bluuebunny/crossref_metadata_2025 huggingface dataset:
Criteria for the resolution and reconstruction of acoustic impedance
Authors: Carrion Philip M. , Patton Waldo A.
Published: February 2008

We derive approximate quantitative criteria for the resolution and reconstruction of the acoustic impedance for horizontally stratified media calculated from band‐limited seismic data both without and with noise. The first criterion, for noise‐free data, relates the calculated acoustic impedance to the true acoustic impedance using only the DC (zero frequency) level of the seismic source or wavelet. The second criterion, for noisy data, predicts the band of uncertainty of the calculated impedance. The third criterion is the combination of the first two. One of the most important results of this paper is that the average shape of the acoustic impedance can be estimated from data without wavelet deconvolution, if the D.C. component of the wavelet function is not zero.
A search for correlatable, isotopically light carbon and nitrogen components in lunar soils and breccias
Authors: Norris S. J. , Swart P. K. , Wright I. P. , Grady M. M. , Pillinger C. T.
Published: February 2008

Using stepped heating extraction techniques, determinations of carbon and nitrogen content and δ13C and δ15N values have been obtained for selected lunar soils and breccias. Only nitrogen data have been gathered for representative splits separated by size, density and magnetic properties from 12023. A plot of the total δ13C (after terrestrial contamination is removed) versus δ15N values for bulk samples reveals little evidence for a correlation between isotopically light carbon and isotopically light nitrogen of putative ancient solar wind origin. Soil 12023 is used to examine the current interpretation for the stepped release profile of nitrogen from bulk lunar samples. Mature agglutinates, postulated by previous workers to be the host of the light nitrogen, are shown to have a very constant δ15N value which is heavy rather than light. The actual host of the light nitrogen in 12023 has not been identified. The lowest values encountered during the study were found associated with the finest soil, but none of these was as low as for some temperature steps of the bulk soil. Interpretations regarding the origin of light nitrogen, if it is not present in agglutinates, await the results of more definitive efforts to identify the host phase.
53Mn profiles in four Apollo surface cores
Authors: Nishiizumi K. , Murrell M. T. , Arnold J. R.
Published: February 2008

53Mn data are presented for four Apollo cores with an emphasis on the past 107‐year history of these samples: (1) Core 15011 has excess 53Mn down to a depth of at least 9 cm, which is probably due to the continuous addition of near‐surface irradiated material. High 53Mn was also observed at 17 cm, which suggests that this might have been the surface at this site, 7–10 m.y. ago. The soil found covering the 15011 core tube keeper appears to be surface soil, but most likely not from the top of 15011. (2) The 53Mn profile for 64002 above 12 cm is relatively flat and in excess of that calculated for a static core, which suggests that the upper part of this core was deposited rapidly about 2 m.y. ago. As this soil appears to be mature, well‐irradiated local material, it seems unlikely that it is ejecta from South Ray crater, unless South Ray crater is much older than 2 m.y. (3) Results for the Apollo 17 drill stem show a large excess of 53Mn from at least 3 cm downwards. Some magnetic separates obtained from this core have very high 53Mn activities, probably due to the presence of agglutinates that were recently irradiated very near the surface. These results are consistent with the suggestion of the Battelle‐Northwest group that this core sampled a young crater that had partially filled due to the slumping of surface irradiated material. (4) The 53Mn content of the upper part of 74002 is similar to that of trench samples collected nearby and indicates that the gray, orange, and black soils at this site have been exposed together near the surface for at least the last 10 m.y.
Thorium concentrations in the lunar surface: IV. Deconvolution of the Mare Imbrium, Aristarchus, and adjacent regions
Authors: Etchegaray‐Ramirez Maria I. , Metzger Albert E. , Haines Eldon L. , Hawke B. Ray
Published: February 2008

The distribution of Th over the Mare Imbrium and northern Oceanus Procellarum portions of the Apollo 15 lunar ground track has been modeled by deconvolving several fields of orbital gamma ray spectroscopy data. Including a prior study of the Apenninus region, a continuous swath from 10°E to 60°W in the northwest quadrant has now been analyzed. In the Aristarchus region, the crater dominates the Th distribution with a concentration of 20 ppm. Other enhancements are seen on the Aristarchus Plateau and south of the plateau. The concentration across the Aristarchus Plateau is not uniform. The average Th concentration in Oceanus Procellarum is less to the west than to the east of the Aristarchus Plateau. Substantial enhancements are found in mare regions around Brayley, and at the ejecta blankets of Timocharis and Lambert. Th in the Eratosthenian mare regions is generally low with one notable exception lying roughly between the craters Euler and Carlini. The existence of enhanced Th concentrations in mare basalt regions suggests that reservoirs of some late stage mare basalts incorporated KREEP‐rich material during formation or transit.
The effect of rupture complexity on estimates of source size
Authors: Boatwright John
Published: February 2008

