Modern Approaches in Geophysics – serie

Structural geologists are well aware of the fact that isotropic rocks are quite exceptional in nature. Whicheverorigin, sedimentary,metamorphicormagmatic, rocks are shaped with a plane of mineral flattening, the foliation in geologists' jargon, and with a line ofmineral elongation, the lineation. Just like a good quarryman, a trained structural geologistwill detectapreferredorientationin an apparently isotropic granite. Preferred mineral orientation and thus structural anisotropy are the rule in nature. Consideringthe largevariationsinelasticcoefficientsofrock-forming minerals,itcould be predicted that, in turn, seismic anisotropy should exist and be important, provided thatdomains withasimilarstructural signatureare largeenough to affectseismic waves. This is why, in 1982 at a conference held in Frankfurt, which was oneofthe fIrst meetings devoted to the subject of seismic anisotropy, I asked Don Anderson the question of why seismologists had not considered earlier in their models the obvious constraint of anisotropy. I still remember Don's answer: "Adolphe, we knew that our isotropic models were not very good but we had no other choice.It is simply that, so far, computerswere not largeenough tointegrate the anisotropy parameter". Changingisotropic glassesfor anisotropic ones permits us to obtain betterand more realistic seismic modelsofthe Earth's interior, but, maybe more importantly, it has, for a seismologist, the farreaching consequenceofsteppinginto the fIeld ofgeodynamics.

This volume is devoted to the quantitative physical modelling of subduction and subduction-related processes. It presents a description of the modelling method (including similarity criteria, and a novel applied experimental technique), results from model experiments, theoretical analysis of results on the basis of continuum mechanics, and their geodynamic interpretation. Subduction is modelled in general as well as applied to particular regions using both 2-D and 3-D approaches, with both slab-push and slab-pull driving forces. The modelling covers all stages from subduction initiation to `death', different regimes of subduction producing back arc extension and compression, blocking of subduction and jumps of subduction zone, arc-continent collision and continental subduction. This work is intended for geologists and geophysicists interested in geodynamics of the convergent plate boundaries and in the mechanics of the lithosphere.

Recent advances in the power of inversion methods, the accuracy of acoustic field prediction codes, and the speed of digital computers have made the full field inversion of ocean and seismic parameters on a large scale a practical possibility. These methods exploit amplitude and phase information detected on hydrophone/geophone arrays, thereby extending traditional inversion schemes based on time of flight measurements. Full field inversion methods provide environmental information by minimising the mismatch between measured and predicted acoustic fields through a global search of possible environmental parameters. Full Field Inversion Methods in Ocean and Seismo-Acoustics is the formal record of a conference held in Italy in June 1994, sponsored by NATO SACLANT Undersea Research Centre. It includes papers by NATO specialists and others. Topics covered include: · speed and accuracy of acoustic field prediction codes · signal processing strategies · global inversion algorithms · search spaces of environmental parameters · environmental stochastic limitations · special purpose computer architectures · measurement geometries · source and receiving sensor technologies.

This work represents a treatment of both classical and modern problems of pulse propagation. The authors provide a physical insight in the intriguing problem of pulse propagation in non-equilibrium media (unstable or admitting attenuation). A refined analysis of the acoustic-gravity waves generation in a compressible stratified fluid is also presented. The solution describes sophisticated wave pictures near the front of the perturbation where previously known methods fail. Finally a detailed account of a relatively new field of investigation related to continuous spectrum waves in shear flows is given.

The text describes a system developed for the processing and interpretation of geophysical fields under conditions of uneven relief, variable geological medium, arbitrary magnetization (polarization) and an unknown level of the normal field. The following procedures are developed and elaborated: methods of terrain correction and use of terrain relief complexity for revealing of additional geological information; methods for picking out the useful anomalies against background noises; and advanced methods for the solution of inverse and direct geophysical problems. The developed system and its components have been successfully applied in complicated conditions of the Caucasus and other regions, during prospecting for economic minerals, study of depth structure and near-surface inhomogeneities. The book is intended for researchers, scientists and students in the field of Earth's sciences, specialists in prospecting for hidden mineral deposits and near-surface geophysics.

