Converted-wave seismology in anisotropic media revisited,Part I: Basic theory     

Xiangyang Li  Jianxin Yuan 《应用地球物理》2005,2(1):26-40

We have developed new basic theories for calculating the conversion point and the travel time of the P-SV converted wave (C-wave) in anisotropic, inhomogeneous media. This enables the use of conventional procedures such as semblance analysis, Dix-type model building and Kirchhoff summation, to implement anisotropic processing, and makes anisotropic processing affordable. Here we present these new developments in two parts: basic theory and application to velocity analysis and parameter estimation. This part deals with the basic theory, including both conversion-point calculation and moveout analysis. Existing equations for calculating the PS-wave (C-wave) conversion point in layered media with vertical transverse isotropy (VTI) are strictly limited to offsets about half the reflector depth (an offset-depth ratio, xlz, of 0.5), and those for calculating the C-wave traveltimes are limited to offsets equal to the reflector depth (x/z=l.0). In contrast, the new equations for calculating the conversion-point extend into offsets about three-times the reflector depth (x/z=3.0), those for calculating the C-wave traveltimes extend into offsets twice the reflector depth (x/z=2.0). With the improved accuracy, the equations can help in C-wave data processing and parameter estimation in anisotropic, inhomogeneous media. This work is funded by the Edinburgh Anisotropy Project (EAP) of the British Geological Survey. First author: Xiangyang Li, Mr. Li is currently a professorial research seismologist (Grade 6) and technical director of the Edinburgh Anisotropy Project in the British Geological Survey. He also holds a honorary professorship in multicomponent seismology at the School of Geosciences, University of Edinburgh. He received his BSc(1982) in Geophysics from Changchun Geological Institute, China, an MSc (1984) in applied geophysics from East China Petroleum Institute (now known as the China University of Petroleum), and a PhD (1992) in seismology from the University of Edinburgh. During 1984–1987, he worked as a lecturer with the East China Petroleum Institute. Since 1991, he has been employed by the British Geological Survey. His research interests include seismic anisotropy and multicomponent seismology.  相似文献   

Analysis of Short-Period Rayleigh Waves Recorded in the Bohemian Massif Area During Celebration 2000 Experiment     

M. Malinowski 《Studia Geophysica et Geodaetica》2005,49(4):485-500

The aim of this paper is to show the application of short-period surface waves recorded during deep seismic sounding experiment for constraining shallow velocity structure of the crust. Phase velocity of fundamental mode Rayleigh waves, observed along the CELEBRATION 2000 experiment profile CEL09, were obtained by a p-ω method and has been subsequently inverted for one-dimensional shear velocity models for the top 2 km. Multiple filter technique applied to one shot gather was used to carry out a joint inversion of phase and group velocity data and to provide γ_R data to be used for Q_β inversion. Validity of obtained V_S and Q_β models was confirmed by the reflectivity method. Noticeably, no clear dispersive wawes were observed in the Tepla-Barrandian Unit. Quasi-2D model based on the individual 1D V_S models is well correlated with the surface geology. Lower V_S are observed in the Saxothuringian Zone in comparison to the Moldanubian Zone. In the vicinity of the Central Bohemian and Moldanubian Plutons, the near-surface V_S values are relatively low, but below 1 km depth, they are higher than in surrounding areas. We interpret it as the result of the weathering and cracks within the granitoid rocks.  相似文献   

Book Review     

A. Udías 《Journal of Seismology》2005,9(3):381-381

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Retrospective Assessment of Bottom Deposits in Kondopoga Bay,Lake Onega   总被引：1，自引：0，他引：1  

N. A. Belkina 《Water Resources》2005,32(6):629-639

Long-term observations of the chemical composition of bottom sediments in Kondopoga Bay, Lake Onega, are considered. The present-day state of bottom sediments is characterized, and regularities of variations in the composition and properties of sediments occurring in the zone of influence of wastewaters from a pulp and paper plant (PPP).  相似文献   

Assessing the Comparability of Ammonium,Nitrate and Sulfate Concentrations Measured by Three Air Quality Monitoring Networks     

Edith L Gego  P. Steven Porter  John S. Irwin  Christian Hogrefe  S. Trivikrama Rao 《Pure and Applied Geophysics》2005,162(10):1919-1939