A general technique is proposed for estimating rupture geometry from measurements of body wave durations, wherein measurements of the overall signal duration or the duration of a single pulse identified in all of the arrivals are inverted to estimate the geometry of the overall rupture or of a specific subevent, respectively. The complexity of a waveform is determined by comparing the overall signal duration to the duration of the most prominent pulse in the waveform; this complexity is used to estimate the ratio of the average rupture velocity to the subevent rupture velocity. The shear waves radiated by eight moderate (3.6≤ML≤4.9) multiply recorded aftershocks of the 1975 Oroville, California, earthquake are analyzed using measurements of the corner frequency, the characteristic frequency, the pulse duration, and the signal duration. Comparison of these four different estimates of source size indicates that the corner frequency and the characteristic frequency are more sensitive to the dominant subevent size than to the overall event size. The difference between the estimates of source size determined from the signal duration measurements and the spectral measurements increases as the rupture complexity increases.
Triple correlation of the gravity field of the Earth
Authors: Bertotti Bruno , Sacerdote Fausto
Published: February 2008

In this work we discuss the triple correlation function on a sphere, having in view its application to the gravity field of the earth. This is done mainly in the short‐wavelength limit, which requires a special mathematical technique, the “high‐frequency approximation.” In order to test the significance of the triple correlation coefficients in any given earth model we define a random earth, in which the phases of the harmonic coefficients are random and, on the average, there is no triple correlation. The numerical value of a given coefficient can be then compared with its root mean square value; it will be larger (and hence significant) if the phases are correlated in triplets. A significant test of triple correlation in relation, for example, to elongated structures in the crust must extend to values of ℓ of order radius of the earth/crust thickness; we believe that the presently available earth models are not yet sufficiently reliable for this.
The seismic structure across an active oceanic/continental transform fault zone
Authors: Horn J. R. , Clowes R. M. , Ellis R. M. , Bird D. N.
Published: February 2008

A seismic structural section across the southern Queen Charlotte transform fault zone, which separates the oceanic Pacific plate from the continental America plate off western Canada, has been determined from an offshore‐onshore refraction experiment. Two explosion profiles, one parallel and one perpendicular to the fault strike, were recorded on three ocean bottom seismographs (OBS) and seven land‐based seismographs (LBS). Assuming lateral homogeneity along the parallel profile recorded over oceanic crust at one OBS, one‐dimensional amplitude modeling produced a velocity model with the characteristics of standard ocean crust. The partially reversed perpendicular profile recorded at two OBS's and one good quality LBS extended across the fault zone, which in bathymetric cross section shows two linear fault escarpments separated by a flat terrace. An initial velocity structure, provided by time term analysis of the complete data set, was modified by ray tracing until the travel time data for the three stations were satisfied by one seismic structural section. This model shows three distinctive crustal blocks (the oceanic, terrace, and continental blocks) separated by two major, crustally pervasive faults, the outer and inner Queen Charlotte faults. The rock units composing the terrace block have lower velocities at equivalent depths than those of the blocks on either side. This may have resulted from deformation associated with oblique convergence and/or the effects of a jump in the position of the active Queen Charlotte fault from its outer to inner positions about 1–0.5 Ma ago. Depth to the base of the crustal section increases from 12 to 18 km below sea level across the terrace transition zone, representing an eastward dip of about 20°. The seismic model, after conversion to a density model, agrees well with the gravity anomaly along the profile. The interpreted structural section is consistent with recent tectonic models that require a component of convergence along the transform fault zone.
Initiation and collapse of active circulation in a hydrothermal system at the Mid‐Atlantic Ridge, 23°N
Authors: Gallinatti Barbara Cosens
Published: February 2008

Gabbro and basalt, collected from an area south of the Kane Fracture Zone along the Mid‐Atlantic Ridge, have three stages of alteration which record the cooling of a hydrothermal system: (1) Stage 1. Penetration of seawater began between 400° and 550°C, altering pyroxene to fibrous green amphibole. (2) Stage 2. Propylitic alteration formed along connected fractures between 250° and 300°C. As fracture density increased, the Fe/Mg ratio of chlorite increased, the final result being an Fe chlorite‐quartz‐sulfide breccia. (3) Stage 3. Late smectite veinlets formed at low temperatures (≤200°C) after active circulation ceased The study focuses on stage 2 alteration. By assuming local equilibrium between alteration minerals and the hydrothermal fluid, constraints can be placed on the fluid composition responsible for stage 2 alteration, the stage associated with deposition of sulfides. The following activities of species in solution were determined for the system FeO Na2O‐CaO‐MgO‐Al2O3‐SiO2‐H2O at 350 bars and 250°C: log a (Ca++)/a2 (H+) = 8.0, log a (Na+)/a (H+) = 5.0, log a (Fe++)/a2 (H+) = 1.7, log a (Mg++)/a2 (H+) = 6.0. Log a (SiO2) was set at quartz saturation (−2.3 at 350 bars and 250°C). Fluid inclusions record the introduction of a low temperature, seawater‐salinity fluid during formation of the latest quartz veins associated with stage 2 alteration. Mixing of this and the hydrothermal fluid caused a drop in temperature and increase in oxidation state, resulting in increased precipitation of quartz, pyrite and chalcopyrite. The salinities of fluid inclusions trapped in quartz during stage 2 alteration are as much as 3 times that of seawater. Concentration of a fluid initially of seawater salinity may be the result of boiling at ≥350°C and ≤3000 m depth.
Magnetic properties of the Bay of Islands ophiolite suite and implications for the magnetization of oceanic crust
Authors: Swift B. Ann , Johnson H. Paul
Published: February 2008

