bluuebunny/crossref_metadata_2025_split huggingface dataset:
Frequency dependence of QLg and its relation to crustal anelasticity in the Basin and Range Province
Authors: Mitchell Brian J. 
Published: February 2008

The high observed frequency dependence of Q for 1‐hz Lg waves (f0.4–0.6) in the Basin and Range province can be explained by a frequency‐independent layered model of intrinsic Q for shear waves (Qμ) which has very low values in the upper crust and rapidly increasing values at greater depths. By contrast, earlier work in the eastern United States indicated Qμ values in the upper crust which are high and which vary with frequency. The Qμ model which best explains reported values of QLg and its frequency dependence in the Basin‐and‐Range consists of an 8‐km thick low‐Q layer (60 or less) overlying Q values as high as 1000 or more at mid‐crustal depths. This Qμ distribution is best explained by an upper crust which contains fluids in interconnected cracks overlying a lower crust where higher lithostatic pressure has closed those cracks.These results indicate that whereas the frequency dependence of Qμ is an intrinsic property of crustal material, the frequency dependence of QLg arises from both the intrinsic frequency dependence of crustal material and its layered structure. A notation is suggested which distinguishes between the frequency dependence of QLg and Qμ.
Signature of burst particle precipitation on VLF signals propagating in the Antarctic Earth‐ionosphere waveguide
Authors: Cotton P. D. , Smith A. J. 
Published: February 2008

The burst precipitation of energetic electrons (≥40 keV), induced by interactions with lightning‐generated whistler mode waves, has been observed to cause phase and amplitude perturbations on subionospheric VLF signals (“Trimpi” events). With a knowledge of the propagation characteristics of the subionospheric signal, analysis of the perturbation details can lead to estimates of the energy, extent, and location of the precipitation.Trimpi events have been observed on VLF signals propagating at high latitudes (L ≥ 4) over Antarctica, on 3.79‐kHz signals transmitted from the horizontal dipole at Siple station. A mode theory computer model for propagation of VLF waves in the Antarctic Earth‐ionosphere waveguide is used to illustrate the characteristics of 3.79‐kHz signals as they propagate from Siple toward VLF receivers at Halley and South Pole stations. To simulate the effects of precipitation, localized depressions in the ionospheric reflection height are introduced over the great circle propagation paths in the model, and it is seen that, while the amplitude and phase perturbations of some specific events are accurately reproduced, large positive amplitude (up to 6 dB) Trimpi events at Halley cannot be reproduced. Calculations are presented which show that signals echoing from precipitation patches located away from the great circle path could be the cause of such signatures.
Introduction to Middle Tertiary Cordilleran Volcanism: Magma Sources and Relations to Regional Tectonics
Authors: Lipman Peter W. , Glazner Allen F. 
Published: February 2008

Cenozoic magmatism in the North American Cordillera has attracted the attention of volcanologists, structural geologists, and petrologists for more than a century. From horseback reconnaissance in the 1800s, when a hand lens was the analytical instrument of choice [e.g., von Richthofen, 1868; King, 1878] to today's studies, where mass spectrometers, electron microprobes, and computers are essential tools, attention has focused on the broad regional extent, large volumes, and complexly shifting space‐time‐composition patterns of Tertiary magmatism in the Cordillera.Cordilleran igneous rocks provide key information on regional geologic history, primary geologic constraints on many types of ore deposits, and the basis for development of broad concepts applicable to global magmatism and plate tectonics. Studies of Cordilleran igneous rocks have been especially intense in the past few decades, fueled by improved analytical techniques and by societal concerns such as the search for geothermal and mineral resources and evaluation of volcanic hazards.
Middle atmosphere response to the 27‐day solar rotation as observed by lidar
Authors: Keckhut P. , Chanin M. L. 
Published: February 2008

The response of the middle atmosphere temperature to short term solar UV radiation related to the 27‐day period of the sun has been studied by Rayleigh Lidar at mid‐latitude in the height range 30–90 km. Among the 9 sequences, each of 3 to 4 months duration, which corresponds to clear solar signature, two types of behavior have been found: either the temperature response is positively correlated with the solar UV flux in the whole height range, or the response reverses abruptly from positive to negative within the height interval 40–60 km. It is important to notice that this second type of behavior is observed as well in summer or in winter, i.e. even in the absence of planetary wave activity, but has only been seen during the Westward phase of the QBO.If such a change of the temperature is confirmed to be solar induced, this response to change in the UV flux is clearly different from the one we observed for the 11‐year solar cycle. Therefore the 27‐day signature of atmospheric structure should not be used as a proxy for the 11‐year variation.
Thermal expansion of molten Fe2SiO4 at high pressure
Authors: Agee Carl B. 
Published: February 2008