Digital signal processing has become an integral part of observational seismology. Seismic waveforms and the parameters commonly extracted from them are influenced strongly by the effects of numerous filters, both within the earth and within the recording system. With the advent of numerous software tools for the processing of digital seismograms, seismologists have unprecedented power in extracting information from seismic records. These tools are often based on sophisticated theoretical aspects of digital signal processing which, to be used properly, need to be understood. This book is aimed at observational seismologists and students in geophysics trying to obtain a basic understanding of those aspects of digital signal processing that are relevant to the interpretation of seismograms. It covers the basic theory of linear systems, the design and analysis of simple digital filters, the effect of sampling and A/D conversion, the calculation of "trueground motion", and the effects of seismic recording systems on parameters extracted from digital seismograms. It contains numerous examples and exercises together with their solutions.

In seismology an earthquake source is described in terms of a fault with a particular rupture size. The faulting process of large earthquakes has been investigated in the last two decades through analyses of long-period seismo­ grams produced by advanced digital seismometry. By long-period far-field approximation, the earthquake source has been represented by physical parameters such as s~ismic moment, fault dimension and earthquake mag­ nitude. Meanwhile, destruction often results from strong ground motion due to large earthquakes at short distances. Since periods of strong ground motion are far shorter than those of seismic waves at teleseismic distances, the theory of long-period source process of earthquakes cannot be applied directly to strong ground motion at short distances. The excitation and propagation of high-frequency seismic waves are of special interest in recent earthquake seismology. In particular, the descrip­ tion and simulation of strong ground motion are very important not only for problems directly relevant to earthquake engineering, but also to the frac­ ture mechanics of earthquake faulting. Understanding of earthquake sources has been developed by investigating the complexity of faulting processes for the case of large earthquakes. Laboratory results on rock failures have also advanced the understanding of faulting mechanisms. Various attempts have been made to simulate, theoretically and empirically, the propagation of short-period seismic waves in the heterogeneous real earth.

Paleomagnetic data are useful in many applications in Earth Science from determining paleocurrent directions to analyzing the long-term behavior of the geomagnetic field. In this volume, an attempt has been made to draw together the various principles and practices within paleomagnetism in a consistent and up-to-date manner. It includes many practical examples that illustrate various applications of paleomagnetism. A companion software package implements the theory explained in the text. The text is aimed at professional Earth Scientists using paleomagnetic data for their research. It is also suitable for use as a text book for students in courses with a paleomagnetic content. In addition, this volume will be of value to other professionals with an interest in the analysis of vector and tensor data in general.

This work provides a broad overview of the fundamental issues involved in seismic event location, and presents a variety of location methods and applications at a wide range of spatial scales. Three important themes in the book are: seismic monitoring for a Comprehensive Nuclear-Test-Ban Treaty (CTBT), seismic event location in three-dimensional Earth models, and methods for multiple-event location. Each chapter contains background material to help readers less familiar with the topics covered, as well as to provide abundant references for readers interested in probing deeper into a topic. However, most of the emphasis is on recent advances in methodology and their application. The book is intended primarily for academic and professional researchers and graduate students in seismology.

Digital signal processing has become an integral part of observational seismology. Seismic waveforms and the parameters commonly extracted from them are strongly influenced by the effects of numerous filters, both within the earth and within the recording system. With the advent of numerous software tools for the processing of digital seismograms, seismologists have unprecedented power in extracting information from seismic records. These tools are often based on sophisticated theoretical aspects of digital signal processing which, to be used properly, need to be understood. This book is aimed at observational seismologists and students in geophysics trying to obtain a basic understanding of those aspects of digital signal processing that are relevant to the interpretation of seismograms. It covers the basic theory of linear systems, the design and analysis of simple digital filters, the effect of sampling and A/D conversion, the calculation of 'true ground motion', and the effects of seismic recording systems on parameters extracted from digital seismograms. It contains numerous examples and exercises together with their solutions.CD-ROM Included The second edition contains the Digital Seismology Tutor by Elke Schmidtke (University of Potsdam) and Frank Scherbaum, a Java applet with all the tools to reproduce and/or modify the examples and problems from this book. Furthermore, a treatment of sigma-delta modulation with new problems and exercises has been added.