Rock magnetic properties, opaque mineralogy, and degree of metamorphism were determined for 101 unoriented samples from the North Arm and Blow‐Me‐Down massifs of the Bay of Islands ophiolite complex, Newfoundland. The weathered and metamorphosed extrusive basalt samples have a weak, secondary magnetization arising from oxidation and exsolution of ilmenite of unknown origin. The initial magnetization of the underlying sheeted dike complex appears to have been destroyed by hydrothermal alteration soon after formation. The magnetic intensity of the gabbroic samples increases as the degree of alteration increases, with the highly altered upper metagabbros having an average intensity of 3×10−3 emu/c3. Because magnetization of the metagabbro samples is related to nonpervasive, variable alteration, these crustal units are unlikely to make a significant contribution to lineated magnetic anomalies. A compilation of our results and other studies suggests a model in which oceanic crust magnetization results from an upper extrusive basalt source layer, roughly 600 m thick, with no contribution from a deeper source layer recognizable from these Bay of Islands data.
Ground magnetic survey in the Coso Range, California
Authors: Roquemore Glenn R.
Published: February 2008

A ground magnetic study was completed in the Coso volcanic field to investigate faulting and associated hydrothermal alteration patterns. The magnetic intensity contours match general geologic patterns in varying rock types. Hydrothermally altered rocks along intersecting fault zones show up as strong magnetic lows that form a triangular‐shaped area. This area is centered in an area of highest heat flow and is a site of concentrated fumarolic activity. In the Coso volcanic field the combination of high heat flow, fumarolic activity, magnetic lows, and hydrothermal alteration along faults suggests that hot fluid filled fractures with high permeability.
Introduction to the Special Section on Fault Behavior and the Earthquake Generation Process
Authors: Coppersmith Kevin J. , Schwartz David P.
Published: February 2008

This special section is a direct outgrowth of an AGU Chapman Conference on Fault Behavior and the Earthquake Generation Process that was convened in Snowbird, Utah, from October 11 to 15, 1982. The body of information concerning the behavior of faults in space and time, especially with regard to earthquake recurrence, fault zone geometry, and the mechanical and physical properties of fault zones that control rupture processes has been increasing at an enormous rate. And, perhaps more importantly, our understanding of these subjects has direct societal application in the mitigation of earthquake hazards, especially the identification of potential seismogenic sources and the characterization of these sources in terms of quantitative estimates of the location and probability of earthquake occurrence. The motivation behind the conference was the desire to pause and reflect on the recent progress in the field and to evaluate, and perhaps identify, potentially important new areas of research.
Structure and variability of oceanic crust on the flanks of the East Pacific Rise between 11° and 13°N
Authors: Bratt Steven R. , Purdy G. M.
Published: February 2008

We use over 500 seismograms collected by five ocean bottom seismometers to examine the structure and variability of 0.5‐m.y.‐old crust in the Rivera Ocean Seismic Experiment (ROSE) area of the East Pacific Rise between 11° and 13°N. There are no significant differences among the first arrival travel times for 10 independent refraction line segments along the isochron. Amplitude patterns recorded on the individual lines, however, suggest that structural boundaries within the upper crust vary by hundreds of meters in depth over lateral distances of tens of kilometers within this 200‐km segment of lithosphere. On the basis of the modeling of amplitude patterns at ranges of 5–10 km and of comparisons with the upper crust sampled at Deep Sea Drilling Project hole 504B and in ophiolite complexes, layer 2 can be divided into three units: 2A corresponds to extrusive volcanics with a steep velocity gradient, 2B to extrusives with a near‐zero velocity gradient, and 2C to a complex region of transition from extrusives to sheeted dikes. The total thickness of layer 2 varies by about 0.7 km over the length of the line. Another amplitude peak which varies in range between 14 and 21 km may be related to the downward transition from sheeted dikes to isotropic gabbros within layer 3. The variability of these two amplitude patterns provides direct evidence that the along‐strike structure of oceanic crust in the ROSE area is definably heterogeneous and that the process of crustal accretion is likewise variable on the scale resolved by amplitude and travel time information.
S‐P wave travel time residuals and lateral inhomogeneity in the mantle beneath Tibet and the Himalaya
Authors: Molnar Peter , Chen Wang‐Ping
Published: February 2008

