bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seismicity and tectonic stress in the south‐central Pacific
Authors: Okal Emile A. , Talandier Jacques , Sverdrup Keith A. , Jordan Thomas H. 
Published: February 2008

The 15‐station French Polynesian Seismic Network is used to study the intraplate seismicity of the South‐Central Pacific Ocean for the period January 1, 1965 to December 31, 1979. The overall pattern of seismicity shows a clustering of earthquakes at approximately 30 distinct localities, occurring both as discrete events and in swarms. Three localities are associated with known centers of active vulcanism (Moua Pihaa and Rocard seamounts in the Tahiti‐Méhétia area and Macdonald seamount in the Austral Islands). A set of eight localities is distributed along the tectonic axis of the Tuamotu Archipelago and its northwestward extention into the Line Islands, and a set of five is roughly aligned with the northeastern edge of the Tuamotu platform; both sets may be related to load inhomogeneities in the lithosphere. However, much of the seismicity is not correlated with major bathymetric features. With the exception of one isolated event, for example, none of the recorded activity occurs along the major fracture zones that cross the study area.Only three localities have been the sites of two or more earthquakes with body‐wave magnitudes greater than 5.0; these we designate Regions A, B and C. Excluding Hawaii, Regions A, B and C are the most intense centers of seismicity within the Pacific plate interior, and together they account for more than 90% of the seismic energy release in the South‐Central Pacific. An analysis of water multiples from events in Regions A, B and C indicates hypocentral depths within the oceanic crust. Eight focal mechanisms have been obtained; these all have nearly horizontal, NW‐trending compressional axes, oriented approximately parallel to the direction of Pacific plate motion. The uniformity of this orientation over the large distances separating the epicenters (>2000 km) suggests that the mechanisms are indicative of a regional tectonic stress field, rather than locally disturbed stress patterns. These data thus provide additional constraints on the force balance models of plate tectonics.
Adiabats of quartz, coesite, olivine, and magnesium oxide to 50 kbar and 1000 K, and the adiabatic gradient in the Earth's mantle
Authors: Boehler R. 
Published: February 2008

The adiabats of olivine, magnesium oxide, and quartz were measured up to 50kbar and 1000 K. An end‐loaded piston‐cylinder apparatus with an in situ pressure gauge and a very fine thermocouple was used to measure (∂T/∂P)s during adiabatic compression. A power law between (∂T/∂P)s and compression yields values of the power n = −∂ ln (∂T/∂P)s/∂ ln ρ that agree with previous results from salts, metals, and fluids. Assuming constant values for n, the adiabtic gradient for an olivine upper mantle and a magnesium oxide lower mantle was calculated. The results agree well with some previous theoretical estimates. The volume dependence of the Grüneisen parameter γ was calculated from the thermodynamic equation ∂ ln γ/∂ ln ρ = ∂B/∂P − n, where B is the isothermal bulk modulus. γ is found to a good approximation to be proportional to volume.Table 6 is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document J82‐002; $1.00. Payment must accompany order.
Further efforts to limit lunar internal temperatures from electrical conductivity determinations
Authors: Hood L. L. , Herbert F. , Sonett C. P. 
Published: February 2008

