Multiple scattering of seismic waves in fractured media: Velocity and effective attenuation of the coherent components ofP waves andS waves     

Ian Lerche  David Petroy 《Pure and Applied Geophysics》1986,124(6):975-1019

We show that the multiple scattering by small fractures of seismic waves with wavelengths long compared to the fracture size and fracture spacing is indistinguishable from multiple-scattering effects produced by regular porosity, except for an orientation factor due to fracture alignment. The fractures reduce theP-wave andS-wave velocities and produce an effective attenuation of the coherent component of the seismic waves. The attenuation corresponds to 1000/Q of about unity for a Gaussian spectrum of fractures, and it varies with frequencyf asf ³. For a Kolmogorov spectrum of fractures of spectral index the attenuation is an order of magnitude or so larger and varies with frequency asf ^3-v The precise degree of attenuation depends upon the matrix properties, the fracture porosity, the degree of fracture anisotropy, the type of fluid filling the fractures, and the incidence angle of the wave.For fracture porosities less than about 15% theP-wave andS-wave velocities are decreased by the order of 5–10% with a lesser dependence on the type of fluid filling the fractures (gas, oil, or brine) and with a dependence on both the degree of anisotropy and the incident angle made by the wave. The tendency of fractures to occur perpendicularly to bedding suggests that the best way to measure seismically fractured rock behavior in situ is by using the travel-time delay and reflection amplitude. As both the offset and the azimuth of receivers vary from a shot, the travel-time delay and reflection amplitude should both show an elliptical pattern of behavior—the travel-time delay in response to the varying seismic speed, and the reflection amplitude in response to angular variations in the multiple scattering. Observations of attenuation at several frequencies should permit (a) determination of the spectrum of fractures (Gaussian versus Kolmogorovian) and (b) determination of the contribution of viscous damping to the effective attenuation.  相似文献   

Stress　relaxation　and　attenuation　of　fluid－saturated　sandstone　at　low　frequency   总被引：3，自引：0，他引：3  

席道瑛  刘爱文  刘卫 《地震学报(英文版)》1995,8(4):585-591

Ｓｔｒｅｓｓｒｅｌａｘａｔｉｏｎａｎｄａｔｔｅｎｕａｔｉｏｎｏｆｆｌｕｉｄ－ｓａｔｕｒａｔｅｄｓａｎｄｓｔｏｎｅａｔｌｏｗｆｒｅｑｕｅｎｃｙＤａｏ－ＹｉｎｇＸＩ（席道瑛），Ａｉ－ＷｅｎＬＩＵ（刘爱文）ａｎｄＷｅｉＬＩＵ（刘卫）（Ｕｎｉｖｅｒｓｉｔｙｏ...  相似文献   

Coda waves: A review     

M. Herraiz  A. F. Espinosa 《Pure and Applied Geophysics》1987,125(4):499-577

The analysis and interpretation of coda waves have received increasing attention since the early seventies. In the past few years interest in this subject has spread worldwide, and the study of high-frequency seismic coda waves has become a very important seismological topic. As a conclusion of the studies accomplished in this time, coda waves are considered the result of scattering processes caused by heterogeneities acting on seismic waves.P andS waves play a particularly important role in this interaction. The process introduces an attenuation which, added to the intrinsic absorption, gives the observed apparent attenuation. Therefore, coda waves constitute a thumbprint left by the heterogeneities on the seismograms. Coda waves offer decisive information about the mechanism of how scattering and attenuation take place. This review describes coda waves in detail, and summarizes the work done in this subject to 1986. The relation between coda waves and attenuation in the context of research on seismic scattering problems is stressed. Particular attention has been given to the application of coda waves to estimate source and medium parameters. The state-of-the-art of the temporal variations of coda wave shape, and the possible use of these variations as an earthquake precursor also are presented. Care has been taken to introduce the statistical models used to deal with the heterogeneities responsible for scattering.  相似文献   

中小震近场地震动估计中地震动衰减关系的适用性分析   总被引：9，自引：1，他引：9  

李小军  阎秀杰  潘华 《地震工程与工程振动》2005,25(1):1-7

核工程场地设计基准地震动确定中涉及弥散地震的地震动估计，这导致中小震近场地震动估计成为被关注的研究课题。本文基于一些中小震近场地震动记录资料，分析和探讨了国内外多种地震动衰减关系对中小震近场地震动估计的适用性问题，并结合我国几个核工程地震问题研究工作的实践对中小震近场地震动衰减关系确定的思路和原则提出了建议。  相似文献   