The average S wave travel time residuals from 11 earthquakes each in Tibet and the Himalaya imply that there are marked lateral variations in structure beneath Tibet and the Himalaya. Average S‐P wave residuals, measured with respect to the Jeffreys‐Bullen (J‐B) tables, for each of 11 earthquakes in the Himalaya are less than +1 s. Average J‐B S‐P residuals from 10 of 11 earthquakes in Tibet, however, are greater than +1 s, even when corrected for the large crustal thickness of Tibet. The largest values, 2.5, 3.2, 3.8, 4.5, and 4.9 s, are for five events in central and northern Tibet, and they imply that the average velocities in the crust and upper mantle of these portions of Tibet are 4–10% lower than those beneath the Himalaya. Therefore it is unlikely that a shield structure underlies these parts of Tibet, unless these S‐P residuals are due to variations in structure deeper than 250 km. S‐P residuals from two other events each in western and eastern Tibet are 1–2 s late and hence suggest that velocities beneath these areas are also somewhat lower than beneath shields. The mean S wave velocity seems not only to be different beneath Tibet and the Himalaya but also seems to increase from a minimum beneath northern Tibet to values close to those of the average earth toward the east, south, and west.

Appendix A is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009. Document B84‐010; $2.50. Payment must accompany order.
The two‐dimensional Gaussian beam synthetic method: Testing and application
Authors: Nowack R. , Aki K.
Published: February 2008

The Gaussian beam method of Červený et al. (1982) is an asymptotic method for the computation of wave fields in inhomogeneous media. The method consists of tracing rays and then solving the wave equation in “ray‐centered coordinates.” The parabolic approximation is applied to find the asymptotic local solution in the neighborhod of each ray. The approximate global solution for a given source is then constructed by a superposition of Gaussian beams along nearby rays. The Gaussian beam method is tested in a two‐dimensional inhomogeneous medium using two approaches. One is the application of the reciprocal theorem for Green's functions in an arbitrarily heterogeneous medium. The discrepancy between synthetic seismograms for reciprocal cases is considered as a measure of the error. The other approach is to apply Gaussian beam synthesis to cases for which solutions are known by other approximate methods. This includes the soft basin problem that has been studied by finite difference, finite element, discrete wavenumber, and glorified optics. We found that the results of these tests were in general satisfactory. We have used the Gaussian beam method for two applications. First, the method is used to study volcanic earthquakes at Mount Saint Helens. The observed large differences in amplitude and arrival time between a station inside the crater and stations on the flanks can be explained by the combined effects of an anomalous velocity structure and a shallow focal depth. The method is also applied to scattering of teleseismic P waves by a lithosphere with randomly fluctuating velocities.
Granitic terrains viewed remotely by shuttle infrared radiometry: Some compositional predictions
Authors: Baird Alex K.
Published: February 2008

Ratios of intensities of near‐infrared spectral bands, measured in reflectance, quantitatively predict the iron content of granitic rocks. Such data from the 1.60‐ and 1.05‐μm bands of the shuttle multispectral infrared radiometer have been used to study granitic rocks along orbits crossing Baja California, Mexico, and the Eastern Desert of Egypt. Both regions are arid and relatively to essentially free of vegetation, and there is no indication in the spectra that surface chemical alteration masks the true composition of the unweathered rock. Predicted values of iron are consistent with known compositional types of most of the rocks along the orbital paths. Results demonstrate that the near‐infrared method used is a powerful technique to average the variability of these rocks on the scales of meters to kilometers.
Modeling crater topography and albedo from monoscopic Viking Orbiter images: 1. Methodology
Authors: Davis Philip A. , Soderblom Laurence A.
Published: February 2008

A new photoclinometric technique for extraction of topographic data from single planetary images is presented that overcomes many previous limitations of photoclinometry. The procedure fully compensates for oblique viewing geometry prevalent in spacecraft images. Albedo variations have been one of the most serious obstacles in the application of photoclinometry to planetary surfaces. This problem is overcome in the topographic solution by simultaneously utilizing brightness data from a pair of profiles; both segments are assumed to have the same topographic and albedo variations along their lengths. Profile directions are chosen where the orientation of downslope or upslope is obvious, thus resolving a major ambiguity in photoclinometry. This requirement is particularly easy to satisfy for craters and not very difficult for many irregular features. An additional procedure is presented that eliminates even the requirement of topographic symmetry along the pair of profiles. If two profiles have the same relief but their shapes are very different, another method can be used in an iterative process to derive topographic profiles; however, this procedure does, require that the albedo not vary along the profiles. Test results indicate that both procedures have an accuracy and precision of approximately 2° for slopes of typical bowl‐shaped craters, which translates to approximately 5% for depths.
Geochemistry of Muong‐Nong type tektites: IV. Selected trace element correlations
Authors: Koeberl C. , Kluger F. , Kiesl W.
Published: February 2008

