ALBERT

Beschreibung / Inhaltsverzeichnis: PREFACE Seismic imaging is the process through which seismograms recorded on the Earth's surface are mapped into representations of its interior properties. Imaging methods are nowadays applied to a broad range of seismic observations: from nearsurface environmental studies, to oil and gas exploration, even to long-period earthquake seismology. The characteristic length scales of the features imaged by these techniques range over many orders of magnitude. Yet there is a common body of physical theory and mathematical techniques which underlies all these methods. The focus of this book is the imaging of reflection seismic data from controlled sources. At the frequencies typical of such experiments, the Earth is, to a first approximation, a vertically stratified medium. These stratifications have resulted from the slow, constant deposition of sediments, sands, ash, and so on. Due to compaction, erosion, change of sea level, and many other factors, the geologic, and hence elastic, character of these layers varies with depth and age. One has only to look at an exposed sedimentary cross section to be impressed by the fact that these changes can occur over such short distances that the properties themselves are effectively discontinuous relative to the seismic wavelength. These layers can vary in thickness from less than a meter to many hundreds of meters. As a result, when the Earth's surface is excited with some source of seismic energy and the response recorded on seismometers, we will see a complicated zoo of elastic wave types: reflections from the discontinuities in material properties, multiple reflections within the layers, guided waves, interface waves which propagate along the boundary between two different layers, surface waves which are exponentially attenuated with depth, waves which are refracted by continuous changes in material properties, and others. The character of these seismic waves allows seismologists to make inferences about the nature of the subsurface geology. Because of tectonic and other dynamic forces at work in the Earth, this first-order view of the subsurface geology as a layer cake must often be modified to take into account bent and fractured strata. Extreme deformations can occur in processes such as mountain building. Under the influence of great heat and stress, some rocks exhibit a taffy-like consistency and can be bent into exotic shapes without breaking, while others become severely fractured. In marine environments, less dense salt can be overlain by more dense sediments; as the salt rises under its own buoyancy, it pushes the overburden out of the way, severely deforming originally flat layers. Further, even on the relatively localized scale of exploration seismology, there may be significant lateral variations in material properties. For example, if we look at the sediments carried downstream by a river, it isclear that lighter particles will be carried further, while bigger ones will be deposited first; flows near the center of the channel will be faster than the flow on the verge. This gives rise to significant variation is the density and porosity of a given sedimentary formation as a function of just how the sediments were deposited. Taking all these effects into account, seismic waves propagating in the Earth will be refracted, reflected and diffracted. In order to be able to image the Earth, to see through the complicated distorting lens that its heterogeneous subsurface presents to us, in other words, to be able to solve the inverse scattering problem, we need to be able to undo all of these wave propagation effects. In a nutshell, that is the goal of imaging: to transform a suite of seismograms recorded at the surface of the Earth into a depth section, i.e., a spatial image of some property of the Earth (usually wave speed or impedance). There are two main types of spatial variations of the Earth's properties. There are the smooth changes (smooth meaning possessing spatial wavelengths which are long compared to seismic wavelengths) associated with processes such as compaction. These gradual variations cause ray paths to be gently turned or refracted. On the other hand, there are the sharp changes (short spatial wavelength), mostly in the vertical direction, which we associate with changes in lithology and, to a lesser extent, fracturing. These short wavelength features give rise to the reflections and diffractions we see on seismic sections. If the Earth were only smoothly varying, with no discontinuities, then we would not see any events at all in exploration seismology because the distances between the sources and receivers are not often large enough for rays to turn upward and be recorded. This means that to first order, reflection seismology is sensitive primarily to the short spatial wavelength