bluuebunny/crossref_metadata_2025_split huggingface dataset:
The conference on magnitude of deviatoric stresses in the Earth's crust and uppermost mantle
Authors: Hanks Thomas C. , Raleigh C. Barry 
Published: February 2008

The magnitude of deviatoric stresses in the earth's crust and uppermost mantle, and especially the magnitude of shear stresses that resist plate motions across the major plate boundaries, is a matter of central importance to solid earth geophysics. Since currently available estimates vary by at least a factor of 10, even when the same features or set of observations are involved, such fundamental issues as the driving mechanism(s) of plate tectonics and the energetics of crustal faulting are entirely unresolved. More generally, there is very little in the study of active geologic processes of geophysical interest that does not involve material deformation of some kind or another; in understated terms the analysis of material deformation to reveal causative processes is poorly constrained when the magnitude of the deviatoric stresses involved is so uncertain.Apart from the obvious problem of our inability to measure directly deviatoric stresses in the earth's crust and uppermost mantle through all but a small fraction of its depth—or sample directly this region in any other way at the present time—a confounding difficulty exists in the great range of time scales involved in geophysical processes of interest, from fractions of seconds for the spontaneous failure of small crustal earthquakes to billions of years for the relaxation of certain topographic and gravimetric features of the continental crust. It is probably naive then to expect that the same magnitude of deviatoric stresses should exist for all these geologic processes, given the great range of time scales over which they operate. Moreover, the earth's crust and uppermost mantle are heterogeneous enough, especially in continental regions, that significant spatial variations probably exist as well. Certainly, an important problem is whether the actual variations in space and time of deviatoric stresses in the earth's crust and uppermost mantle can be large enough to accommodate the order of magnitude differences as presently perceived or whether our present perceptions are only imagined, in one sense or another. Even so, we can be assured that at least some of our perceptions must be imagined, when deviatoric stress estimates differing by an order of magnitude or more are offered to explain the same basic processes or the same observations of them.
Lu‐Hf constraints on the evolution of lunar basalts
Authors: Fujimaki Hirokazu , Tatsumoto Mitsunobu 
Published: February 2008

Very low Ti basalts and green glass samples from the moon show high Lu/Hf ratios and low Hf concentrations. Low‐Ti lunar basalts show high and variable Lu/Hf ratios and higher Hf concentrations, whereas high‐Ti lunar basalts show low Lu/Hf ratios and high Hf concentrations. KREEP basalts have constant Lu/Hf ratios and high but variable Hf concentrations. Using the Lu‐Hf behavior as a constraint, we propose a model for the mare basalts evolution. This constraint requires extensive crystallization of the primary lunar magma ocean prior to formation of the lunar mare basalt sources and the KREEP basalts. Mare basalts are produced by the melting of the cumulate rocks, and KREEP basalts represent the residual liquid of the magma ocean.Lu and Hf concentrations and the Hf isotopic data of lunar rocks suggest that assimilation cannot be accepted as a major process to explain the diversity of the lunar mare basalts. The urKREEP hypothesis is also unnecessary. Both high‐ and low‐Ti basalts show enough iron enrichment to be regarded as melting products of the last stage cumulate rocks from the lunar magma ocean. The KREEP basalts are also rich in iron and may be regarded as the final, residual liquid left after the crystallization of the major portion of the primary lunar magma ocean.
Gas exchange on Mono Lake and Crowley Lake, California
Authors: Wanninkhof Rik , Ledwell James R. , Broecker Wallace S. , Hamilton Mike 
Published: February 2008

Gas exchange coefficients have been determined for freshwater Crowley Lake and for saline Mono Lake through the use of a man‐made purposefully injected gas, sulfur hexafluoride (SF6). The concentration decreased from an initial value of 40×10−12 mol/L to 4×10−12 mol/L for Mono Lake and from 20×10−12 mol/L to 1×10−12 mol/L for Crowley Lake over a period of 6 weeks. Wind speed records from anemometers on the shore of each lake enabled us to determine the relationship between the gas exchange coefficient k and wind speed u. The average wind speed and average exchange coefficient for the experiment were identical for the two lakes (uav=2.9 m/s, kav=2.5 cm/h), despite a large difference in size and chemical composition.From laboratory experiments and theoretical calculations it is estimated that for wind speeds observed over Mono Lake from July until December 1984 the exchange of CO2 occurred 2–½ times faster than without chemical enhancement. This is a factor of 4 lower than needed to explain the high invasion rate of 14C produced by nuclear bomb tests.
Dispersive digital filters
Authors: Robinson Enders A. , Treitel Sven 
Published: February 2008

