bluuebunny/crossref_metadata_2025 huggingface dataset:
A comprehensive meteorologically oriented methodology for the prediction of wave propagation parameters in telecommunication applications beyond 10 GHz
Authors: Capsoni C. , Fedi F. , Paraboni A.
Published: February 2008

This paper presents a new approach for the prediction of propagation parameters (such as rain attenuation, site diversity gain, interference by rain scattering, etc.) in telecommunication applications beyond 10 GHz. It consists of a comprehensive theory allowing the full exploitation of the large amount of meteorological data available today. The method is based on a recently devised statistical model of the rain horizontal structure (Capsoni et al., this issue), whose parameters can be determined on the basis of the local statistical distribution of the point rainfall intensity. A test of the ability of this method in predicting attenuation statistics is performed using data collected in Europe with the satellites SIRIO and OTS (COST 205, 1985). The excellent results obtained encourage the application of the model to the statistical prediction of other parameters pertaining to propagation.
Data and theory for a new model of the horizontal structure of rain cells for propagation applications
Authors: Capsoni C. , Fedi F. , Magistroni C. , Paraboni A. , Pawlina A.
Published: February 2008

A large population of radar‐measured ground rain cells is used to devise and assess a rain cell model for use in some of the future telecommunication applications. The model is based on cells of exponential profile (which is shown to reproduce best the point rain rate CDF); both rotational and biaxial symmetries are considered for the horizontal cross sections. Furthermore, the proposed model contains analytical expressions for the joint probability densities of the parameters which define the cell, i.e., peak rain intensity, cell size and axial ratio. Finally, an algorithm is given for adapting the model to the characteristics of any given site: this algorithm requires as input the local cumulative distribution of point rainfall and provides the spatial number densities (i.e., the average number of cells per square kilometer and per unit range of the parameters) which this distribution would produce. The model offers the possibility of predicting the statistics of many propagation parameters (such as attenuation or interference by rain scattering) which are determined by the rain cell characteristics and their frequency of occurrence.
Daily observations of the development of the ionospheric equatorial anomaly by means of differential Doppler shift method
Authors: Huang Yinn‐Nien , Cheng Kang , Chen Sen‐Wen
Published: February 2008

The differential Doppler frequency shifts observed by receiving coherent radio signals at frequencies of 150 and 400 MHz transmitted from the polar orbiting satellites of U.S. Navy Navigation Satellite System have been used to deduce the latitudinal variations of the ionospheric total electron content (TEC) near the ionospheric equatorial anomaly crest region. All latitudinal variations of TEC thus obtained for each passage of an NNSS satellite are used to construct daily contour plots of TEC in a latitude versus local time coordinates. It has been shown that these contour plot of TEC can be used to investigate the behavior of TEC around equatorial anomaly crest region. Some results are presented and discussed.
Proton cyclotron echoes and spurs observed on Alouette II and ISIS II
Authors: Horita R. E.
Published: February 2008

Proton cyclotron echoes and spurs observed on the topside sounder ionograms on the Canadian Alouette and ISIS satellites are phenomena related to the proton cyclotron frequency. They appear on the ionograms at apparent ranges which lead to a frequency close to the proton cyclotron frequency; the frequency is calculated by taking the reciprocal of the time elapsed between the transmission of the sounder pulse and the reception of the signal at the satellite. Most proton cyclotron echoes and spurs occur at frequencies below the electron plasma frequency, ƒN; the echoes occur predominantly at frequencies slightly above the electron cyclotron frequency, ƒH, while the spurs occur predominantly when a harmonic of ƒH is near ƒN. Over 1000 ionograms exhibiting proton cyclotron echoes and/or spurs were examined and were classified depending on apparent range and shape of the echoes or spurs. The major classifications were echoes only, spurs only, and spur‐echo combinations. The subclassifications include one new type of spur which occurs at frequencies above ƒN. The classifications also reveal the absence of echoes with apparent ranges less than those corresponding to the calculated proton gyroperiod in the vicinity of the satellite. These results are compared with theories for the generation mechanism for proton cyclotron echoes and spurs.
Effects of propagation on the return stroke radiation fields
Authors: Cooray Vernon
Published: February 2008

It is shown that a simple mathematical model could be used to predict the propagation effects on the radiation fields to a high accuracy under most of the cases of interest. Propagation effects on a large collection of radiation fields from first return strokes measured over seawater are studied by using this mathematical model. The theoretical results are compared with the available experimental data and a good agreement is found between them. One important conclusion of the study is that the localization of the lightning return strokes by the time of arrival method could be greatly improved, under low conducting ground conditions, by selecting one of the following as reference points in the time measurement: (1) a point in the initial rising part of the radiation field whose amplitude is less than about 50% of the initial peak or (2) the peak of the first or the second derivative of the radiation field.
Scattering by parallel plates
Authors: Shimoda M. , Itakura T.
Published: February 2008