Digital signal processing has become an integral part of observational seismology. Seismic waveforms and the parameters commonly extracted from them are strongly influenced by the effects of numerous filters, both within the earth and within the recording system. With the advent of numerous software tools for the processing of digital seismograms, seismologists have unprecedented power in extracting information from seismic records. These tools are often based on sophisticated theoretical aspects of digital signal processing which, to be used properly, need to be understood. This book is aimed at observational seismologists and students in geophysics trying to obtain a basic understanding of those aspects of digital signal processing that are relevant to the interpretation of seismograms. It covers the basic theory of linear systems, the design and analysis of simple digital filters, the effect of sampling and A/D conversion, the calculation of 'true ground motion', and the effects of seismic recording systems on parameters extracted from digital seismograms. It contains numerous examples and exercises together with their solutions. The second edition contains the Digital Seismology Tutor by Elke Schmidtke (University of Potsdam) and Frank Scherbaum, a Java applet with all the tools to reproduce and/or modify the examples and problems from this book as well as a treatment of sigma-delta modulation with new problems and exercises.

This work on electromagnetic resonance phenomena describes a general approach to physical problems, ways to solve them, and properties of the solutions obtained. Attention is given to the discussion and interpretation of formal and experimental data and its links to global atmospheric conditions such as the dynamics of global thunderstorm activity, variations of the effective height of the lower ionosphere, and so forth. Schumann resonance is related to worldwide thunderstorm activity, and simultaneously, to global properties of the lower ionosphere. Transverse resonance is predominantly a local phenomenon containing information on the local height and conductivity of the lower ionosphere and on nearby thunderstorm activity. Transient events in ELF-VLF radio propagation are also treated. These are natural pulsed radio signals and/or abrupt changes of manmade VLF radio signals. The transients associated with cloud-to-ionosphere discharges (red sprites, blue jets, trolls) are discussed, and clarification of the underlying physical ideas and their practical applications to pioneer results achieved in the field recently are emphasised.

Paleomagnetic data is useful in many applications in earth science from determining paleocurrent directions to analyzing the long-term behaviour of the geomagnetic field. In this book, an attempt has been made to draw together the various principles and practices within paleomagnetism in a consistent and up-to-date manner. It includes many practical examples that illustrate various applications of paleomagnetism. A companion software package implements the theory explained in the text.

This volume opens up new perspectives on the physics of the Earth's interior for graduate students and researchers working in the fields of geophysics and geodesy. It looks at our planet in an integrated fashion, linking the physics of its interior to the geophysical and geodetic techniques that record, over a broad spectrum of spatial wavelengths, the ongoing modifications in the shape and gravity field of the planet. Basic issues related to the rheological properties of the Earth's mantle and to its slow deformation will be understood, in both mathematical and physical terms, within the framework of an analytical normal mode relaxation theory. Fundamentals of this theory are developed in the first, tutorial part. The second part deals with a wide range of applications, ranging from changes in the Earth's rotation to post-seismic deformation and sea-level variations induced by post-glacial rebound. In the study of the physics of the Earth's interior, the book bridges the gap between seismology and geodynamics.

This volume opens up new perspectives on the physics of the Earth's interior for graduate students and researchers working in the fields of geophysics and geodesy. It looks at our planet in an integrated fashion, linking the physics of its interior to the geophysical and geodetic techniques that record, over a broad spectrum of spatial wavelengths, the ongoing modifications in the shape and gravity field of the planet. Basic issues related to the rheological properties of the Earth's mantle and to its slow deformation will be understood, in both mathematical and physical terms, within the framework of an analytical normal mode relaxation theory. Fundamentals of this theory are developed in the first, tutorial part. The second part deals with a wide range of applications, ranging from changes in the Earth's rotation to post-seismic deformation and sea-level variations induced by post-glacial rebound. In the study of the physics of the Earth's interior, the book bridges the gap between seismology and geodynamics.