features in the velocity model. We usually assume that we know the smoothly varying part of the velocity model (somehow) and use an imaging algorithm to find the discontinuities. The earliest forms of imaging involved moving, literally migrating, events around seismic time sections by manual or mechanical means. Later, these manual migration methods were replaced by computer-oriented methods which took into account, to varying degrees, the physics of wave propagation and scattering. It is now apparent that all accurate imaging methods can be viewed essentially as linearized inversions of the wave equation, whether in terms of Fourier integral operators or direct gradient-based optimization of a waveform misfit function. The implicit caveat hanging on the word "essentially" in the last sentence is this: people in the exploration community who practice migration are usually not able to obtain or preserve the true amplitudes of the data. As a result, attempts to interpret subtle changes in reflector strength, as opposed to reflector position, usually run afoul of one or more approximations made in the sequence of processing steps that makes up a migration (trace equalization, gaining, deconvolution, etc.) On the other hand, if we had true amplitude data, that is, if the samples recorded on the seismogram really were proportional to the velocity of the piece of Earth to which the geophone were attached, then we could make quantitative statements about how spatial variations in reflector strength are related to changes in geological properties. The distinction here is the distinction between imaging reflectors, on the one hand, and doing a true inverse problem for the subsurface properties on the other. Until quite recently the exploration community was exclusively concerned with the former, and today the word "migration" almost always refers to the imaging problem. The more sophisticated view of imaging as an inverse problem is gradually making its way into the production software of oil and gas exploration companies, since careful treatment of amplitudes is often crucial in making decisions on subtle lithologic plays (amplitude versus offset or AVO) and in resolving the chaotic wave propagation effects of complex structures. When studying migration methods, the student is faced with a bewildering assortment of algorithms, based upon diverse physical approximations. What sort of velocity model can be used: constant wave speed v? v(x), v(x, z), v(x, y, z)? Gentle dips? Steep dips? Shall we attempt to use turning or refracted rays? Take into account mode converted arrivals? 2D (two dimensions)? 3D? Prestack? Poststack? If poststack, how does one effect one-way wave propagation, given that stacking attenuates multiple reflections? What domain shall we use? Time-space? Time-wave number? Frequency-space? Frequency-wave number? Do we want to image the entire dataset or just some part of it? Are we just trying to refine a crude velocity model or are we attempting to resolve an important feature with high resolution? It is possible to imagine imaging algorithms that would work under the most demanding of these assumptions, but they would be highly inefficient when one of the simpler physical models pertains. And since all of these situations arise at one time or another, it is necessary to look at a variety of migration algorithms in daily use. Given the hundreds of papers that have been published in the past 15 years, to do a reasonably comprehensive job of presenting all the different imaging algorithms would require a book many times the length of this one. This was not my goal in any case. I have tried to emphasize the fundamental physical and mathematical ideas of imaging rather than the details of particular applications. I hope that rather than appearing as a disparate bag of tricks, seismic imaging will be seen as a coherent body of knowledge, much as optics is...

Beschreibung / Inhaltsverzeichnis: PREFACE The four-year period of activity of the Groupement de Recherche 942 (GDR) of the Centre National de la Recherche Scientifique (CNRS) came to an end in December 1993. This GDR was a scientific association grouping research teams from the academic sphere -- i.e. the Unités de Recherches Associées 723 & 724 of the CNRS as well as the Universities of Orléans and Paris-Sud -- and from the industrial world: Elf-Aquitaine Production, TOTAL and the Institut Français du Pétrole (IFP). The aim of the GDR was to understand the processes and the causes of organic carbon fossilization in sediments, especially when they can be modified by environmental conditions such as climate, eustatism, productivity etc., factors which can alko interact. This goal implies the simultaneous study of ancient geological formations (hydrocarbon source rocks from the famous Kimmeridge Clay Formation) and recent