A Monte Carlo procedure is used to generate a representative set of eighteen electrical conductivity profiles that are consistent with previously published lunar transfer function data in the frequency range 10−5 to 10−3 Hz. The electrical conductivity is most strongly constrained by these data in the approximate depth range 450 to 1350 km. Published laboratory electrical conductivity versus temperature data (extrapolated to higher and lower temperatures) are applied to convert the eighteen electrical conductivity profiles into temperature profiles for a series of radially homogeneous olivine‐pyroxene mixtures ranging from 100% olivine [(Mg/(Mg + Fe) = 0.91] to 100% aluminous orthopyroxene (6.8 wt% Al2O3). The 100% olivine composition yields selenotherms that approach the Ringwood‐Essene solidus at depths near 500 km while the addition of aluminous orthopyroxene (either 1.9 or 6.8 wt% Al2O3) in concentrations exceeding 15–30 vol% leads to cooler selenotherms that approach the solidus only at depths greater than about 1000 km. The shape of the temperature‐depth profiles is not found to be strongly sensitive to the olivine/pyroxene ratio if the assumption of radial homogeneity is valid at depths greater than 450–500 km.On the basis of independent geophysical constraints (low seismic shear wave attenuation in the upper mantle, maintenance of mascon anisostasy over 3–4 b.y., locations of the deep moonquake foci), the profile envelopes for compositions containing more than 15–30 vol% aluminous orthopyroxene are considered to be most probable. A comparison of the latter with present day selenotherms calculated according to thermal history models indicates the greatest consistency with the model of Toksöz et al. [1978] which assumed initial partial melting and differentiation to a depth of 500 km and significant radial heat transport by subsolidus convection only during the first few b.y. of lunar history.
Small‐scale features in the Earth's magnetic field observed by Magsat
Authors: Cain Joseph C. , Schmitz Dave Ray , Muth Lorant 
Published: February 2008

A spherical harmonic expansion to degree and order 29 is derived using a selected magnetically quiet sample of Magsat data. Global maps representing the contribution due to terms of the expansion above n = 13 at 400 km altitude are compared with previously published residual anomaly maps and shown to be similar, even in polar regions. An expansion with such a high degree and order displays all but the sharpest features seen by the satellite and gives a more consistent picture of the high‐order field structure at a constant altitude than do component maps derived independently.The appendix is available with the entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009. Document B83‐008; $2.50. Payment must accompany order.
A note on the rate sensitivity of frictional sliding of westerly granite
Authors: Solberg P. , Byerlee J. D. 
Published: February 2008

The frictional sliding of simulated faults containing crushed Westerly granite was studied in a series of constant stepped velocity experiments. Confining pressures were varied from 0.00733 to 7.33 μm/s. The strain rate sensitivity B, that is, the slope of the frictional stress change Δμ with the logarithm of the change in velocity, (log10 (V2/V1)), was found to be low and pressure dependent, increasing with increased confining pressure to a maximum of approximately 0.01 at 300 MPa confining pressure.Creep curves are available with entire article on microfiche. Order from the American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009. Document B83‐011; $2.50. Payment must accompany order.
Effects of compression direction on the plasticity and rheology of hydrolytically weakened synthetic quartz crystals at atmospheric pressure
Authors: Linker Mark F. , Kirby Stephen H. , Ord Alison , Christie John M. 
Published: February 2008

A hydrothermally grown synthetic quartz crystal with 370±60 ppm hydroxyl impurity was cut into right rectangular prisms in eight crystallographic orientations. We compressed the prisms under constant axial force corresponding to a uniaxial stress of 140.0±0.5 MPa, and temperatures of 510° and 750°C. All but one of the samples sustained permanent axial strains of 2–3%. We established the operating slip systems from specimen shape change, slip bands and dislocation etch pits on polished surfaces, crystallographic orientation changes, stress optical features in thin sections, and transmission electron microscopy. The observed creep behavior and plasticity divided the samples into three groups: (1) Crystals compressed at 45° to [0001] and [
] and those compressed ⊥(
) and ⊥(
) deformed principally by slip parallel to [0001]. Creep rates were relatively high and were not strongly sensitive to test temperature. Dislocation arrays approximately parallel to (
) are common. Dislocation loops are elongate parallel to [0001], indicating that the edge segments were more mobile than the screw segments. (2) The second group of samples were loaded normal to [0001] in three orientations: ⊥(
), ⊥(
), and at 45° to (
). These samples deformed primarily by {
} 〈a〉 slip with some evidence for secondary slip on the other systems. They were more creep resistant than the first group and displayed a much higher sensitivity of creep rate to test temperature. Dislocation loops are very elongate parallel to [0001], indicating that the screw dislocation segments were much more mobile than the edge segments. (3) A sample compressed parallel to [0001] at 750°C crept at a barely detectable rate (∼10−9 s−1) and no optical scale slip features were observed. These results confirm our earlier work on one orientation each from groups 1 and 2, which indicated a strong creep anisotropy for this same crystal. This creep anisotropy parallels a remarkably similar anisotropy in the diffusivity of impurities in quartz, suggesting a causal relationship between impurity diffusion and creep associated with hydrolytic weakening.Appendix Tables A1‐A5 are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009. Document B84‐004; $2.50. Payment must accompany order.
Morphology of large valleys on Hawaii: Evidence for groundwater sapping and comparisons with Martian valleys
Authors: Kochel R. Craig , Piper Jonathan F. 
Published: February 2008

