bluuebunny/crossref_metadata_2025_split huggingface dataset:
An experiment in the use of trained neural networks for regional seismic event classification
Authors: Pulli Jay J. , Dysart Paul S. 
Published: February 2008

A neural network employing the back propagation learning paradigm has been developed as an experiment in the automatic classification of small regional earthquakes and quarry explosions. The network has been used in the analysis of 66 events recorded by the NORESS array in southern Norway. The input vector consists of three broadband discriminants including the spectral ratios of Sn/Pn and Lg/Pn waves, and the mean cepstral variance of Pn, Sn, and Lg. Two hidden layers are used, consisting of 8 and 2 units. The output vector consists of two units which correspond to the classification of explosion or earthquake.The network was first trained using input vectors from the entire dataset. The network was able to perfectly model the training set with no classification errors. For comparison, an optimum linear classifier used with the same dataset resulted in 5 errors and 19 uncertain classifications. Next, the network was trained with half of the events and tested with the remaining half. This resulted in 5 errors and 2 uncertain classifications. This compares with 5 errors and 18 uncertain events for the optimum linear classifier. The apparent advantage of the neural network over the optimum linear classifier is the network's ability to model complex decision regions and in the reduction of the number of uncertain events.
Mechanism of parallel electric fields inferred from observations
Authors: Yeh H.‐C. , Hill T. W. 
Published: February 2008

An analysis of satellite data from regions of upward Birkeland (magnetic‐field‐aligned) current shows that the typical magnetic‐field‐aligned potential drop in the auroral zone is no larger than required to provide direct acceleration of magnetospheric electrons by the field‐aligned electric field against the upward magnetic mirror force to produce the observed upward Birkeland current. A model of simple electrostatic acceleration without anomalous resistivity predicts observable relations between parallel current and parallel potential drop and between energy deposition and parallel potential drop. The temperature, density, and species of the unaccelerated charge carriers are the relevant parameters of the model.Simultaneous measurements of electron precipitation and ion drift velocities on the satellites Atmosphere Explorer C and D were used to test these relations. In a steady state the divergence of ionospheric currents must be compensated by Birkeland currents. The model current‐voltage relation was applied to predict the densities of the primary charge carriers (i.e., plasma sheet electrons above the acceleration region for upward currents). In cases involving thin arc structures, where the reliable estimation of the divergence of ionospheric current is difficult and the steady‐state assumption may not apply, the precipitating energy flux versus voltage relation was used instead to predict the densities of the unaccelerated plasma sheet electrons. Within the experimental uncertainties, reasonable agreement is found between these predicted densities and those inferred directly from the simultaneous data of the Low‐Energy Electron Experiment. These results are interpreted as indicating that anomalous resistivity is not important in determining the magnitude of the field‐aligned potential drop in the auroral zone.
Evidence supporting the approximation γρ = const for the Grüneisen parameter of the Earth's lower mantle
Authors: Anderson Orson L. 
Published: February 2008

There has been no uniform acceptance of one theoretical formulation of the Grüneisen parameter formula over another. The application of a Grüneisen function to the earth's interior for temperature calculations by one author has been to some extent arbitrary, or at least held in doubt by others. In this paper, using only the seismic data of the earth, an argument is presented which supports the contention that an acceptable empirical law for the lower mantle is

urn:x-wiley:01480227:media:jgrb2944:jgrb2944-math-0001
where γ is the Grüneisen parameter and ρ is the density, where q is close to unity. Because of the range of the compression, no great error is made by taking q to be exactly unity for simplicity in the empirical formulae. However, a value of q anywhere in the band 0.8 < q < 2.2 is acceptable on the basis of the seismic data. By assuming the rule γρ = const, it is shown that it follows that αKT is independent of temperature and pressure and therefore depth in the lower mantle. The term α is the volume thermal expansivity, and KT is the isothermal bulk modulus.
Shallow earthquakes and active tectonics in eastern Afghanistan
Authors: Prevot R. , Hatzfeld D. , Roecker S. W. , Molnar P. 
Published: February 2008

