Geophysical Aspects Research Articles

Bistatic observations of Titan's surface with the Huygens probe radio signal

Huygens provided an unanticipated bistatic radio scattering experiment from Titan's surface. After a successful entry and descent on Titan, on 14 January 2005, the probe remarkably survived the landing and continued radioing from the surface to the overflying Cassini, until the orbiter set below Titan's local horizon. Here we report high‐quality measurements of the 2098 MHz (14.3 cm) postlanding radio signal, focusing on the striking variations observed in signal strength. The mechanism that creates this fading pattern is physically interpreted as multipath interference between the direct signal and the signal reflected on Titan's surface. The geophysical aspects that could bear on the signal analysis are described.

Estimating mud expulsion rates from temperature measurements on Håkon Mosby Mud Volcano, SW Barents Sea

The Håkon Mosby Mud Volcano (HMMV), located on the Norwegian–Barents–Svalbard continental margin in 1250 m water depth, has been identified and described as a structure caused by upward transport of mud, pore water and gas [e.g. Eldholm, O., Sundvor, E., Vogt, P.R., Hjelstuen, B.O., Crane, K., Nilsen, A.K., Gladczenko, T.P., 1999. SW Barents Sea continental margin heat flow and Håkon Mosby Volcano. Geo-Marine Letters 19, 29–37]. During RV Polarstern expedition ARK XIX/3b in 2003, an integrated study took place to investigate the detailed morphology, biology, chemistry and geophysical aspects of HMMV [Klages, M., Thiede, J., Foucher, J.-P., 2004. The Expeditions ARK XIX 3a, 3b and 3c, Berichte zur Polarforschung, 488.]. In this paper, we describe a detailed survey involving more than 100 temperature gradient measurements in order to reveal the temperature structure of HMMV. Values of apparent heat flow up to 3000 mW/m 2 and absolute temperatures up to 25.8 °C have been detected. These enormously high heat flux values do not reflect deep-seated thermal gradients but are a result of surface mud flows. The occurrence and abundance of mud flows varies in different areas within the HMMV inner crater. A combination of very shallow, ROV-derived temperature measurements, a large number of intermediate depth temperature gradients and nine deep penetrating gravity corers allows us to reconstruct the history of activity of HMMV. Modeling of the observed temperature gradients indicates vigorous activity with very recent mud flows. Furthermore, the supply of energy and material from the HMMV is estimated to have an annual mass volume of ∼15,000 m 3. From the thermal corona of HMMV and the observed horizontal heat flux, it is possible to deduce that the long term temperature of the mud pond is stable at a temperature approximately similar to the recent maximum temperature of 25 °C.

G‐Cubed: A snapshot today and a look to the future

<i>G‐Cubed</i>: A snapshot today and a look to the future

Specific features of the deep structure of the Novo-Elkhov and Romashkin hydrocarbon fields based on geoelectric data

In recent decades, problems of the active role of fluid factor in the structural transformations of lithosphere matter and its influence on the genesis of oil and ore deposits have been discussed in several publications [1‐3]. In our work, we present experimental results of electromagnetic studies, which allow us to analyze the structural‐tectonic links between the location of large (Romashkin and Novo-Elkhov) oil fields with trends in the distribution of electrical conductivity σ of rocks at depths from 10 m to 100‐120 km. Along with the mineral composition of rocks, conductivity σ is an important physical parameter that characterizes the rheological properties of the medium, such as convective heat and mass transport, filtration of melts in the asthenosphere, viscous and brittle deformations in the crust, hydrothermal circulation, and others. This new information about the composition and state of the Earth’s interior significantly complements the data on seismometry, deep seismic profiling, gravimetry, and other geophysical methods. Choice of the study region was not accidental. Both oil fields are located in the sedimentary cover of the South Tatarstan Dome (STD) in the East European Platform, where crystalline rocks of the basement are located comparatively not very deep (1750‐1850 m) below the surface. This territory has been studied well in the geological and geophysical aspects. Numerous wells drilled in this region include two superdeep ones (Fig. 1, wells 20000 and 20009). Borehole 20000 recovered soft and fissured basement rocks in the depth interval 4700‐5099 m, characterized by the circulation of highly mineralized solutions saturated with gases and hydrocarbons [2]. High level of low-temperature hydrothermal processing of the basement with the indications of hydrocarbon-containing fluids was found in Borehole 20009 at great depths [1]. Thus, geostructural factors of the STD indicate that geoelectric prospecting can be successfully used for solving the problem formulated in our work. Before the beginning of the work, we had some data concerning the electrical resistivity ( ρ ) of the sedimentary cover based on the borehole logging data [2] and the transient field sounding method [4]. However, they do not allow us to find the relation between the fluid saturation of the medium with specific features of the geotectonic structure in the consolidated part of the section. Such problems can be solved by applying the methods of deep geoelectric prospecting, including magnetotelluric methods.

