Distances In Excess Research Articles

Comparison of Radio Imaging Method (RIM) Electromagnetic Wave Tomography with In-Mine Geological Mapping in the Liddell, Bulli and Wongawilli Coal Seams

The radio imaging method (RIM) of coal seam mapping relies on the natural waveguide effect exhibited by coal seams to electromagnetic wave propagation. Whenever coal seams are disrupted by a natural geological discontinuity, the waveguide disruption causes a measurable change in the wave attenuation. Attenuation measurements can be analysed directly or, if sufficient data are available by tomography, to indicate the location of the anomaly and its likely severity. Such information is of vital importance in modern underground coal mining. In February, 1987 a series of trial surveys were conducted in three Australian mines by a survey team from Stolar Inc. of the USA. The results showed that the natural wave attenuation is 46 dB/100 m in the Liddell Seam, 36 dB/100 m in the Wongawilli Seam and 13 dB/100 m in the Bulli Seam. In the Bulli Seam propagation over distances in excess of 600 m is possible. The surveys were conducted over test sites where dykes and other geological features exist. Wave propagation was clearly disrupted by the dykes and it was possible to image their location by tomographic means. An application for RIM in Australian mines has been clearly indicated.

Laboratory studies of homing orientation in the eastern red-spotted newt, Notophthalmus viridescens

The orientation behaviour of adult male eastern red-spotted newts (Notophthalmus viridescens) was studied in laboratory tests. Newts were collected from ponds located 10-30 km from the laboratory, and housed in water-filled, all-glass aquaria located in a greenhouse or outdoors adjacent to the laboratory building. The aquaria were aligned on the magnetic north-south axis. Newts were tested in a dry, enclosed arena in four magnetic fields: the ambient magnetic field (magnetic north at North) and three altered fields (magnetic north rotated to East, West or South). Newts tested during January-March exhibited weak bimodal magnetic orientation along the axis of the holding tank. However, during the spring migratory period (April until early May), the bimodal response shifted to coincide with the direction of the pond from which the newts had been collected. Much stronger unimodal orientation was elicited by elevating the water temperature to 33-34 degrees C immediately prior to testing. If newts were held in a training tank with an artificial shoreline at one end and exposed to elevation of water temperature after several days of stable water temperatures, they exhibited unimodal shoreward orientation and did not show the seasonal switch to homing behaviour observed in the earlier tests. If, however, the elevation of water temperature followed a period of fluctuating water temperature (over a 20 degrees C range), the newts exhibited strong unimodal orientation in the direction of the pond from which they had been collected. These results suggest that newts possess a navigational system that enables them to home from distances in excess of 20 km. Moreover, these experiments provide the first opportunity to examine the sensory basis of navigational ability in any animal under controlled laboratory conditions.

The role of helicopter noise-induced vibration and rattle in human response

Our understanding of community reaction to helicopter noise is incomplete and inadequate. While A-weighting appears to work outdoors and at modest noise levels, and the community response in terms of percentage of population highly annoyed can be correlated with respect to the day/night average sound level (DNL) descriptor, questions remain as to the role of perceived building vibrations and rattle in human response to helicopter noise. Does hearing windows, ceiling tiles, or objects in the room rattle or does the general perception of building vibration increase the public’s adverse response to helicopter noise? To answer these questions, this study examined the role of vibration and rattle in human response to helicopter noise. Results showed that the A-frequency-weighting is generally adequate to assess community response to helicopter noise when no vibration or rattle is induced by the noise. When rattle or vibrations are induced by the helicopter noise, however, A-weighting does not assess the community response adequately. In this study, slant distance (distance of closest approach between the helicopter and the location on the ground) offers the best correlation with high levels of rattle. High levels of rattle usually would not be induced for slant distances in excess of 1000 ft, but high levels of rattle would nearly always be produced for slant distances shorter than 500 ft. The result suggests a decibel offset on the order of 10 dB or more is required to assess helicopter noise properly when little vibration or rattle is produced. When no rattles are induced by the noise, there is no offset. No housing or noise-sensitive land uses should be located in zones where high levels of vibration or rattle are induced by helicopter noise; the offset is at least on the order of 20 dB. This high vibration and rattle zone potentially can be delineated by helicopter type and slant distance. For the Army Huey aircraft in level flyover, this zone boundary is at a slant distance between 500 and 1000 ft. The slant distance zone boundary is expected to differ with type of aircraft and operation.

