复杂条件下薄煤层弱反射波的精细处理与分析     

王树敏  黄蓉  姚磊 《安徽地质》2009,19(4):264-267

通过对淮北某矿区利用三维地震勘探技术开展深部薄煤层细微构造的分析研究,找到了在复杂地质条件下,如何处理资料以提高薄煤层弱反射波的信噪比和分辨率的方法,从而对主采煤层下部薄煤层的构造形态做出精细解释。  相似文献   

Interpretation of ambiguous reflection data by imaging processes: An example profile crossing steep submarine valley at the sea bottom     

Zakir Kanbur   《Journal of Asian Earth Sciences》2009,35(6):516-523

The determination of the geometry of a vertical structure is one of the most important problems in the conventional stacking process used as an imaging process. The horizontal layers in depths of the earth are easily displayed in the seismic time section, but the dipping and folded layers are not correctly displayed in the reflection data. The present study addresses the same problem for the data collected from a profile of a steep marine valley and that of an offshore extension of the Ganos fault at the westernmost part of the Tekirdağ basin, Marmara Sea, NW Turkey. In the previous studies, the fault was interpreted as a low-angle reverse fault juxtaposing between the Plio-Quaternary and the Miocene strata in the time migration section. However, the results of the extensive analyses in this study show that the close position of a newly interpreted Miocene anticline to the synformal structure of the sea bottom makes the data ambiguous, whereas the subvertical fault and the other events coming away from the fault plane causes complexity. To eliminate misinterpretation due to ambiguity and complexity as in the previous analysis, the data are reinterpreted by pre-stack Kirchhoff depth migration in addition to the conventional stacking process. The new interpretation is checked through the synthetics data created from the model having appropriate parameters of the data used. The results have shown the existence of an anticline that is cored by the Miocene strata and overlain by the Plio-Quaternary strata 200 m below the sea bottom. The Ganos fault is imaged as disturbing all the layers down the way and as having a listric geometry and steeper dip angle (75° N) at shallow depths but decreasing downward. This study examples the importance of considering the problems of the complex geometry and choosing appropriate imaging technique for analyzing seismic reflection data collected over an area with known vertical fault and related tectonic complexity.  相似文献   

Experimental and numerical investigations on zigzag porous screen breakwater     

J. S. Mani 《Natural Hazards》2009,49(2):401-409

Pile supported porous breakwaters are commonly adopted for shielding small-scale harbors, such as marinas, fishing harbors, and recreational harbors from external waves. To improve efficiency of such breakwaters, attempts have been made to provide a filter screen containing porous material. Possible alternative to the existing pile supported screen breakwaters is the zigzag breakwater. This article details on the numerical and experimental investigations carried out on the performance of zigzag porous screen breakwater. Results related to the wave amplification in front of the structure, wave reflection, and transmission, forces exerted by the waves on the structure are discussed. The studies clearly indicate that the transmission coefficient of the order of 0.5 can be achieved for H _i/gT ² > 0.008 for 50% submergence, whereas the reflection coefficient can be effectively reduced to 0.2. Reduction in wave force is of the order of 50% which is primarily due to reduction in reflection coefficient. Substantial reduction in wave force contributes directly to reduction in the cost of construction of the breakwater, a definite advantage over other similar breakwaters.  相似文献   

On the distance to the Ophiuchus star‐forming region     

E.E. Mamajek 《Astronomische Nachrichten》2008,329(1):10-14

The Ophiuchus molecular cloud complex has produced in Lynds 1688 the richest known embedded cluster within ∼300 pc of the Sun. Unfortunately, distance estimates to the Oph complex vary by nearly ∼40% (∼120–165 pc). Here I calculate a new independent distance estimate of 135±8 pc to this benchmark star‐forming region based on Hipparcos trigonometric parallaxes to stars illuminating reflection nebulosity in close proximity to Lynds 1688. Combining this value with recent distance estimates from reddening studies suggests a consensus distance of 139±6 pc (4% error), situating it within ∼11 pc of the centroid of the ∼5 Myr old Upper Sco OB subgroup of Sco OB2 (145 pc). The velocity vectors for Oph and Upper Sco are statistically indistinguishable within ∼1 km s^–1 in each vector component. Both Oph and Upper Sco have negligible motion (<1 km s^–1) in the Galactic vertical direction with respect to the Local Standard of Rest, which is inconsistent with the young stellar groups having formed via the high velocity cloud impact scenario. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

