基于激发极化弛豫时间谱的浸染型海底多金属硫化物岩石物性评价方法

海底多金属硫化物主要分布于洋中脊,是极具潜力的新型战略资源,其中以浸染型最难识别,探索有效的勘探评价方法必要且紧迫.弛豫时间谱起源于石油勘探中的激发极化测井,在金属矿尤其是海底多金属硫化物中的研究明显不足.本文将本征半导体极化理论引入原本以薄膜极化理论为基础的传统弛豫时间谱中,提出了一种评价浸染型海底多金属硫化物岩石物性尤其是激发极化特性的新方法,并通过理论和岩石物理实验数据的分析对比来验证方法的有效性.结果表明,该方法能有效评价浸染型海底多金属硫化物岩石的激发极化特性,包括对岩石弛豫时间常数、极化率等常规物性的评价,以及岩石中不同极化源的识别,此外还可以确定岩石中金属硫化物的含量和粒径;根据岩石物理实验结果,将海底多金属硫化物岩石的弛豫时间谱分为四种典型类型,能够反映多种分布形态的金属硫化物共存时岩石的激发极化特性;断电延时是影响激发极化特性评价的重要因素,稍大的断电延时就会导致浸染型金属硫化物的激发极化效应被大幅低估.该方法对海底多金属硫化物的激发极化测井解释具有指导作用.

     

Simple method for combined studies of macroseismic intensities and focal mechanisms

A simple method is presented for the computation of theoretical models of the macroseismic field, approximately valid close to the epicentre of a weak crustal earthquake. It is assumed that the intensity is logarithmically proportional to the energy flux of a complete directS wave. A circular source is used, whose energy-flux directivity is weak and thus simply predictable. The focal mechanism influences the solution through standard far-field double-couple radiation patterns. For the wave propagation in the layered crust the ray method is used, and a simple absorption correction is applied. Conversion coefficients at the earth's surface are included. To speed up repeated computations of the theoretical macroseismic fields for varying focal mechanisms, the ray quantities are computed (and stored) separately. This makes the program fast and simple enough even for routine applications on small microcomputers, whenever observed macroseismic fields, focal mechanisms, and hypocentre locations need joint interpretation.     

Depth of detection of highly conducting and volume polarizable targets using induced polarization

We define the apparent frequency effect in induced polarization (IP) as the relative difference between apparent resistivities measured using DC excitation on the one hand and high‐frequency excitation (when the IP effect vanishes) on the other. Assuming a given threshold for the minimum detectable anomaly in the apparent frequency effect, the depth of detection of a target by IP can be defined as that depth below which the target response is lower than the threshold for a given electrode array. Physical modelling shows that for the various arrays, the depth of detection of a highly conducting and volume polarizable target agrees closely with the depth of detection of an infinitely conducting and non‐polarized body of the same shape and size. The greatest depth of detection is obtained with a two‐electrode array, followed by a three‐electrode array, while the smallest depth of detection is obtained with a Wenner array when the array spread is in‐line (i.e. perpendicular to the strike direction). The depth of detection with a Wenner array improves considerably and is almost equal to that of a two‐electrode array when the array spread is broadside (i.e. along the strike direction).     

Coefficients of volume recombination and some derived characteristics of air ions

Summary General formulas derived for the recombination and combination coefficients of charged and uncharged aerosol particles can be adapted for calculation of the recombination coefficient of small air ions by using an appropriate correction term in the exponential function and by introducingThomson's factor of enhancement of the capturing cross-section due to the central electrical forces acting between the oppositely charged ions.By using this corrected formula for the recombination coefficient, some characteristics of the ions to be recombined can be calculated when values of the recombination coefficients measured in dependence on the pressure are applied.     

Temperature-driven fluid flow in porous media using a mixed finite element method and a finite volume method

We present a numerical scheme for the computation of conservative fluid velocity, pressure and temperature fields in a porous medium. For the velocity and pressure we use the primal–dual mixed finite element method of Trujillo and Thomas while for the temperature we use a cell-centered finite volume method. The motivation for this choice of discretization is to compute accurate conservative quantities. Since the variant of the mixed finite element method we use is not commonly used, the numerical schemes are presented in detail. We sketch the computational details and present numerical experiments that justify the accuracy predicted by the theory.     

一种前兆异常预报效能的检验方法

给出了一种地震前兆预报效能的检验方法,以北京板桥水位观测资料为例,通过与随机异常和以一定时间间隔周期出现的均匀异常的预报效能进行对比,对其异常的预报效能进行了系统检验。 结果表明,北京板桥水位观测5日均值,通过维纳滤波后的残差值高于1倍均方差异常,对张北—唐山一带中等以上地震具有一定预报效能。以异常出现后80天的时宽做预报,此时 R 值可达0.43,可信度为70％以上。这一方法可用于对其他前兆观测台站或单测项预报效能的检验。     

Optimization of a precise integration method for seismic modeling based on graphic processing unit

General purpose graphic processing unit(GPU) calculation technology is gradually widely used in various fields.Its mode of single instruction,multiple threads is capable of seismic numerical simulation which has a huge quantity of data and calculation steps.In this study,we introduce a GPU-based parallel calculation method of a precise integration method(PIM) for seismic forward modeling.Compared with CPU single-core calculation,GPU parallel calculating perfectly keeps the features of PIM,which has small bandwidth,high accuracy and capability of modeling complex substructures,and GPU calculation brings high computational efficiency,which means that high-performing GPU parallel calculation can make seismic forward modeling closer to real seismic records.     