The past fifteen years has witnessed an explosive growth in the fundamental research and applications of artificial neural networks (ANNs) and fuzzy logic (FL). The main impetus behind this growth has been the ability of such methods to offer solutions not amenable to conventional techniques, particularly in application domains involving pattern recognition, prediction and control. Although the origins of ANNs and FL may be traced back to the 1940s and 1960s, respectively, the most rapid progress has only been achieved in the last fifteen years. This has been due to significant theoretical advances in our understanding of ANNs and FL, complemented by major technological developments in high-speed computing. In geophysics, ANNs and FL have enjoyed significant success and are now employed routinely in the following areas (amongst others): 1. Exploration Seismology. (a) Seismic data processing (trace editing; first break picking; deconvolution and multiple suppression; wavelet estimation; velocity analysis; noise identification/reduction; statics analysis; dataset matching/prediction, attenuation), (b) AVO analysis, (c) Chimneys, (d) Compression I dimensionality reduction, (e) Shear-wave analysis, (f) Interpretation (event tracking; lithology prediction and well-log analysis; prospect appraisal; hydrocarbon prediction; inversion; reservoir characterisation; quality assessment; tomography). 2. Earthquake Seismology and Subterranean Nuclear Explosions. 3. Mineral Exploration. 4. Electromagnetic I Potential Field Exploration. (a) Electromagnetic methods, (b) Potential field methods, (c) Ground penetrating radar, (d) Remote sensing, (e) inversion.

The present book is the author's third on the subject of vertical seismic profiling (VSP). Ten years have elapsed since the pUblication of the fIrst book. During this period, VSP has become the principal method of seismic observations in boreholes and the chief method of experimental studies of seismic waves in the real earth. VSP combines borehole studies in the seismic frequency band, well velocity surveys, proximity or aplanatic surveys, all of which previously existed as separate methods. The high effectiveness ofVSP, its great practical value, the express nature and clarity of the results obtained have all contributed towards a very rapid acceptance of the method. In the USSR VSP has been used in an overwhelming majority of areas and is being used increasingly in many foreign countries as well. This has been greatly facilitated by the translation into English and the publication in the U. S. A. by the Society of Exploration Geophysicists of the book Vertical Seismic Profiling (Tulsa, Oklahoma, 1974). As the method has become more familiar, it has attracted growing interest outside the USSR This has been substantiated by the special seminar on VSP (Oklahoma, 1979) which was organized for 22 U. S. companies and universities and presented by the author.

Advances in seismology and extensions of its application have made it increasingly necessary to perform high-sensitivity observationsonartificial earth tremors (explosions) or on natural ones. This implies in particular to investigating the seismic conditions in large industrial centres. There are many major cities with a million inhabitants or more in seismically-active regions. In the USSR, this applies to the capitals of the Union Republics such as Alma Ata, Frunze, Tashkent, Dushanbe, and Ashkhabad, as well as to dozens of local entres and cities with extensive industrial development. Seismic classification and earthquake forecasting have to be considered in relation to the extension or building of cities in such regions, and this would be impossible without detailed investigation of the seismicity, which involves upgrading the instru­ mental observation network. The demand for detailed information on the seismicity increases with every extension to the construction. A successful solution here can be implemented only by taking account of some specific factors, the main one being the high level of seismic noise due to the activities in large centres, which restricts the sensitivity of the apparatus and makes it impossible to record weak local earth tremors, which are of particular interest in periods of relative seismic calm. Stations at sufficiently great distances from the city do not sense the city noise, but they also fail to record weak local earth tremors. Also, the accuracy ofobservation falls for those tremors that can be recorded because of the great distances between stations.

Although considera bIe efforts are now being made to find new sources of energy, alI the experts are agreed that hydrocarbons will have to provide the greater part of our energy needs for a generation ahead. Exploration for and production of hydrocarbons therefore pose a serious problem for our future, as much for the quantitative satisfaction of our requirements as for our search for self-sufficiency in energy. As a direct result of improvements in technology throughout the world, geophysics has progressively enlarged its field of influence in the realms of exploration and production. But amongst the various geophysical methods available, seismic reflection has gradually become accepted as the basic tool of the oiI prospector. Reflection seismology has reached and consolidated this position because it has shown itself to be capable of adapting to the increasing complexity of the requirements of exploration. Initially directed towards geometric mapping of the sub-surface, it became the means of detection of structural traps in geotectonically quiescent regions, and thereafter in increasingly complex surroundings. It has enabled us to clothe the structural framework with a lithology, initially approximate, but becoming more and more precise, assisting the explorer to locate stratigraphic traps. Further developments enable us under favourable circumstances to estimate the quality of the deposits and to detect the presence of fluids and of their interfaces; it then becomes an unrivalled tool for the producer, both in the development of deposits and in the application of enhanced recovery methods.