Understanding the concept of outlier and its relevance to the assessment of data quality: Probabilistic background theory

Abstract In recent years an increasing interest in the studies on outlier can be observed, however, for the time being there exists no general definition of outlier. In the present paper we introduced a generic descriptive definition of outlier. We observed that the outlier problems had so far been treated in statistical way without paying proper attention to probabilistic-theoretic backgrounds. In view of this gap, we made an attempt to establish a probabilistic background theory. Within this framework, the large deviations are considered as probabilistic-theoretic model of outlier, and the interrelationship of the laws of large numbers, the central limit theorems and the large deviations are clarified. These considerations are specialized for the case of statistical sample, which is important from the point of view of the assessment of data quality. Some methodological and historical aspects of geodesy, geophysics and astronomy are mentioned, too. We revealed that the data analysis carried out by Kepler in the process of discovery of his famous elliptic law of planetary motion has relevance to the outlier problem. This methodologically interesting fact is a new result in the history of geosciences. We established that the accuracy of Chebyshev inequality increases as the deviation of the random variable involved from its expectation, increases. The possibility of application of Chebyshev inequality to the outlier problem is pointed out.

Some snapshots from fifty years of geophysics

A person lucky enough to have worked in different aspects of geophysics in Australia over the last fifty years is sure to have a treasure trove of rich memories. Australia has the great good fortune to be a whole continent within one national boundary, and to be a marvellous laboratory for geophysical methods. The developments in geophysics which have taken place in Australia have been based, and have indeed been possible, because of strong rigorous traditions existing in mathematics, physics and geology. A perspective to the present state of geophysics is obtained be re-visiting various geophysical experiences over fifty years. The path followed commences with trigonometrical surveying (which allows the fifty years time span!) and progresses through various aspects of magnetic and electromagnetic measurements. Part of the journey takes place on land, some is airborne, and some is by sea. Developments in electronics, and computers, have made geophysics a rapidly-developing and exciting subject. The last fifty years of exploration work in Australia have taken place against the proving and acceptance of continental drift, plate tectonics and mantle convection. It has therefore been a time of remarkable intellectual stimulation and activity, of the widest possible importance to humankind.