Density and viscosity gradients in zoned magma chambers, and their influence withdrawal dynamics

The liquid being sampled from a draining reservoir of density-stratified fluid, such as an erupting zoned magma chamber, is derived from a relatively thin withdrawal layer adjacent to the level of the chamber outlet. This is a consequence of the buoyancy force associated with the density gradient inhibiting vertical motion so that the opportunity for widely separated density levels (compositions) to be tapped and mingled syneruptively is suppressed. Density gradients in zoned chambers of 0.02 – 10 kgm −3/m are suggested by data from caldera-forming eruptions. Viscosity gradients can be specified for a given density gradient using calculated relationships between viscosity and density. Published compositional and geothermometric data are used to show that zoned high-silica rhyolites decrease in viscosity upward because of the roofward concentration of dissolved volatiles. Other zoned calc-alkaline magmas increase in viscosity upward because of decreasing temperature and concentration of network modifying cations. A method is developed of calculating the scale of the withdrawal layer thickness, δ, for given kinematic viscosity, eruption rate, and density and viscosity gradients. The method is systematized by the identification of specific flow regimes describing the action of either viscous or inertial forces in balancing the buoyancy force. Thin withdrawal layers are favoured by small eruption rates, small viscosity, and by large density gradients. For particularly steep density gradients, however, the consequently large viscosity gradient plays a role in determining the withdrawal layer thickness. Withdrawal layer thicknesses of the order of 100 m are calculated for typical pyroclastic eruptions of zoned acid magma, and are mostly independent of the viscosity gradient. The vertical scale at which a zoned chamber is instantaneously being tapped during an eruption is equal to the scale of the withdrawal layer thickness. Thus, an eruption that causes collapse of a caldera block through a height that is less than that of the withdrawal layer scale will produce magmas from deeper levels than that to which the chamber roof sinks. In this case the eruption is said to oversample the chamber with respect to the amount of caldera collapse and will produce an essentially constant range of compositions throughout. Alternatively, if the caldera collapse distance is much greater than δ then the selective withdrawal process leads to successive levels of the chamber being “skimmed off” (on a scale δ). This allows the compositional stratigraphy of the chamber to be inverted by the eruptive process, with little opportunity for syneruptive mixing between diverse magma compositions. The geological record shows that most calderas associated with zoned magmas collapsed through vertical distances in excess of 100 m (the characteristic estimate for δ) and, in agreement with our modelling of selective withdrawal, show smooth correlations between composition, or temperature, and the order of eruption.

High-Speed CMI Optical Intraoffice Transmission System: Design and Performance

This paper presents the design and performance features of a successfully developed optical intraoffice transmission system operating at 100-400 Mbits/s. The keys to the commercial realization of this simple, highly reliable, and low-cost system are the employment of the 1.3 μm LED and graded-index multimode fiber. Additionally important, the system makes use of coded mark inversion (CMI) coding to ensure bit sequence independence (BSI) and good error-monitoring capability. Experimental results have clarified the optimum bandwidth of the low-pass filter at the receiver end and the commercially attainable transmission distance. Furthermore, an available system gain of 15.4 dB is demonstrated through 400 Mbit/s transmission experiments. This value enables transmission over distances in excess of 4 km through multimode fiber (900 MHz \cdotp km, 0.8 dB/km).

Geochemical exploration for mineralized breccia pipes in northern Arizona, U.S.A.