Muong‐Nong type tektites are distinct from other tektites in their shape, size, petrographical characteristics, and chemistry. Volatile elements are enriched, but other trace elements do not show large differences when compared to normal splash‐form tektites. We have analyzed nineteen Muong‐Nong type tektites for 40–50 elements. We discuss fifteen nonvolatile elements in this paper. They show that the Muong‐Nong type tektites are very restricted in chemical composition and are almost indistinguishable from the Australasian tektites. Elemental ratios calculated from the data reported here show the same genetic connection. All elementary abundances and ratios are fully consistent with terrestrial sediments. The nonvolatile elements may record more about the conditions of the origin.
Petrography and classification of Ca, Al‐rich and olivine‐rich inclusions in the Allende CV3 chondrite
Authors: Kornacki Alan S. , Wood John A.
Published: February 2008

A detailed, systematic petrographic survey of all (189) Ca, Al‐rich and olivine‐rich inclusions larger than ∼0.2 mm in diameter in 17 thin sections of Allende was performed by optical and scanning electron microscopy. Most of these inclusions are aggregates containing varying proportions of three distinct constituents, termed concentric objects, chaotic material, and inclusion matrix. A new classification system for Allende inclusions is proposed. Olivine‐rich inclusions occur in two textural varieties: unrimmed olivine aggregates (Type 1A inclusions) and rimmed olivine aggregates (Type 1B inclusions). We classify Ca, Al‐rich inclusions (CAI's) on the basis of the size and abundance of their constituent concentric objects (rather than their grain size) into unrimmed complex CAI's (Type 2 inclusions), rimmed complex CAI's (Type 3 inclusions), and simple CAI's (Type 4 inclusions). Several of the inclusion classes grade into each other. Some fundamental relationships among various types of Allende inclusions are discussed. We suggest that the term ‘coarse‐grained,’ even if used only in a relative sense, is too restrictive for some members of one class of inclusion (simple CAI's) and is inappropriate for most members of another class (melilite‐rich complex CAI's).
Radar altimetry of Mercury: A Preliminary analysis
Authors: Harmon J. K. , Campbell D. B. , Bindschadler D. L. , Head J. W. , Shapiro I. I.
Published: February 2008

Measurements of Mercurian topography based on Arecibo radar observations are presented. The data, which were obtained from 1978 to 1984, cover much of the equatorial zone of Mercury between 12°N and 5°S latitude. Over thirty continuous altitude profiles were obtained, each spanning from 20 to 90 degrees of longitude at a resolution of 0.15° (longitude) by 2.5° (latitude). Radar depths for large craters support previous indications from imagery that Mercurian craters are shallower than lunar craters of the same size. One very large (800 km) impact basin shows some distinct topographic structure, although its relative shallowness suggests postimpact modification by isostatic relaxation or volcanic filling. The plains of Tir Planitia appear topographically smooth to the radar. These plains extend well into the hemisphere not imaged by Mariner 10, possibly forming part of a large annulus of smooth plains around Caloris Basin. The circum‐Caloris smooth plains are strongly down‐bowed, indicating subsidence under a load. This and other similarities to lunar maria suggest a volcanic origin for these plains. Additional areas of topographically smooth terrain have been found in both the imaged and unimaged hemispheres. Several ridges, scarps, and fault zones have been identified in the altimetry. Three mapped arcuate scarps show heights of about 700 m and cross‐sectional widths of about 70 km. One of these features is clearly a ridge, while the other two scarps have a more ridge‐like appearance than is suggested by images. One large‐scale topographic drop of 3 km correlates well with a mapped system of faults and intracrater scarps. The equatorial zone of Mercury shows 7 km of maximum relief, although the typical elevation difference between highlands and lowlands is closer to 3 km. Three major highland areas are found, the largest two of which are roughly antipodal and aligned within about 10° of the “hot poles” of Mercury. The unimaged hemisphere, possessing both large craters and topographically smooth areas, does not appear to be markedly different in its topography from the imaged hemisphere. No evidence has been found for another Caloris‐type impact structure in the unimaged hemisphere.
Errors in minimum plate velocity determined from paleomagnetic data
Authors: Bryan Phillip , Gordon Richard G.
Published: February 2008

In prior studies paleomagnetic data have been used to determine ancient minimum velocities of the continents. The greatest minimum velocities, ∼50 km/m.y., exceed the present‐day absolute velocities of the major continents. This result is important because the observation that present‐day oceanic plates move faster than present‐day continental plates can be treated as a major constraint on plate dynamics. However, these prior studies are limited because they ignore known errors in the paleomagnetic data. In this paper we present a technique for incorporating these errors and using them to estimate 95% confidence limits on the minimum velocities. This new technique was applied to Pennsylvanian to Cretaceous paleomagnetic data from North America and to the ancient geometry of Laurasia. When errors are considered, minimum velocities are 10 to 50 km/m.y. lower than when errors are ignored. Additional uncertainties owing to a hypothesized clockwise rotation of the Colorado Plateau, a source of many of the data, are considered and found to alter the minimum velocities only negligibly. Allowing for uncertainties in the pole positions, uncertainties in ages, and the uncertainty due to possible rotation of the Colorado plateau, we estimate that Laurasia moved at least 48 km/m.y. from Early Jurassic to Early Cretaceous time, and at least 43 km/m.y. from Pennsylvanian through Late Triassic time. There is only a 5% risk that the true minimum velocities are lower than these lower bounds. These velocities are less than the peak velocities over short intervals found in prior analyses, but exceed the average velocities previously found for Triassic and Jurassic time. These newly estimated velocities are still much higher than the present velocities of the continents and, as in the prior studies, imply that the slow motion characteristic of major continents at present is not a fundamental attribute of plate motions.
Reservoir processes and fluid origins in the Baca Geothermal System, Valles Caldera, New Mexico
Authors: Truesdell Alfred H. , Janik Cathy J.
Published: February 2008

