The nucleation and rupture process of the 1981 Gulf of Corinth earthquakes from deconvolved broad-band data   总被引：1，自引：0，他引：1  

R. E. Abercrombie  I. G. Main  A. Douglas  P. W. Burton 《Geophysical Journal International》1995,120(2):393-405

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Relation Between Hydraulic Conductivity and Texture in a Carbonate Aquifer: Regional Continuity   总被引：1，自引：0，他引：1  

Charles W. Rovey II  Douglas S. Cherkauer 《Ground water》1994,32(2):227-238

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Thematic Section: Diagenesis and very low-grade metamorphism: Proceedings of the 29th IGC Symposium     

Koichi Aoyagi  Douglas Robinson 《Island Arc》1993,2(4):238-239

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Pre- and post-orogenic extensional settings for burial-type metamorphism     

Douglas  Robinson 《Island Arc》1993,2(4):280-287

Abstract Extensional basins are formed in a variety of geotectonic settings and in some cases the infills of such basins show the effects of very low grade, burial-type metamorphism. It is proposed that extensional basins with a low grade metamorphic infill can be divided into pre- and post-orogenic types with a different causal mechanism for the metamorphism. In the pre-orogenic setting the extensional process driven by mantle upwelling provides both the mechanism for basin formation and the development of the metamorphism in response to the enhanced thermal flux in such settings. The typical mineral parageneses and facies series found in these low grade metamorphic terranes are more compatible with the counter-clockwise pressure-temperature-time loops postulated for such settings, rather than the clockwise loops associated typically with convergent settings. In the post-orogenic settings, extensional basins formed in over-thickened continental crust during orogenesis have infills in which very low grade metamorphism is also developed. It is proposed that such metamorphism is not linked to the extensional process itself. Instead, it is linked to crustal heating during the process of thickening and orogenesis and is expected to be found only in orogenic belts where widths are in excess of 500 km.  相似文献   

Fan and playa areas in southern California and adjacent parts of Nevada     

Peter Jansson  Douglas Jacobson  Roger B. Le Hooke 《地球表面变化过程与地形》1993,18(2):109-119

In bolsons in the desert regions of southern California and adjacent parts of Nevada, the area underlain by alluvial fan gravels and playa sediments is generally ?1·2 times the area being eroded to produce those sediments. In certain larger basins in the vicinity of Death Valley, however, the depositional area is only about half the size of the erosional area. This reflects the more active tectonic environment in these bolsons. Of the areas underlain by recent sediments in these bolsons, playas make up 2–6 per cent. Smaller playas are found in the Mojave region, and seem to be associated with sedimentary terranes. Conversely, igneous terranes support larger playas. Larger deviations of playa area from these averages are attributable to incorrect identification of bolson boundaries. Fine sediment is either able to pass through the bolson to the next down stream, or is being collected from areas upstream that were not considered to be part of the system. For example, the playa in Death Valley is unusually large. This is in part because the Death Valley playa has been deformed tectonically so parts of it are now eroding, and in part because the outlet of Lake Tecopa was downcut in the geologically recent past, so sediment once trapped there now reaches Death Valley. The size of the playa in Death Valley is still adjusting to these changes.  相似文献   

Results from field testing A curved box girder bridge using simulated earthquake loads     

James A. Richardson  Bruce M. Douglas 《地震工程与结构动力学》1993,22(10):905-922

This paper presents the results of a unique field test on a curved highway overpass. In the test, large horizontal loads were applied to the superstructure of the bridge and quickly released, causing the bridge to vibrate. The resulting large-amplitude vibrations were intended to be similar to the vibrations caused by earthquakes (horizontal accelerations of up to 25 per cent of gravity were measured on the bridge deck). Well-defined lateral, longitudinal, vertical and torsional vibration modes were identified from the test data. The vibration modes were used to verify an analytical model of the bridge's dynamic response. For this paper, the model was verified using only the fundamental vibration mode, which was primarily a horizontal vibration mode. Using a system identification procedure, the dynamic response model was adjusted until its frequency and mode shape matched the measured frequency and mode shape. Parameters in the verified model were compared with the same parameters calculated from information in the structural drawings. Because the fundamental mode represents a horizontal mode, the bridge parameters identified in this paper were those parameters which strongly influence the horizontal response of the bridge.  相似文献   

The nature of particle motion in regional seismograms and its utilization for phase identification     

Zoltan A. Der  Douglas R. Baumgardt  Robert H. Shumway 《Geophysical Journal International》1993,115(3):1012-1024