Thousands of solution-collapse breccia pipe crop out in the canyons and on the plateaus of northern Arizona. Over 80 of these are known to contain U or Cu mineralized rock. The high-grade U ore associated with potentially economic concentrations of Ag, Pb, Zn, Cu, Co and Ni in some of these pipes has continued to stimulate mining and exploration activity in northern Arizona, despite periods of depressed U prices. Large expanses of northern Arizona are comprised of undissected high plateaus; recognition of pipes in these areas is particularly important because mining access to the plateaus is far better than to the canyons. The small size of the pipes, generally less than 600 ft (200 m) in diameter, and limited rock outcrop on the plateaus, compounds the recognition problem. Although the breccia pipes, which bottom in the Mississippian Redwall Limestone, are occasionally exposed on the plateaus as circular features, so are unmineralized near-surface collapse features that bottom in the Permian Kaibab and Toroweap Formations. The distinction between these two classes of circular features is critical during exploration for this unique type of U deposit. Various geochemical and geophysical exploration methods have been tested over these classes of collapse features. Because of the small size of the deposits, and the low-level geochemical signatures in the overlying rock that are rarely dispersed for distances in excess of several hundred feet, most reconnaissance geochemical surveys, such as hydrogeochemistry or stream sediment, will not delineete mineralized pipes. Several types of detailed geochemical surveys made over collapse features, located through examination of aerial photographs and later field mapping, have been successful at delineating collapse features from the surrounding host rock: (1) Rock geochemistry commonly shows low level Ag, As, Ba, Co, Cu, Ni, Pb, Se and Zn anomalies over mineralized breccia pipes; (2) Soil surveys appear to have the greatest potential for distinguishing mineralized breccia pipes from the surrounding terrane. Although the soil anomalies are only twice the background concentrations for most anomalous elements, traverses made over collapse features show consistent enrichment inside of the feature as compared to outside; (3) B. Cereus surveys over a known mineralized pipe show significantly more anomalous samples collected from within the ring fracture than from outside of the breccia pipe; (4) Helium soil-gas surveys were made over 7 collapse features with discouraging results from 5 of the 7 features. Geophysical surveys indicate that scaler audio-magnetotelluric (AMT) and E-field telluric profile data show diagnostic conductivity differences over mineralized pipes as compared to the surrounding terrane. These surveys, coupled with the geochemical surveys conducted as detailed studies over features mapped by field and aerial photograph examination, can be a significant asset in the selection of potential breccia pipes for drilling.

GEOGRAPHIC VARIATION IN ALLOZYMES IN A "RING SPECIES," THE PLETHODONTID SALAMANDER ENSATINA ESCHSCHOLTZII OF WESTERN NORTH AMERICA.

The ring species Ensatina eschscholtzii (a plethodontid salamander) of western North America has a circle of subspecies surrounding the Central Valley of California which come into contact and are sympatric in southern California. We examined 26 proteins in 19 populations (maximum of 10 specimens per population) collected throughout the range in order to gain an understanding of the degree of differentiation in the group. Allozymic differentiation is profound, with genetic distances in excess of 0.5 (Rogers or Nei) between populations. Naturally hybridizing populations differ by genetic distances greater than 0.4. Two general classes of color morphs, blotched and unblotched, are segregated geographically, but they do not form discrete genetic units. Both are deeply differentiated, and genetic distances among populations of either class exceed those measured between the classes where they are sympatric in southern California. This study disclosed little evidence of gene exchange around the ring of populations and sampling of many additional populations in regions between populations sampled thus far will be required to determine whether smooth intergradation occurs. Although genetic distances measured exceed those between some co-occurring species of plethodontid salamanders, we find no evidence of borders between cryptic species.

Simple-pile approach to pile installation in clays : Baligh, M M Proc of the Conference on Analysis and Design of Pile Foundations, San Francisco, California, 1–5 Oct 1984P310–330. Publ New York: ASCE, 1984

This article describes the fundamentals of the approach and presents solutions for the effects of quasi-static deep undrained penetration of a simple solid pile on the deformations and strains in saturated isotropic clays and the deviatoric stresses in the outer soil located at some distance from the pile. Extensions of these solutions including stresses and pore pressures to more realistic conditions (e. g. , anisotropic clays and drained penetration in sands) by the strain path method are outlined. Evaluations of cavity expansion methods indicate that spherical expansion solutions have no direct application to pile installation studies and cylindrical cavity expansion solutions have the potential of providing predictions only in the outer elastic soil located at distances in excess of four to five radii from the pile axis and far behind the pile tip (about 10 radii).

