Analytical wavefront curvature correction to plane‐wave reflection coefficients for a weak‐contrast interface

Most amplitude versus offset (AVO) analysis and inversion techniques are based on the Zoeppritz equations for plane‐wave reflection coefficients or their approximations. Real seismic surveys use localized sources that produce spherical waves, rather than plane waves. In the far‐field, the AVO response for a spherical wave reflected from a plane interface can be well approximated by a plane‐wave response. However this approximation breaks down in the vicinity of the critical angle. Conventional AVO analysis ignores this problem and always utilizes the plane‐wave response. This approach is sufficiently accurate as long as the angles of incidence are much smaller than the critical angle. Such moderate angles are more than sufficient for the standard estimation of the AVO intercept and gradient. However, when independent estimation of the formation density is required, it may be important to use large incidence angles close to the critical angle, where spherical wave effects become important. For the amplitude of a spherical wave reflected from a plane fluid‐fluid interface, an analytical approximation is known, which provides a correction to the plane‐wave reflection coefficients for all angles. For the amplitude of a spherical wave reflected from a solid/solid interface, we propose a formula that combines this analytical approximation with the linearized plane‐wave AVO equation. The proposed approximation shows reasonable agreement with numerical simulations for a range of frequencies. Using this solution, we constructed a two‐layer three‐parameter least‐squares inversion algorithm. Application of this algorithm to synthetic data for a single plane interface shows an improvement compared to the use of plane‐wave reflection coefficients.     

Wave interaction with a wave absorbing double curtain-wall breakwater

This study examines the hydrodynamic performance of a wave absorbing double curtain-wall breakwater. The breakwater consists of a seaward perforated wall and a shoreward impermeable wall. Both walls extend from above the seawater to some distance above the seabed. Then the below gap allows the seawater exchange, the sediment transport and the fish passage. By means of the eigenfunction expansion method and a least square approach, a linear analytical solution is developed for the interaction of water waves with the breakwater. Then the reflection coefficient, the transmission coefficient and the wave forces acting on the walls are calculated. The numerical results obtained for limiting cases agree very well with previous predictions for a single partially immersed impermeable wall, the double partially immersed impermeable walls and the bottom-standing Jarlan-type breakwater. The predicted reflection coefficients for the present breakwater also agree reasonable with previous experimental results. Numerical results show that with appropriate structure parameters, the reflection and transmission coefficients of the breakwater may be both below 0.5 at a wide range of the relative water depth. At the same time, the magnitude of wave force acting on each wall is small. This is significant for practical engineering.     

Application of Spectral Angle Mapper Classification to Discriminate Hydrothermal Alteration in Southwest Birjand,Iran, Using Advanced Spaceborne Thermal Emission and Reflection Radiometer Image Processing

The purpose of this study is to evaluate the Spectral Angle Mapper (SAM) classification method for determining the optimum threshold (maximum spectral angle) to unveil the hydrothermal mineral assemblages related to mineral deposits. The study area indicates good potential for Cu-Au porphyry, epithermal gold deposits and hydrothermal alteration well developed in arid and semiarid climates, which makes this region significant for Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image processing analysis. Given that achieving an acceptable mineral mapping requires knowing the alteration patterns, petrochemistry and petrogenesis of the igneous rocks while considering the effect of weathering, overprinting of supergene alteration, overprinting of hypogene alteration and host rock spectral mixing, SAM classification was implemented for argillic, sericitic, propylitic, alunitization, silicification and iron oxide zones of six previously known mineral deposits: Maherabad, a Cu-Au porphyry system; Sheikhabad, an upper part of Cu-Au porphyry system; Khoonik, an Intrusion related Au system; Barmazid, a low sulfidation epithermal system; Khopik, a Cu-Au porphyry system; and Hanish, an epithermal Au system. Thus, the investigation showed that although the whole alteration zones are affected by mixing, it is also possible to produce a favorable hydrothermal mineral map by such complementary data as petrology, petrochemistry and alteration patterns.     

倾角分解共反射面元叠加方法

共反射面元（Common Reflection Surface）叠加是一种独立于宏观速度模型的零偏移距剖面成像方法,传统的CRS叠加实现是以数据驱动的方式对属性参数进行自动搜索并对其进行优化合成相应的CRS叠加算子,通过该算子进行叠加能够得到信噪比和连续性更高的零偏移距剖面.但是数据驱动的实现方式带来了不可避免的“倾角歧视现象”,它造成了弱有效反射信号损失和运动学特征失真的问题.本文提出的倾角分解CRS叠加方法成功解决了上述问题,使CRS叠加方法更具实用价值.     