The density of molten Fe2SiO4 has been bracketed at 1573,1673,1773, and 1873K in the pressure range 1.1 to 1.6 GPa by observing sinking and floating ruby buoyancy markers in piston‐cylinder experiments. From these data a coefficient of thermal expansion
K−1 was calculated from the relationship:where dρ/dP=0.09±0.01 g cm−3 GPa−1 [Agee, 1992]. The high pressure thermal expansion result for molten Fe2SiO4 reported here is in excellent agreement with the coefficient of thermal expansion (α=7.13×10−5 K−1) from Shiraishi et al. [1978] done at 105 Pa by the double‐bob Archimedean method using iron crucibles in a stream of argon, and the ultrasonically derived (∂α/∂P)T=− 1.8×10−5 K−1 GPa−1 from Rivers and Carmichael [1987].
A study of the chemical degradation of ClONO2 in the stratosphere
Authors: Ravishankara A. R. , Davis D. D. , Smith G. , Tesi G. , Spencer J. 
Published: February 2008

The flash photolysis‐resonance fluorescence technique has been utilized to measure the rate constants for the reactions of chlorine nitrate (ClONO2) with two stratospheric radicals, O(³P) and OH. Both rate constants were measured at a pressure of 20 Torr and a temperature of 245 K. The reactions with their corresponding rate constant in units of cm−3molecule−1s−1 are: O(³P) + ClONO2 → Products, k1 = (2.0 ± 0.2) × 10−13; OH + ClONO2 → Products, k2 = (3.7 ± 0.2) × 10−13.The above results, coupled with the photolysis rate of ClONO2, indicate that these chemical degradation pathways contribute less than 10% to the removal of ClONO2 in the stratosphere.
Determination of the geocentric gravitational constant from laser ranging on near‐Earth satellites
Authors: Lerch Francis J. , Laubscher Roy E. , Klosko Steven M. , Smith David E. , Kolenkiewicz Ronald , Putney Barbara H. , Marsh James G. , Brownd Joseph E. 
Published: February 2008

Laser range observations taken on the near‐earth satellites of Lageos (a = 1.92 e.r.), Starlette (a = 1.15 e.r.), BE‐C (a = 1.18 e.r.) and Geos‐3 (a = 1.13 e.r.), have been combined to determine an improved value of the geocentric gravitational constant (GM). The value of GM is 398600.61 km³/sec², based upon a speed of light, c, of 299792.5 km/sec. Using the IAG adopted value of c equalling 299792.458 km/sec scales GM to 398600.44 km³/sec². The uncertainty in this value is assessed to be ± .02 km³/sec². Determinations of GM from the data taken on these four satellites individually show variations of only .04 km³/sec² from the combined result.The Lageos information dominated the combined solution, and gave the most consistent results in its data subset solutions. The value obtained for GM from near‐earth laser ranging compares quite favorably with the most recent results of the lunar laser and interplanetary experiments.
Long‐term 1.5 GHz amplitude scintillation measurements at the magnetic equator
Authors: Basu Sunanda , Basu Santimay , Mullen John P. , Bushby A. 
Published: February 2008

The diurnal and seasonal behavior of long‐term (approximately 20 months) 1.54 GHz amplitude scintillation measurements under low sunspot conditions observed at Huancayo, Peru are presented. The measurements refer to a low elevation geometry in the E‐W plane at the magnetic equator. The data show clear equinoctial maxima of occurrence and confinement to the pre‐midnight hours. There is a total absence of scintillations during the May‐July period.The present results are critically compared to previously reported GHz measurements in the context of geometry of observations, equatorial irregularity strength variation and spatial structure information obtained from in‐situ data.
Permeability and strength of San Andreas Fault gouge under high pressure
Authors: Morrow C. , Shi L. Q. , Byerlee J. 
Published: February 2008