盆地构造地震地面运动速度和加速度分布特征的数值模拟   总被引：9，自引：1，他引：8       下载免费PDF全文

赵志新  徐纪人 《地球物理学报》2005,48(5):1085-1091

本文用错格实数傅里叶变换的拟谱法的数值模拟方法分析了地震波在冲积扇、盆地等不均匀地震构造体区域的传播过程和地面运动分布. 结果表明, 地震波由岩石区进入盆地结构后,在盆地内上下多次反射振荡,对地面建筑物可能形成多次连续的振动和破坏,仅有极少量地震波能量返回岩石区域中,这是防灾研究中值得注意的地面运动特征;地震波在盆地边界地质构造条件下,形成的地震波体波与次生面波动的叠加干涉形成了大振幅的地面运动,它可能导致建筑物的极大破坏;破坏峰值的空间位置可能远离岩石和盆地沉积层的边界或者地震断层的位置.  相似文献   

天然气水合物--石油天然气的未来替代能源   总被引：4，自引：0，他引：4  

姚伯初  吴能友 《地学前缘》2005,12(1):225-233

天然气水合物是甲烷等天然气在高压、低温条件下形成的冰状固体物质。据估算,全球天然气水合物中碳的含量等于石油、煤等化石能源中碳含量的两倍,这是一个非常诱人的数字。在人类面临化石能源即将枯竭的时候,科学家和各国政府都把眼光投向这一未来能替代化石能源的新能源。南海在新生代构造演化历史、沉积条件、沉积环境等方面都显示这里具有生成和蕴藏巨大天然气水合物资源的条件,因此,这里可能成为中国在不远的将来之新能源基地。  相似文献   

利用宽角反射/折射和深反射探测剖面揭示三河-平谷大震区深部结构特征   总被引：16，自引：5，他引：11       下载免费PDF全文

赵金仁  张先康  张成科  张建狮  杨卓欣  刘宝峰  刘保金  赵成斌 《地球物理学报》2004,47(4):646-653

利用三河—平谷8.0级大震区实施的深地震反射剖面与宽角反射剖面探测方法获得的结果进行了综合研究和解释. 结果表明：两种探测方法给出的地壳基本分层是一致的,在三河—平谷大震区上地壳的埋深为21～23km,莫霍界面的深度为36～37km;该地区基底结构起伏变化较大,浅部断裂发育,在确定的数条断裂构造带中夏垫断裂是一条特征明显、深浅共存的断裂构造带;震源区周围差异明显的速度异常结构和特殊而复杂的地质构造环境意味着这些部位是发生大地震的有利部位;该地区莫霍界面起伏变化和较厚的反射叠层以及局部复杂的楔形反射带的存在等现象表明,该地区地壳结构发生过强烈的挤压、变形,同时也反映出岩浆活动对下地壳结构进行了物质的和结构的强烈改造,从而构成了该地区复杂的地壳深部结构,可将其视为三河—平谷8.0级大地震孕育和发生的深部要素.  相似文献   

High-resolution seismic characterization of the gas and gas hydrate system at Green Canyon 955, Gulf of Mexico,USA     