The scattering of electromagnetic fields from the parallel plates is analysed by the use of a new formulation. All the field representations to formulate the equations are expressed by the formal solutions of the Wiener‐Hopf equation for a plate. The mutual fields defined by the multiple scattering due to the parallel plates can be determined by the continuity condition of fields on the fictitious boundary which is set at an arbitrary position between two plates. Numerical results of the obtained far field are presented and compared with the results by the GTD method.
Polarizability tensors in low‐frequency inverse scattering
Authors: Angell T. S. , Kleinman R. E.
Published: February 2008

The problem treated is that of determining the geometric configuration and constitutive parameters of an object from a knowledge of the low‐frequency scattered far field produced by an incident plane wave. This problem is recast as a constrained optimization problem for a functional defined in terms of the polarizability tensor elements associated with the object. In particular, a method is described for finding the dimensions and orientation of that ellipsoid, the scattering properties of which best approximate the measured far field.
Time‐domain reciprocity theorems for electromagnetic fields in dispersive media
Authors: de Hoop Adrianus T.
Published: February 2008

Time‐domain reciprocity theorems of the time‐convolution and the time‐correlation type for electromagnetic fields in linear, time‐invariant, and locally reacting media are discussed. Inhomogeneous, anisotropic, and arbitrarily dispersive, both active and passive, media are included. The analysis is entirely carried out in space‐time, without intermediate recourse to the frequency or the wave vector domain. The application to inverse source and inverse constituency (or inverse profiling) problems is briefly indicated.
Wideband probing of the transauroral HF channel: Solar minimum
Authors: Wagner L. S. , Goldstein J. A. , Meyers W. D.
Published: February 2008

The Naval Research Laboratory HF Channel Prober is a high‐resolution, computer‐controlled, coded‐pulse sounder designed to study the time variable behavior of the wideband HF radio channel. Multispectral time histories of the channel pulse response and the channel scattering function are tools used in the study. Pulse response delay resolution down to 1 μs and unambiguous Doppler up to ±30 Hz are possible, depending on the choice of experiment format and operating parameters. Measurements were made quarterly between October 1985 and July 1986 on a 2300‐km transauroral path between a transmitter site at Frobisher Bay, Canadian Northwest Territories, and a receiver site near Rome, New York. Data are presented in the form of ionograms, pulse response time histories (power and coherent video), and channel scattering functions. Data for mid‐latitude and transauroral paths are compared, and their similarities and differences are discussed. The mid‐latitude channel is multimodal but is usually characterized by a single specular return per mode. The character of transauroral channel is quite variable, depending strongly on the degree of magnetic disturbance, the location of the midpath reflection point relative to the position of the auroral oval, and the mode. During quiet magnetic conditions, and with the path midpoint well below the auroral oval, channel behavior is shown to resemble a mid‐latitude channel at certain times and a specular multipath channel at other times (i.e., one where each mode comprises several distinct multipath components). Doppler spread in these cases tends to be small. At night, when the midpath point lies within the auroral oval, the return signal is diffuse, and the Doppler spread appears to be larger by an order of magnitude.
Electromagnetic vision‐oriented numerical solution to three‐dimensional inverse scattering
Authors: Caorsi S. , Gragnani G. L. , Pastorino M.
Published: February 2008

The problem of studying the capabilities of a preliminary electromagnetic vision process is considered. A numerical approach is developed on the basis of three‐dimensional electromagnetic scattering inversion. Computer simulations are performed by means of a numerical program implementing the moment method and making use of a pseudoinversion algorithm to overcome ill‐conditioning problems. An investigation volume holding unknown dielectric objects is assumed to be the scene to be visioned. An observation domain is considered for which the electric field vector's components (amplitude and phase) to be measured are obtained via numerical simulations of the direct electromagnetic scattering problem. The effects of the geometrical configurations of the observation domain and the measurement errors are analyzed.
Generalized impedance/resistive boundary conditions for electromagnetic scattering problems
Authors: Rojas R. G. , Al‐hekail Z.
Published: February 2008

Generalized impedance boundary conditions are derived for a planar, homogeneous, magnetic dielectric slab grounded by a perfect electric conducting plane and for a magnetic dielectric coated, perfect electric conducting circular cylinder. By invoking the duality principle, generalized resistive boundary conditions are also obtained for a planar, transparent dielectric slab. In the method followed here, it is not necessary to have a prior knowledge of the Fresnel reflection and/or transmission coefficients of the configuration under study to obtain the generalized boundary conditions. The boundary conditions developed here for the planar slab recover the exact Fresnel reflection and transmission (for the transparent slab) coefficients. Finally, the boundary conditions for the coated cylinder are used to obtain a solution for the scattering of an obliquely incident plane wave field, and this result is compared with the exact solution.
Maximum entropy estimation of Doppler shift and spectral width of VHF radar signals
Authors: Klostermeyer J.
Published: February 2008