The permeability and strength of San Andreas fault gouge from the Cienega Valley was measured under confining pressures up to 2 kbar. The gouge was composed almost entirely of clay minerals, predominantly montmorillonite and mixed‐layer clays. Permeabilities ranged between 1 and 10 nanodarcies for confining pressures of a few hundred bars to 1 kbar, and less than 1 nanodarcy for pressures greater than 1 kbar. Permeability was sensitive to confining pressure and differential stress, but did not depend significantly on accumulated strain.The low strength of saturated clay is often attributed to the buildup of excess pore pressure as the clay is stressed. These experiments, performed under drained conditions where excess pore pressure was not created, suggest that loosely bonded interlayer water in the hydrated clays can generate a pseudo‐pore pressure that serves to lower the strength of the gouge.
A note on a random stress model for seismicity statistics and earthquake prediction
Authors: Caputo Michele 
Published: February 2008

Some of the results of the paper by von Seggern (1980), concerning the reddening of the wavenumber spectrum of the stress difference over the fault as the main shock approaches, depend on an assumption on the coefficient c of the relation log M0 = d + cM.It is shown here that, at least in California, the reddening of the spectrum of a vertical section of the fractal surface (Mandelbrot 1977) begins with the aftershocks sequence, as suggested by von Seggern (1980) but the normal state (k−2, k is the wavenumber) is in the period between aftershocks and the foreshock and, because of the reddening of the spectrum, it is followed by the abnormal state (k−3) associated to the foreshock sequence. Then the major shock introduces a disorder into the local stress field and gives rise to very irregular zeroset areas with "antipersistent" fractal function, with k−0.5 to k−1.4, of the aftershock sequence. At this stage the cycle starts again with the reddening of the power spectrum. In other words there is a reddening which begins with the aftershock sequence, but with k−0.5 to k−1.4 and it ends with the foreshock sequence with k−3.The statistical analysis of fifteen sequences of earthquakes is also presented and it is suggested that the change in the density distribution function of the stress drop may be an indicator of the preparatory phase of large earthquakes.
Photometric and interferometric observations of the Sar arc event of March 5/6, 1981
Authors: Watanabe T. , Kim J. S. 
Published: February 2008

An extraordinary stable auroral red (SAR) arc was observed on the night of March 5/6, 1981 (EST) at a field station near Albany (42.63° N; 73.98°W), New York with a multicolor meridian scanning photometer and a 15‐cm high‐resolution Fabry‐Perot interferometer. The arc was extraordinary in the sense that: (a) it was the most intense arc (∼2.2 kR) observed during the past twelve years at Albany, New York; (b) it was a multiple arc consisting of two SAR arcs (the major arc occurred between zenith angles of 40° (L = 2.7) and 54°S (L = 2.5) throughout the observation period, and the minor arc occurred in close proximity for a duration of only one hour; (c) a visible aurora was not sighted from Albany during the observation period.Thermospheric temperatures were derived from Doppler line profiles of the [OI] 6300Å emission, obtained within the arc and outside the arc at zenith angles of 70°S, 50°N, and 70°N.The temperatures within the arc were quite stable with respect to time, even during the period of very rapid and large decrease in the arc intensity, and they were approximately equal to those measured at 70°N. The temperatures at 70°S, which varied considerably in time, were different from those at 50°N or 70°N. The temperatures within the arc were generally higher than those at 50°N or 70°S. The observed enhancement of the temperatures within the arc is much greater than the value predicted by the two‐dimensional model calculations of the SAR arc.
Determination of timing of volcanic events by secular variation and thermal modeling
Authors: Furlong Kevin P. , Shive Peter N. 
Published: February 2008

The length of time between emplacement of successive lava flows is difficult to determine with high resolution except in regions of very recent or current activity. In paleomagnetic studies, a tacit assumption of the relative timing is made by considering the effects of secular variation to be averaged in samples from a series of flows, a condition which may not in fact be met. Through the combined use of numerical modeling of the cooling history of sequences of lava flows (erupted at any set of arbitrary time intervals) and detailed measurements of the magnetization directions from field samples, constraints can be placed on the length of time between flows.As individual flow units in a sequence cool, the position within each flow of the last point to pass through the blocking temperature is a function of the relative timing of the flows in the sequence. Additionally, the depth into an underlying flow to which magnetic directions are reset is also a function of this relative timing.In addition to the timing information, the approach appears promising for determination of rates of secular variation in the past.
Organic gases in the Norwegian Arctic
Authors: Hov Ø. , Penkett S. A. , Isaksen I. S. A. , Semb A. 
Published: February 2008