Suites of wavelets or filters having identical amplitude spectrums are of interest because of the insight they can yield into the fundamental nature of the seismic pulse. Wavelets of a given suite are obtainable from each other by passing them through an appropriate set of dispersive filters. Such filters are of the pure phase‐shift kind; that is, their amplitude characteristic is constant and independent of frequency, whereas their phase‐lag characteristic is a prescribed function of frequency. In general, the wavelets of a given suite can be distinguished from each other on the basis of the ‘partial energy’ curve. This curve describes how the energy of a wavelet is distributed over the time range of its duration. The ‘minimum‐delay’ wavelet of a suite is the one whose energy is concentrated at its front, whereas the ‘maximum‐delay’ wavelet of the same suite is the one whose energy is concentrated at its end. Wavelets whose energies are concentrated at intermediate positions between these extreme cases are of the ‘mixed‐delay’ type. Of the wavelet members of a given suite, the minimum‐delay wavelet has a phase‐lag characteristic that lies as near as possible to the frequency axis, whereas the maximum delay wavelet has a phase‐lag characteristic which lies as far away as possible from the frequency axis. The phase‐lag characteristics of the mixed‐delay wavelets of a given suite all fall between the phase‐lag characteristics of the minimum‐ and maximum‐delay wavelet members of this suite.Phase‐shift filters may be either one‐sided or two‐sided; that is, phase‐shift filters may have a pure memory component, a pure anticipation component, or both a memory and an anticipation component. Phase‐shift filters with a pure anticipation component are the inverses of corresponding phase‐shift filters with a pure memory component. This paper treats the general class of phase‐shift filters, but with primary emphasis on the important subclass of dispersive filters. The amplitude characteristic of such filters is unity for all frequencies, whereas their phase‐lag characteristic is such that differential delays or advances are introduced into each frequency component. A pulse passed through such a filter will change its shape, even though its amplitude characteristic remains unaltered.We consider the impulsive response of a horizontally stratified, perfectly elastic and homogeneous medium, whose deepest interface is a perfect reflector. Both source and detector are located at the surface, and we treat only normally incident P‐wave motion. Then the reflected response of the layered medium is expressible as the transfer function of a dispersive filter. This means that the partial energy curve of the reflected response lies everywhere below the partial energy curves of an arbitrary source wavelet used to excite the medium.
Rapid estimation of the topographic disturbance to superficial thermal gradients
Authors: Lachenbruch Arthur H. 
Published: February 2008

The Jeffreys‐Bullard theory of the topographic correction to geothermal gradients cannot be applied with confidence if the height of the relief is large relative to the horizontal distance and depth of the measurement points. It cannot be generally applied to shallow probe measurements in the ocean bottom if bold relief occurs on a scale exceeding a few meters, or on continents to observation in shallow boreholes in extremely rugged terrain.In an important special case, where the measurement depth is small relative to the distance to the relief, the ‘superficial’ gradient anomaly may be approximated by the value applicable at zero depth. A fairly general two‐dimensional steady‐state theory for this case can be based on the solution for heat flux through an inclined plane of arbitrary height and slope angle. These two parameters are easily visualized and represented graphically so that models which approximate or bracket real topography can be identified quickly. The results can be applied to stations on planes, valleys, ridges, or benches bounded by irregular slopes. They are valid for points arbitrarily close to slopes of any height or inclination. Finite slope and curvature of the surface at the station can be accommodated if they are not too great. Even if other theories of the topographic correction are applicable, the present method can be useful, as it leads to rapid estimates by graphical means and to useful limits even if the superficial condition is not satisfied.Curvature in an ocean‐bottom temperature profile justifies suspicion of a topographic disturbance from undetected relief. The temperature probe's length should be 2 or 3 times the uncertainty in local elevation difference, and measured curvature should be negligible for reasonable assurance that undetected relief is not causing gradient errors greater than ±10%. Relief not detectable with conventional echo sounders, but of the type observed with deeply towed sounding equipment, can cause heat‐flow anomalies of 50–100%, and relatively little curvature will be indicated by probes a few meters long. The very high oceanic heat flows are difficult to explain by undetected relief, but the very low ones are not.
Understanding and constructively using the effects of underground nuclear explosions
Authors: Rodean Howard C. 
Published: February 2008