Quaternary sediments (the Lac du Bouchet or lake Bouchet maar, Massif Central, France). In the latter case, we benefit from a fine-scale stratigraphical framework as well as a reliable reconstruction of the local and regional environment. This volume is a collection of papers representing oral presentations given on December 7, 1993, at the Société Géologique de France in Paris, during the final meeting of the GDR. These articles thus report the latest developments of the studies carried out under the GDR. However, this is not the first publication of our results, which can be found in the papers referred to in each article. The Kimmeridge Clay Formation was previously studied in 1987, by the Yorkim Group from IFP, Elf-Aquitaine and the British Geological Survey, on the basis of a series of wells drilled across the Cleveland Basin of Yorkshire. In each well, the distribution with depth of the total organic content is cyclic. We have compared some of the organic cycles from two wells (Matron and Ebberston) based on mineralogy, organic and inorganic geochemistry and petrography, at a high resolution scale (centimetric). The main conclusion of this work is that the driving force for organic matter accumulation in the studied cycles was organic phytoplankton productivity. Oxygenation conditions seem to have played a secondary role as a positive feedback action enhancing organic matter storage. Lac du Bouchet is located on the Devès volcanic plateau, 15 km SW of Le Puy en Velay, at an altitude of 1205 m. The depth of the water column is 28 m. The lake has a subcircular shape (1 km in diameter) and a very restricted watershed. This site is exceptionally suitable for research on climate variations and palaeomagnetic field modifications (Euromaars EC Program). The GDR focused on sedimentary organic matter and its relationship to inorganic phases. An important result is that organic matter appears to be a good indicator of palaeoenvironmental reconstructions for over 350 000 years. In addition, the study of early diagenetic reactions in surficial sediments (porewater and solid phase) allows the specification of the processes of organic matter degradation and storage in such an oligothrophic lake.

Beschreibung / Inhaltsverzeichnis: PREFACE In the geologic record, vertical crustal uplift has often resulted in erosional removal of huge thicknesses of sedimentary strata. If the uplift is of a broad regional nature or the uplifted strata remain relatively undeformed and sediments deposited after the uplift are not preserved, the magnitude of uplift and subsequent erosion may be difficult to quantify. This may lead to misinterpretation or omission of chapters of geologic history of a region. Fortunately, a number of indirect methods can be used to infer the thicknesses of missing strata and reconstruct the geologic history. Our book titled "Thick Post-Devonian Sediment Cover Over New York State: Evidence from Fluid-Inclusion, Organic Maturation, Clay Diagenesis and Stable Isotope Studies" uses four techniques of paleotemperature measurements in sedimentary rocks in order to determine burial depths of the existing Paleozoic strata in New York State. Since every technique has its own analytical and interpretative uncertainties, the use of four techniques allowed us to place a better constraint on our results. We show how regionally extensive paleotemperature data can be used to estimate the thicknesses of strata lost from an uplifted sedimentary basin. We also provide a tentative tectonic-, paleogeographic- and depositional history of New York State after the Devonian when the missing strata were deposited...

Beschreibung / Inhaltsverzeichnis: PREFACE The aim of this volume is two-fold. At the more pragmatic level, it is to help answer the many questions about the structure of the Pacific continental margin of North America, which have arisen over the years as a result of continuing field mapping and geophysical surveys. The second objective is methodological - to illustrate the irreplaceable role of geological information among the various data sets used in earth-science studies. The need to address these issues became apparent to the author during the several years he spent taking part in geological and geophysical studies on the west coast of Canada. All too often, results of geologic field mapping disagreed with tectonic predictions from too-straightforward local applications of global plate reconstructions, which due to their generality do not always take a full account of specific character of particular regions. To be sure, the global approach has during the last q~/artercentury greatly expanded the vision of geoscientists, previously restricted to continental regions. However, a negative by-product of this expansion has been a decline of attention paid to local information, as tectonic studies