Brief studies of microearthquakes in four separate parts of eastern Afghanistan reveal a high level of seismicity over a broad area. In general, the activity is not concentrated on well‐defined faults, nor does it define new faults, but seismicity on or close to the Chaman and Sarubi faults attests to their activity. First motions of P waves are consistent with left‐ and right‐lateral strike‐slip motion, respectively, on these two faults. Fault plane solutions and composite solutions of events in different areas throughout the region differ from one another, but in general, the P axes are parallel to the north‐northwest direction of relative motion between India and Eurasia. Several earthquakes beneath Kabul and its immediate surroundings emphasize a need for further study of its seismic hazard.The appendix is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document J80‐001; $1.00. Payment must accompany order.
Paleomagnetism of the Samail Ophiolite, Oman: 1. the sheeted dike complex at Ibra
Authors: Luyendyk Bruce P. , Laws Bruce R. , Day Ron , Collinson Thomas B. 
Published: February 2008

We have studied the rock magnetism and paleomagnetism of 200 oriented samples from the middle Cretaceous sheeted dike sequence of the Samail ophiolite, Oman. The samples are from 28 sites spanning a cross‐strike distance of 30 km. Most of the dikes have undergone green‐schist metamorphism. The natural remanent magnetization (NRM) of the samples is about 1 A/m and Qn is also near 1. Thermal and alternating field demagnetization treatment resolves both normal (north) and reversed (south) polarities. About one third of the samples have low median destructive fields (MDF) less than 100 Oe (7.96×103 A turn/m). These low MDF samples have scattered directions and are classified as undetermined polarities (U). Hysteresis measurements show pseudo‐single domain carriers predominate in all samples, although the low MDF samples are suggested to have the largest grains in the samples studied. Thermomagnetic curves show both magnetite and minor maghemite. Thermal demagnetization and microscopic study reveals that hematite is abundant and is the carrier of the R remanence. In addition, several dikes exhibit both N and R polarities. These facts, coupled with the degree of metamorphism, indicate that part of the remanence is secondary and could be due to hydrothermal metamorphism below the seafloor. We suggest that the N polarity is primary and resides in exsolved magnetite, while the R polarity is secondary and resides primarily in metamorphic‐origin hematite. Several short R events observed in the Albian through Cenomanian magnetostratigraphic record are candidates for the R event in the ophiolite if the R polarity originated near the spreading center. Alternately, nonreproducible self‐reversal is another possible origin for the R polarity. Regardless of whether the reversal originated at the spreading center, secondary magnetization in the dikes considerably increases the directional dispersion. Another major factor affecting dispersion is viscous remanent magnetization (VRM) in the larger magnetite grains. This extreme dispersion disallows the Samail ophiolite dike layer as a significant source for marine magnetic anomalies, regardless of the strength of the NRM or the value of Q.The stable N and R directions yield a paleomagnetic pole which is far sided, suggesting northward movement of the ophiolite. However, the paleomagnetic pole is not as far sided as the contemporaneous Africa pole, which suggests a component of north‐south closure between the ophiolite and Africa prior to northward movement.
Introduction to the seafloor mapping section
Authors: Detrick R. S. 
Published: February 2008