This report describes the unclassified research that is directed toward the understanding of underground nuclear explosion phenomena and that is applied to developing constructive applications for nuclear explosions.The equations of state for geological materials are of fundamental importance in describing the response of these materials to nuclear explosions. These equations are based on geophysical and laboratory measurements of chemical and physical properties and on theoretical calculations for the high‐pressure and high‐temperature conditions not accessible to measurement. Physical measurements of ground motion generated by explosions are used, together with the equations of state, chemical and thermodynamic theory, and the laws of continuum mechanics, to develop mathematical models for predicting explosion phenomena.Postshot exploration is necessary to determine the residual explosion effects, such as heat deposition, rock fracturing, and chimney formation. These explorations give physical and chemical clues that aid in the interpretation of the experiment. Furthermore, the residual effects are of interest in many engineering applications.Safety considerations include airblast and seismic motion that may damage property and radioactivity that may be a health hazard. Significant progress has been made in predicting airblast, ground motion, and radioactivity distribution, but more work needs to be done in order that these hazards be predictable with a known statistical accuracy.Nuclear explosions are intense sources of neutrons; therefore, experiments are conducted to measure neutron cross sections and to produce heavy elements. The heaviest nuclide produced to date by this technique has a mass number of 257. The seismic waves generated by nuclear explosions have been used by geophysicists for more than two decades to determine the internal structure of the earth with a precision not possible with earthquakes. Finally, research is under way to relate the effects of an explosion to its intended use (in the petroleum industry, for example).
Experimental metamorphic petrology
Authors: Hewitt D. A. , Gilbert M. C. 
Published: February 2008

The past quadrennium, 1971–1974 inclusive, has seen a great variety of published work in experimental metamorphic petrology. Numerous phase equilibrium studies as well as many determinations of physical properties of minerals have been produced. Whereas the last report contained 270 references, this report contains over 475, illustrative not only of the activity of the science but also of the wider scope of articles necessary to describe the interactions within modern petrology.In this review, metamorphism has generally been taken to cover the temperature range from 10O°C to the solidus in the appropriate bulk compositions and mineral groups. A few articles containing liquidus data have been referenced when significant subsolidus data were also included. Most of the references are in the English language and from North American—or European‐based publications. Unavoidably, many pertinent foreign experimental data are excluded. Nevertheless, trends in research are thought to be reasonably well displayed. An attempt was made to keep the review as current and useful as possible by including abstracts from the principal meetings, in 1974, of the Geological Society of America and the American Geophysical Union.
The state of stress in the Earth's crust
Authors: Haimson Bezalel C. 
Published: February 2008

This article is limited to a short state of the art report on available methods of stress determination in situ and a summary of findings to date.Stress determination at depth requires the drilling of a hole to the level of interest. Most of the methods employ sophisticated instrumentation down the hole and require overcoring for relieving the stresses. Because of the necessity to overcore, hole length is limited to 30–40 m. Hence these methods are useful only in stress measurements near the surface of the earth or at depth if previous access has been obtained through underground chambers, tunnels, or mine openings. A variety of measuring methods have been developed which determine either changes in hole diameter or strain on the bottom of the hole resulting from the complete relief of the stress due to overcoring.
Thermal structure of the ionosphere
Authors: Brace L. H. 
Published: February 2008

This report presents a brief review of the progress that has been made in the past 4 years or so toward gaining a more complete understanding of the thermal structure of the ionosphere, with particular emphasis on research in the United States.Knowledge of the electron temperature Te and the ion temperature Ti is of fundamental importance in our attempts to understand the processes that occur in the upper reaches of our atmosphere because most thermospheric processes tend to heat or cool the electrons that make up the ionosphere, and the ion temperature is coupled to both the electron temperature and the neutral gas temperature Tn. The current state of theoretical knowledge about the ionosphere temperature has been reviewed by Schunk and Walker [1973], who provided references for the work up to that time.
A review of F region dynamics
Authors: Evans J. V. 
Published: February 2008

The photochemical processes responsible for the formation of the F region of the ionosphere were identified from radio wave reflection and rocket experiments prior to 1960 (for review, see Rishbeth [1967a], D. R. Bates [1973, 1974], and Ratcliffe [1974]). It was long recognized that dynamical processes are also extremely important in governing the F layer, but it was not until the decade between 1960 and 1970 that two of the most important processes for setting the plasma in motion horizontally, namely, thermospheric winds and magnetospheric convection, were recognized and confirmed by observation. During the past 4 years, progress in understanding the dynamics of the F layer has largely been made through experimental measurements that have provided detailed information on these two phenomena.On the theoretical side, there have been considerable advances in developing time‐dependent computer models of the F region which incorporate the photochemical processes, the thermal structure, and the transport arising as a result of neutral winds in an internally self‐consistent manner. These permit one to test the relative importance of various phenomena in contributing to the observed behavior and estimating the magnitude of some parameters which remain poorly known. There have also been important developments in understanding the phenomenon of the escape of plasma at high latitudes into field tubes that have been emptied of ionization; however, many of these ideas still await experimental confirmation.
Precipitation research, 1975–1978
Authors: Court Arnold 
Published: February 2008