The particle motion of regional arrivals is frequently treated in automatic phase-recognition schemes as that appropriate to simple P or S waves incident on an elastic, laterally homogeneous half-space. This model implies that the motion in ' P -type' phases can be described in terms of a single, generalized signal process and ' S -type' phases in terms of two independent processes ( SV and SH ) and thus, all regional arrivals could be fully characterized by three components of motion. In this paper, we present anlyses of the particle-motion patterns of various regional arrivals recorded at the ARCESS array from closely spaced events in the Kola Peninsula. We have found that only Pn -particle motion, described in terms of two independent signal processes, can be reliably characterized by three-component recordings. On the other hand, the various regional arrivals following Pn , such as Pg and Sn and Lg , can only be poorly characterized on the basis of three-component recordings alone. The reason is that these arrivals must be described in terms of more than two independent generalized signal processes, at least three for Pg and Sn , and possibly up to five for Lg . Recognition of these phases will thus require the use of more sensors than signal processes in the observing sensor configuration, such as three-component sensors combined with a small tripartite array. We have investigated the feasibility of adaptive, automatic recognition of regional arrivials by a wavefield extrapolation scheme utilizing such a mini-array. The process, which appear to be promising, adaptively learns the particle-motion patterns of individual arrivals, including complex site-response functions, from examples of closely located regional events.  相似文献   

Privatised Communities: the use of owners corporations in master planned estates in Melbourne     

Robin Goodman  Kathy Douglas 《The Australian geographer》2008,39(4):521-536

This paper contributes to the growing body of work on master planned estates in Australia by addressing the issue of the privatisation of assets and facilities, which in more conventional residential developments are in the public realm, owned and managed by local councils or other public bodies. The paper addresses the trend to place assets presented as lifestyle features, such as community and recreational facilities, open space or landscaping features, in a form of collective private ownership, known in Victoria as owners corporations. The provision of these facilities and assets for residents, however, has a number of implications relating to exclusivity, separation from the wider community, and potential conflicts within the master planned community itself. These issues are examined with reference to data gathered through an investigation of recently established master planned communities in the growth areas of Melbourne.  相似文献   

The influence of lee sediment behind large bed elements on bedload transport rates in supply-limited channels     

Douglas M. Thompson   《Geomorphology》2008,99(1-4):420-432

A coarse surface layer can help to limit bedload transport rates in channels with cobble and gravel beds. In these systems, periodic boulder-sized clasts often exist with small deposits of fine material in the lee of these large bed elements. A combined field and flume study was conducted to investigate the potential impact of lee deposits with distinctly finer sediment-sizes behind boulders on bedload transport rates. Detailed sediment characterizations were performed on surface, subsurface, and lee sediments in two coarse-bedded Connecticut channels. Bedload measurements also were conducted in a series of flows that approached the bankfull level in these two systems to determine transport rates and the size distribution of bedload material. A 6-m long, 0.5-m wide flume was used to model these systems with fine sediment passing over a fixed bed of sediment particles with uniform-sized, large bed elements. Sediment distributions of the lee deposits in the two Connecticut channels indicate that lee deposits may be produced from winnowing of sediments from the surface layer. Lee deposits also exhibit sediment distributions similar to bedload sediment distributions from low to near-bankfull flow in one of the two channels. Bedload sediments in the second channel were finer than lee deposits, presumably from selective entrainment of fines. Flume experiments demonstrate that bedload transport rates are lower for periods of steady flow relative to periods that include either an increase or decrease in discharge. The results show that lee sediments establish a metastable deposit behind each obstruction for a given discharge. Either increases or decreases in discharge disrupt this temporary stability and increase sediment delivery to the main flow. The study suggests that the influence of the rate of change in discharge may be as important as the absolute magnitude of discharge on sediment transport rates at moderate and low discharges in sediment-limited systems with large bed elements.  相似文献   

A test of the possible influence of seabird activity on the <Superscript>210</Superscript>Pb flux in high Arctic ponds at Cape Vera,Devon Island,Nunavut: implications for radiochronology     

N. Michelutti  J. M. Blais  H. Liu  B. E. Keatley  M. S. V. Douglas  M. L. Mallory  J. P. Smol 《Journal of Paleolimnology》2008,40(3):783-791

A large seabird colony of northern fulmars (Fulmarus glacialis) at Cape Vera on Devon Island in the Canadian high Arctic has been shown to act as an effective biological pump, transporting large quantities of marine-derived nutrients and contaminants to the ponds beneath their nesting sites. Previous research has shown that seabirds also have the potential to elevate radionuclide concentrations in their immediate surroundings. Here, we assess the influence of the Cape Vera seabird colony on the ²¹⁰Pb budgets of six affected ponds and one control site, and discuss potential implications with respect to ²¹⁰Pb dating methodologies. In general, fluxes of ²¹⁰Pb at Cape Vera were similar to, or less than, those measured at other Arctic locations not influenced by seabirds. Plots of unsupported ²¹⁰Pb activity versus depth showed a number of non-monotonic features in all sediment cores, necessitating the use of the constant-rate-of-supply (CRS) model to derive age-depth profiles. We conclude that seabird activity has not dramatically increased the ²¹⁰Pb flux to the ponds at Cape Vera. Overall, the low flux of excess ²¹⁰Pb made accurate dating problematic for some of the study cores, necessitating the use of independent dating markers (e.g., ¹³⁷Cs and PCB concentrations) to verify the reliability of the chronologies.  相似文献