Broad Absorption Line QSOs

Observational constraints on models for broad absorption line (BAL) QSOs are discussed. The picture which emerges is one in which the broad absorption line region (BALR) contributes to the broad emission line region (ELR) as a high ionization component. Depending on QSO luminosity, the limits on the distance of the BALR from the central source are 1–1000 pc. A highly metal enriched and disk-like geometry for the region is indicated. The similarity between the absorption in some radio quiet BAL QSOs and the associated complexes of absorption in some radio loud QSOs may indicate that the BALR outflow can affect the region surrounding a QSO out to distances in excess of several hundred kpc.

Tomato Springs: The Identification of a Jasper Trade and Production Center in Southern California

AbstractIn this report I present evidence of a prehistoric trade network that operated between the inland desert and coastal regions of southern California. Jasper, a nonlocal commodity from sources in the inland deserts, was found in large quantities at the Tomato Springs site, a prehistoric coastal village. This lithic material appears to have been of some value to the inhabitants of the coastal region, as evidence indicates that it was procured in quantity for a period of approximately 4,500 years over distances in excess of 175 km. The available data indicate that jasper trade between the inland deserts and the coast does not fit any distance-decay models proposed for trade in spite of the distances under consideration.

Asteroids in cometary orbits

Orbital integrations are presented for a total of 14 asteroids with perihelia inside 1.7 AU and with aphelion distances in excess of 4 AU, 10 of which were discovered in 1979–1984. The integrations were normally extended over approximately ±1000 years in a three-body model (Sun-Jupiter-asteroid). The effects of uncertainties of starting orbits are not treated in this work, and as far as the real asteroids are concerned, the results should be regarded mostly as preliminary indications. A wide variety of orbital evolutions is found, and some of them evidently belong to the cometary, chaotic type. Three such cases are identified with certainty (1983 SA, 1983 XF, and 1984 BC) and two or three more with various degrees of likelihood. An asteroidal motion is found for the well-observed object 1979 VA. A stable libration around the 2 1 resonance is found for 1981 FD, which obviously adds to the Griqua group. A long-lasting libration around the 5 3 resonance performed by 1982 YA is probably unstable. Temporary librations are also found for 1983 SA ( 4 3 resonance) and 1983 XF ( 2 1 resonance), but these objects appear to transit into irregular motions with close approaches to Jupiter (less than 0.01 AU for 1983 XF). A very rapid large-amplitude ω libration around 90° is found in the future motion of 1983 VA. If this will indeed occur for the real asteroid, the object will oscillate with a period of only 750 years between a main-belt orbit of very high inclination and a low-inclination Apollo-type orbit.