安徽地区地震波衰减、场地响应及震源新参数的测定   总被引：5，自引：2，他引：5  

沈小七  刘杰  陈宇卫  刘东旺  黄显良  王行舟 《地震地磁观测与研究》2005,26(3):1-10

根据安徽数字地震台网7个地震台的143条波形资料,研究了安徽地区的衰减模型和各台站的场地响应。采用三段几何衰减模型拟合,得到了安徽及邻近地区的几何衰减函数,得到安徽地区非弹性衰减Q值随频率f的关系为Q(f)=235.3×f0.616;7个台站的场地响应均无明显的放大效应,这与它们均处于岩石地基相符;并在本地区地震预测研究中尝试使用新参数,进行了初步的应用。  相似文献   

Arbitrary high-order finite volume schemes for seismic wave propagation on unstructured meshes in 2D and 3D     

Michael Dumbser  Martin Käser  Josep de la Puente 《Geophysical Journal International》2007,171(2):665-694

  相似文献   

The light transmission and seiche depth of Izmir Bay,western Turkey     

Erdem Sayin  Sezgi Adalioglu  Canan Eronat 《Journal of Earth System Science》2007,116(1):57-71

Izmir Bay is one of the most polluted estuaries in the whole Mediterranean Sea. The inner part of the Bay (Inner Bay) is heavily affected by domestic and industrial discharge. As a result of these loads, strong eutrophication occurs in the Inner Bay, which is temporally anaerobic. The ecologically sensitive approach of the local authorities during the last decade has given rise to a wide variety of monitoring and research studies on this bay. On the other hand, the municipality of Izmir started to operate wastewater treatment facilities since January 2000. The Institute of Marine Sciences and Technology — Izmir (IMST) with its research vessel R/V K Piri Reis has been conducting an intensive monitoring program since 1988 and especially during the recent few years. These investigations provide an opportunity for the evaluation of the performance of the wastewater treatment plant in terms of the change in the optical properties of Izmir Bay water in a positive manner. The turbidity values measured in these monitoring studies indicate that the values have changed drastically after January 2000. Their spatial variation indicates that the values decrease from the Inner Bay towards the Aegean Sea. The turbidity (light transmission) values are measured with an automatic CTD (conductivity, temperature and depth) system during each cruise. The seiche disc depth measurement is carried out only occasionally. The accuracy of the seiche disc depth is dependent on certain daylight conditions and depends on the operator. The seiche disc depth (D _s) is an important parameter to estimate primary production of organic matter (hereafter called production). A relation between light transmission (turbidity) value and seiche disc depth (D _s) is found with very good agreement. The correlations are very high (approximately 0.94) with slight seasonal variation.  相似文献   

滇西地区中强地震的余震衰减     

钱晓东  秦嘉政  刘祖荫 《地震研究》2001,24(2):109-114

研究了滇西地区8次中强地震余震序列的衰减特征，得出了余震序列频度衰减符合修正的大森定律：（n）t=k/(t c)^p关系；余震衰减的快慢与大地热流值成正相关关系；强余震前中、小余震活动会出现平静或增强现象，即频度残差小于（平静）或大于（增强）其二倍方差，且持续一段时间，其后发生强余震的可能性较大。  相似文献   

The level of deterrence provided by data from the SPITS seismometer array to possible violations of the Comprehensive Test Ban in the Novaya Zemlya region   总被引：1，自引：0，他引：1  

David Bowers  Peter D. Marshall  Alan Douglas 《Geophysical Journal International》2001,146(2):425-438

  相似文献   

Three-dimensional Q structure in Jiashi earthquake region of Xinjiang     

Fan Ji-chang  Li Song-lin  Lai Xiao-ling  Deng Hong-zhao 《地震学报(英文版)》2001,14(6):611-619

3-D S-waveQ structure in Jiashi earthquake region is inverted based on the attenuation of seismic waves recorded from earthquakes in this region in 1998 by the Research Center of Exploration Geophysics (RCEG), CSB, and a rough configuration of deep crustal faults in the earthquake region is presented. First, amplitude spectra of S-waves are extracted from 450 carefully-chosen earthquake records, called observed amplitude spectra. Then, after instrumental and site effect correction, theoretical amplitude spectra are made to fit observed amplitude spectra with nonlinear damped least-squares method to get the observed travel time overQ, provided that earthquake sources conform to Brune’s disk dislocation model. Finally, by 3-D ray tracing method, theoretical travel time overQ is made to fit observed travel time overQ with nonlinear damped least-squares method. In the course of fitting, the velocity model, which is obtained by 3-D travel time tomography, remains unchanged, while onlyQ model is modified. When fitting came to the given accuracy, the ultimateQ model is obtained. The result shows that an NE-trending lowQ zone exists at the depths of 10–18 km, and an NW-trending lowQ zone exists at the depths of 12–18 km. These roughly coincide with the NE-trending and the NW-trending low velocity zones revealed by other scientists. The difference is that the lowQ zones have a wider range than the low velocity zones. Foundation item: Joint Seismological Science Foundation of China (957-07-414) and State Key Basic Research Development and Programming Project (95-13-02-02). Contribution No. RCEG200105, Research Center of Exploration Geophysics, China Seismological Bureau.  相似文献