have increasingly relied on simply fitting the development of a particular region into this or that prefabricated tectonic template. Direct geological observations have limitations of their own. The observer in most cases deals with products of geologic processes, rather than with the processes themselves. Field mapping provides local information, and many years of effort are needed before a regional overview becomes possible. Geologic mapping is restricted to the ground surface, and even the deepest drillholes cannot sample more than the outermost shell of the Earth. The factual side of geologic mapping is usually limited to determination of rock types and their relationships in areas of exposure. Conclusions about the three-dimensional structure of a region and its evolution are still mostly inferential. Broad incorporation into geological studies of geophysical data, assisted by ever-more-sophisticated modern computers, provides a huge volume of information unobtainable in other ways. Geophysical methods quickly afford regional coverage or images of the Earth's deep interior. Geophysical methods have prompted the application in geological sciences of methodologies borrowed from exact sciences, such as mathematics and physics. Particularly important has been quantitative modeling, which allows a scientist to use the known parameters of a system to predict others. But in taking this approach too far, one encounters a dangerous pitfall. A model is a simplified representation of a natural phenomenon. The quality of this or that representation is relative, and a representation is never perfect. To incorporate all characteristics of a geologic phenomenon, in a parametrized form, into a numerical or physical imitation is impossible. This requires one to rely on simplifying assumptions, and a model is no better than the assumptions at its base. Unrealistic assumptions lead to unrealistic models. When a disagreement arises between model predictions and observations - such as those from geologic field mapping - a modeler may be tempted to downplay the differences or the significance of the offending observations. It becomes tempting to underestimate the role of an experienced geologist as a principal arbiter of the realism of a model. But it is geological data and geological control that provide the ultimate means of testing abstract models. From this methodological position, the present study of the western North American continental margin is organized as follows: 1. Geological information, available from field mapping and drilling, is gathered and summarized. 2. Current geophysical models for this region are considered, with particular attention to their underlying assumptions. 3. The available data, geological and geophysical, are synthesized into an internally consistent geologic-evolution concept. 4. This concept is tested by comparison with direct geological observations from field mapping and drilling. Because most current data sets and models cover northwestern Washington and western British Columbia, particular attention was paid to these areas. Fortunately, these areas contain many keys that help understand the structure of the entire western North American continental margin, which has baffled scientists for decades. The author does not claim to have resolved all these problems, but he does believe he has made a useful contribution to understanding continental-oceanic plate interrelations at this continental margin. Rigidity of lithospheric plates is a critical assumption in current models of plate evolution. The lithophere of a plate is created at spreading centers manifested in the global system of mid-ocean ridges. It moves away from the place of its birth towards boundaries with other plates, with which it can interact in a variety of ways. Some interactions are of strike-slip type, with two plates simply sliding past each other. However, to compensate for the creation of new lithosphere at spreading centers, older lithosphere at some plate boundaries descends into the mantle as it is overriden by other plates. At such plate boundaries lie subduction zones. If both regimes occur along a single plate boundary, the transition between them must be abrupt. Unless it can be tied to a change in orientation of the boundary, it must be associated with a junction of not two, but three different plates. Such a template was used to interpret the structure and tectonic evolution of the western North American continental margin in the late 1960s and thereafter (Atwater, 1970; McManus et al., 1972; Barr and Chase, 1974; Riddihough and Hyndman, 1976). To satisfy the principles of rigid-plate tectonics, both regimes have to exist along this continental margin. Also needed in rigid-plate reconstructions is a plate triple junction somewhere between the areas of proven ongoing subduction (in