Runoff and groundwater sapping processes are important, to varying degrees, in the initiation and evolution of terrestrial and Martian valleys. The resulting channel morphology and valley morphometry appear to be distinctive, depending upon which of the two processes are dominant. Our field reconnaissance and morphometric studies of runoff and sapping valleys on the slopes of Hawaii and Molokai in Hawaii indicate that valley types can be distinguished using remotely sensed data similar to the Viking orbital imagery of Mars. Principal components analysis of morphometric data clearly separate runoff valleys from sapping valleys. Hawaiian sapping valleys, like their possible Martian analogs, are characterized by: (1) steep valley walls and flat floors, (2) amphitheater heads, (3) low drainage density, (4) paucity of downstream tributaries, (5) low frequency of up‐dip tributaries, and (6) strong evidence of structural and stratigraphic control on valley patterns.The large Hawaiian sapping valleys are fed by groundwater from high‐level dike‐impounded aquifers breached by channel incision. Flume experiments in weakly cemented sand have produced similar channels by groundwater sapping. In addition, we have mimicked the sequence of valley evolution observed in Hawaii and have shown the importance of groundwater piracy as a major process for widening valley heads. These experiments are useful in testing fundamental ideas concerning how sapping valleys evolve in response to variable structure and stratigraphy. They also provide a model for developing geomorphic criteria useful in the recognition of landforms generated by groundwater sapping.
Siderophile elements in planetary mantles and the origin of the Moon
Authors: Drake Michael J. 
Published: February 2008

The origin of the moon is examined in the context of theories of planetary accretion and of siderophile element abundances inferred for the upper mantles of the earth, moon, and shergottite parent body (SPB=Mars?). The lunar origin hypotheses examined are collisional ejection in a giant impact, and coaccretion from a circumterrestrial disk of metal‐depleted material.If the moon originated in a giant impact, the impactor must have contained free metal and was most probably differentiated with siderophile elements segregated into a core, in order to account for the low absolute and generally nonchondritic relative abundances of moderately and noble siderophile elements in the lunar mantle. If impactor metal was accreted to the earth's upper mantle during the impact and if it perfectly scavenged siderophile elements from the upper mantle into the core, then it is necessary to postulate a late‐stage chondritic “veneer” in order to account for the high absolute and chondritic relative abundances of noble siderophile elements in the present‐day upper mantle of the earth. These elements are less abundant in the mantles of the moon and SPB than in the earth, and they may not be present in chondritic ratios. If they are present in chondritic ratios (the scatter in noble siderophile element data permits this possibility), they are present at approximately 10−3 and 10−4 × CI concentrations in the SPB and moon, respectively. In either case, the noble siderophile elements present a problem for the chondritic “veneer” version of the collisional ejection hypothesis because they are not present in any reservoir in the moon at the required abundance levels.If the impactor metal that was accreted to the earth imperfectly scavenged siderophile elements from the earth's mantle, it is not necessary to postulate a late stage “veneer.” However, the giant impact would substantially melt or vaporize the earth's mantle, yet there is no evidence in samples derived from the upper mantle for large‐scale vertical compositional zoning that might be expected to result from crystallization in a gravity field, by analogy with the moon and with terrestrial layered intrusions. Mantle nodules from all over the world are homogeneous with respect to compatible siderophile elements such as Ni, Co, and Ir at the hand specimen scale.Coaccretion hypotheses of lunar origin are inherently less testable using siderophile elements than collisional ejection hypotheses because abundances of these elements in the mantles of the earth and SPB are less useful as constraints. At present, none of the hypotheses of lunar origin satisfactorily accounts for siderophile element concentrations in the mantles of the earth, moon, and SPB.
The 1987 Whittier Narrows, California, earthquake: A Metropolitan shock
Authors: Hauksson Egill , Stein Ross S. 
Published: February 2008