Air samples for determination of halocarbons and light hydrocarbons were collected at Spitsbergen in July 1982 and in March 1983. With the exception of ethene and propene, which appear to originate mainly from natural sources, hydrocarbon concentration levels were generally one order of magnitude higher for the March 1983 samples than for the summer samples. This is explained by difference in atmospheric reactivity, and particularly by direct transport of polluted air masses from the Soviet Union during March 1983.The spring samples from Spitsbergen were more abundant in alkanes and less abundant in solvents than air sampled at Barrow by Rasmussen et al. (1983) in March 1982. Ny‐Ålesund is a good site to measure air coming off the Soviet Union and Europe. Continued sampling could provide valuable information about questions related to global climate, Arctic haze and the chemical composition of the troposphere.
A seafloor magnetotelluric sounding in the Tasman Sea
Authors: Ferguson I. J. , Filloux J. H. , Lilley F. E. M. , Bindoff N. L. , Mulhearn P. J. 
Published: February 2008

This paper reports an analysis of electromagnetic data from a site occupied on the floor of the Tasman Sea during an Australia‐U.S. research program, the Tasman Project of Seafloor Magnetotelluric Exploration. This site (37°33′S, 155°58′E, depth 4450 m) is in the central portion of the Tasman Sea, and near both a fossil spreading ridge and the Tasmantid Seamount Chain. The extensive electric and magnetic data sets, covering 60 days, exhibit the signals of a most energetic oceanic environment. Conspicuous features of the electric field include an unusually large component induced by mesoscale fluid motions, as well as sporadically occurring high‐frequency signal probably induced by ocean turbulence.These motional fields contribute a significant background noise to the ionospheric storm and substorm magnetic activity from which the seafloor magnetotelluric impedance tensor is estimated, but permit a usable frequency band of 0.06 to 5.5 cph. Over this band the seafloor impedance is found to exhibit frequency‐independent skew and anisotropy. The skew suggests the presence of some nearby lateral conductivity heterogeneity. The anisotropy is characterised by a principal axes ratio of 3.5, the major axis being oriented 24° clockwise from true north.Tentative inversion of the data implies the presence of an unusually high conductance in the uppermost seafloor. Altogether, information on upper mantle conductivity may reach a 500 km depth. The principal magnetotelluric axes are approximately aligned with both the trend of the seamount chain and with the Australian coastline. The ensemble of data from eight other sites occupied in the project should permit an assessment of the relative contribution of these two features.
Measurements in the marine boundary layer near a coastal front
Authors: Riordan A. J. , SethuRaman S. , Davis J. M. , Viessman S. 
Published: February 2008

Measurements taken from aboard ship and from nearby fixed sites during a March 1985 research cruise near Cape Hatteras document some interesting boundary layer features of the coastal front which have been largely unexplored. The front, although commonly associated with the development of coastal cyclones is nevertheless shallow and often difficult to detect due to the scarcity of routinely available observations offshore.During the particular case described, the coastal front, undetected by routine analyses, divides air masses of quite different character. To the east of the surface wind shift line a warm, statically unstable boundary layer is associated with strong fluxes of latent heat from the sea surface. To the west, however, the boundary layer is cold and stable with negligible air‐sea heat exchange. A low‐level jet in the frontal zone carries the warm moist air westward toward eastern North Carolina. Subsequent moderate precipitation and cyclone passage may be associated with the frontal boundary.
Global relationship between oceanic geoid and seafloor depth: New results
Authors: Cazenave Anny , Dominh Kien 
Published: February 2008