Oregon and southern Washington) and transform plate motion (along the southeastern Alaska margin; Atwater, 1970; McManus et al., 1972). Such a triple junction has been placed off Queen Charlotte Sound offshore British Columbia (Keen and Hyndman, 1979; Riddihough et al., 1983), where a spreading center has been postulated between the Pacific and Explorer oceanic plates (Hyndman et al. 1979; Riddihough, 1984). Off northern Vancouver Island, a transform boundary between the Explorer and Juan de Fuca oceanic plates has been postulated, but both these plates are assumed to be subducting beneath Vancouver Island (Hyndman et al., 1979; Riddihough and Hyndman, 1989)o With the assumed universality of the rigid-plate model, "broad similarity" has been suggested between the geology of western Oregon and that of western British Columbia, and the Cascadia zone of active subduction has been extended as far north as the mouth of Queen Charlotte Sound (Riddihough, 1979, 1984). An accretionary sedimentary prism (Yorath, 1980) - or even an accretionary complex containing several exotic "terranes" (Davis and Hyndman, 1989) - has been postulated off Vancouver Island. Geological observations onshore and offshore (Shouldice, 1971; Tiffin et al., 1972) have come to be considered too "surficial" to be of major consequence for large-scale tectonic modeling (Yorath et al., 1985a,b; Yorath, 1987). Variants of the principal geophysical model for this area during the last decade (Clowes et al., 1987; Hyndman et alo, 1990; Spence et al. 1991; Yuan et al., 1992; Dehler and Clowes, 1992) have become increasingly distant from geological observations. As new model variants emerged, they were checked for internal consistency, compatibility with neighboring local models and fidelity to the overall assumed tectonic picture. However, detailed geological work continued, and many of its results proved incompatible with the conventional wisdom (Gehrels, 1990; Babcock et al., 1992, 1994; Allan et al., 1993; Lyatsky, 1993a). Importantly, questions arose about the applicability in this region of the conventional, simple rigid-plate assumption, as it was shown to be unable to account for all the geological and geophysical peculiarities in some areas (Carbotte et al., 1989; Allan et al., 1993; Davis and Currie, 1993). New solutions were made necessary by new findings and by rediscovery of forgotten old data (see Lyatsky et al., 1991; Lyatsky, 1993b). Without aiming to resolve all the outstanding debates, tectonic implications of the geologic mapping and drilling results in this region are considered in the following chapters. These results are integrated with geochemical and geophysical data. Interpretations of these data, made by this author and by other workers, are verified by geological observations and by geologically plausible extrapolations from these observations. In searching for solutions consistent with all the information, the author has restricted himself to analyzing continental-crust structures along this continental margin. He believes, however, that future models for the offshore regions of the northeastern Pacific should consider the results obtained herein.

Beschreibung / Inhaltsverzeichnis: The subject of the book is an indepth description of the theory and mathematical models behind the application of the Global Positioning System in geodesy and geodynamics. The text has been prepared by leading experts in the field, contributing their particular points of view. Unlike a collection of disjoint papers, the text provides a continous flow of ideas and developments. The mathematical models for GPS measurements are developed in the first half of the book, followed by the description of GPS solutions for geodetic applications on local, regional and global scales.

Beschreibung / Inhaltsverzeichnis: The book gives a general overview of recent approaches to debris flows. Problems of both occurrences and dynamics of debris flow are treated, taking into account new results from theoretical and experimental research and field observations. Finally, the functioning of the main control devices are reconsidered in the light of the state of the art. Contents: Observation and Measurement for Debris Flow - Introduction, Prediction of Debris Flow for Warning and Evacuation, Large and Small Debris Flows - Occurence and Behaviour, Field Survey for Debris Flow in Volcanic Area.- Dynamics of Debris Flow - Introduction, A Comparison Between Gravity Flows of Dry Sand and Sand-Water Mixtures, Review Dynamic Modeling of Debris Flows, Dynamics of the Inertial and Viscous Debris Flows, Selected Notes on Debris Flow Dynamicss.- Control Measures for Debris Flow - Introduction, Development of New Methods for Countermeasures against Debris Flows, Torrent Check Dams as a Control Measure for Debris Flows, On the Dynamic Impact of Debris Flows.