水库渗漏通道的伪随机流场法与双频激电法综合探查

正确快速的探测水库堤坝渗漏在保证防洪工程安全上具有重要意义,而查明渗漏入口和渗漏途径又是难点中的重点,本文简述了伪随机流场法的基本原理,重点探讨了当水库坝体中存在诸多金属管,且渗漏水为承压水形式时,传统流场法难以解决实际问题时,作者首先采用流场法对水库大坝进行电流场分布的检测后,再结合双频激电法,详细的分析和对比检测的数据,从得到的探测曲线分析表明,通过流场法与双频激电法的结合,极大地提高了流场法区分金属管和地层渗漏通道的能力,为以后的相关工程应用提供了很好的范例.     

A method for rapid evaluation of magnetic anomalies over thin sheets

A method for rapid evaluation of magnetic anomalies over thin sheets is presented. This method is based on characteristic distancesX _3/4,X _1/2,X _1/4 at which the anomaly falls off to 3/4, 1/2, and 1/4 of the total (peak to peak) amplitude, respectively. Simple mathematical relations using these characteristic distances are presented to estimate the death and dip of the sheet. This method is fast and does not require prior knowledge of the base level and the origin. A few field examples are included to show the applicability and efficacy of the method.     

Resistivity and induced polarization response of a thin sheet

The relevant potential theory is given for a current point source in the presence of a conductive slab embedded in a homogeneous host region of infinite extent. The thin sheet representation is obtained from the exact integral formulation by a simple mathematical limit process. The same result is also deduced directly at the outset by applying a thin sheet boundary condition. The apparent resistivity for a two electrode array is then computed for the case where the bore hole intersects the thin sheet at right angles. The corresponding results for the dilution factor, relevant to the induced polarization response, are also obtained. It is shown that the apparent resistivity and the dilution factor are constant when the potential and the current electrode straddle the sheet but there is a characteristic decrease as the electrodes move away from the sheet.     

Wavelet packet polarization method for an automatic detection of P and S wave arrivals

A new method is proposed for detecting P and S wave arrivals in the problem of passive seismic monitoring. This method is based on the wavelet packet decomposition of three-component seismic traces, their automatic quality control, and the calculation of the principal components of the traces in overlapping packet frequency bands and in scale-dependent moving time windows. The wave arrivals times are estimated by means of a robust iterative procedure of adjusting hyperbolic traveltime curves to the initial estimates of arrival times determined from the maximum values of the multilevel measure of the nonstationarity of each trace. The method has been developed for applications in the cases of a large number of bad single-component traces and a high noise level. To illustrate its application, the method is applied to the data set of the Cotton Valley experiment on the seismic monitoring of hydraulic fractures in a fractured gas reservoir.     

An analytical method of analysing the oscillatory pressure head measured at any depth in a well casing

When a slug test is conducted in a highly permeable aquifer, a shallow pressure transducer in the well casing produces an oscillatory pressure head that is representative of the water level fluctuation, whereas a deep pressure transducer in the well casing yields an oscillatory pressure head that is different from the water level change. Although the solutions for shallow and deep pressure head are different, it is found that the ratios of the subsequent extremity displacements are in an identical relationship (an extremity can be a maximum or a minimum in the oscillatory pressure head). Based on this relationship, an analytical data analysis method for the determination of the hydraulic conductivity is developed for both shallow and deep pressure transducer data. This analytical method is applied to the pressure head measured at different depths in the well casing of a well partially penetrating an unconfined coarse sand aquifer. Satisfactory results are obtained, validating the applicability of this analytical method for pressure transducer data at any depth in a well casing. Copyright © 2007 John Wiley & Sons, Ltd.     

Quantifying felt events: A joint analysis of intensities, accelerations and dominant frequencies

Recent seismic events for which macroseismic intensities and accelerometric records are simultaneously available are investigated in order to derive empirical relationships between intensities and ground accelerations. 20 events with local magnitudes 3.0 to 5.4 are selected in a single country (France), in order to have homogeneous intensity data. Records are obtained in about 50 stations. Relationships are first established between intensities, magnitudes and distances on one side, between S-wave horizontal peak ground accelerations (PGA), magnitudes and distances R on the other side. They show that the PGA decays with distance roughly as R ⁻², in agreement with previous studies, and that PGA and intensities lead to different attenuation models. An intensity-acceleration relationship is established from direct observations, and from a combination of the previous relationships. It reveals that the intensity felt depends not only on the PGAs, but also on the distance. This may be explained by the frequency dependent attenuation of the waves, and by a different sensitivity of humans to the different frequencies. The influence of frequency on the felt intensity is then investigated, and a relation between intensity, PGA and frequency is established. It shows that the acceleration needed to be felt with a given intensity is larger at high frequency than at low frequency.Finally, as sound also contributes to earthquake perception, the P-wave displacement is analysed in an attempt to find in which conditions a perceptible sound is generated. The perturbation in air pressure induced by the P-wave is compared to the threshold of hearing in two frequency ranges, 20–40 Hz and 40–60 Hz. The maximum distance of perceptibility as a function of magnitude deduced from the P-wave displacement alone is found to be below the experimental distances of perception reported in the macroseismic enquiries.