Light lithophile elements in martian basalts: Evaluating the evidence for magmatic water degassing     

Christopher D.K. Herd  Allan H. Treiman  Charles K. Shearer 《Geochimica et cosmochimica acta》2005,69(9):2431-2440

Whether water has played a role in the petrogenesis of martian basalts remains a subject of significant debate. Estimates of pre-eruptive water concentrations in martian magmas are impeded by the effects of degassing and shock. However, zoning trends of light lithophile elements (LLE) in pyroxene have been interpreted as evidence for the degassing of magmatic water, on the basis of the soluble behavior of these elements in hydrothermal fluids. We provide ion microprobe analyses of LLE in pyroxene in the Zagami and Shergotty martian basalts, complemented by detailed electron microprobe analyses and major-element X-ray maps, to independently verify the zoning of LLE and its relationship to texture and major-element variations. Our results corroborate previous results; specifically, that Li concentrations are lower in rims than cores of Shergotty and Zagami pyroxene. In contrast, we see no evidence for a core-to-rim decrease in B. In the absence of further data, we interpret the decrease in Li as reflecting either loss after crystallization of pyroxene cores, consistent with magmatic degassing, or the diffusive preferential loss of Li from pyroxene rims, possibly as a result of shock. Because the partitioning behavior of Li between hydrous fluid, minerals, and melt under relevant conditions of pressure, temperature, and melt composition is unknown, the viability of the water degassing hypothesis depends on experiments establishing the compatibility of Li in hydrous fluid associated with martian basaltic melt and the incompatibility of Li in pyroxene at elevated pressures.  相似文献   

Survey and monitoring of landslide displacements by means of L-band satellite SAR interferometry   总被引：2，自引：2，他引：2  

Tazio Strozzi  Paolo Farina  Alessandro Corsini  Christian Ambrosi  Manfred Thüring  Johannes Zilger  Andreas Wiesmann  Urs Wegmüller  Charles Werner 《Landslides》2005,2(3):193-201

This paper illustrates the capabilities of L-band satellite SAR interferometry for the investigation of landslide displacements. SAR data acquired by the L-band JERS satellite over the Italian and Swiss Alps have been analyzed together with C-band ERS-1/2 SAR data and in situ information. The use of L-band SAR data with a wavelength larger than the usual C-band, generally considered for ground motion measurements, reduces some of the limitations of differential SAR interferometry, in particular, signal decorrelation induced by vegetation cover and rapid displacements. The sites of the Alta Val Badia region in South Tyrol (Italy), Ruinon in Lombardia (Italy), Saas Grund in Valais (Switzerland) and Campo Vallemaggia in Ticino (Switzerland), representing a comprehensive set of different mass wasting phenomena in various environments, are considered. The landslides in the Alta Val Badia region are good examples for presenting the improved performance of L-band in comparison to C-band for vegetated areas, in particular concerning open forest. The landslides of Ruinon, Saas Grund, and Campo Vallemaggia demonstrate the strength of L-band in observing moderately fast displacements in comparison to C-band. This work, performed with historical SAR data from a satellite which operated until 1998, demonstrates the capabilities of future planned L-band SAR missions, like ALOS and TerraSAR-L, for landslide studies.  相似文献   

The Seismic Project of the National Tsunami Hazard Mitigation Program     

David H. Oppenheimer  Alex N. Bittenbinder  Barbara M. Bogaert  Raymond P. Buland  Lynn D. Dietz  Roger A. Hansen  Stephen D. Malone  Charles S. McCreery  Thomas J. Sokolowski  Paul M. Whitmore  Craig S. Weaver 《Natural Hazards》2005,35(1):59-72

In 1997, the Federal Emergency Management Agency (FEMA), National Oceanic and Atmospheric Administration (NOAA), U.S. Geological Survey (USGS), and the five western States of Alaska, California, Hawaii, Oregon, and Washington joined in a partnership called the National Tsunami Hazard Mitigation Program (NTHMP) to enhance the quality and quantity of seismic data provided to the NOAA tsunami warning centers in Alaska and Hawaii. The NTHMP funded a seismic project that now provides the warning centers with real-time seismic data over dedicated communication links and the Internet from regional seismic networks monitoring earthquakes in the five western states, the U.S. National Seismic Network in Colorado, and from domestic and global seismic stations operated by other agencies. The goal of the project is to reduce the time needed to issue a tsunami warning by providing the warning centers with high-dynamic range, broadband waveforms in near real time. An additional goal is to reduce the likelihood of issuing false tsunami warnings by rapidly providing to the warning centers parametric information on earthquakes that could indicate their tsunamigenic potential, such as hypocenters, magnitudes, moment tensors, and shake distribution maps. New or upgraded field instrumentation was installed over a 5-year period at 53 seismic stations in the five western states. Data from these instruments has been integrated into the seismic network utilizing Earthworm software. This network has significantly reduced the time needed to respond to teleseismic and regional earthquakes. Notably, the West Coast/Alaska Tsunami Warning Center responded to the 28 February 2001 Mw 6.8 Nisqually earthquake beneath Olympia, Washington within 2 minutes compared to an average response time of over 10 minutes for the previous 18 years.  相似文献   

An envelope for Mohr's circle in seismically excited three‐dimensional structures     