Empirical investigations show that at low and moderate signal‐to‐noise ratios, maximum entropy (ME) Doppler shift and spectral width estimates of VHF radar signals have significantly higher accuracies than conventional periodogram estimates with noise thresholding. The variances of the ME estimates decrease with decreasing spectral width and clearly indicate a limiting signal‐to‐noise ratio below which the Doppler shift estimates are dominated by cosmic and instrumental noise rather than fluctuating radar signals. Two criteria are derived empirically that yield estimates of the optimum ME prediction error filter lengths for computing the Doppler shift and spectral width of individual radar signals. At small signal‐to‐noise ratios the Doppler shift criterion produces variances that are close to the minimum variance bounds of spectral methods. Fast ME algorithms for computing signal power, Doppler shift, and spectral width are described. At large signal‐to‐noise ratios the ME Doppler shift estimator is faster than the corresponding periodogram estimator based on a fast Fourier tranform, whereas at low signal‐to‐noise ratios, it is slower. For computing a typical height profile of the mean radial velocity in the troposphere and lower stratosphere, the ME estimator is as fast as the periodogram estimator, whereas for a height profile of the mean spectral width, it needs approximately 3 times as much computation time as the periodogram estimator.
Ionospheric incoherent scatter measurements with the middle and upper atmosphere radar: Techniques and capability
Authors: Sato Toru , Ito Atsuo , Oliver William L. , Fukao Shoichiro , Tsuda Toshitaka , Kato Susumu , Kimura Iwane
Published: February 2008

The MU (middle and upper atmosphere) radar of Japan is a 46.5‐MHz pulse‐modulated monostatic Doppler radar with an active phased array antenna which consists of 475 crossed yagis. This system has been used primarily, since its initial observations with a partial system in 1983, to observe back‐scatter from irregularities in the atmospheric index of refraction in the mesosphere, stratosphere, and troposphere (MST radar). However, this system was also designed to be able to observe the incoherent scattering (IS) from ionospheric plasma as well. We report here the capability of this system for IS measurements. This paper describes the observational technique employed for MU radar IS measurements, examines the expected accuracy of the plasma parameter measurements, and presents sample results to demonstrate the current capability.
Effect of geomagnetic disturbances on the VHF nighttime scintillation activity at equatorial and low latitudes
Authors: Dabas R. S. , Lakshmi D. R. , Reddy B. M.
Published: February 2008

VHF nighttime scintillation observations from a chain of stations extending from the equator to 21°N magnetic latitude along 84°E longitude in the Indian zone and at Lunping (23.0°N; 122°E; magnetic latitude 14.9°N subionospheric) in the Far Eastern zone, have been examined during five individual geomagnetic storms of varying strength. The usual nighttime scintillation activity during the main phase of the storm was found to be unaffected. For cases in which recovery phase of the storm starts during midnight to dawn local time sector and where the Dst value goes below −100 nT, strong postmidnight scintillations extending well beyond sunrise hours were observed at locations from 84°E to 122°E longitudes and in a wide latitudinal belt (i.e., up to 21°N magnetic latitude) particularly in the Indian zone. Under similar circumstances ionosonde data, from the equatorial region of both the zones, show considerable postmidnight increase in h′F as well as in spread F. However, at all locations, in cases of those storms whose recovery phases start during local daytime hours, on the following night scintillation and spread F activities were found to be suppressed completely or partially depending upon the maximum negative excursion of Dst. The effect was found to be more pronounced for cases in which Dst reaches below −100 nT. The same is also true for the first two categories of storms for the following night after the recovery phase sets in. The above results were further confirmed by examining Lunping scintillation and Manila ionosonde data for another 52 cases of geomagnetic storms observed during 1977 to 1983. The results are interpreted in terms of the reversal of the equatorial electric field directions under magnetically disturbed conditions.
Diffraction analysis of a proposed dual‐reflector feed for the spherical reflector antenna of the Arecibo Observatory
Authors: Kildal Per‐Simon , Skyttemyr Svein Andreas
Published: February 2008

A proposed dual‐reflector feed for the spherical reflector antenna in Arecibo is presented. This is analyzed over a large frequency range: at the lower frequencies by physical optics (PO) integration, and at the higher ones by a geometrical optic (GO) ray tracing technique described in another work. The latter calculations are extended with the transition region theory (TRT) to include edge diffraction. The results clearly demonstrate the usefulness of the time efficient TRT method. However, they also show that PO integration is important, as this has detected an underillumination of the central region of the aperture. This effect is related to a similar problem with the line feeds, but can in the present case be reduced by moving the subreflectors away from the paraxial focus.
Effects of chiral microstructure on em wave propagation in discrete random media
Authors: Varadan Vasundara V. , Ma Yushieh , Varadan Vijay K.
Published: February 2008

In this paper we examine the role of chirality or handedness on em (electromagnetic) wave propagation in a discrete random dielectric composite. Although chirality is manifested naturally by certain molecules and polymers at optical wavelengths, it must be introduced artificially at microwave frequencies. A discrete random medium is considered in which the inclusion phase is described by new constitutive equations, D = εE + βε∇×E and B = μ H + β μ ∇ × H. The new material constant β (meters), called the chirality parameter, arises due to the introduction of handedness in the material of which the inclusions are made. The influence of this parameter on the effective phase velocity and the attenuation of em waves is studied using a multiple scattering formalism that has previously been used successfully to describe dielectric composites that were nonchiral. The role of chirality in altering the propagation characteristics is readily apparent by comparing results for chiral and nonchiral media that are otherwise identical. Numerical results are presented for spherical inclusions made of a chiral material, for various concentrations and frequencies.
On the variability of sporadic E
Authors: Paul Adolf K.
Published: February 2008

