sand throughout the transects and lateral coarsening at two of the transects, however, suggests that sediment transport by convection is also important.  相似文献   

Effects of a diel oxygen cycle on nitrogen transformations and greenhouse gas emissions in a eutrophied subtropical stream   总被引：2，自引：0，他引：2  

John A. Harrison  Pamela A. Matson  Scott E. Fendorf 《Aquatic Sciences - Research Across Boundaries》2005,67(3):308-315

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Evaluation of an Inexpensive Small-Diameter Temperature Logger for Documenting Ground Water–River Interactions     

Adam N. Johnson  Brian R. Boer  William W. Woessner  Jack A. Stanford  Geoffrey C. Poole  Steven A. Thomas  Scott J. O'Daniel 《Ground Water Monitoring & Remediation》2005,25(4):68-74

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