Airborne fine particulate matter across the United States is monitored by different networks, the three prevalent ones presently being the Clean Air Status and Trend Network (CASTNet), the Interagency Monitoring of PROtected Visual Environment Network (IMPROVE) and the Speciation and Trend Network (STN). If combined, these three networks provide speciated fine particulate data at several hundred locations throughout the United States. Yet, differences in sampling protocols and samples handling may not allow their joint use. With these concerns in mind, the objective of this study is to assess the spatial and temporal comparability of the sulfate, nitrate and ammonium concentrations reported by each of these networks. One of the major differences between networks is the sampling frequency they adopted. While CASTNet measures pollution levels on seven-day integrated samples, STN and IMPROVE data pertain to 24-hour samples collected every three days. STN and IMPROVE data therefore exhibit considerably more short-term variability than their CASTNet counterpart. We show that, despite their apparent incongruity, averaging the data with a window size of four to six weeks is sufficient to remove the effects of differences in sampling frequency and duration and allow meaningful comparison of the signals reported by the three networks of concern. After averaging, all the sulfate and, to a lesser degree, ammonium concentrations reported are fairly similar. Nitrate concentrations, on the other hand, are still divergent. We speculate that this divergence originates from the different types of filters used to collect particulate nitrate. Finally, using a rotated principal component technique (RPCA), we determined the number and the geographical organization of the significant temporal modes of variation (clusters) detected by each network for the three pollutants of interest. For sulfate and ammonium, the clusters’ geographical boundaries established for each network and the modes of variations within each cluster seem to correspond. RPCA erformed on nitrate concentrations revealed that, for the CASTNet and IMPROVE networks, the modes of variation do not correspond to unified geographical regions but are found more sporadically. For STN, the clustered areas are unified and easily delineable. We conclude that the possibility of jointly using the data collected by CASTNet, IMPROVE and STN has to be weighed pollutant by pollutant. While sulfate and ammonium data show some potential for joint use, at this point, combining the nitrate data from these monitoring networks may not be a judicious choice.  相似文献   

Magnetosheath Interaction with the High Latitude Magnetopause     

S. Savin  A. Skalsky  L. Zelenyi  L. Avanov  N. Borodkova  S. Klimov  V. Lutsenko  E. Panov  S. Romanov  V. Smirnov  YU. Yermolaev  P. Song  E. Amata  G. Consolini  T. A. Fritz  J. Buechner  B. Nikutowski  J. Blecki  C. Farrugia  N. Maynard  J. Pickett  J. A. Sauvaud  J. L. Rauch  J. G. Trotignon  Y. Khotyaintsev  K. Stasiewicz 《Surveys in Geophysics》2005,26(1-3):95-133

We present both statistical and case studies of magnetosheath interaction with the high-latitude magnetopause on the basis of Interball-1 and other ISTP spacecraft data. We discuss those data along with recently published results on the topology of cusp-magnetosheath transition and the roles of nonlinear disturbances in mass and energy transfer across the high-latitude magnetopause. For sunward dipole tilts, a cusp throat is magnetically open for direct interaction with the incident flow that results in the creation of a turbulent boundary layer (TBL) over an indented magnetopause and downstream of the cusp. For antisunward tilts, the cusp throat is closed by a smooth magnetopause; demagnetized ‘plasma balls’ (with scale ∼ few R_E, an occurrence rate of ∼25% and trapped energetic particles) present a major magnetosheath plasma channel just inside the cusp. The flow interacts with the ‘plasma balls’ via reflected waves, which trigger a chaotization of up to 40% of the upstream kinetic energy. These waves propagate upstream of the TBL and initiate amplification of the existing magnetosheath waves and their cascade-like decays during downstream passage throughout the TBL. The most striking feature of the nonlinear interaction is the appearance of magnetosonic jets, accelerated up to an Alfvenic Mach number of 3. The characteristic impulsive local momentum loss is followed by decelerated Alfvenic flows and modulated by the TBL waves; momentum balance is conserved only on time scales of the Alfvenic flows (1/f_A ∼12 min). Wave trains at f_A∼1.3 mHz are capable of synchronizing interactions throughout the outer and inner boundary layers. The sonic/Alfvenic flows, bounded by current sheets, control the TBL spectral shape and result in non-Gaussian statistical characteristics of the disturbances, indicating the fluctuation intermittency. We suggest that the multi-scale TBL processes play at least a comparable role to that of macro-reconnection (remote from or in the cusp) in solar wind energy transformation and population of the magnetosphere by the magnetosheath plasma. Secondary micro-reconnection constitutes a necessary chain at the small-scale (∼ion gyroradius) edge of the TBL cascades. The thick TBL transforms the flow energy, including deceleration and heating of the flow in the open throat, ‘plasma ball’ and the region downstream of the cusp.  相似文献   