GPR reflection characteristics and depositional models of mud volcanic sediments—Wushanting mud volcano field, southwestern Taiwan

Ground penetrating radar (GPR) survey was conducted in the Wushanting mud volcano field (Yanchao, Kaohsiung) using a 500 MHz antennae, which allowed high-resolution imaging of subsurface structures. Seven GPR reflection characteristics are recognized. Sigmoid GPR reflection patterns resulted from a recent mud lobe deposited above an underlying older mud lobe front. Contorted GPR facies resulted from recent mud flow which encountered obstacles. Subparallel reflections resulted from mud volcano deposits of limited flowability, low velocity and gentle gradient. Hummocky reflection patterns are formed by interfingering of recent mud lobes building onto low land. Disrupted GPR facies were due to lateral breaks of continuity from mud cracks, which, according to field observation, can provide channels for erosion and form deeper erosion gullies. GPR time slices of different depths are rendered as a three-dimensional model. Approximately orbicular GPR reflection characteristics can indicate arcuate stacked mud lobe fronts of different periods. Some depositional models to explain GPR reflection characteristics can be founded upon observations of recent sedimentary phenomena. The models of this study may be applied to paleoenvironments and the depositional evolution of mud volcanoes in similar geological settings.     

A non-reflecting boundary condition for the finite element modeling of infinite reservoir with layered sediment

The design of seismic resistant concrete gravity dam necessitates accurate determination of hydrodynamic pressure developed in the adjacent reservoir. The hydrodynamic pressure developed on structure is dependent on the physical characteristics of the boundaries surrounding the reservoir including reservoir bottom. The sedimentary material in the reservoir bottom absorbs energy at the bottom, which will affect the hydrodynamic pressure at the upstream face of the dam. The fundamental parameter characterizing the effect of absorption of hydrodynamic pressure waves at the reservoir bottom due to sediment is the reflection coefficient. The wave reflection coefficient is determined from parameters based on sediment layer thickness, its material properties and excitation frequencies. An analytical or a closed-form solution cannot account for the arbitrary geometry of the dam or reservoir bed profile. This problem can be efficiently tackled with finite element technique. The need for an accurate truncation boundary is felt to reduce the computational domain of the unbounded reservoir system. An efficient truncation boundary condition (TBC) which accounts for the reservoir bottom effect is proposed for the finite element analysis of infinite reservoir. The results show the efficiency of the proposed truncation boundary condition.     

Effective sub-Zechstein salt imaging using low-frequency seismics — Results of the GRUNDY 2003 experiment across the Variscan front in the Polish Basin

The extent of the Variscan deformation front is one of the key problems of the regional geology of the Central European Permian Basin system, particularly in its Polish part. Conventional reflection seismics usually fails to produce a satisfactory image of the pre-Permian strata due to the shielding effect of Zechstein (Upper Permian) evaporites. Thus we used a novel seismic acquisition technique to study the base of the Permian complex and its Variscan basement. In the GRUNDY 2003 experiment we combined wide-angle reflection–refraction measurements with the near-vertical reflection seismics by the use of the constant geophone array with dense (100 m) receiver spacing occupying 50-km long profile. 3D design of the experiment, covering 50 × 10 km area, helped in eliminating the effect of out-of-plane propagations and local inhomogeneities. An effective integration of traveltime tomography, CDP reflection processing and prestack depth migration of wide-angle reflections applied to our data, allowed us to present the model in which we deduced the contact zone of the Variscan overthrust structure (Variscan front) with its molasse-filled foredeep. The latter might be a gas-generation zone, which is of a great importance for hydrocarbons prospecting in this area.     

深地震反射剖面数据子库

深地震反射剖面数据子库（简称SB1）,系国土资源部深部地球物理探测数据库下属子库之一。经过需求分析,数据标准格式设计,采用Microsoft Access97作为开发平台的深地震反射剖面数据子库,具备关系型数据库固有的一切功能。SB1由用户查询,维护管理和报表打印等3个子系统组成。SB1收录了1996年以前,即原地质矿产部和国土资源部地球物理工作者执行深部地质计划和前沿科技计划等专项计划获得的大量深地震反射剖面调查原始记录,处理成果与解释成果。经调研数据分布和保存状况,依照“深地震反射剖面数据入库技术规定”完成了深地震反射剖面数据收集,整理及登录。迄今为止,SB1共收录国土资源部深地震反射资料累计测线19条,剖面长度859km与入库原始记录数据量35.8GB;原始记录,数据处理等入库数据记录格式皆统一采用地震勘探专业通用的SEG－Y格式;并采用通用的刻录格式ISO9660共刻录数据光盘30张。SB1管理系统的库文件及其用户指南,管理员手册,系统盘说明等文档也已刻录成系统光盘,为数据共享以及其它应用提供了方便条件。     

东闯金矿自然金矿物学研究

东闯金矿自然金以其不依赖硫化物而存在的特殊产状、巨粒的形态有别于小秦岭其他金矿的自然金。本文在叙述成矿地质背景的基础上,着重论及了它的产状、化学成分、物理性质等特征;给出了自然金X射线衍射数据;提供了完整的自然金反射率色散曲线;计算了自然金的颜色指数并指出了它们与成色之间的关系;同时也对该矿区金在热液中搬运、沉淀方式作了探讨。     

对绿色会计几个问题的认识与思考

本文对绿色会计的概念与产生、确认和计量等几个问题，提出了自己的认识，并就我国实行绿色会计进行了思考。