This book is about marine seismic sources, their history, their physical principles and their deconvolution. It is particularly accented towards the physical aspects rather than the mathematical principles of signature generation in water as it is these aspects which the authors have found to be somewhat neglected. A huge amount of research has been carried out by both commercial and academic institutions over the years and the resulting literature is a little daunting, to say the least. In spite of this, the subject is intrinsically very simple and relies on a very few fundamental physical principles, a somewhat larger number of heuristic principles and a refreshingly small amount of blunderbuss mathematics. As such it is still one of those subjects in which the gifted practical engineer reigns supreme and from which many of the important advances have originated. In Chapter 1 of the book, the underlying physics and concepts are discussed, including pressure and wave propagation, bubble motion, virtual images and the factors determining choice of source. In marine reflection seismology, almost all of the seismic data acquired currently is done with either the airgun or the watergun, which rely on the expulsion of air and water respectively to generate acoustic energy. As a consequence, the discussion in this chapter is geared towards these two sources, as is much of the rest of the book.

Methods to eonstruet images of an objeet from "projeetions" of x-rays, ultrasound or eleetromagnetie waves have found wide applieations in eleetron mieroseopy, diagnostie medicine and radio astronomy. Projeetions are measurable quantities that are a funetiona- usually involving a line integral - of physieal properties of an objeet. Convolutional methods, or iterative algorithms to solve large systems of linear equations are used to reeonstruet the objeet. In prineiple, there is no reasan why similar image reeonstruetions ean not be made with seismie waves. In praetiee, seismic tomography meets with a number of diffieulties, and it is not until the last deeade that imaging of transmitted seismie waves has found applicatian in the Earth sciences. The most important differenee between global seismie tomography and mare eonventional applieations in the laboratory is the faet that the seismologist is eonfronted with the lack of anything resembling a well-eontrolled experimental set-up. Apart from a few nuelear tests, it is not in our power to locate or time seismie events.Apart from a few seabattom seismographs, our sensors are located on land -and even there the availability of data depends on eultural and politieal factors. Even in exploratian seismics, praetieal faetors such as the east of an experiment put strong limitations on the eompleteness of the data set.

Methods to eonstruet images of an objeet from "projeetions" of x-rays, ultrasound or eleetromagnetie waves have found wide applieations in eleetron mieroseopy, diagnostie medicine and radio astronomy. Projeetions are measurable quantities that are a funetiona- usually involving a line integral - of physieal properties of an objeet. Convolutional methods, or iterative algorithms to solve large systems of linear equations are used to reeonstruet the objeet. In prineiple, there is no reasan why similar image reeonstruetions ean not be made with seismie waves. In praetiee, seismic tomography meets with a number of diffieulties, and it is not until the last deeade that imaging of transmitted seismie waves has found applicatian in the Earth sciences. The most important differenee between global seismie tomography and mare eonventional applieations in the laboratory is the faet that the seismologist is eonfronted with the lack of anything resembling a well-eontrolled experimental set-up. Apart from a few nuelear tests, it is not in our power to locate or time seismie events.Apart from a few seabattom seismographs, our sensors are located on land -and even there the availability of data depends on eultural and politieal factors. Even in exploratian seismics, praetieal faetors such as the east of an experiment put strong limitations on the eompleteness of the data set.

This Oosterbeek conference was one in a long series of topical conferences starting with the Upper Mantle Project Symposia on Geophysical Theory and Computers in the 1960s, and thence their successors, the conferences on Mathematical Geophysics, until the present.