Charles Menun 《地震工程与结构动力学》2004,33(9):981-998

A previously developed response‐spectrum‐based procedure for computing the envelope that bounds the time‐varying realizations of Mohr's circle at any prescribed location within a two‐dimensional structure is extended for use with three‐dimensional structures subjected to as many as three translational components of ground acceleration. The proposed envelope, which is completely defined by quantities that are routinely used and calculated in conventional response spectrum analyses, is developed for the general case in which the principal directions of the earthquake, along which the ground accelerations are uncorrelated, are unknown. The accuracy of the proposed envelope is evaluated by comparing it to the results of an ensemble of time‐history analyses performed on a concrete arch dam using simulated accelerograms. It is found that the proposed envelope has a level of accuracy that is suitable for structural design and analysis. The largest observed difference between the simulated and predicted mean envelopes is less than 5%. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

May 2004     

J. C. Green  Charles H. Shaw 《Environmental Geology》2004,45(7):1036-1038

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Preliminary Method Development and Evaluation of a Statewide Assessment of Ground Water and Surface Water Interactions     

Richard C. Berg  Donald A. Keefer  Misganaw Demissie  Ganapathi Ramamurthy  Charles A. Job 《Ground Water Monitoring & Remediation》1997,17(3):64-69

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Generation of the teleseismic P-wave coda from Aleutian earthquakes     

Charles H. Estabrook  Michael Weber  Rainer Kind 《Geophysical Journal International》1997,130(2):349-364

We investigate large-amplitude phases arriving in the P -wave coda of broad-band seismograms from teleseisms recorded by the Gräfenberg array, the German Regional Seismic Network and the Global Seismic Network. The data set consists of all events m _b≤ 5.6 from the Aleutian arc between 1977 and 1992. Earthquakes with large-amplitude coda waves correlate with the presence of oceanic crust in the source region. The amplitudes sometimes approach those of the P wave, much larger than predicted by theory. Modelling indicates that phases in the P -wave coda cannot be P -wave multiples beneath the source and receiver, or underside reflections, which precede PP , from upper-mantle discontinuities. Among the events, seismograms are very similar, where the arrival times of the unusual phases agree approximately with the predicted times of S -to- P conversions from the upper-mantle discontinuities under the source. Because the large-amplitude phases in the P -wave coda have little, if any, dependence on event depth and have predominantly an SV -wave radiation pattern towards the receiver, we suggest that they originate as SV and/or Rayleigh waves and are enhanced by lateral heterogeneity and multipathing from the subducting Aleutian slab.  相似文献   

Scale Dependency of Hydraulic Conductivity Measurements   总被引：8，自引：0，他引：8  

Charles W. Rovey II  Douglas S. Cherkauer 《Ground water》1995,33(5):769-780

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Periglacial geomorphology edited by J. C. Dixon and A. D. Abrahams,Binghamton Symposia,No 22, John Wiley and Sons,Chichester, 1992. No. of pages: xiii + 354. Price: £60.00. ISBN 0-471-93342-2     

Charles Harris 《地球表面变化过程与地形》1993,18(5):470-470

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An evaluation of the global variations in the major element chemistry of arc basalts   总被引：2，自引：0，他引：2  

Terry Plank  Charles H. Langmuir 《Earth and Planetary Science Letters》1988,90(4):349-370

Arc volcanoes occur at convergent margins with a wide range in subduction parameters, and variations in these parameters might be expected to lead to variations in the chemistry of magmas parental to arcs. Major element analyses from approximately 100 volcanic centers within 30 arcs, normalized to 6% MgO to minimize the effects of crystal fractionation, display wide variations. Na₂O and CaO at 6% MgO (Na_6.0 and Ca_6.0) correlate remarkably well with the thickness of the overlying crust. These systematics are consistent with two possible models. In the first model, the crust behaves as a chemical filter; where the crust is thick, magmas crystallize at higher pressure and interact more extensively with the arc crust. Modeling of high-pressure crystallization and assimilation, however, does not reproduce the associated variations in Na_6.0 and Ca_6.0 without calling upon complicated combinations of fractionating phases and assimilants. In the second model, crustal thickness determines the height of the mantle column available for melting beneath arc volcanoes. If melting begins beneath arcs at similar depths, then the column of mantle that undergoes decompression melting is much shorter beneath the thickest arc crust. The shorter mantle column for arcs built on thick crust will lead to smaller extents of melting in the mantle, and hence higher Na_6.0 and lower Ca_6.0 in the parental magmas. Modeling shows that variations in the extent of melting in the mantle can easily account for the associated variations in Ca_6.0 and Na_6.0. The abundances of the other major elements at 6% MgO do not correlate well with crustal thickness, or any other subduction parameter. Co-variation of some of these other major elements (e.g., Si_6.0 and Fe_6.0) within individual arcs suggests that they are strongly influenced by local crustal level processes that obscure partial melting systematics. Correction for the crustal processes improves the relationship between Na_6.0 and Ca_6.0 that is so readily explained by partial melting. The extents of melting in the mantle beneath arc volcanoes estimated from the ranges in Na_6.0 and Ca_6.0 are remarkably similar to those estimated beneath mid-ocean ridges. This observation provides further evidence that the mantle wedge, and not the slab, melts beneath arc volcanic fronts.  相似文献