Radiation patterns of torsionally vibrating seismic sources

The radiation patterns available in the literature for seismic surface sources are restricted to far‐field, low‐frequency solutions for undamped half‐space models. A theoretical study of the radiation pattern of a circular baseplate vibrating torsionally on the surface of an N-layered anelastic medium demonstrates that the patterns in the literature do not reasonably represent the radiated field of a source on a damped layered medium. The radiation pattern of a source is a measure of the strength of the output signal as a function of direction and is determined by calculating the displacements at points along the arc of a circle at a specified radial distance from the source. The solution for the displacement due to a vibrator or a plane‐layered anelastic medium is obtained by solving the elastodynamic wave equation using Fourier and Hankel transforms. The displacement is expressed in terms of an inverse Hankel transform which is performed numerically. The shape of the torsional radiation pattern in a half‐space is a function of frequency, baseplate radius, shear‐wave velocity, and radial distance between the source and the observation points. As frequency increases, the source beams more energy in a near‐vertical direction, and less in directions near the horizontal. Vertical beaming also increases as baseplate radius increases and as shear‐wave velocity decreases. The radiated field approaches an asymptotic far‐field radiation pattern at radial distances in excess of 5 to 8 baseplate radii. In a layered medium, constructive and destructive interference of direct, reflected, and refracted waves results in a characteristic lobate structure in the radiated field. A minimum occurs just below the layer interface due to the combined effects of reflections and refractions. As frequency increases, a greater proportion of energy penetrates the layer interface and enters the underlying medium. At frequencies typically used in exploration seismology the majority of the signal from a torsional source is trapped in the surface layer. The shape of the radiation pattern at a given distance from the source is a function of the density, velocity, and Q contrasts between layers. For a given acoustic impedance contrast, more energy is trapped in the surface layer if the contrast is caused primarily by a velocity rather than a density change since the velocity contrast results not only in reflections but also in refractions and Love waves. A variation in Q between layers further distorts the radiated field. The pattern for a layered model does not asymptote to a far‐field pattern until the radial distance is much greater than the total thickness of the layers in the model. Radiation pattern modeling for layered media may help resolve the discrepancies between theoretical patterns and field measurements and may provide a means of optimizing the radiated field of a surface source or source array in terms of its directivity and the partitioning of energy between various wave types.

Optical spiral structure at L = 30 deg to 70 deg. I - New observations of distant early-type stars

view Abstract Citations (7) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical spiral structure at L = 30 to 70. I. New observations of distant early-type stars. Forbes, D. Abstract Photoelectric UBV photometry has been obtained for 86 early-type stars fainter than photographic magnitude 11, within the range of galactic longitude 30° - 70°, and classified as OB+ or OB in the Luminous Stars catalogues of the Hamburg and Warner and Swasey Observatories. MK spectrograms of 68 of these stars have also been obtained. Color excesses and distances are derived for those stars in the sample with spectral types B1.5 V or earlier and/or luminosity class Iab and brighter. Several of the stars observed are B and A supergiants with heliocentric distances in excess of 8 kpc. Publication: The Astronomical Journal Pub Date: April 1984 DOI: 10.1086/113537 Bibcode: 1984AJ.....89..475F Keywords: B Stars; Early Stars; O Stars; Spectral Energy Distribution; Stellar Spectrophotometry; Ubv Spectra; Astronomical Catalogs; Electrophotometers; Main Sequence Stars; Stellar Evolution; Stellar Luminosity; Supergiant Stars; Astronomy full text sources ADS | data products SIMBAD (85)

Plate Tectonics, Organic Matter, and Basin Evaluation for Petroleum Potential: ABSTRACT

Application of plate-tectonic concepts to sedimentary basin development has been important in petroleum geology. Physical aspects have been stressed, but a complete classification must include the amount, type, and distribution of organic matter because this is the material that generates petroleum. Organic matter can be classified into two broad categories: (1) land-derived (terrestrial) organic matter that may include major amounts of lignin and surface coatings which give gas or waxy crudes respectively, and (2) aquatic organic matter which commonly is dominantly of algal origin and generates normal crudes. The relative amounts of these two types of organic matter, and hence the relative amounts of oil and gas, depend on the depositional environment and this can be r lated to plate-tectonic setting. Rifts that form in the early stages of continental breakup receive high percentages of terrestrially derived organic matter initially, but aquatic organic matter becomes quantitatively more significant as the rift widens and marine conditions develop. Thus pull-apart continental margins develop a vertical profile from terrestrial organic matter deep to aquatic organic matter shallow. The deeper continentally derived sedimentary sections of these margins produce waxy crudes, gas, and some condensate reflecting the character of the organic matter. Pull-apart margins and rifts with waxy crudes were within 20° of the equator at the time of rifting. They include the Sirte, Cambay, Reconcavo, Gabon, and Cuanza basins. When rifting occurred farther from the equator, gas-dominated provin es were developed, such as northwest Australia, offshore Newfoundland, Baltimore Canyon, and the central Viking graben. Rivers transport continental sediments and organic matter to continental margins, and the association of transported terrestrial organic matter with clastic sediments makes deltas one of the most gas-prone depositional environments. Organic materials are not distributed uniformly in deltas because terrestrial organic matter has its highest concentration nearshore whereas aquatic material is also produced in large amounts offshore. This separation and distribution lead to gas fields near paleoshorelines and oil farther out. As the delta progrades, terrestrial organic matter is deposited over the previously deposited aquatic organic matter. This profile of organic matter type is exactly the opposite of that developed on passive continental margins and leads to the opposite trend for the distribution of oil and gas with depth. Although organic-matter type exercises initial control over the nature of the hydrocarbons generated, the composition may be changed later by maturation and migration. Maturation is the thermally induced trend from oil to gas and the depth for this conversion will depend on geothermal gradient. Migration distance is also controlled by plate-tectonic setting with distances in excess of 100 km being well documented for structurally simple interior basins. In contrast, migration distances are much shorter when migration pathways are interrupted, for example, by block faulting in rifts and growth faults in deltas. End_of_Article - Last_Page 1356------------