At the Baca geothermal field in the Valles caldera, New Mexico, 19 deep wells were drilled in an attempt to develop a 50‐MWe (megawatts electric) power plant. The chemical and isotopic compositions of steam and water samples have been used to indicate uniquely the origin of reservoir fluids and natural reservoir processes. Two distinct reservoir fluids exist at Baca. These fluids originate from the same deep, high‐temperature (335°C), saline (2500 mg/kg Cl) parent water but have had different histories during upflow. One fluid (from wells 4 and 13) is isotopically light, high in radiogenic noble gases, CO2 and HCO3, and low in Ca. It has a temperature of 290°–295°C and a reservoir chloride near 1900 mg/kg. This fluid resulted from rapid upward flow through 1.1‐ to 1.4‐m.y.‐old Bandelier Tuff reservoir rocks after long residence in pre‐Bandelier (>7 m.y.) sediments and Precambrian basement rocks and 25% dilution with high‐altitude cold groundwater from Redondo Peak. The other water (from wells 15, 19, and 24) moved slowly through the Bandelier Tuff and cooled conductively (with minor steam loss for well 19) from 335°C to 280°–260°C. Apparently, short residence in old basement rocks has left this water with low radiogenic gases. Conductive cooling without mixing has kept the original chloride and relatively heavy isotope composition of the deep water. The recharge to the deep parent water is not well understood but may be from lower elevation precipitation outside the Valles caldera area. Gases are in equilibrium in all‐liquid reservoir fluids at near reservoir temperatures, and the concentrations of atmospheric gases are similar to those of air‐saturated water, indicating little boiling and steam loss. All water, solutes, and gases in the reservoir fluids originate from air‐saturated meteoric recharge water, watermineral reactions, and rock leaching, with the possible exception of excess 3He that must have an ultimate mantle source. This gas could originate directly from magma or from leaching of intrusive volcanic rocks beneath the Bandelier.
Geodesy by radio interferometry: Determinations of baseline vector, Earth rotation, and solid earth tide parameters with the Mark I Very Long Baseline Radio Interferometry System
Authors: Ryan J. W. , Clark T. A. , Coates R. J. , Ma C. , Wildes W. T. , Gwinn C. R. , Herring T. A. , Shapiro I. I. , Corey B. E. , Counselman C. C. , Hinteregger H. F. , Rogers A. E. E. , Whitney A. R. , Knight C. A. , Vandenberg N. R. , Pigg J. C. , Schupler B. R. , Rönnäng B. O.
Published: February 2008

We analyzed 37 very long baseline radio interferometry experiments performed between 1972 and 1978 and derived estimates of baseline vectors between six sites, five in the continental United States and one in Europe. We found no evidence of significant changes in baseline length. For example, with a statistical level of confidence of approximately 85%, upper bounds on such changes within the United States ranged from a low of 10 mm/yr for the 850 km baseline between Westford, Massachusetts, and Green Bank, West Virginia, to a high of 90 mm/yr for the nearly 4000 km baseline between Westford and Goldstone, California. We also obtained estimates for universal time and for the x component of the position of the earth's pole. For the last 15 experiments, the only ones employing wideband receivers, the root‐mean‐square differences between our values and the corresponding ones published by the Bureau International de l'Heure are 0.0012 s and 0.018 arc sec respectively. The average value we obtained for the radial Love number h for the solid earth is 0.62±0.02 (estimated standard error).
Temporal change in attenuation intensity before and after the Eastern Yamanashi Earthquake of 1983 in central Japan
Authors: Sato Haruo
Published: February 2008

A crutal earthquake of magnitude 6.0 took place on August 8, 1983, in the middle of the Kanto‐Tokai microearthquake observation network of the National Research Center for Disaster Prevention in central Japan. By analyzing vertical seismograms of microearthquakes occurring in a small volume in the aftershock region, we measured temporal change in attenuation intensity for a period from 22 months before to 9 months after the main shock. Attenuation change was estimated by using two different kinds of analyses. In the first analysis, station magnitude calculated from the maximum amplitude at each station was compared with the average of station magnitudes. Deviations of station magnitude from the average magnitude at five stations in the vicinity of the aftershock area are found to have increased after the main shock compared with that before. In the second analysis, S coda duration from the origin time was measured and was compared with the average magnitude. The increase of S coda duration for the same average magnitude is found after the main shock at two stations close to the main shock epicenter. The simplest interpretation of the results is that the attenuation intensity in the upper crust in the close vicinity of the focal region decreased after the main shock for frequencies f from 2 to 20 Hz: ΔQs−1 = −1.4×10−2f−1. Since other precursors appeared in the preparation stage, it is possible to interpret the change in Qs−1 as a precursor. The attenuation intensity would have been anomalously large before the main shock.
Acoustic imaging and the juxtaposition of waves
Authors: DuBroff Richard E.
Published: February 2008

