Estimating azimuthal stress‐induced P‐wave anisotropy from S‐wave anisotropy using sonic log or vertical seismic profile data          下载免费PDF全文

Olivia Collet  Boris Gurevich  Guy Duncan 《Geophysical Prospecting》2016,64(5):1305-1317

Most sedimentary rocks are anisotropic, yet it is often difficult to accurately incorporate anisotropy into seismic workflows because analysis of anisotropy requires knowledge of a number of parameters that are difficult to estimate from standard seismic data. In this study, we provide a methodology to infer azimuthal P‐wave anisotropy from S‐wave anisotropy calculated from log or vertical seismic profile data. This methodology involves a number of steps. First, we compute the azimuthal P‐wave anisotropy in the dry medium as a function of the azimuthal S‐wave anisotropy using a rock physics model, which accounts for the stress dependency of seismic wave velocities in dry isotropic elastic media subjected to triaxial compression. Once the P‐wave anisotropy in the dry medium is known, we use the anisotropic Gassmann equations to estimate the anisotropy of the saturated medium. We test this workflow on the log data acquired in the North West Shelf of Australia, where azimuthal anisotropy is likely caused by large differences between minimum and maximum horizontal stresses. The obtained results are compared to azimuthal P‐wave anisotropy obtained via orthorhombic tomography in the same area. In the clean sandstone layers, anisotropy parameters obtained by both methods are fairly consistent. In the shale and shaly sandstone layers, however, there is a significant discrepancy between results since the stress‐induced anisotropy model we use is not applicable to rocks exhibiting intrinsic anisotropy. This methodology could be useful for building the initial anisotropic velocity model for imaging, which is to be refined through migration velocity analysis.  相似文献   

The Struggle to be Temperate: Climate and "Moral Masculinity" in Mid-Nineteenth Century Ceylon   总被引：1，自引：1，他引：0  

James S. Duncan 《Singapore journal of tropical geography》2000,21(1):34-37

This paper examines a particular type of imperial literature, the writing of the plantation in mid-nineteenth century Ceylon. These writings, by and for the male planting community, were written to recruit, instruct and entertain, and drew upon discourses of tropicality and moral masculinity. But discourses are constrained by the material conditions under which they are put into practice. Consequently, writings about a place such as highland Ceylon recognised the divergence of this place from the archetypal tropics. Accounts, nevertheless, remained within the conceptual grid that Livingstone (1991) has termed the "morality of climate." These texts were also pervaded by the discourse of moral masculinity. More particularly, the narrative structure of these writings was inflected by the masculinist adventure novel, which was cross-cut by concerns of race, class, religion and nationality. The tropical highlands were represented as an adversary that presented a moral test of the planters' manhood, race and class.  相似文献   

The transition region and coronal explorer   总被引：5，自引：0，他引：5  

Handy  B.N.  Acton  L.W.  Kankelborg  C.C.  Wolfson  C.J.  Akin  D.J.  Bruner  M.E.  Caravalho  R.  Catura  R.C.  Chevalier  R.  Duncan  D.W.  Edwards  C.G.  Feinstein  C.N.  Freeland  S.L.  Friedlaender  F.M.  Hoffmann  C.H.  Hurlburt  N.E.  Jurcevich  B.K.  Katz  N.L.  Kelly  G.A.  Lemen  J.R.  Levay  M.  Lindgren  R.W.  Mathur  D.P.  Meyer  S.B.  Morrison  S.J.  Morrison  M.D.  Nightingale  R.W.  Pope  T.P.  Rehse  R.A.  Schrijver  C.J.  Shine  R.A.  Shing  L.  Strong  K.T.  Tarbell  T.D.  Title  A.M.  Torgerson  D.D.  Golub  L.  Bookbinder  J.A.  Caldwell  D.  Cheimets  P.N.  Davis  W.N.  Deluca  E.E.  McMullen  R.A.  Warren  H.P.  Amato  D.  Fisher  R.  Maldonado  H.  Parkinson  C. 《Solar physics》1999,187(2):229-260

The Transition Region and Coronal Explorer (TRACE) satellite, launched 2 April 1998, is a NASA Small Explorer (SMEX) that images the solar photosphere, transition region and corona with unprecedented spatial resolution and temporal continuity. To provide continuous coverage of solar phenomena, TRACE is located in a sun-synchronous polar orbit. The ∼700 Mbytes of data which are collected daily are made available for unrestricted use within a few days of observation. The instrument features a 30-cm Cassegrain telescope with a field of view of 8.5×.5 arc min and a spatial resolution of 1 arc sec (0.5 arc sec pixels). TRACE contains multilayer optics and a lumogen-coated CCD detector to record three EUV wavelengths and several UV wavelengths. It observes plasmas at selected temperatures from 6000 K to 10 MK with a typical temporal resolution of less than 1 min.  相似文献   