The analysis of digital ionograms taken in short‐time intervals shows rapid changes of sporadic E parameters. This is directly visible in the variation of the top frequency or maximum electron density of such layers. Angle of arrival data which were available with those ionograms also showed fast changes of the apparent direction and often large deviations from vertical propagation.
Distribution of irregularities in the northern polar region determined from HILAT observations
Authors: MacDougall John W.
Published: February 2008

Three years' observations of the HILAT satellite from stations Sondre (Sondre Stromfjord), Churchill, and Tromso have been used to study the distributions of scintillations over the northern polar region. Two regions showed enhancement. One was an enhancement of phase scintillations when the line of sight to the satellite lay along an L shell and the observing station was under the auroral oval. The second enhancement is revealed most clearly by amplitude scintillations and maximizes in an annular region several degrees poleward of the auroral oval. The L shell enhancement is most likely associated with large‐scale “blobs” of ionization in the auroral zone, whereas the second enhancement appears to be due to kilometer scale irregularities generated in the polar cap.
New phenomena observed by EISCAT during an RF ionospheric modification experiment
Authors: Isham B. , Kofman W. , Hagfors T. , Nordling J. , Thidé B. , LaHoz C. , Stubbe P.
Published: February 2008

An ionospheric HF‐modification experiment was carried out near Tromsø, Norway, using the Max‐Planck‐Institut für Aeronomie (MPI) heating facility and the EISCAT 933‐MHz incoherent scatter radar (ISR). The MPI heater was normally operated at 4.04 MHz and modulated 20‐s on, 40‐s off. The ISR observed waves propagating parallel to B0, and chirped as well as normal plasma line observations were performed. Heater‐induced plasma lines were observed only in the first 10‐s integration interval, indicating a strong overshoot. These lines are unusual in that multiple simultaneous lines were observed, normally originating within one kilometer of the critical region but sometimes from lower heights, and that the frequency of the most constant line is offset some 250 kHz from the heating frequency, with the other lines occurring at greater frequency offsets. The natural, photoelectron‐enhanced plasma line was not observed; however, the background plasma was diagnosed via ion line observations and comparisons to chirped observations performed at EISCAT in May 1986 indicate that increased Landau damping may be responsible for both the strong induced‐line overshoot and the lack of a distinct natural line. Finally, ion power profile observations show the existence of a topside enhanced ion line at the critical density corresponding to the heater frequency. We believe this is due to strong O to Z‐mode coupling parallel to B0 and a low ƒ0F2.
Current flow into a three‐dimensionally anisotropic conductor
Authors: Wait James R.
Published: February 2008

A point source of direct current, in an anisotropic unbounded homogeneous conductor, is considered. The conductivities in three orthogonal directions are arbitrary. The solution is extended to deal with planar interfaces. Also, the relevance to resistivity sounding of a layered Earth is pointed out.
A model for the prediction of differential rain attenuation on adjacent Earth‐space propagation paths
Authors: Kanellopoulos J. D. , Houdzoumis V. A.
Published: February 2008

The main propagation effect on interference between adjacent Earth‐space paths is differential rain attenuation. In the present paper a method to predict the rain differential attenuation statistics is proposed which is based on a model convective rain cell structure of the rainfall medium. The assumption that the point rainfall statistics follow a lognormal form is also adopted. The results of this method are compared with the available simulation data for the differential attenuation over pairs of paths in the Montreal area. The agreement has been found to be quite encouraging. The sensitivity of various parameters affecting the differential attenuation statistics is also examined.
High‐latitude irregularity spectra deduced from scintillation measurements
Authors: Wernik A. W. , Liu C. H. , Franke S. J. , Gola M.
Published: February 2008

High‐latitude scintillation data show that the strength and spectral index of intensity scintillation are dependent on the propagation geometry. It will be shown that anisotropic irregularity spectra, with different indices along and across the magnetic field, lead to geometrical effects similar to those observed. In general, the spectrum along the magnetic field is steeper than that across the field, and the difference is more pronounced for nighttime conditions. Spectral anisotropy can be interpreted as a size‐dependent irregularity anisotropy. Our data indicate that large‐scale irregularities in the daytime and nighttime ionosphere are almost isotropic, while small‐scale irregularities are anisotropic and considerably more so at night than during the day. It will be shown that anisotropic irregularity spectra could account for the observed scintillation and in situ temporal spectra with frequency‐dependent slope. The effect depends strongly on the geometry.
Field tests of a lower tropospheric wind profiler
Authors: Ecklund W. L. , Carter D. A. , Balsley B. B. , Currier P. E. , Green J. L. , Weber B. L. , Gage K. S.
Published: February 2008