Introduction to this special section—Seismic survey design

It is probably true to say that many consider seismic survey design a niche topic in geophysics. Practitioners of this science inhabit a world halfway between that of the geophysicist and that of the operations specialist. They have to consider the geophysical aspects of design as well as the constraints placed upon them by the environment, the recording equipment and, of course, their budgets. While all geophysicists should understand the principles of survey design, few will actually be directly involved in a design study. However, effects of the design are felt all the way through the process, from acquisition to data processing and interpretation. An understanding of the inevitable trade-offs and compromises made during acquisition will help geophysicists to understand the limitations and nature of their data. In addition, as oil companies strive for efficiency and seek to acquire higher-quality and more cost-effective seismic surveys, greater emphasis is being placed on the design process. Given the significance of the topic, staying abreast of its developments is important. That is one of the objectives of this special section. A factor that makes survey design such a fascinating subject is that the “rules” are continually changing—not the fundamental rules of geophysics but what can actually be achieved in the field. As new acquisition systems and techniques appear, they alter the limitations placed on survey designers. The increasing numbers of channels available in both land and marine acquisition is an obvious example. Channel count has been rising since the earliest days of seismic prospecting, allowing not only larger spreads but also denser sampling. Not surprisingly, increasing channel counts and denser sampling are subjects covered in more than one of the papers in this special section. In addition to channel counts, it is worth reflecting on some other major influences in the last decade …

Giant tortoises are not so slow: rapid diversification and biogeographic consensus in the Galápagos.

Isolated oceanic archipelagos have played a major role in the development of evolutionary theory by offering a unique setting for studying spatial and temporal patterns of biological diversification. However, the evolutionary events that cause associations between genetic variation and geography in archipelago radiations are largely unknown. This finding is especially true in the Galápagos Islands, where molecular studies have revealed conflicting biogeographic patterns. Here, we elucidate the history of diversification of giant Galápagos tortoises by using mtDNA sequences from 802 individuals representing all known extant populations. We test biogeographic predictions based on geological history and assess the roles of volcano emergence and island formation in driving evolutionary diversification. Patterns of colonization and lineage sorting appear highly consistent with the chronological formation of the archipelago. Populations from older islands are composed exclusively of endemic haplotypes that define divergent monophyletic clades. Younger populations, although currently differentiated, exhibit patterns of colonization, demographic variation and genetic interchange shaped by recent volcanism. Colonization probably occurs shortly after a volcano emerges through range expansion from older volcanoes. Volcanism can also create temporal shifts from historical to recurrent events, such as promoting gene flow by creating land bridges between isolated volcanoes. The association of spatial and temporal patterns of genetic variation with geophysical aspects of the environment can best be attributed to the limited dispersal and migration of tortoises following an oceanographic current. The endangered giant Galápagos tortoises represent a rapid allopatric radiation and further exemplify evolutionary processes in one of the world's greatest natural laboratories of evolution.

Kazim M. Ergin (1915-2002)

The international community of Earth scientists was saddened by the death of Professor Dr. Kazim M. Ergin on 24 November 2002. Dr. Ergin possessed the rare distinction of excelling professionally in both the applied and theoretical aspects of geophysics, with accomplishments both in industry and in academia. He was born in 1915 in the city of Gaziantep, Turkey. In 1937, while attending the University of Istanbul and pursuing a degree in mathematics, he was awarded a scholarship from the Mineral Research and Exploration (MTA) Institute to study geology in Germany. After a short while there, his studies were interrupted by World War II. Fortunately, he was able to resume his education at the Massachusetts Institute of Technology, where he was awarded a B.S. in Geology. He then moved to Caltech to pursue graduate work toward the degrees of M.S. and Ph.D. At Caltech he studied under world-renowned theoretical seismologist Beno Gutenberg and several other prominent scientists. Upon receiving his M.S. degree (1943), …

An Introduction to Geophysical Exploration: Third Edition

Finding a modern textbook that covers all aspects of exploration geophysics is difficult, but An Introduction to Geophysical Exploration certainly fills the bill. Appropriate for an introductory course addressing a range of techniques the book's breadth is demonstrated by comprehensive inclusion of non‐seismic exploration methods. In fact, half of the book is devoted to non‐seismic methods, providing students with a permanent reference to these infrequently applied exploration methods.This book came to my attention while I was ordering textbooks for a course in exploration geophysics only to find that the text of my choice was out of print. I quickly substituted An Introduction to Geophysical Exploration, and it has served the class well, including senior‐level undergraduates and first‐year graduate students in both soft‐rock geology and geophysics. The material is comprehensive and well organized. The non‐seismic topics include not only chapters on potential fields— one each on gravity and magnetic methods— but also chapters on electrical and electromagnetic methods, including ground‐penetrating radar (GPR). Short chapters on radiometric surveying and borehole logging are also provided.