Boundary conditions involving acoustic pressure waves and their normal derivatives are used to develop an acoustic imaging criterion. This criterion is actually a testing procedure which operates upon the sum of the incident and reflected acoustic waves associated with reflection from an unknown acoustic boundary. One of the outputs from this procedure is used to reconstruct the unknown acoustic reflector while a second output from this procedure estimates the acoustic wavespeed on the opposite (transmission) side of the boundary. The calculation of the reflected acoustic wave as a function of spatial position and temporal frequency (which is a prerequisite for applying the testing procedure) is analogous to the downward continuation calculation used in conventional migration of seismic data. After using some simple examples to demonstrate the concepts involved in this procedure, the method is applied to computer generated synthetic data.
A compositional study of the Aristarchus Region of the Moon using near‐infrared reflectance spectroscopy
Authors: Lucey P. G. , Hawke B. R. , Pieters C. M. , Head J. W. , McCord T. B.
Published: February 2008

Newly obtained near‐infrared reflectance spectra for features on or near the Aristarchus Plateau demonstrate the diversity of compositions in the region. Highland units are of three probable compositions: a feldspar and clinopyroxene assemblage; a probable clinopyroxene, olivine, and possibly feldspar assemblage; and an assemblage composed of olivine or olivine and feldspar. The feldspar‐clinopyroxene assemblage is tentatively correlated with the major Th anomaly centered on Aristarchus crater. The regional pyroclastic deposits on the plateau are composed of greater than 90% Fe2+‐bearing glass. The Aristarchus cratering event fully penetrated any mare or pyroclastics in the target. Evidence for mare‐related material is found in the ejecta on the mare side of the mare‐plateau contact.
Mapping of carbon concentrations in the Allende meteorite with the 12C(d,p)13C method
Authors: Van Der Stap C. C. A. H. , Heymann D. , Vis R. D. , Verheul H.
Published: February 2008

We have “mapped” carbon concentrations in a 4.2 × 4.2 mm area of the Ailende meteorite with the 12C(d,p)13 C nuclear method. The x,y resolution perpendicular to the deuteron beam was 65 μm; the depth resolution was 0.6 μm. The matrix of the meteorite contains about 1 wt % carbon, which is uniformly distributed at the 65‐μm level of resolution. The matrix contains most, perhaps close to all, C of this meteorite. The coarse‐grained constituents, such as chondrules, show a very strong enhancement of C in the depth range 2 to about 0 μm; the matrix does not show this enhancement. The enhancement may be due to contamination of the coarse‐grained areas or else to migration of C in solid solution from the interiors of comparatively large crystals to their freshly polished surfaces.
Cosmogenic neutron‐capture‐produced nuclides in stony meteorites
Authors: Spergel M. S. , Reedy R. C. , Lazareth O. W. , Levy P. W. , Slatest L. A.
Published: February 2008

The distribution of neutrons with energies below 15 MeV in spherical stony meteoroids is calculated using the ANISN neutron‐transport code. The source distributions and intensities of neutrons are calculated using cross sections for the production of tritium. The meteoroid's radius and chemical composition strongly influence the total neutron flux and the neutron energy spectrum, whereas the location within a meteoroid only affects the relative neutron intensities. Meteoroids must have radii of more than 50 g/cm2 before they have appreciable fluxes of neutrons near thermal energies. Meteoroids with high hydrogen or low iron contents can thermalize neutrons better than chondrites can. Rates for the production of 60Co, 59Ni, and 36Cl are calculated with these neutron fluxes and evaluated neutron‐capture cross sections and are reported for carbonaceous chondrites with high hydrogen contents, L‐chondrites, and aubrites. For most meteoroids with radii <300 g/cm2, the production rates of these neutron‐capture nuclides increase monotonically with depth. The highest calculated 60Co production rate in an ordinary chondrite is 375 atoms/min/g‐Co at the center of a meteoroid with a 250 g/cm2 radius. The production rates calculated for spallogenic 60Co and 59Ni are greater than the neutron‐capture rates for radii less than ∼50–75 g/cm2. Only for very large meteorpids and chlorine‐rich samples is the neutron‐capture production of 36Cl important. The results of these calculations are compared with those of previous calculations and with measured activities in many meteorites.
High energy irradiations simulating cosmic‐ray‐induced planetary gamma ray production: I. Fe target
Authors: Metzger Albert E. , Parker Richard H. , Yellin Joseph
Published: February 2008