The brightest superassociations in spiral and irregular galaxies as extragalactic distance indicators

view Abstract Citations (59) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The brightest superassociations in spiral and irregular galaxies as extragalactic distance indicators Wray, J. D. ; de Vaucouleurs, G. Abstract The brightest blue knots (superassociations) detected by composite U,B,V color photography in spiral and irregular galaxies have absolute magnitudes B1 ranging from -10 to -15, which are from 3 to 5 magnitudes brighter than the brightest single stars. The absolute magnitude of the brightest blue knot M10 (corrected for galactic extinction) depends on the corrected color index (B-V)T0 and luminosity index Λc of the galaxy, being brighter in the bluer and most luminous galaxies. In a first approximation a two-parameter solution gives M10 = M1C + 2(Λc -1)+2.5 [(B-V)T0-0.5] where 1C> = -13.4 ± 0.2 from a sample of 78 galaxies having known distance moduli 18.3 < μ0 < 32.0. In a second approximation allowing for internal extinction a three parameter solution gives M10 = M1* +2(Λc -0.8)+2.8 [(B-V)T0 -0.5] +0.7 (log R25 -0.2) where R25 is the isophotal axis ratio of the galaxy and 1*> > = -13.0 ± 0.2. Distances derived from B1 and M1C or M1* are in good systematic agreement with distances derived from primary, secondary and tertiary indicators, but with a rather large dispersion (σ ≅ 0.55 mag) due in part to errors in the preliminary photometry (σ ≅ 0.4 mag). With some refinements and better photometry this new distance indicator appears capable of providing distance moduli with mean errors ≲0.5 mag out to distances in excess of 100 megaparsecs. Publication: The Astronomical Journal Pub Date: January 1980 DOI: 10.1086/112625 Bibcode: 1980AJ.....85....1W Keywords: Astrometry; Galactic Structure; Luminous Intensity; Spiral Galaxies; Stellar Luminosity; Hydrogen Clouds; Magnitude; Star Clusters; Stellar Spectrophotometry; Astrophysics full text sources ADS | data products NED (81)

Compositions of halo clusters and the formation of the galactic halo

A method of abundance determination based on reddening-independent properties of low-resolution spectral scans is described and applied to 177 red giants in 19 globular clusters, most of which are at galactocentric distances in excess of 8 kpc. The general properties of the halo-cluster system inferred from the abundance results are examined. It is found that the distribution over abundance of the halo globular clusters is independent of galactocentric distance for distances exceeding 8 kpc and that the clusters exhibit differences in the morphology of their color-magnitude diagrams that are uncorrelated with metal abundance. The characteristics of the system of halo clusters are compared with implications of some simple conceptual schemes for the formation of the Galaxy. It is suggested that the halo clusters originated within transient protogalactic fragments that gradually lost gas while undergoing chemical evolution and continued to fall into the Galaxy after the collapse of its central regions had been completed.