The widespread use of echo sounders on oceanographic research vessels in the years following World War II revolutionized marine geology by providing a technique for routinely measuring the depth of the seafloor along a ship's track. Within two decades, Precision Depth Recorders (PDRs) had been used to identify the major morphotectonic features in the ocean basins, and compilations of depths measured on thousands of cruise tracks yielded the first reliable global maps of seafloor topography [e.g., Heezen and Tharp, 1960, 1968; Chase et al., 1971]. The existence of these maps played an important role in the development and acceptance of the ideas of seafloor spreading and plate tectonics in the mid and late 1960s.During the past decade the emphasis in marine geology has shifted away from the reconnaissance geographical surveys of the 1950s and 1960s toward much more detailed studies aimed at investigating the important volcanic, tectonic, and sedimentological processes operating in the ocean basins. With this change has come the need for much higher‐resolution bathymetry maps and new techniques for rapidly surveying large areas of the seafloor. The result has been the development of a suite of new seafloor mapping tools with names like Deep Tow, Sea Beam, Sea MARC I and II, GLORIA, and Seasat. These new tools have provided some remarkable new images of the seafloor and promise to revolutionize our understanding of geological processes in the ocean basins in much the same way that the introduction of the precision depth recorder did 40 years ago.
Introduction to Special Section on Geophysical Investigations of Proposed Radioactive Waste Disposal Sites
Authors: Oliver H. W. 
Published: February 2008

A symposium on “Geophysical Investigations of Proposed Radioactive Waste Disposal Sites” was held at the Fall Meeting of the American Geophysical Union, December 13, 1982. Since then, five of the papers presented at the symposium have been published in the Journal of Geophysical Research and an additional six papers are included in this issue. Three of the current papers involve geophysical research at Yucca Mountain, Nevada; two papers are on subsurface structure and fracturing of the Strath‐Halladale granite in northern Scotland, a prime candidate for rad waste storage in the United Kingdom; and a general paper is included on the application of various geophysical methods for characterizing all the potential storage sites in the United States under consideration by the U.S. Department of Energy.In 1982, the following nine sites in the United States (Figure 1) were under consideration by the U.S. Department of Energy for the first U.S. repository of high‐level radioactive waste (HLW). The host rock at each site is noted in parentheses (from NW to SE): Hanford, Washington (Miocene basalt flows); Yucca Mountain, Nevada (Tertiary tuff); Davis Canyon, Utah, (bedded salt); Lavender Canyon, Utah (bedded salt); Deaf Smith, Texas (Permian bedded salt); Swisher County, Texas (Permian bedded salt); Vacherie dome, Louisiana (domal salt); Richton dome, Mississippi (domal salt); and Cypress Creek dome, Mississippi (domal salt)
The origins of sulfur compounds in the atmosphere of a zone of high productivity (Gulf of Guinea)
Authors: Delmas Robert , Servant Jean 
Published: February 2008

Recent observations have suggested substantial emission of sulfur compounds by oceanic water which could explain the presence of SO2 and SO=4 in the air above these waters. The emission is thought to increase with the productivity of the oceanic zones. This point is discussed in relation to the Gulf of Guinea, a zone of high productivity. During the first two campaigns between Dakar, Abidjan, and the Gulf of Guinea SO=4 concentrations were measured in the air. Between Abidjan and the Gulf of Guinea the atmospheric SO=4 concentrations decreased from 800 to 400 ng m−3.During the third campaign, between Abidjan and the South Equatorial Current (latitude 1°S), the H2S and SO2 concentrations were measured. The mean H2S concentration was 20 ng m−3, and that of SO2 varied between 120 and under 50 ng m−3. The origins of SO2 and SO=4 in the air of this area are discussed through the daily variations of the H2S content of the air and a contribution from the forested zones of West Africa.
Introduction
Authors: Hughes B. A. , Gasparovic R. F. 
Published: February 2008

The synthetic aperture radar (SAR) flown on the Seasat satellite in 1978 yielded a rich collection of radar imagery exhibiting surface expressions from a variety of oceanic phenomena. These images have stimulated substantial research efforts to develop a quantitative understanding of the process by which surface waves, bathymetric features, internal waves, fronts, eddies, and ship wakes modify microwave energy back‐scattered from the sea surface and manifest their presence as intensity variations in SAR images.Conceptually, the process can be subdivided into three generic problem areas: (1) hydrodynamics, which concentrates on describing how the phenomenon of interest alters the surface wave roughness characteristics; (2) microwave backscattering, which addresses the manner in which surface roughness variations are encoded in electromagnetic energy reflected from the sea surface; and (3) the SAR image formation process, which accounts for the effects of imaging geometry and scatterer motion on the coherence properties of the backscattered radiation.
Solar wind and interplanetary magnetic field
Authors: Dessler A. J. 
Published: February 2008