Beschreibung / Inhaltsverzeichnis: PREFACE The objective of this book is to introduce the practitioner as well as the more theoretically interested reader into the integration problem of spatial information for Geo-lnformation Syslems. Former Get-Information Systems are restricted to 2D space. They realize the integration of spatial information by a conversion of vector and raster representations. This, however. leads to conceptual difficulties because of the two totally different paradigms. Furthermore, the internal topology of the get-objects is not considered. In recent years the processing of 3D information has played a growing role in Get-Information Systems. For example, planning processes for environmental protection or city planning are dependent on 3D data. The integration of spatial reformation will become even more impoaant in the 3D context and with the development of a new generation of open GISs. This book is intended to respond to some of these requirements. It presents a model for the integration of spatial information for 3D Geo-lnformation Systems (3D-GISs). As a precondition for the integration of spatial information, the integration of different spatial representations is emphasized. The model is based on a three-level notion of space that likewise includes the geometry, metrics and the topology of get-objects. The so called extended complex (e-complex) is introduced as a kernel of the model. Its internal basic geometries are the point, the line, the triangle and the tetrahedron. It is shown how a convex e-complex (ce-complex) is generated by the construction of the convex hull and the "'filling" of lines, triangles and tetrahedra, respectively. As we know from computer geometry, this results in substantially simpler geometric algorithms. Additionally, the algorithms gain by the explicit utilization of the topology of the ce-complex. This book also builds a bridge from the GIS to the object-oriented database technology, which will likely become a key technology for the development of a new generation of open Geo-lnformation Systems. In the so-called GEtmodel kernel "building blocks" are introduced that s~mplify the development of software architectures for geo-applications. A geological application in the Lower Rhine Basin shows the practical use of the introduced geometric and topological representation for a 3D-GIS...

Beschreibung / Inhaltsverzeichnis: PREFACE Through the last few decades inversion concepts have become an integral past of experimental data interpretation in several branches of science. In numerous cases similar inversion-like techniques were developed independently in separate disciplines, sometimes based on different lines of reasoning, and sometimes not to the same level of sophistication. This fact was realized early in inversion history. In the seventies and eighties "generalized inversion" and "total inversion" became buzz words in Earth Science, and some even saw inversion as the panacea that would eventually raise all experimental science into a common optimal frame. It is true that a broad awareness of the generality of inversion methods is established by now. On the other hand, the volume of experimental data varies greatly among disciplines, as does the degree of nonlinearity and numerical load of forward calculations, the amount and accuracy of a priori information, and the criticality of correct error propagation analysis. Thus, some clear differences in terminology, philosophy and numerical implementation remain, some of them for good reasons, but some of them simply due to tradition and lack of interdisciplinary communication. In a sense the development of inversion methods could be viewed as an evolution process where it is important that "species" can arise and adapt through isolation, but where it is equally important that they compete and mate afterwards through interdisciplinary exchange of ideas. This book was actually initiated as a proceedings volume of the "Interdisciplinary Inversion Conference 1995", held at the University of Aarhus, Denmark. The aim of this conference was to further the competition and mating part of above-mentioned evolution process, and we decided to extend the effect through this publication of 35 selected contributions. The point of departure is a story about geophysics and astronomy, in which the classical methods of Backus and Gilbert from around 1970 have been picked up by helioseismology. Professor Douglas Gough, who is a pioneer in this field, is the right person to tell this success story of interdisciplinary exchange of research experience and techniques [1-31] (numbers refer to pages in this book). Practitioners of helioseismology like to stress the fact that the seismological coverage on the Sun in a sense is much more complete and accurate than it is on Earth. Indeed we witness vigorous developments in the Backus & Gilbert methods (termed MOLA/SOLA in the helioseismology literature) [32-59] driven by this fortunate data situation. Time may have come for geophysicists to look into helioseismology for new ideas. Seismic methods play a key role in the study of the Earth's lithosphere. The contributions in [79 - 130,139 - 150] relate to reflection seismic oil exploration, while methods for exploration of the whole crust and the underlying mantle axe presented in [131 - 138, 151 - 166]. Two contributions [167 - 185] present the application of inversion for the understanding of the origin of petroleum and the prediction of its migration in sedimentary basins. Inversion is applied to hydrogeophysical and environmental problems [186 - 222], where again developments are driven by the advent of new, mainly electromagnetic, experimental techniques. The role of inversion in electromagnetic investigations of the lithosphere/astenosphere system as well as the ionosphere axe exemplified in [223 - 238]. Geodesy has a fine tradition of sophisticated linear inversion of large, accurate sets of potential field data. This leads naturally to the fundamental study of continuous versus discrete inverse formulations found in [262-275]. Applications of inversion to geodetic satellite data are found in [239 - 261]. General mathematical and computational aspects are mainly found in [262 - 336]. Nonlinearity in weakly nonlinear problems may be coped with by careful modification of lineaxized methods [295 - 302]. Strongly nonlinear problems call for Monte Carlo methods, where the cooling scedule in simulated annealing [303 - 311,139 - 150] is critical for convergence to a useful (local) minimum, and the set of consistent models is explored through importance sampling [89 - 90]. The use of prior information, directly or indirectly, is a key issue in most contributions, ranging from Bayesian formulations based a priori covariances e.g. [98 - 112,122 - 130, 254 - 261], over more general but also less tractable prior probability densities [79 - 97], to inclusion of specific prior knowledge of shape [284 - 294, 312 - 319]. Given the differences and similarities in approach, can we benefit from exchange of ideas and experience? In practice ideas and experience seldom jump across discipline boundaries by themselves. Normally one must go and get them the hard way, for instance by reading and understanding papers from disciplines far from the home ground. Look at the journey into the interdisciplinary cross-field of inversion techniques as a demanding safari into an enormous hunting ground. This book is meant to provide a convenient starting point.