A small, portable 915‐MHz wind‐profiling Doppler radar has been developed at the National Oceanic and Atmospheric Administration's Aeronomy Laboratory. This radar provides high‐resolution wind profiles from near the surface upward to 2–3 km in clear air. Results of field trials in Colorado and Illinois are presented. These field trials include comparisons with 405‐MHz and 50‐MHz wind‐profiling Doppler radars. Wind measurements made by the different wind profilers are in very good agreement. Since the radar is very sensitive to heavy clouds and rain, it can be used to monitor the height of the melting layer and the vertical extent of hydrometeors. The small radar also provides temperature profiles up to 1 km when operated with an acoustic source in the radio acoustic sounding system (RASS) mode.
Three‐antenna poststatistic steering using the MU radar
Authors: Palmer Robert D. , Woodman Ronald F. , Fukao Shoichiro , Tsuda Toshitaka , Kato Susumu
Published: February 2008

This paper derives useful expressions for the synthesized beam statistics using poststatistic steering (PSS), when three antennas are used in a spatial interferometer configuration for two‐dimensional steering. These antennas may have arbitrary position and can have nonorthogonal baselines. The use of three (noncollinear) antennas allows altitude dependent two‐dimensional steering. This technique is verified using spatial interferometer data obtained in October 1989 using the MU radar, including PSS in directions parallel and perpendicular to the wind direction, which is a very convenient advantage of the technique.
Development of forearcs of intraoceanic subduction zones
Authors: Lundberg Neil
Published: February 2008

The uplifted Costa Rican forearc landward of the Middle America Trench and the Mariana forearc drilled on IPOD leg 60 both lack the thick clastic sequences, complex deformation, and abundant evidence of accretion which characterize more widely known forearcs that border continents. Both regions contain significant in situ accumulations of pelagic and hemipelagic sediments in place of thick trench and trench slope basin sequences composed of terrigenous turbidites. The Nicoya Peninsula of Costa Rica contains no significant melange terranes. Deformation of the mafic igneous basement and its thin cover of pelagic, hemipelagic, and first‐cycle volcanogenic material is mild overall, with discrete zones of intense deformation disrupting otherwise well‐preserved stratigraphic sections. Intraoceanic subduction zones lacking longitudinal trench feed are sites of little or no accretion of sediments, and recently suggested experimental and theoretical models of subduction zone processes involving flow melanges are inappropriate for intraoceanic forearcs. Intraoceanic forearcs generally lack high‐grade exotic components such as blueschist and eclogite tectonically incorporated as blocks in lower‐grade matrix, although uplift and erosion of the forearc basement may provide detritus of amphibolite and ultramafic rock to the trench and trench slope.
Influence of plate subduction on isostatic compensation in northern California
Authors: McNutt Marcia K.
Published: February 2008

The isostatic gravity map for northern California calculated by the U.S. Geological Survey on the assumption of Airy compensation reveals a residual correlation between gravity and topography. Peaks in the Klamath and Siskiyou Mountains west of 122.25°W and north of 40°N are associated with isostatic gravity highs in excess of 100 gu (gravity units), while to the east the Cascade volcanoes Lassen and Shasta display gravity lows less than −300 gu. Admittance calculations which determine the correlation between Bouguer gravity and topography demonstrate that some of the difference in isostatic gravity signature for the Klamaths and Cascades can be attributed to density variations in surficial rock types. The admittance estimates at wavelengths less than 50 km suggest that the mafic and metamorphosed units in the Klamath block are at least 80 kg/m³ more dense on average than the standard Bouguer reduction density of 2670 kg/m³. In addition, longer wavelength response estimates require some differences in the nature of the isostatic compensation for features in eastern versus western sections of northern California. Interpretations of the response functions in addition to direct modeling of a representative east‐west cross‐section indicates that the Klamath Mountains are rootless structures supported by the rigidity of the underlying Gorda plate, while the Cascades are locally compensated by shallower, low‐density material within the North American plate. Seismicity studies, heat flow data, and gravity structures south of this region are also consistent with this model.
Cenozoic thermal evolution and tectonics of the Coast Mountains of British Columbia: 1. Fission track dating, apparent uplift rates, and patterns of uplift
Authors: Parrish Randall R.
Published: February 2008