On the relationship between age and dynamics in elliptical galaxies   总被引：1，自引：0，他引：1  

Duncan A. Forbes  Trevor J. Ponman 《Monthly notices of the Royal Astronomical Society》1999,309(3):623-628

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Contrasting beach-ridge systems in different types of coastal settings     

Manuel F. Isla  Damián Moyano-Paz  Duncan M. FitzGerald  Lautaro Simontacchi  Gonzalo D. Veiga 《地球表面变化过程与地形》2023,48(1):47-71

Beach-ridge systems are geomorphological features common in every type of coast and have been widely interpreted as geo-archives of past sea-level, climatic, or tectonic changes. These relict morphological elements are well-known by their facies, architecture, stratigraphy, and evolution. However, the coastal context where beach ridges are formed has never been evaluated. Coastal beach-ridge systems were classified into four main types corresponding to deltaic strandplains, non-deltaic strandplains, spits, and barrier islands. Our study consisted of three scales of analysis: (1) the entire beach-ridge system; (2) beach-ridge sets; and (3) individual beach ridges. Several beach-ridge systems having formed in different types of coastal settings are compared by their present characteristics. Geomorphic data generated from processing and interpreting satellite images combined with previous studies are used to quantify multi-scale attributes of beach-ridge systems. These attributes include the area, length, width, number of sets, number of ridges per set, set rotation, ridge spacing, and ridge elevation. Our findings demonstrate that significant differences define beach-ridge systems including deltaic strandplains, large non-deltaic strandplains, small non-deltaic strandplains, large spits (cuspate forelands), small spits (flying spits, bay-mouth spits and tombolos) and barrier islands. A more comprehensive characterization of the factors controlling beach-ridge variability will improve our ability to recognize the sedimentary record of ancient of these systems. The proposed basic platform can be used to isolated different beach-ridge types and systems to facilitate future process and morphodynamic studies.  相似文献   

Book Review: Resource and Environmental Management by Bruce Mitchell,Addison Wesley Longman,Harlow 1997. No. of pages: xvii+298. Price: £18.99 (pb). ISBN 0-582 23796-3.     

Duncan McGregor 《地球表面变化过程与地形》1998,23(2):193-194

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Sedimentology,stratigraphy and architecture of the Nicobar Fan (Bengal–Nicobar Fan System), Indian Ocean: Results from International Ocean Discovery Program Expedition 362     

Kevin T. Pickering  Hugo Pouderoux  Lisa C. McNeill  Jan Backman  Farid Chemale  Steffen Kutterolf  Kitty L. Milliken  Hideki Mukoyoshi  Timothy J. Henstock  Duncan E. Stevens  Charlie Parnell  Brandon Dugan 《Sedimentology》2020,67(5):2248-2281

Drill sites in the southern Bay of Bengal at 3°N 91°E (International Ocean Discovery Program Expedition 362) have sampled for the first time a complete section of the Nicobar Fan and below to the oceanic crust. This generally overlooked part of the Bengal–Nicobar Fan System may provide new insights into uplift and denudation rates of the Himalayas and Tibetan Plateau. The Nicobar Fan comprises sediment gravity-flow deposits, mostly turbidites, that alternate with hemipelagite drapes and pelagite intervals of varying thicknesses. The decimetre-thick to metre-thick oldest pre-fan sediments (limestones/chalks) dated at 69 Ma are overlain by volcanic material and slowly accumulated pelagites (0.5 g cm⁻² kyr⁻¹). At Expedition 362 Site U1480, terrigenous input began in the early Miocene at ca 22.5 Ma as muds, overlain by very thin-bedded and thin-bedded muddy turbidites at ca 19.5 Ma. From 9.5 Ma, sand content and sediment supply sharply increase (from 1–5 to 10–50 g cm⁻² kyr⁻¹). Despite the abundant normal faulting in the Nicobar Fan compared with the Bengal Fan, it offers a better-preserved and more homogeneous sedimentary record with fewer unconformities. The persistent connection between the two fans ceased at 0.28 Ma when the Nicobar Fan became inactive. The Nicobar Fan is a major sink for Himalaya-derived material. This study presents integrated results of International Ocean Discovery Program Expedition 362 with older Deep Sea Drilling Project/Ocean Drilling Program/International Ocean Discovery Program sites that show that the Bengal–Nicobar Fan System experienced successive large-scale avulsion processes that switched sediment supply between the Bengal Fan (middle Miocene and late Pleistocene) and the Nicobar Fan (late Miocene to early Pleistocene). A quantitative analysis of the submarine channels of the Nicobar Fan is also presented, including their stratigraphic frequency, showing that channel size/area and abundance peaked at ca 2 to 3 Ma, but with a distinct low at 3 to 7 Ma: the intervening stratigraphic [sub]unit was a time of reduced sediment accumulation rates.  相似文献   