Beschreibung / Inhaltsverzeichnis: PREFACE The sedimentology of Chalk describes processes that caused the rhythmic vertical variation in grain size, structures and authigenic mineral concentrations in Late Cretaceous and Early Tertiary, subtropical, shallow marine, fine-grained, detrital bioclastic carbonates of northwest Europe. In particular, attention is paid to the sedimentology of the Tuffaceous Chalk of Maaslricht (The Netherlands), a coarsegrained variety of Chalk that resembles the Chalk (coccolithic mudstones) as well as modern shallow marine carbonate sands. Numerical models are presented that enable the simulation of the genesis of flint nodule layers, hardgrounds and complex wavy bedded sequences, such as the K/T boundary sequence of Stevns Klint (Denmark). The aim of this book is to show how depositional and early diagenetic features, which are observed in small-scale Chalk outcrops, can be used to reconstruct the large-scale dynamics of the northwest European continent during the Late Cretaceous and Early Tertiary...

Beschreibung / Inhaltsverzeichnis: PREFACE The ocean has always been reluctant to reveal its secrets. Its size and the inaccessibility of its deeper regions have made their safeguard a reasonably simple matter with the result that significant misconceptions persisted for many years. Two of the most widespread of these concerned the featureless nature of the sea floor and the silence of the deep ocean. Underwater acoustics has played a key role in discrediting both and in so doing introduced new and exciting developments in oceanography and geophysics. In the years following World War II, echosounders and subbottom profilers based on new active sonar technology, revealed the true nature of the seafloor topography and led to the major advances represented by plate tectonics. Research driven by the requirements of passive sonar, on the other hand, was to demonstrate that the sea was not silent but was characterised by a complex noise spectrum. Many individual mechanisms and sources ranging from man-made, biological and geophysical activity to the intrinsic noise of the sea itself were found to contribute to this spectrum. A major component, which is the subject of this book, was to remain unrecognised to underwater acoustics until noise measurements could be made effectively at very low frequencies, although its presence had been indicated by seismology long before these measurements were possible. By virtue of its geographical isolation in the Southern Ocean, New Zealand has provided an ideal environment for long-range propagation and ambient noise investigations and numerous studies have been reported. Our interest in the subject of this book was aroused initially in the course of one such experiment in 1966. For the first time it had been possible to extend the recording bandwidth to 1 Hz and the improved performance of this new system was anticipated eagerly. However the main purpose of the experiment was nearly aborted by the appearance of a new and unsuspected noise component at frequencies below 10 Hz. Due primarily to technical limitations in the equipment then available, a subsequent programme, designed to identify the properties and origin of the source more clearly, was not productive and was soon abandoned. An opportunity to revisit the problem arose some 10 years later, when the University of Auckland became involved in a major environmental study in support of the development of an offshore gas field in Cook Strait. The technology then available provided an opportunity to examine afresh the relationship between sea state and the seismo-acoustic response generated. An initial trim demonstrated the potential of the site. Accordingly a long-term programme, involving the parallel measurement of the oceanwave field and acoustic response, was undertaken in a series of student research theses. The data so gathered were of sufficiently high quality to ultimately establish wave-wave interactions as the source of the acoustic effects observed and to identify many of its characteristics. This result was soon to be confirmed by other studies. As the noise data accumulated, however, it became apparent that certain refinements to the theories describing the mechanism were required. Our attempts to provide these refinements