Spectral analyses of high‐frequency Pn,Sn phases recorded on ocean bottom seismographs

Spectrograms of high‐frequency Pn,Sn phases recorded on ocean bottom seismographs contain frequencies in Pn and Sn wavetrains as high as 10 Hz and 7 Hz, respectively, at distances in excess of 3700 km. These and other observations confirm earlier evidence for remarkable efficiencies of Pn and Sn propagation, with Sn often more efficient (higher apparent Q) than Pn.

Atmospheric electric space charge generated by the surf

Measurements of potential gradients in the atmosphere have confirmed earlier findings, made by different methods, that positive space charge is released into the atmosphere by the surf action. A simple theoretical model is used in special cases to estimate the density of surf generated space charge and the thickness of the layer. The average density is about +420 pC m −3 and the average layer thickness 4.5 m. It is suggested that under suitable atmospheric conditions it may be possible to detect the presence of surf generated space charge at distances in excess of 20 km from the surf.

High-frequency Pnand Snphases recorded in the western Pacific

One hundred sixty-four (164) high-frequency Pn phases and 126 high-frequency Sn phases recorded on a short-period seismograph temporarily operated at Ponape are used to complement and extend prior investigations of the Western Pacific mantle. Pn and Sn phases are well recorded out to distances of 20° for moderate-sized earthquakes (Mb ≃ 5) for travel paths entirely within the relatively homogeneous geophysical provinces of the Northwestern Pacific Basin or the Ontong Java Plateau. For comparable events, Pn and Sn phases are generally more prominent for travel paths in the Northwestern Pacific Basin than in the Ontong Java Plateau. Pn and Sn propagation is much less efficient but still possible for travel paths that cross island arc-trench systems or island chains. For distances beyond 20°, Pn and Sn are observed only for large earthquakes (Mb ≥ 6.0) or for moderate-sized earthquakes having substantial focal depths (>200 km). At all distances, Pn is generally more prominent on the seismograms than Sn. The maximum distance at which Pn and Sn phases are recorded is 37.84° (4208 km). Sn velocities for the Northwestern Pacific Basin (>130 m.y. old) and for the Ontong Java Plateau (60 to 130 m.y. old) are 4.77±0.03 km/s and 4.70±0.07 km/s, respectively. Corresponding velocities for Pn are 8.33±0.05 km/s and 8.52±0.14 km/s. A suggestion of more than one Pn, Sn wave guide is provided by Pn phases at distances in excess of 30°. The Pn velocity for these phases is 7.87±0.33 km/s.

Stable isotopic fractionation, climate change and episodic stagnation in the eastern Mediterranean during the late Quaternary

Fluctuations in the δ 18O composition of planktonic foraminifers in eastern Mediterranean piston cores indicate cycles with amplitudes much greater than those which can be attributed alone to global ice-volume changes. Isotopic values become markedly negative within lithostratigraphic levels characterized by the apparition of organicrich sapropels These owe their origin to the development of euxinic bottom water during episodes of basin-wide stagnation. The depletion of δ 18O in many of the sapropels is accompanied by the occurrence of poorly diversified planktonic faunas, and both phenomena are attributed to a strong dilution of the local eastern Mediterranean surface water mass by a combination of glacial run off from large continental ice sheets and by an important increase of regional precipitation synchronous with the transition from pleniglacial to kataglacial climate. Although sapropel accumulation occurs generally during intervals of warming of the Mediterranean region as determined from a quantitative evaluation of planktonic foraminiferal assemblages, the pre-125,000 years, local warming of eastern Mediterranean surface water lagged the acme of glacial melting by up to 15,000 years. Climatic and isotopic cycles are correlative within the eastern Mediterranean for lateral distances in excess of 1000 km and, except for amplitude and phase, they are in most aspects remarkably similar to those recorded in the equatorial Pacific and Caribbean.