The high relief of the Coast Mountains of British Columbia has been produced in part by rapid late Neogene uplift. The relationship of this uplift to the presently diverse and complex plate tectonic regime off the west coast of British Columbia, however, is not clear‐cut. To study this problem, the areal patterns, rates, and total amounts of Cenozoic uplift from 50° to 55°N have been determined by using fission track dating of zircon and apatite separated from rocks collected at high and low altitudes along several traverses through the mountains. Accepting closure temperatures of 105°C ± 10°C and 175°C ± 20°C for apatite and zircon, respectively, and a likely closure temperature difference between zircon and apatite of 70° ± 15°C, paleogeothermal gradients have been measured at Kemano (
°C/km 35 Ma ago) and near Ocean Falls‐King Island (
°C/km 20 Ma ago). Subcrustal heat flow is suggested to have significantly increased in the late Neogene near King Island. Uplift rates in the axial part of the northern (52°–55°N) Coast Mountains were 0.1–0.2 km/Ma from 25 to 15 Ma ago; this uplift was temporally and tectonically related to part of the subsidence in the adjacent Queen Charlotte basin. Uplift rates increased somewhat in the Late Miocene to about 0.4 km/Ma, probably due to passage of the Anahim “hot spot” beneath the area. Late Miocene‐Recent erosion in the north (52°–55°N) has reduced summit altitudes and been more extensive than farther south. Despite this, relicts of Miocene river valleys and topography are still locally preserved, partly beneath 7–10 Ma basalts. The area of the present southern (50° to 52°N) Coast Mountains was near sea level and experienced very low uplift rates (<0.1 km/Ma) throughout the middle Cenozoic (30–10 Ma), despite its more active volcanism. Late Miocene basaltic lavas that were erupted onto a mature erosion surface near Taseko Lakes were elevated and warped by rapid Pliocene‐Pleistocene uplift (>0.5 km/Ma) of the southern Coast Mountains. The profile of this uplift was broadly plateaulike, and this uplift led to the inversion of the Miocene coastal topography. Middle Cenozoic uplift from 52° to 55°N was probably the result of denudation and diminishing uplift after the terminal Paleocene‐Eocene orogenic episode which grossly thickened the crust. This middle Cenozoic erosion resulted in the restoration of a normal crustal thickness. Late Neogene uplift in the Coast Mountains was the result of thermal expansion in the mantle caused by a mantle hot spot near 53°N and changes in the geometry of the subducted slab farther south.
Geophysical anomalies along strike of the Southern Appalachian Piedmont
Authors: Cook Frederick A.
Published: February 2008

Bouguer gravity anomalies and aeromagnetic anomalies display a northward increase of values in the Charlotte and Carolina slate belts from Georgia to Virginia. Analysis of these data with constraints imposed by seismic reflection, seismic refraction, conductivity measurements, and surface geology imply that this increase is due to a corresponding increase in the percentage of mafic rocks in the upper crust. A regional trend in the Bouguer field is determined for an observed eastward decrease in crustal thickness based on seismic refraction measurements. A comparison of the calculated regional with surface boundaries shows that in places the crustal thinning occurs more than 50 kilometers west of the Inner Piedmont‐Charlotte belt transition. The comparison also shows that the crustal thinning may take place west of exposed Grenville basement. The evidence thus indicates that the southern Appalachian gravity gradient is not likely related to a crustal or lithospheric suture. The evidence further indicates that, because the upper crustal and deep crust/upper mantle variations are independent in terms of spatial position, the upper crust of the Charlotte/slate belts is decoupled from the lower crust, perhaps at subhorizontal boundaries seen on reflection data.
Structure of the Southern Keweenawan Rift from COCORP Surveys across the midcontinent geophysical anomaly in northeastern Kansas
Authors: Serpa L. , Setzer T. , Farmer H. , Brown L. , Oliver J. , Kaufman S. , Sharp J. , Steeples Don W.
Published: February 2008

COCORP profiling across the midcontinent geophysical anomaly in northeastern Kansas reveals structural basins and other features of the Precambrian Keweenawan rift buried beneath the Phanerozoic cover. The 40‐km‐wide main basin is asymmetric, with a maximum depth of 3 km on the east and 8 km on the west. The basin fill is characterized by a lower layered sequence of strong continuous west dipping reflectors which may be correlated with Middle Keweenawan interbedded volcanic and clastic rocks exposed along the MGA in the Lake Superior region. Overlying this layered sequence is a zone of weak, discontinuous reflectors correlated here with the predominantly clastic rocks characteristic of the Upper Keweenawan sequence near Lake Superior. A second tilted but shallower basin lies to the east of the main basin and appears to be filled predominantly with clastic sedimentary rocks. The character of the seismic data, the seismic velocity distribution, and gravity modeling suggest that mafic intrusions lie beneath the main rift basin. Normal faults associated with the rift dip at moderate angles to the east. Palinspastic reconstruction indicates that the rift basin formed by the rotation of fault bounded blocks during crustal extension. Although reactivation of preexisting structures appears to have occurred in many other rifts profiled by COCORP, the evidence is inconclusive on this point in the case of the Kansas data. The structures mapped by COCORP surveys in Kansas and elsewhere suggest that asymmetric sequences of layered reflectors are characteristic, and perhaps diagnostic, of rift basin deposits in general.
Rheological controls on the geometry of deep faults and the tectonic delamination of the continental crust
Authors: White S. H. , Bretan P. G.
Published: February 2008

Recent seismic reflection profiles indicate that the deep faults in the continental crust may decouple deep within the crust or at the Moho. In the contribution it is argued that the decoupling horizons were initially zones across which variations in flow strength occur due to mineralogical differences in the principal rock types. These can result in the tectonic delamination of the crust and at the Moho. Calculations reveal marked strength differences across the Moho. Once initial delamination occurs, weak planes of mylonite develop along such surfaces and are preferentially reactivated during any subsequent deformation. It is postulated that during tectonism, the continental crust (1) does not act, at depth, as a single rigid entity, (2) should not be considered as being firmly attached to the upper mantle and (3) is capable of moving independantly of the upper mantle.
Thermomechanical models of active rifting
Authors: Moretti Isabelle , Froidevaux Claude
Published: February 2008