Just 3 hours after the Whittier Narrows earthquake struck, it became clear that a heretofore unseen geological structure was seismically active beneath metropolitan Los Angeles. Contrary to initial expectations of strike‐slip or oblique‐slip motion on the Whittier fault, whose north end abuts the aftershock zone, the focal mechanism of the mainshock showed pure thrust faulting on a deep gently inclined surface [Hauksson et al., 1988]. This collection of nine research reports spans the spectrum of seismological, geodetic, and geological investigations carried out as a result of the Whittier Narrows earthquake.Although unseen, the structure was not unforeseen. Namson [1987] had published a retrodeformable geologic cross section (meaning that the sedimentary strata could be restored to their original depositional position) 100 km to the west of the future earthquake epicenter in which blind, or subsurface, thrust faults were interpreted to be active beneath the folded southern Transverse Ranges. Working 25 km to the west, Hauksson [1987] had also found a surprising number of microearthquakes with thrust focal mechanisms south of the Santa Monica mountains, another clue to a subsurface system of thrust faults. Finally, Davis [1987] had presented a preliminary cross section only 18 km to the west of Whittier Narrows that identified as “fault B” the thrust that would rupture later that year. Not only was the earthquake focus and its orientation compatible with the 10–15 km depth and north dipping orientation of Davis' proposed thrust, but fault B appears to continue beneath the northern flank of the Los Angeles basin, skirting within 5 km of downtown Los Angeles, an area of dense commercial high‐rise building development. These results are refined and extended by Davis et al. [this issue].
Experimental sea slicks: Their practical applications and utilization for basic studies of air‐sea interactions
Authors: Hühnerfuss Heinrich , Garrett W. D. 
Published: February 2008

Practical applications of organic surface films added to the sea surface date back to ancient times. Aristotle, Plutarch, and Pliny the Elder describe the seaman's practice of calming waves in a storm by pouring oil onto the sea [Scott, 1977]. It was also noted that divers released oil beneath the water surface so that it could rise and spread over the sea surface, thereby suppressing the irritating flicker associated with the passage of light through a rippled surface.From a scientific point of view, Benjamin Franklin was the first to perform experiments with oils on natural waters. His experiment with a ‘teaspoonful of oil’ on Clapham pond in 1773 inspired many investigators to consider sea surface phenomena or to conduct experiments with oil films. This early research has been reviewed by Giles [1969], Giles and Forrester [1970], and Scott [1977]. Franklin's studies with experimental slicks can be regarded as the beginning of surface film chemistry. His speculations on the wave damping influence of oil induced him to perform the first qualitative experiment with artificial sea slicks at Portsmouth (England) in October of 1773. Although the sea was calmed and very few white caps appeared in the oil‐covered area, the swell continued through the oiled area to Franklin's great disappointment.
Distribution of and changes in industrial carbon dioxide production
Authors: Rotty Ralph M. 
Published: February 2008