Proceedings of the Summer School organized in Strasbourg, France, July 15-August 1, 1986, by European Mediterranean Seismological Centre and Institute de Physique du Globe de Strasbourg

Recent advances in the power of inversion methods, the accuracy of acoustic field prediction codes, and the speed of digital computers have made the full field inversion of ocean and seismic parameters on a large scale a practical possibility. These methods exploit amplitude and phase information detected on hydrophone/geophone arrays, thereby extending traditional inversion schemes based on time of flight measurements. Full field inversion methods provide environmental information by minimising the mismatch between measured and predicted acoustic fields through a global search of possible environmental parameters. Full Field Inversion Methods in Ocean and Seismo-Acoustics is the formal record of a conference held in Italy in June 1994, sponsored by NATO SACLANT Undersea Research Centre. It includes papers by NATO specialists and others. Topics covered include: · speed and accuracy of acoustic field prediction codes · signal processing strategies · global inversion algorithms · search spaces of environmental parameters · environmental stochastic limitations · special purpose computer architectures · measurement geometries · source and receiving sensor technologies.

This book represents a comprehensive treatment of both classical and modern problems of pulse propagation. The authors provide a physical insight in the intriguing problem of pulse propagation in non-equilibrium media (unstable or admitting attenuation). A refined analysis of the acoustic-gravity waves generation in a compressible stratified fluid is also presented. The solution describes sophisticated wave pictures near the front of the perturbation where previously known methods fail. Finally a detailed account of a relatively new field of investigation related to continuous spectrum waves in shear flows is given. Audience: This volume will be of use to researchers and scientists with a background in wave motion, fluid mechanics and calculus including elementary aspects of asymptotic methods. A major source of information for academians specialized in acoustics, hydrodynamics and geophysics.

The book describes a system developed for the processing and interpretation of geophysical fields under conditions of uneven relief, variable geological medium, oblique magnetization (polarization) and an unknown level of the normal field. This is the main difference from other books. The following procedures are developed and elaborated: methods of terrain correction and use of terrain relief complexity to reveal additional geological information; methods to select the useful anomalies against background noises; and advanced methods for the solution of inverse and direct geophysical problems. The developed system and its components have been successfully applied to complicated conditions in the Caucasus and other regions, during prospecting for economic minerals, studies of depth structure and near-surface inhomogeneities. Audience: The book is intended for researchers, scientists and students in the field of Earth's Sciences, specialists in prospecting for hidden mineral deposits and near-surface geophysics.

In seismology an earthquake source is described in terms of a fault with a particular rupture size. The faulting process of large earthquakes has been investigated in the last two decades through analyses of long-period seismo­ grams produced by advanced digital seismometry. By long-period far-field approximation, the earthquake source has been represented by physical parameters such as s~ismic moment, fault dimension and earthquake mag­ nitude. Meanwhile, destruction often results from strong ground motion due to large earthquakes at short distances. Since periods of strong ground motion are far shorter than those of seismic waves at teleseismic distances, the theory of long-period source process of earthquakes cannot be applied directly to strong ground motion at short distances. The excitation and propagation of high-frequency seismic waves are of special interest in recent earthquake seismology. In particular, the descrip­ tion and simulation of strong ground motion are very important not only for problems directly relevant to earthquake engineering, but also to the frac­ ture mechanics of earthquake faulting. Understanding of earthquake sources has been developed by investigating the complexity of faulting processes for the case of large earthquakes. Laboratory results on rock failures have also advanced the understanding of faulting mechanisms. Various attempts have been made to simulate, theoretically and empirically, the propagation of short-period seismic waves in the heterogeneous real earth.

Advances in Seismic Event Location provides a broad overview of the fundamental issues involved in seismic event location, and presents a variety of state-of-the-art location methods and applications at a wide range of spatial scales. Three important themes in the book are: seismic monitoring for a Comprehensive Nuclear-Test-Ban Treaty (CTBT), seismic event location in three-dimensional Earth models, and methods for multiple-event location. Each chapter contains background material to help readers less familiar with the topics covered, as well as to provide abundant references for readers interested in probing deeper into a topic. However, most of the emphasis is on recent advances in methodology and their application. Audience: The book is intended primarily for academic and professional researchers and graduate students in seismology.