A series of 6 GeV proton irradiations at the Argonne National Laboratory's Zero Gradient Synchrocyclotron included the bombardment of two thick Fe targets for the purpose of simulating the cosmic ray bombardment of planetary objects in space. Cosmic ray bombardment leads to characteristic gamma ray production, from which, by measuring their energy and intensity, surface composition may be derived. In this experiment, gamma ray energy spectra were obtained with a germanium solid state detector during the bombardment. The spectra show much detail, with 46 of the gamma ray lines ascribed to the Fe targets. The background includes recoil‐broadened lines due to energetic neutron interactions in the Ge detector. A comparison with values predicted by modeling shows good agreement for Fe lines from neutron inelastic scattering and spallation reactions, and less satisfactory agreement for neutron capture reactions, the latter found to be due primarily to the difference in composition between the Fe target and the mean lunar abundance used in the modeling. Analysis of the irradiation results combined with continuum data obtained in lunar orbit indicates that 100 hours of measurement with a state‐of‐the‐art instrument should generate a spectrum containing approximately 20 lines due to Fe alone, with a 2σ sensitivity for detection of about 0.2%.
Recent developments in conventional high‐pressure methods
Authors: Graham E. K.
Published: February 2008

Over the last decade, high‐pressure‐temperature experiments in mineral physics generally have employed either diamond anvil, shock wave, or conventional pressure generation methods. In the latter category, one would include standard hydrostatic fluid vessels, piston‐cylinder devices, “belt” and “girdle” apparatus, and multianvil units. Recent emphasis in the use of such systems has centered on improvements in volume, pressure, and temperature capabilities, as well as the achievement of more hydrostatic pressure environments. Because the pressure generation level of conventional equipment is rather limited, in comparison to diamond anvil and shock wave methods, focus has been placed on the usage of working volume in terms of material synthesis and the measurement of physical properties. In this regard, the design of internal pressure cell‐specimen capsule arrangements has been improved to allow X ray and ultrasonic measurements to hydrostatic pressures in excess of 6 GPa. Mineral data derived from such measurements should provide the bases for more accurate representations of the equation of state in the lower mantle and core by virtue of the inclusion of higher‐order elastic properties.
On the colors of Jupiter's satellite Io: Irradiation of solid sulfur at 77 K
Authors: Steudel Ralf , Holdt Gabriele , Young Andrew T.
Published: February 2008

The colors of seven sulfur allotropes at 77 K have been investigated both before and after irradiation by a high‐pressure mercury lamp. S8 is white at 77 K but turns intense yellow within a few minutes on irradiation through quartz or DURAN. On warming, the yellow species (presumably chain‐like sulfur diradicals characterized by an absorption at 430 nm) decomposes near 260 K and polymeric sulfur (S∞) is formed; the sample color changes gradually to the very similar color of an S8–S∞ mixture, resulting in no visually detectable color change with temperature from 77 K to 260 K. This is consistent with the lack of posteclipse brightening on Io. Other sulfur forms also turn intense yellow (S7, S10), grayish yellow (S12, S20, S∞), or brownish yellow (S6) on irradiation at 77 K, and these colors also change to the normal colors of the starting materials on warming to 298 K. We suggest that the yellowish features on Io are caused by the effect of solar radiation on elemental sulfur. The yellow color thus produced may subsequently be modified by deposits of SO2 frosts and volcanic ash.
Linked evolutionary data arrays: A logical structure for petrologic modeling of multisource, multiprocess magmatic systems
Authors: Bryan Wilfred B.
Published: February 2008

Models of multiprocess, open magmatic systems can be tested in a stepwise procedure in which two‐dimensional data arrays representing a single stage in the set of processes are linked to a specific member of another array that represents either a preceding or a subsequent step in the model. Data within each array may be ordered according to variation in one or more components known or inferred to be especially sensitive to the process in question. In some cases, several processes operating concurrently, such as mixing plus crystal fractionation, can be accommodated within a single array. The essential steps in organizing data and testing models are (1) grouping sample data according to their assumed association with each process; (2) ordering of data within each array to reflect the “degree of evolution” or the extent to which the process has operated; and (3) defining the composition or compositions that represent the “branch points” linking each array to other arrays representing a previously completed or a subsequent process. This leads to a conceptual structure of linked evolutionary arrays, which collectively relate the starting and final compositions of a given magmatic system. Variation within major element data arrays and the linkage between them can be tested using an extension of the least squares algorithm, which selects the “best” branch point according to the minimum sum of squared residuals criterion. These capabilities have been incorporated in a program called MULTIFIT, written in Microsoft BASIC for use in an IBM or compatible microcomputer. A subroutine based on the Rayleigh equations permits evaluation of trace element variation consistent with the best major element result. It is emphasized that, while MULTIFIT utilizes concepts that are familiar to most petrologists and geochemists, and can be applied to a variety of problems, it may not be the best approach for poorly constrained models involving partial melting or complex mixing. An adaptation of inverse modeling methods may be more appropriate for such problems. Advantages and disadvantages of the materials balance approach used in MULTIFIT are discussed, a simple example is given, and the equations utilized by MULTIFIT are summarized. It is shown that an extension of the same concept may be useful for defining trace element partition coefficients in magmatic systems.