A new global transfer function (admittance) between oceanic geoid and seafloor depth has been derived for the wavelength band 1000‐4000 km, after removal of lithospheric cooling effects using the most recently published crustal ages of the oceans. In this wavelength band, the admittance is positive, reaches a maximum of ∼ 5m/km around 2750 km wavelength, then decreases to ∼ 2.5 m/km, on the average, at shorter wavelengths (between 2500 km and 1000 km). These values are systematically higher by 30‐40% than those we derived in a previous study using crustal ages of poorer quality.In view of these new results, we cannot exclude that part of the signal at the 2750 km wavelength is of convective origin, unlike the conclusions of the previous study. On the other hand, at shorter wavelengths, the observed admittance can still be interpreted in terms of crustal thickening and sediment loading.
Distribution of major stratospheric warmings in relation to the quasi‐biennial oscillation
Authors: Dunkerton Timothy J. , Delisi Donald P. , Baldwin Mark P. 
Published: February 2008

Data from 1953 to the present indicate that major warmings in the northern hemisphere winter have not occurred when the equatorial monthly mean zonal winds are deep westerly, i.e., westerly over more than about 5/8 of the 10–85 mb layer. Sixteen winters have had a major warming in the last 35 years. Six January–February periods had deep equatorial westerlies but did not experience a major warming.Major warmings do not require deep equatorial easterlies, nor is the occurrence of a major warming significantly correlated with the sign of the zonal mean wind at any particular level between 10 and 50 mb, although as noted by previous investigators, more than half of the observed major warmings have occurred when the equatorial flow is easterly at a given level between 10 and 50 mb. We suggest that a more relevant QBO statistic may be found in the depth of QBO wind regimes.The previously proposed connection between the equatorial quasi‐biennial oscillation and the major warmings of the northern hemisphere winter is supported by these observations.
Evidence for anisotropy in north east Africa, from geographical and azimuthal distribution of Rayleigh wave velocities, and average upper mantle structure
Authors: Hadiouche Ouiza , Jobert Nelly 
Published: February 2008

Long period surface waves from WWSSN, GDSN, SRO and GEOSCOPE stations are analysed to obtain the dispersion of surface waves in the North‐East of Africa. Lateral variations of Rayleigh wave velocities are retrieved simultaneously with the average azimuthal anisotropy. As a first result, the low velocity anomaly under the Red Sea is apparent at all periods. A second result is a nearly North‐South direction of maximum group and phase velocities. This azimuthal anisotropy direction is in agreement with the direction of absolute plate motion in this region.Anisotropy is also evidenced by simultaneous inversion of Love and Rayleigh wave dispersion along the path TAM‐AGD. In the resulting models, isotropic and anisotropic, very low mantle SV‐wave velocities extend up to the Moho. For SH waves, we find a strong discrepancy with SV waves, SH‐wave velocities being higher by 5% down to 200 km under the crust. This is characteristic of lithospheric polarization anisotropy.The S‐wave anisotropy (polarization and azimuthal) found in this region, including the Red Sea, is compatible with the absolute motion of the African plate: it can be interpreted, considering the low lithospheric S‐velocities, as a consequence of plastic flow in the weak lithosphere of an anomalous mantle. This anisotropy, evidenced here on S waves, may be due, as Pn and lithospheric S‐wave anisotropy found in other continental areas, to dynamical processes related to plate motion.
Constraints and interpretation of 87Sr/86Sr ratios in Cenozoic dolomites
Authors: Vahrenkamp Volker C. , Swart Peter K. , Ruiz Joaquin 
Published: February 2008

Replacement dolomitization by seawater has been modeled in order to quantify the Sr‐isotope signature in Cenozoic dolomites as a function of precursor mineralogy and 87Sr/86Sr ratio, reaction stoichiometry and 87Sr/86Sr ratio of the dolomitizing fluids. High Sr carbonates, such as aragonite, may introduce a significant precursor memory into an otherwise seawater dominated Sr‐isotope signature if small quantities of seawater per unit volume of precursor carbonate are involved. Dolomitization of low Sr carbonates (i.e. low‐Mg calcite) are shown to create an isotopic signature indistinguishable from that of the seawater involved in the reaction. Therefore, by comparison with the Sr‐isotope evolution curve of seawater, the‐ 87Sr/86Sr ratios of the dolomites can be used to record the oldest possible age of dolomitization and the youngest age of deposition.The implications for this approach have been applied to data obtained from a dolomitized core from Little Bahama Bank, Bahamas. Two periods of dolomitization are recognized, one in the early Late Miocene involving Middle Miocene or older rocks, and a second one around 2.4 Ma ago affecting early Pliocene carbonates.