The burning of fossil fuels is believed to be the major source responsible for an observed increase in the concentration of carbon dioxide in the atmosphere now measured at many locations around the world. This paper revises earlier published data on the annual amounts of carbon released to the atmosphere during the period 1950–1978 and updates the record through 1980. A latitudinal distribution of the fossil fuel source is presented as an aid in explaining the differences in the observed CO2 concentrations at several stations.Data from Mauna Loa Observatory, the South Pole, and elsewhere around the world [Keeling et al., 1978a, b; Bolin and Bischof, 1970; Herbert, 1980] show an increase in the concentration of carbon dioxide in the atmosphere. Attempts to deduce from these records information about the global carbon cycle depend upon data pertaining to the sources of CO2 introduced by man‐burning of fossil fuels and conversion of the world's forests. The latitudinal distribution of the fossil fuel production of CO2 should be an important aid in carbon‐cycle analysis.Observations in the atmosphere show that the Northern Hemisphere CO2 concentration is increasing more rapidly than the Southern Hemisphere concentration and that the most rapid increase is at 50°–60°N latitude. The greatest seasonal variation also occurs in this latitude band. This paper updates and documents the fossil fuel sources of CO2. It revises global CO2 emission values for 1950–1978 published earlier; it demonstrates that a change in the rate of increase of annual CO2 emissions occurred in 1973; and it attempts to delineate the regional distribution of this source of CO2.
Time series regression of sea level on weather
Authors: Groves Gordon W. , Hannan E. J. 
Published: February 2008

Analysis of sea‐level and weather records by frequency is done by the usual methods of spectrum analysis, whereupon a regression analysis is performed in each frequency band. The very complete array of existing statistical procedures, for testing hypotheses and allocating confidence intervals, is then available, suitably modified to take account of the fact that the regression coefficients are complex numbers. Associated statistics, such as partial and multiple coherences and residual spectral matrices, may be treated similarly. The combination of estimates from neighboring frequency bands is also discussed.These methods are used to study records of sea level, surface atmospheric pressure, and wind components at Kwajalein and Eniwetok in the Marshall Islands. An 8 × 8 spectral matrix of these variables covering the frequency range of 0 to 0.85 cycles per day is the starting point for the study. The spectra are characteristic of other sea‐level and weather spectra at islands in low latitudes. There is good coherence between the two islands, especially in sea level and atmospheric pressure. At each island there is the usual strong coherence between sea level and pressure, with moderate coherence between sea level and wind at each island. Several regression models of sea level on the weather records are considered in order to study oceanic influences on the sea‐level records free from local weather noise. However, the spatial coherence of the residual sea level is less than that of the original sea‐level records, apparently because most of the original spatial coherence results from coherent weather patterns and not from coherent water motions. If the computed statistical relations are taken as the true relations, the results are not compatible with a simplified theory of free planetary barotropic waves on the surface of an ocean of constant depth. Because of statistical uncertainty, however, little can be deduced regarding the presence or absence of planetary waves.
Coherence and band structure of inertial motion in the sea
Authors: Munk Walter , Phillips Norman 
Published: February 2008

It is now well established by observation that a peak in the spectrum of horizontal motion should be anticipated everywhere in the ocean near the local inertia frequency, 2ω sine (latitude). The theory of wave motion in a weakly stratified, rotating ocean of constant depth explains this observation either by the existence of a frequency condensation point in wave‐number space or, alternatively, by the vanishing of the meridional group velocity. This explanation is independent of a specific generating mechanism, such as tidal forcing. The details of the wave structure and dispersion relation are readily obtained when, as seems both likely and desirable, it is permissible to ignore the discrete normal‐mode‐producing effects of distant lateral boundaries.This theory predicts a spectral peak slightly above the inertia frequency, and this displacement depends on the zonal and vertical wave numbers. The peak frequency in the North Atlantic measurements by Fofonoff and Webster implies vertical modes of O(10) and a zonal wave number of O (several hundred cycles per earth circumference). When these numbers are applied to a simple coherence model, assuming phase independence between different wave numbers, one can account for the observed lack of coherence between stations separated in depth or longitude. This theory also defines a latitudinal scale; for vertical wave number 10 this is, typically, of O(25 km), which is in qualitative agreement with Hendershott's observations in the eastern North Pacific.The present theoretical model is appropriate for random distributed sources. The observations, however, indicate a higher degree of intermittency than is implied by this model. We conclude that both random distributed sources and intermittent discrete sources must be taken into account for a satisfactory description of the phenomena.