A brief history is presented of some of our ideas regarding the solar wind. The basic physical principles of supersonic expansion are discussed. An analogy is drawn with the flow of an ideal gas through a rocket‐engine nozzle. Supersonic expansion of a stellar corona requires a stellar and coronal temperature lower than a specified maximum. For temperatures above this maximum, subsonic expansion should result. The thermal structure of the sun is such that only supersonic expanion occurs although subsonic expansion is, in principal, allowed.The present status of relevant experiments and theory regarding the solar wind and interplanetary magnetic field is discussed. In particular, attention is drawn to a comparison between theoretical predictions and actual measurements. It is concluded that measurements are consistent with theory for the component of field projected on the ecliptic plane. However, a serious discrepancy is noted between theory and experiment with regard to a possible component perpendicular to the sun's equatorial plane.Wave motion in the solar wind is discussed briefly. It is shown that, under certain conditions, relative wave amplitudes should grow with increasing heliocentric distance.Finally, ideas concerning the ultimate fate of the supersonic solar wind are reviewed.
Measurement of gravity at sea and in the air
Authors: Lacoste Lucien J. B. 
Published: February 2008

General problems of gravity measurement at sea are discussed. A treatment of the effects of vertical accelerations shows that gravity meter nonlinearities cause errors that ordinarily are proportional to the square of the vertical acceleration. In a treatment of horizontal accelerations, similarities and differences that exist between gimbal supported and stabilized platform gravity meters are pointed out. It is shown that optimization of the parameters of a stabilized reference can reduce gravity meter errors by two or more orders of magnitude at long periods. A method for correcting for inadequate period of a stabilized reference is given. The Schuler‐tuned stabilized platform is briefly described. The theory of inherent type cross coupling and examples of imperfection type cross coupling are given.Theory and significant details of construction are given for the LaCoste and Romberg (L&R) gravity meter and stabilized platform. Tests on L&R air‐Sea gravity meters made during the last decade are discussed. The largest error in earlier work is shown to have been due to vertical accelerations. A method of correcting for these errors is described. Tests indicate that presently attainable accuracy of L&R gravity meters is appreciably better than 1 mgal.
Low‐frequency waves in the magnetosphere
Authors: Helliwell R. A. 
Published: February 2008

In the magnetosphere are found low‐frequency (100–100,000 Hz) electromagnetic waves generated externally by lightning and ground‐based transmitters and internally by energetic charged particles. Dispersion and anisotropy characterize the medium, and both ducted and nonducted paths of propagation are found. Lightning‐generated ducted ‘whistlers,’ observed on the ground, give information on the distribution of electrons and the latitudinal drift motions of ducts in the magnetosphere. Nonducted whistlers observed in satellites give information on electron and ion concentrations, the earth's magnetic field, and wave damping by energetic particles.Noise generated in the magnetosphere (or ionosphere) includes steady noise, or hiss, and the structured forms known as discrete emissions. In the auroral zone, hiss is seen in close association with the aurora and over a frequency range of at least 4 kHz to several hundred kHz. It has been attributed tentatively to incoherent Cerenkov radiation from the incoming auroral particles. At middle latitudes, noise from the magnetosphere is mostly of the discrete type with associated hiss and appears to be limited to frequencies below the minimum gyrofrequency on the path of propagation. A related type of noise, called ‘polar chorus,’ appears at high latitudes below about 1500 Hz. Discrete emissions may occur spontaneously or be triggered by whistlers or man‐made signals from the ground. The upper cutoff frequency is controlled by the minimum gyrofrequency on the path of propagation, indicating that the region of generation lies in the equatorial plane. Discrete emissions have been attributed to cyclotron resonance between whistler‐mode waves and electrons. Emissions offer new possibilities for studying wave‐particle interactions in the earth's magnetosphere and in other plasmas, both natural and man‐made.
Spectral studies of tropospheric wave disturbances in the tropical western Pacific
Authors: Wallace J. M. 
Published: February 2008