Geological and geophysical evidence (in particular thermal and gravity anomalies) suggests the presence of hot mantle material below the zones of continental rifting. Using a thermomechanical numerical model we quantify the lithospheric thinning caused by such a deep thermal anomaly. The mantle is assumed to be an incompressible non‐Newtonian fluid with temperature‐ and pressure‐dependent viscosity. The index power law is 3 in the mantle and 7 in the crust. This yields a viscosity minimum at the base of the lithosphere and therefore favors rapid convective thinning. The corresponding mass displacements disturb the lithosphere. The stresses at the bottom of the crust are used to quantify the vertical movements and the tectonic regime within the continental crust. The heat flow anomalies are also computed. The present work indicates that these deep geodynamic processes can induce well‐localized extensive tectonic stresses and the thinning of the lithosphere on a short time scale. This analysis also suggests that the subsidence in the rift valley is mainly due to crustal thinning while the uplift of the shoulders of the rift is a consequence of the advection of hot material from the asthenospheric channel. A regional extensional stress enhances the convective phenomena and favors the crustal thinning but is not necessary. A decrease in this far‐field force drastically increases the uplift of the shoulders and reduces the width of the rift valley. This case may be representative of the African rift.
Significance of Klamath rocks between the Franciscan Complex and Coast Range Ophiolite, northern California
Authors: Jayko A. S. , Blake M. C.
Published: February 2008

Small fault‐bounded slabs of low‐grade (prehnite‐pumpellyite‐bearing) slate, metagraywacke, and greenstone occur between the Coast Range ophiolite and South Fork Mountain Schist for at least 60 km south of the Klamath Mountains, northern California. The metagraywacke slabs differ from typical Franciscan Complex metagraywacke to the west by the absence of blueschist‐facies minerals and the abundance of quartz and chert clasts, and they differ from sandstone and mudstone of the Great Valley sequence to the east by the presence of a penetrative cleavage and low‐grade metamorphism. The metasedimentary rock in the slabs is petrographically identical to the Jurassic Galice Formation, which occurs along the western and southern margins of the Klamath Mountains. Upward drag along a west dipping reverse fault best explains the present structural position of the slabs and is consistent with available geological and geophysical data. These data imply that the Coast Range ophiolite structurally overlies Sierran‐Klamath basement at least locally.
Central Japan Triple Junction revisited
Authors: Le Pichon Xavier , Huchon Philippe
Published: February 2008

We show that the two‐dimensional kinematic discussion of McKenzie and Morgan's TTT‐type triple junction is not sufficient, as it ignores the interaction of the sinking plates. We derive a relation for the three‐dimensional existence of TTT triple junctions and show that it is satisfied at the unstable central Japan triple junction. We then use the geometry of the subducting Pacific plate beneath the Philippine Sea and Eurasian plates to show that the present situation did not hold before about 3 Ma. Before that time, the triple junction was probably located north of the present one and very close to the pole of relative motion. Finally, we discuss the geological implications of this model.
Realizability and stability of TTT Triple Junctions
Authors: Hamano Yozo
Published: February 2008

I derive a condition for the realizability of a TTT triple junction by considering the three dimensional structure of the junction. This condition and the stability condition derived by McKenzie and Morgan (1969) can be used as a basis for discussing the evolution of TTT‐type triple junctions.
The style of Late Cenozoic deformation at the eastern front of the California Coast Ranges
Authors: Wentworth Carl M. , Zoback Mark D.
Published: February 2008

The 1983 Coalinga earthquake occurred at the eastern boundary of the California Coast Ranges in response to northeast directed thrusting. Such movements over the past 2 Ma have produced Coalinga anticline by folding above the blind eastern tip of the Coalinga thrust zone. The 600‐km length of the Coast Ranges boundary shares a common structural setting that involves westward upturn of Cenozoic and Cretaceous strata at the eastern front of the Coast Ranges and a major, southwest facing step in the basement surface beneath the western Great Valley. Like Coalinga anticline, Pliocene and Quaternary folding and faulting along the rest of the boundary also result from northeast–southwest compression acting nearly perpendicular to the strike of the San Andreas fault. We suggest that much of this deformation is related to active thrusts beneath the eastern Coast Ranges. The step in the basement surface beneath the Great Valley seems to have controlled the distribution of this deformation and the shape of the Coast Ranges boundary.
Proterozoic contraction/extension tectonics of the southern SÃO Francisco Region, Minas Gerais, Brazil
Authors: Marshak Stephen , Alkmim Fernando F.
Published: February 2008