Geophysical aspects of very long baseline neutrino experiments

Several proposed experiments will send beams of neutrinos through the Earth along paths with a source–receiver distance of hundreds or thousands of kilometers. Knowledge of the physical properties of the medium traversed by these beams, in particular the density, will be necessary in order to properly interpret the experimental data. Present geophysical knowledge allows the average density along a path with a length of several thousand kilometers to be estimated with an accuracy of about ±5%. Physicists planning neutrino beam experiments should decide whether or not this level of uncertainty is acceptable. If greater accuracy is required, intensive geophysical research on the Earth structure along the beam path should be conducted as part of the preparatory work on the experiments.

Neural networks as an intelligence amplification tool: A review of applications

The sophisticated algorithms we use to process, analyze, and interpret geophysical data automate tasks we used to do by hand, transform data into domains where patterns are more obvious, and allow us to calculate quantities where we used to rely on intuition or back‐of‐envelope estimates. But, the crux of the exploration problem is still interpretation—associating abstract patterns with geologic formations of economic value. Artificial neural networks are able to couple the speed and efficiency of the computer with the pattern recognition and association capabilities of the brain to aid the exploration process. The key concept to understand in the application of neural network technology is that they should not be used as an artificial intelligence tool to replace a human interpreter; rather, neural networks are an intelligence amplification toolkit that allows the interpreter to focus on the important information.More than 102 neural network papers have been published by SEG since 1988, and more than 550 neural network papers pertaining to any aspect of geophysics were published in that same time period. Neural network applications in exploration geophysics can generally be divided into two eras. The focus through 1994 was largely on learning what neural networks could do with different data sets, and how to prepare data for them and analyze the results. Networks were usually trained with synthetic data and then tested with field data. The second era, from 1995 to the present, has focused on some specific application areas such as reservoir characterization. The current emphasis is to integrate neural networks within a comprehensive interpretation scheme instead of as a stand‐alone application. Neural network technology has helped us turn data into information by allowing us to find nontrivial correlations between geophysical data and petrophysical properties; relate detailed changes in wavelet morphology to small‐scale changes in lithology; and find features in the wavelets that allow us to locate first breaks, track horizons, identify gas chimneys, or trace faults; and attenuate multiples. As the science and engineering of data acquisition progresses, neural networks will play an increasingly vital role in helping us find relevant information in the vast streams of data under the constraints of lower costs, less time, and fewer people.

Euler, the theory of gravitation and some geophysical aspects

Euler's results concerning the theory of gravitation are discussed in this paper in order to give an insight into the scientific problems of Euler's age and his relation to Newton's work. Geophysical aspects are emphasized in his work.

Nielsen Receives 2001 Horton medal

Donald R. Nielsen was awarded the Robert E. Horton Medal at the AGU Spring Meeting Honors Ceremony, which was held May 31, 2001, in Boston, Massachusetts. The medal recognizes outstanding contributions to the geophysical aspects of hydrology.

Whither geophysical technology: A true paradigm shift?

Fast, inexpensive personal computers can and will revolutionize all aspects of exploration geophysics. Computational power, graphical display, data storage, and man-machine interaction will rapidly evolve to a new and radically different paradigm from what we see today. What was once viewed as an environment suitable only for personal use now performs at a level exceeding that of the first Crays. Internal storage resources easily handle data volumes of almost any size.

Wolman receives 2000 Robert E. Horton Medal

M. Gordon Wolman was awarded the Robert E. Horton Medal at the AGU Spring Meeting Honors Ceremony, which was held on June 2, 2000, in Washington, D.C. The medal recognizes outstanding contributions to the geophysical aspects of hydrology.