Analysis of Many-Year Variations in River Runoff into the Arctic Ocean     

Yu. A. Simonov  A. V. Khristoforov 《Water Resources》2005,32(6):587-593

Statistical analysis of long-term hydrological observations has shown that the interannual variations in the total river runoff into the Arctic Ocean can be considered as a stationary process. Similar are the variations in the annual runoff of the Ob, Lena, and rivers of the northwestern Asia. However, some components of the total runoff into the Arctic Ocean feature distinct and fairly complicated disturbances in the homogeneity of runoff variations. For example, variations in the annual runoff of the Yenisei River have a distinct nonmonotonic trend: the runoff systematically decreased till the late 1950s and increased since the late 1960s. The rivers of the European part of the Arctic Ocean drainage basin featured a decrease in the amplitude of variations in runoff during the past decades. Rivers of the northwestern America and northeastern Asia featured a regular increase in the amplitude of runoff variations and their autocorrelation since the late 1960s.  相似文献   

Observed Evolution of Linear and Nonlinear Effects at the Dahan Downhole Array,Taiwan: Analysis of the September 21, 1999 M 7.3 Chi-Chi Earthquake Sequence     

Huey-Chu Huang  Shin-Wei Huang  Hung-Chie Chiu 《Pure and Applied Geophysics》2005,162(1):1-20

— In this paper, the site characteristics of the Dahan downhole array are studied by analyzing the September 21, 1999 M 7.3 Chi-Chi earthquake sequence including the main shock and some aftershocks. The four-level array (0 m, 50 m, 100 m and 200 m) is located to the north of Hualien City in eastern Taiwan. Polarization analysis is used to check the orientation errors of the seismometers at different levels of depth. If the surface instrument is chosen as reference, the angle between the major polarization axes of the surface and any downhole records is the orientation error that must be corrected for the downhole accelerographs. The orientation errors at depths of 50 m, 100 m and 200 m are 32°, 120° and –84°. After the corrections, the coherency between the surface and downhole records is substantially improved. Spectral ratio analysis shows that the predominant frequency of the Chi-Chi main shock shifts to a lower frequency. We also simulate ground motions at different depths by using the Haskell method with a linear velocity structure model. The record at surface is chosen as the input motion. Compared with the observed data, ground acceleration can be well reproduced for the aftershocks (weak-motion events) of the September 21, 1999 M 7.3 Chi-Chi earthquake. However, for the Chi-Chi main shock, the synthetic waveform cannot match well with the observation neither in amplitude nor in phase. This indicates that large ground shaking probably induced the nonlinear site effect at that time, and the model used cannot support it.Acknowledgement. The authors would like to express their thanks to Dr. L.F. Bonilla and one anonymous reviewer for their valuable suggestions. This research was supported by the National Science Council under grant number NSC 89-2921-M-194-007. The Institute of Earth Sciences, Academia Sinica supplied the strong-motion data. The support of these organizations is gratefully acknowledged.  相似文献   

A Nonlinear Model of Contaminant Transformations in an Aquatic Environment     

B. M. Dolgonosov  T. N. Gubernatorova 《Water Resources》2005,32(3):291-304

A nonlinear model of the decomposition of a multicomponent contaminant is developed with allowance made for the distribution of components over their reactivity. Model application is illustrated by the analysis of published empirical data on organic matter biodegradation in water column and bottom sediments, in an activated-sludge bioreactor, and the biological absorption and enzymatic destruction of organic matter by macrophytes. Photodestruction, chemical destruction, and sedimentation are also considered. The nonlinear model is compared with a first-order reaction equation.__________Translated from Vodnye Resursy, Vol. 32, No. 3, 2005, pp. 322–336.Original Russian Text Copyright © 2005 by Dolgonosov, Gubernatorova.  相似文献   

Freshwater Deficiency and the World Market     

V. I. Danilov-Danilyan 《Water Resources》2005,32(5):572-579

The causes of freshwater deficiency are considered, the main causes being poor environmental conditions and excessive water consumption. The problem of water deficiency is shown to be insoluble without the development of intense water use, conservation, and protection. Based on studying water as a commodity, it is asserted that the market mechanism is not sufficient to cope with water deficiency. The potential of the international water market is shown to be very limited in contrast to the market of water-efficient processes and water-retaining products.  相似文献