Tropospheric wave disturbances in the tropical western Pacific have been subjected to intensive analysis during three separate seasons. These all show evidence of spectral peaks in the 4‐ to 5‐day range and at periods longer than 10 days. In this review I attempt to synthesize the results for these three seasons, together with the analysis of a fourth season, into a tentative description of the various types of wave disturbances in this region. The conclusions are outlined below.It appears that there are two types of tropical disturbances that contribute to the 4‐ to 5‐day peaks: synoptic‐scale, westward‐propagating waves with phase speeds on the order of 6‐7 degrees per day, and planetary‐scale equatorial waves that extend into the lower stratosphere. There are also one or more wave types associated with the low‐frequency spectral peaks.All the tropical waves exhibit a similar vertical structure, with a phase reversal in the wind field between upper and lower troposphere. There are warm temperature anomalies at 300 mb, above the low‐level troughs, in qualitative agreement with the thermal‐wind equation. These warm anomalies coincide with the regions of maximum rising motion. As distinguished from tropical waves, the subtropical disturbances do not exhibit a phase reversal in the wind field between upper and lower tropospheric levels. The troughs of these waves appear to be colder than their surroundings at 300 mb.The available potential energy the tropical waves derive from condensation heating is immediately converted into kinetic energy by the synoptic‐scale divergent wind field. This appears to be the dominant energy source for these waves. The leakage of wave energy upward through the tropopause appears to be at least an order of magnitude smaller than the rate of energy generation.The spectral results indicate that most of the synoptic‐scale mass convergence into regions of disturbed weather takes place above the subcloud layer. Although the vertical distribution of latent heat release displays the same gross features in different regions, a simple linear proportionality between boundary‐layer convergence and condensation heating (as is usually assumed in the CISK hypothesis) does not appear to exist.
Chlorofluoromethanes in the environment
Authors: Rowland F. S. , Molina Mario J. 
Published: February 2008

The molecules CF2Cl2 and CFCl3 are released into the atmosphere following their extensive use as propellants for aerosol spray cans and in refrigeration. Since they are chemically inert and have low solubility in water, these chlorofluoromethanes have very long atmospheric residence times and can be detected throughout the troposphere in amounts roughly corresponding to the integrated world industrial production to date. The most important sink for atmospheric CFCl3 and CF2Cl2 appears to be photolytic dissociation in the stratosphere by ultraviolet radiation around 2000 Å. Upon photolysis the chlorofluoromethanes release chlorine atoms, which initiate an extensive catalytic chain reactionCl + O3 → ClO + O2ClO + O → Cl + O2leading to the net destruction of O3 in the stratosphere. This chain reaction can be diverted through reaction of ClO with NO, which interconnects the NOx and ClOx catalytic cycles. The Cl‐ClO chain is interrupted by the reaction of Cl with methane or other hydrogenous species to form HCl, and it is renewed by reaction of OH with HCl. One‐dimensional diffusion calculations show that present O3 depletion levels resulting from the presence of the chlorofluoromethanes are of the order of 1%. This depletion would increase up to 15 or 20% if the chlorofluoromethane injection were to continue indefinitely at present rates. Furthermore, the calculations show that the full stratospheric effect of the photodissociation of CF2Cl2 and CFCl3 is not immediately felt after their introduction at ground level because of the delay required for upward diffusion to the 25‐ to 30‐km level. If the atmospheric injection of these compounds were to terminate only after causing an observable depletion of stratospheric ozone, the depletion would intensify for sometime thereafter and would remain significant for a period of a century or more.