《Marine and Petroleum Geology》2017

The Pliocene and Pleistocene sediments at lease block Green Canyon 955 (GC955) in the Gulf of Mexico include sand-rich strata with high saturations of gas hydrate; these gas hydrate accumulations and the associated geology have been characterized over the past decade using conventional industry three-dimensional (3D) seismic data and dedicated logging-while-drilling (LWD) borehole data. To improve structural and stratigraphic characterization and to address questions of gas flow and reservoir properties, in 2013 the U.S. Geological Survey acquired high-resolution two-dimensional (2D) seismic data at GC955. Combined analysis of all available data improves our understanding of the geological evolution of the study area, which includes basin-scale migration of the Mississippi River sediment influx as well as local-scale shifting of sedimentary channels at GC955 in response to salt-driven uplift, structural deformation associated with the salt uplift, and upward gas migration from deeper sediments that charges the main gas hydrate reservoir and shallower strata. The 2D data confirm that the sand-rich reservoir is composed principally of sediments deposited in a proximal levee setting and that episodes of channel scour, interspersed with levee deposition, have resulted in an assemblage of many individual proximal levee deposit “pods” each with horizontal extent up to several hundred meters. Joint analysis of the 2D and 3D data reveals new detail of a complex fault network that controls the fluid-flow system; large east-west trending normal faults allow fluid flow through the reservoir-sealing fine-grained unit, and smaller north-south oriented faults provide focused fluid-flow pathways (chimneys) through the shallower sediments. This system has enabled the flow of gas from the main reservoir to the seafloor throughout the recent history at GC955, and its intricacies help explain the distributed occurrences of gas hydrate in the intervening strata.  相似文献   

Identification and characterization of fluid escape structures (pockmarks) in the Estremadura Spur,West Iberian Margin     

《Marine and Petroleum Geology》2017

Located on the West Iberian margin, between Cabo Carvoeiro and Cabo da Roca, the Estremadura Spur is a trapezoidal promontory elongated in an east-west direction, extending until the Tore seamount. Recently a field with more than 70 pockmarks was discovered in the NW region of the Estremadura Spur outer shelf (Lourinhã Monocline). Pockmarks are the seabed culminations of fluid migration through the sedimentary column and their characteristic seabed morphologies correspond to cone-shaped circular or elliptical depressions. The characterization of these features and the understanding of the associated fluid escape process are the main objectives of this work. Here we characterize these structures to understand their structural and stratigraphic control based on: 1) Seismic processing and interpretation of the high resolution 2D single-channel sparker seismic dataset, 2) Bathymetric and Backscatter interpretation and 3) ROV direct observation of the seafloor.The analysis of the seismic profiles allowed the identification of six seismic units, disturbed by the migration and accumulation of fluids. The Estremadura Spur outer shelf has been affected by several episodes of fluid migration and fluid escape during the Pliocene-Quaternary that are expressed by a vast number of seabed and buried pockmarks. At present, the pockmarks are mainly inactive, as the seabed pockmarks are covered by recent sediments. It is concluded that the migration of fluids to the seabed occurred over the Pliocene-Quaternary, as indicated by the buried pockmarks at different depths below the seabed. The vertical stacking of various pockmarks suggests a cyclical fluid flow activity that can possibly be the result of the eustatic sea level variations and the subsequent changes of the hydrostatic pressure.  相似文献   

Northern Hemisphere Stratospheric Polar Vortex Extremes in February under the Control of Downward Wave Flux in the Lower Stratosphere          下载免费PDF全文

《大气和海洋科学快报》2012,(3):183-188

Using ECWMF ERA-40 and Interim reanalysis data, the planetary wave fluxes associated with the February extreme stratospheric polar vortex were studied. Using the three-dimensional Eliassen-Palm (EP) flux as a measure of the wave activity propagation, the authors show that the unusual warm years in the Arctic feature an anomalous weak stratosphere-troposphere coupling and weak downward wave flux at the lower stratosphere, especially over the North America and North Atlantic (NANA) region. The extremely cold years are characterized by strong stratosphere-troposphere coupling and strong downward wave flux in this region. The refractive index is used to examine the conception of planetary wave reflection, which shows a large refractive index (low reflection) for the extremely warm years and a small refractive index (high reflection) for the extremely cold years. This study reveals the importance of the downward planetary wave propagation from the stratosphere to the troposphere for explaining the unusual state of the stratospheric polar vortex in February.  相似文献