Naming rights,place branding,and the tumultuous cultural landscapes of neoliberal urbanism     

Reuben Rose-Redwood  Jani Vuolteenaho  Craig Young  Duncan Light 《Urban geography》2019,40(6):747-761

ABSTRACT

In recent decades, urban policymakers have increasingly embraced the selling of naming rights as a means of generating revenue to construct and maintain urban infrastructure. This practice of “toponymic commodification” first emerged with the commercialization of professional sports during the second half of the 20th century and has become an integral part of the policy toolkit of neoliberal urbanism more generally. As a result, the naming of everything from sports arenas to public transit stations has come to be viewed as a sponsorship opportunity, yet such naming rights initiatives have not gone uncontested. This special issue examines the political economy of urban place naming through a series of case studies that consider how the commodification of naming rights is transforming the cultural landscapes of contemporary cities. In this introductory article, we provide an overview of the geographies of toponymic commodification as an emerging research focus within the field of critical urban toponymies and propose several theoretical approaches that can enhance our understanding of the commodification of naming rights as an urban spatial practice. We then discuss the main contributions in this special issue and conclude by exploring potential directions for future research on the geographies of urban toponymic commodification.  相似文献   

Systematic variation in the apparent burning area of thermonuclear bursts and its implication for neutron star radius measurement     

Sudip Bhattacharyya  M. Coleman Miller  Duncan K. Galloway 《Monthly notices of the Royal Astronomical Society》2010,401(1):2-6

Precision measurements of neutron star radii can provide a powerful probe of the properties of cold matter beyond nuclear density. Beginning in the late 1970s, it was proposed that the radius could be obtained from the apparent or inferred emitting area during the decay portions of thermonuclear (type I) X-ray bursts. However, this apparent area is generally not constant, preventing a reliable measurement of the source radius. Here, we report for the first time a correlation between the variation of the inferred area and the burst properties, measured in a sample of almost 900 bursts from 43 sources. We found that the rate of change of the inferred area during decay is anticorrelated with the burst decay duration. A Spearman rank correlation test shows that this relation is significant at the  <10⁻⁴⁵  level for our entire sample, and at the  7 × 10⁻³⁷  level for the 625 bursts without photospheric radius expansion. This anticorrelation is also highly significant for individual sources exhibiting a wide range of burst durations, such as 4U 1636–536 and Aql X-1. We suggest that variations in the colour factor, which relates the colour temperature resulted from the scattering in the neutron star atmosphere to the effective temperature of the burning layer, may explain the correlation. This in turn implies significant variations in the composition of the atmosphere between bursts with long and short durations.  相似文献   

Formation of interstellar clouds: Parker instability with phase transitions     

Telemachos Ch. Mouschovias  Matthew W. Kunz  Duncan A. Christie 《Monthly notices of the Royal Astronomical Society》2009,397(1):14-23

We numerically follow the nonlinear evolution of the Parker instability in the presence of phase transitions from a warm to a cold H  i interstellar medium in two spatial dimensions. The nonlinear evolution of the system favours modes that allow the magnetic field lines to cross the galactic plane. Cold H  i clouds form with typical masses  ≃10⁵ M_⊙  , mean densities  ≃20 cm⁻³  , mean magnetic-field strengths  ≃4.3 μG  (rms field strengths  ≃6.4 μG  ), mass-to-flux ratios  ≃0.1–0.3  relative to critical, temperatures  ≃50 K  , (two-dimensional) turbulent velocity dispersions  ≃1.6 km s⁻¹  and separations  ≃500 pc  , in agreement with observations. The maximum density and magnetic-field strength are  ≃10³ cm⁻³  and  ≃20 μG  , respectively. Approximately 60 per cent of all H  i mass is in the warm neutral medium. The cold neutral medium is arranged into sheet-like structures both perpendicular and parallel to the galactic plane, but it is also found almost everywhere in the galactic plane, with the density being highest in valleys of the magnetic field lines. 'Cloudlets' also form whose physical properties are in quantitative agreement with those observed for such objects by Heiles. The nonlinear phase of the evolution takes ≲30 Myr, so that, if the instability is triggered by a nonlinear perturbation such as a spiral density shock wave, interstellar clouds can form within a time suggested by observations.  相似文献