The southern São Francisco region comprises the southern portion of the São Francisco craton, which is underlain by Archean basement, and its fringing Proterozoic orogenic belts. Included in this region are three geologic provinces: the Quadrilátero Ferrífero (QF), the São Francisco Basin, and the Cordilheira do Espinhaço. We synthesize preliminary results of ongoing structural analysis, reconnaissance field studies, and published reports to provide a concise review of the geology of the region and to propose a working tectonic model for its Proterozoic evolution. Interpretation of superimposed folds, faults, and foliations leads to the conclusion that the southern São Francisco region records the effects of four principal tectonic events that occurred subsequent to deposition of the Lower Proterozoic Minas Supergroup. The first event resulted in formation of a northwest‐verging fold‐thrust belt. The second event led to development of high‐angle reverse faults, open folds, and basement uplift. The third event is manifested in the QF by the formation of normal faults and by the intrusion of mafic dikes; these extensional structures may be associated with formation of the sedimentary basins east and south of the São Francisco craton. The final event resulted in formation of a west‐verging fold‐thrust belt that affected the QF, the Cordilheira Espinhaço, and the São Francisco basin. The events that we describe can be tentatively associated with regionally recognized orogenic periods (Trans‐Amazonian, Uruaçuano, Brasiliano).
Pre‐Eocene Synmetamorphic Structure in the Mindoro‐Romblon‐Palawan Area, West Philippines, and implications for the history of southeast Asia
Authors: Faure Michel , Marchadier Yves , Rangin Claude
Published: February 2008

The structure of the pre‐Eocene rocks, considered as the “basement” of the Philippines, has been investigated in the Mindoro‐Lubang, Romblon‐Tablas‐Sibuyan, and North Palawan areas. In the former two areas the same pre‐Eocene succession of units is recognized from top to bottom: (1) a pre‐Eocene olistostrome; (2) an ophiolitic nappe; (3) a schistose sequence (pelites, sandstones, basic schists and marbles); and (4) a gneissic unit. The nature of the contact between the olistostrome and the underlying units is unclear, but the ophiolite and the schistose sequence form two thrust sheets of oceanic origin thrust upon the gneissic unit that is considered a part of a continental basement called the West Philippines Block. Small‐scale structures show that the early deformation stage is characterized by a submeridian (0°–N40°E) lineation formed in greenschist to amphibolite facies conditions during the thrusting. Kinematic analysis show that the thrusting was from north to south. In North Palawan, metamorphic rocks with similar microtectonic and kinematic characteristics are found. They are overlain by a Late Jurassic olistostrome which is correlated with the olistostromes found in Calamian, North Mindoro, Carabao, and Buruanga peninsula (North Panay). The microstructural features and the presence of the olistostrome suggest that the North Palawan, Mindoro, Tablas, Romblon, Sibuyan, and Carabao islands belong to the same North Palawan block of Hamilton (1979) which is a continental fragment rifted from Asia in Cenozoic times. It is assumed that the Western Panay and Zamboanga areas, which are characterized by Mesozoic ophiolites and metamorphic rocks, also belong to the North Palawan Block. All these islands experienced, to some extent, the same Mesozoic geohistory: the south verging thrusting is interpreted as the result of an oblique collision of the West Philippines Block with Asia. The contemporaneous left‐lateral strike‐slip faulting and the calc‐alkaline magmatism widespread along the Chinese margin are also included in the geodynamic model.
Rock magnetic properties and structural development in the core of the Hazara‐Kashmir Syntaxis, NE Pakistan
Authors: Bossart Paul , Ottiger Robert , Heller Friedrich
Published: February 2008

Paleomagnetic and structural analyses have been conducted on three well‐exposed sections through a 6–8 km thick pile of molassic red beds (Murree formation) in the lowermost tectonic unit of the Hazara‐Kashmir Syntaxis. Micropaleontological age determinations of the lowermost Murree sediments indicate Late Paleocene deposition (55 m.y.). From south to north, the sections are situated in the Jhelum, Neelum (both in Azad Kashmir), and Kaghan (northeastern Pakistan) valleys. Thermal demagnetization experiments suggest that haematite with high unblocking temperatures carries stable characteristic remanence directions. The relationship between finite strain and magnetic fabric was established by mapping deformed reduction spot strain markers and by measuring the anisotropy of magnetic susceptibility (AMS). For the Jhelum valley the weakly tectonized Murree beds are characterized by flattened AMS ellipsoids resulting from diagenetic compaction. Inclination values suggest that the Murree foreland basin started to develop at about 8°N during the early suturing of India and the development of island arcs to the north. India has moved northward by at least 2600 km since collision with Eurasia in the Paleocene. Declination values suggest 45° of clockwise rotation of the block supporting the Murree formation relative to the Indian craton. For the Neelum and Kaghan valleys, quantitative strain mapping shows a progressive increase of deformation northward. NRM directions rotate passively toward the cleavage plane which parallels the foliation of the AMS ellipsoids. NRM directions and AMS ellipsoids are deformed because of superposition of tectonic strain on a primary compactional strain. The AMS pattern is interpreted in light of this superposition, and a regional deformation path from south to north is suggested. A tectonic rotation model is proposed which is consistent with the transport directions around the Hazara‐Kashmir Syntaxis and the rotation of thrust sheets indicated by the NRM data. This model relates the convergent transport directions with the mean indentation direction of India into Asia.