Precipitation research in the United States during the past quadrennium, 1975–1978, has been directed at all three steps of a scientific discipline: description, explanation, and prediction. Most of the work, however, has been in describing, in various ways, the occurrence of precipitation: instruments and measurements, stochastic and analytic models, and accounts of extremes of precipitation or lack thereof: deep snows, cloudbursts and hurricane rains causing floods, unusually wet periods and droughts.These observed precipitation patterns were explained, somewhat, in a few papers as arising from variations in the inputs to general circulation models (changes in atmospheric dust or in sea surface temperatures) as well as from local causes: changes due to urbanization, irrigation, or industry, and to the apparent effects of weather modification experiments and operations. Prediction has made considerable progress by using multivariate regressions (“Model Output Statistics”) to relate the probability of precipitation (“PoP"), and even its amount in quantitative precipitation forecasts ("QPF”), to the various predictions, 12, 24, and 36 hours in advance, of operational circulation models (PE, LFM, etc.). Each of these aspects of precipitation research will be discussed in the order given.
Internal waves, finestructure, microstructure, and mixing in the ocean
Authors: Gregg M. C. , Briscoe Melbourne G. 
Published: February 2008

Progress in measuring, interpreting, and understanding oceanic internal gravity waves and fine and microstructure is reviewed; we emphasize the quadrennium 1975–1978. The context is how these subjects contribute to oceanic mixing. The overlap between the areas is examined, as is the relevance of the subjects to other aspects of oceanography.Present trends and suggestions for future work are included, and we offer some speculation on possible progress during the next quadrennium, which may be substantial especially for finestructure understanding.
Planetary surfaces
Authors: Mutch Thomas A. 
Published: February 2008

This review paper has several aims: first, briefly to characterize planetary photogeology as a scientific discipline; second, to provide some sense of the rapid emergence of this field; third, to systematically review the literature over the past few years; and fourth, to identify the more significant problems for future analysis.To some degree, the four sections dictated by these goals speak to different audiences. Those unfamiliar with the progress in our understanding of planetary surfaces may be best entertained by a broad overview. Those involved in related science may find more useful the brief citations of the recent literature.
The Global Atmospheric Research Programs's Atlantic Tropical Experiment
Authors: Greenfield Richard S. , Fein Jay S. 
Published: February 2008

The Global Atmospheric Research Program (GARP) was described in some detail in the last U.S. National Report (Perry, 1975). The latest GARP activities are discussed in another contribution to this report. In this section, we will describe the major research activities that followed the GARP Atlantic Tropical Experiment (GATE) of 1974.From the beginning of GARP, the tropics were identified for special attention. The tropical zones, of course, are the primary source of heat driving the general circulation of the atmosphere. The phenomena that transmit the necessary energy to the middle latitudes are not adequately treated in the large‐scale models of the general circulation. To a large extent this inadequacy is due to significant gaps in our understanding of the physical processes involved in deep cumulus convection and the interactions between convection and the other dominant scales of atmospheric phenomena. GATE was designed to obtain data that permit research on the effects of smaller scale tropical systems on the larger scale circulations. The ultimate objective of GATE is to improve and verify tropical numerical models.
Synthetics and theoretical seismology
Authors: Harkrider David G. 
Published: February 2008

In the near field, discrete‐finite wave number schemes are economic since they involve fewer wave numbers than most wave number integration schemes. The number of wave numbers is determined by the range and the location of artificial reflectors or fictitious sources inherent in discrete wave number techniques. The number and spacing of wave numbers in wave number integration schemes are determined by the desired accuracy.The vertical integration schemes used in the near field have been either spectral (Apsel, 1979, Bouchon, 1981) as in the regional techniques or finite‐element (Olson,1982) and finite‐difference in the time domain as in the Alexseev‐Mikhailenko method. The finite element schemes have the disadvantage in that the vertical step size is determined by the desired maximum frequency content, which in turn determines the time step required for stability. This time step is usually many times smaller than the time increment associated with the maximum frequency.
Heliospheric shocks (excluding planetary bow shocks)
Authors: Mihalov J. D. 
Published: February 2008

Even though it took place less than halfway through the last four year period, the AGU Chapman Conference in Napa Valley, California, during February, 1984, highlighted in many ways current U. S. contributions to the study of heliospheric shocks. Considerable recent progress in the theoretical understanding of these discontinuities has been summarized in the collections of the review papers from the Conference, so that those excellent papers have been an important source for the preparation of this Report.In addition, detailed analyses of ISEE‐3 interplanetary shock observations, and reports on additional data from the outer heliosphere, particularly major disturbances during 1982, have been published since the last Quadrennial Report, and are summarized hereafter. The Pioneer and Voyager spacecraft in the outer heliosphere also have traveled closer to the heliospheric boundary, and further inferences of the boundary location have been made, although it has not yet been directly detected. In addition, details are not yet available concerning the type of shock transition with which it may be associated. More general characteristics of shocks in the outer heliosphere, and out of the solar equatorial plane to ∼25 deg latitude or more, are available from the Pioneer and Voyager data. Also, collection and analyses of data from the inner heliosphere have been extended. Finally, new analyses and observations of coronal shocks have been done, and theoretical studies of this phenomenon have been advanced.