Brutsaert receives 1999 Horton Medal

Wilfried H. Brutsaert was awarded the 1999 Horton Medal at the AGU Fall Meeting Honors Ceremony, which was held on December 15, 1999, in San Francisco, California. The Horton Medal is given for outstanding contributions to geophysical aspects of hydrology.

Preliminary results of the ultralong-range sounding of ionospheric irregularities using the ducted mode

We present preliminary experimental results concerning transequatorial propagation (TEP) of HF waves upon chirp sounding over the 11950-km path alice Springs (Australia)-Yoshkar-Ola (Russia). The measurements were made in August, 1998. Two anomalous signals with delays of 3.0 and 4.5 ms with respect to the main mode were observed during night time (21:30–23:00 UT). The maximum observed frequencies (MOF) of these signals were 2–3 MHz greater than the main-mode MOF. Simulations allowed us to identify these signals as the ducted signals trapped in theFE interlayer duct due to radiowave refraction on a negative gradient of the electron density and that escaped from the duct due to the scattering by small-scale field-aligned irregularities of the subpolar ionosphere. We discuss radiophysical and geophysical aspects concerning localization of the irregularities responsible for scattering and perspectives of using the ducted mode for over-the-horizon diagnostics of the inhomogeneous structure of the ionosphere with a global network of chirp sounders and HF radars.

Geophysical Aspects of Problems in Interpretations of Icelandic Radiocarbon Dates of Archaeological Samples

The philosophy behind the radiocarbon dating method is briefly described from an historical standpoint, including normalizations, secular activity variations and calibrations. Special attention is paid to the global atmospheric radiocarbon activity differences (regional variations of the radiocarbon in carbon dioxide), which have long been under scrutiny. Apart from carbon dioxide of volcanic origin or from wells, these are chiefly attributed to oceanic circulation and the exchange between the carbon dioxide in the atmosphere and that in the oceans.

The Emergence of the Diversity of Igneous Rocks As A Geological Problem: Part One—Early Speculations

Speculation about igneous rock diversity began in the first half of the nineteenth century after acceptance of the existence of ancient volcanism and the recognition of two fundamental types of lava: basalt and trachyte. Before 1850, George Poulett Scrope (1797-1876), Charles Darwin (1809-1882), and James Dwight Dana (1813-1895) attributed diversity to intumescence of gas-rich lava, crystal settling, and differential fusion of minerals. In the 1850s, Robert Bunsen (1811-1899) maintained that lava is derived from two deep normal trachytic and normal pyroxenic sources. Wolfgang Sartorius von Waltershausen (1809-1876), Joseph Durocher (1817-1860), and Ferdinand von Richthofen (1833-1905) universalized Bunsen's sources by postulating a density-stratified Earth in which a layer of acid, feldspathic material rested above a layer of basic, basaltic material. Exploration of the complex volcanic terranes of western America in the 1860s and 1870s undermined the two-source theories and opened the way for the concept of fusion of already solid crust. Prior to 1880, speculations about diversity were typically suggested by naturalists, chemists, and geological generalists with strong interests in the geomorphic or geophysical aspects of Earth. Consequently, the problem of diversity was a peripheral concern to most of those proposing hypotheses. The hypotheses characteristically reflected the professional interests of their proposers. The content of the early speculations was further shaped by the nature of the field areas studied by proposers, and by their views on the correlation between geologic age and igneous rock type. Those, like Scrope, Darwin, Dana, Joseph Jukes (1811-1869), Carl Bernhard von Cotta (1808-1870), and Clarence Dutton (1841-1912), who rejected such correlations, located the source of igneous rock diversity at the surface, within a volcano, or within the acid crust. Those, like Bunsen, von Waltershausen, Durocher, von Richthofen, and Clarence King (1842-1901), who accepted the Wernerian idea that there had been changes in igneous rock type through time were more inclined to attribute diversity to multiple lava sources at great depth.