have been reported in a number of contributions in recent years. The accounts of these and similar contributions by others have unfortunately appeared in the literature in a somewhat disjointed manner, with the result that the evolution of the subject has not been easy to follow. This book attempts to present a more coherent account of the subject and its development. Most of the early experimental and theoretical results from our group have arisen from two key Ph.D. theses, due to Dr. K.C. Ewans and Dr. C.Y. Wu. The painstaking and careful instrumentation development and data analysis provided by Dr. Ewans were critical to the definitive correlation which we were able to establish between wind field, seastate and the acoustic response so generated. Dr. Wu's thesis presented the first phase of our attempt at the resolution of certain key theoretical issues, which were identified in the course of the experimental programme. Both studies owe much to the support of Shell BP Todd Oil Services Ltd., acting for Maui Development Ltd., and to the University of Auckland. The support of the Electricity Corporation of New Zealand Ltd. during a later experimental investigation of the Southern Ocean wave field is also acknowledged...

Beschreibung / Inhaltsverzeichnis: This book contains revised refereed papers selected from the presentations at the First International Workshop on Graphics Recognition, held in University Park, PA, USA, in August 1995. The 23 full papers included are divided into sections on low-level processing, vectorization and segmentation of scanned graphics documents; symbol and diagram recognition, map processing, interpretation of engineering drawings. Each section contains both survey articles to assess the state of the art, and research papers presenting novel results. One section is devoted to a contest held to determine the best algorithm for detection of dashed lines in drawings. The final chapter summarizes the conclusions and recommendations of the discussions held during the workshop.

Beschreibung / Inhaltsverzeichnis: This book presents the proceedings of the Sixth International Conference on Computer Analysis of Images and Patterns, CAIP '95, held in Prague, Czech Republic in September 1995. The volume presents 61 full papers and 75 posters selected from a total of 262 submissions and thus gives a comprehensive view on the state-of-the-art in computer analysis of images and patterns, research, design, and advanced applications. The papers are organized in sections on invariants, segmentation and grouping, optical flow, model recovery and parameter estimation, low level vision, motion detection, structure and matching, active vision and shading, human face recognition, calibration, contour, and sessions on applications in diverse areas.

Beschreibung / Inhaltsverzeichnis: PREFACE In recent years, there has been increasing interest from geoscientists in potassic igneous rocks. Academic geoscientists have been interested in their petrogenesis and their potential value in defining the tectonic setting of the terranes into which they were intruded, and exploration geoscientists have become increasingly interested in the association of these rocks with major epithermal gold and porphyry gold-copper deposits. Despite this current interest, there is no comprehensive textbook that deals with these aspects of potassic igneous rocks. This book redresses this situation by elucidating the characteristic features of potassic (high-K) igneous rocks, erecting a hierarchical scheme that allows interpretation of their tectonic setting using whole-rock geochemistry, and investigating their associations with a variety of gold and copper-gold deposits, worldwide. About twothirds of the book is based on a PhD thesis by Dr Daniel MOiler which was produced at the Key Centre for Strategic Mineral Deposits within the Department of Geology and Geophysics at The University of Western Australia under the supervision of Professor David Groves, the late Dr Nick Rock, Professor Eugen Stumpfl, Dr Wayne Taylor, and Dr Brendon Griffin. The remainder of the book was compiled from the literature using the collective experience of the two authors. The book is dedicated to the memory of Dr Rock who initiated the research project but died before its completion...