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451.
本文研究了可微算子C_o-半群T(t)的n阶微分算子T~(n)(t)的谱性质,讨论了T~(n)(t)的谱点与T(t)的谱点的关系,给出了T~(n)(t)的谱集的一种构造。 相似文献
452.
PRELIMINARY STUDY ON THE CONDUCTIVITY STRUCTURE OF THE CRUST AND UPPER MANTLE: THIRD REPORT ON THE GEOSCIENCE TRANSECT FROM XIANGSHUI, JIANGSU, TO MANDAL, NEI MONGOL 下载免费PDF全文
The features of deep conductivity structure along Xiangshui-Mandal Geoscience Transect are described in this paper basing on newly obtained magnetotelluric data. Large resistivity contrasts can be found on both borders of North China platform. The depth of the crustal high conductivity layer changes abruptly from 21 km to 34 km beneath Nei Mongol fold system on the northwestern end of the transect. While it is absent beneath Subei-Jiaonan terrane on the southeastern end of the transect 相似文献
453.
Bernard Chouet 《Pure and Applied Geophysics》1990,132(1-2):289-310
A simple model of single acoustic scattering is used to study the dependence of the shape of local earthquake coda on the anelastic and scattering structures of the lithosphere. The model is applied to the coda of earthquakes located near Stone Canyon, central California, and provides an explanation for the features observed in the data, which include an interesting temporal variation in the coda shape. A surficial layer with aQ of 50 and thickness of 10 or 25 km underlain by a zone with aQ of 1000 extending to the bottom of the lithosphere, together with a scattering scale length,a, that varies with depthz according to the relationa=0.3 exp[-(z/45)2] are found to constitute the simplest structure of the medium compatible with the coda data and with body and surface wave attenuation data. The profile of heterogeneity sizes implies that the scattering strength increases strongly with depth, a constraint required by the necessity to boost the energy of the later coda without forcing the intrinsicQ to be excessively high in the uppermost mantle. This constraint is viewed as an artifact of the single scattering model which overstimates the scattering coefficient due to the neglect of multiple scattering. The observed temporal variation of the signal is difficult to explain by a simple change of the intrinsicQ at some depth. Rather, it is suggested that the scattering properties at depth changed with time through a variation of the fractional rms velocity fluctuation on the order of one percent. 相似文献
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455.
下切古河谷高分辨率层序地层学研究的进展 总被引:18,自引:1,他引:18
基面抬升、溯源堆积、依次退积叠置是下游河段古河谷厚层连续沉积产生的关键。基于此点,对现有古河谷沉积模式和高分辨率层序地层学研究的若干问题作了讨论。 相似文献
456.
"羊里磁异常"自1967年发现以来,由于所处地质环境为矽卡岩型铁矿成矿有利地段,且紧邻已知的温石埠铁矿,以及"羊里磁异常"规模较大且具备低缓磁异常的特点,一直受到地质界的广泛关注,地勘单位在该区做了大量的铁矿找矿工作,但对"羊里磁异常"勘查中一直未取得突破性进展,该文从高精度重磁角度对"羊里磁异常"进行了定量解释以及定量计算,并通过钻探验证等技术手段,进一步推断"羊里磁异常"是由古近纪含磁铁碎屑的砂砾岩以及闪长岩共同引起的,对该异常的认识更进了一步。 相似文献
457.
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459.
准噶尔盆地吉木萨尔凹陷芦草沟组为一套优质陆相烃源岩, 是我国当前页岩油气研究的热点地区之一.基于吉木萨尔凹陷18口井芦草沟组约为580 m岩心观察、薄片观察、地球化学测试等数据, 对芦草沟组烃源岩岩石类型、地球化学特征等方面开展了研究与评价, 结果表明: 1)芦草沟组烃源岩整体上为优质烃源岩, 且以Ⅰ-Ⅱ型有机质类型为主, 处于低熟至成熟阶段; 2)烃源岩主要划分为5种类型, 包括纯页岩、白云质页岩、纯泥岩, 白云质泥岩和粉砂质泥岩, 其有机质类型和丰度存在一定差异.综合研究得出, 吉木萨尔凹陷芦草沟组优质有效烃源岩的有机质丰度下限值为2.0%, 并认为TOC≥2.0%的烃源岩段也是该区页岩油发育的有利层段. 相似文献
460.
From river to shelf,anatomy of a high‐frequency depositional sequence: The Late Pleistocene to Holocene Tiber depositional sequence 下载免费PDF全文
Salvatore Milli Marco Mancini Massimiliano Moscatelli Francesco Stigliano Mattia Marini Gian Paolo Cavinato 《Sedimentology》2016,63(7):1886-1928
The Late Pleistocene/Holocene Tiber delta succession represents the most recent and one of the best preserved, high‐frequency/low‐rank depositional sequences developed along the Latium continental margin of the Italian peninsula. Several previous studies have established a robust data set from which it has been possible to describe the stratigraphic architecture of the entire Tiber depositional sequence from the landward to seaward sectors and over a distance of 60 km. The Tiber depositional sequence shows many characteristics found in other Late Pleistocene to Holocene deltaic and coastal successions of the Mediterranean area. The stratigraphic architecture of the Tiber depositional sequence is controlled mainly by glacioeustasy, although factors such as tectonic uplift, volcanism and subsidence, exert an influence at a local scale. The resulting depositional model allowed discussion of some important points such as: (1) the genesis of the Tiber mixed bedrock‐alluvial valley, extending from the coastal plain to the innermost portion of the shelf, recording (i) multiple episodes of incision during relative sea‐level fall, and (ii) a downstream increase of depth and width of the valley during the base‐level fall and the subsequent base‐level rise; (2) the different physical expression of the Tiber depositional sequence boundary from landward to seaward, and its diachronous and composite character; (3) the maximum depth reached by the Tiber early lowstand delta at the end of the sea‐level fall is estimated at ca 90 m below the present sea‐level and not at 120 m as suggested by previous works; (4) the backward position of the Tiber late lowstand delta relative to the deposit of early lowstand; (5) the change of the channel pattern and of the stacking pattern of fluvial deposits within the Lowstand Systems Tract, Transgressive Systems Tract and Highstand Systems Tract. All of these features indicate that the Late Pleistocene/Holocene Tiber delta succession, even if deposited in a short period of time from a geological point of view, represents the result of the close interaction among many autogenic and allogenic factors. However, global eustatic variations and sediment supply under the control of climatic changes can be considered the main factors responsible for the stratigraphic architecture of this sedimentary succession, which has been heavily modified by human activity only in the last 3000 years. 相似文献