bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging radar polarization signatures: Theory and observation
Authors: van Zyl Jakob J. , Zebker Howard A. , Elachi Charles
Published: February 2008

We have converted a conventional synthetic aperture radar system into an imaging radar polarimeter by employing two orthogonally polarized antennas and recording both the amplitude and absolute phase measurements of the received electric fields. This enables us to measure the complete complex scattering matrix for each individual resolution element in the radar image. The Stokes matrix, derived from the scattering matrix, is then used to synthesize the scattering coefficient for any desired combination of transmit and receive antenna polarizations, allowing us to measure the variation of the scattering coefficient with polarization. This polarization information can be displayed in a new and useful way, producing the polarization signature for each point in an image. Comparison of the theoretical and observed polarization signatures permits identification of the dominant scattering mechanisms contributing to the measured radar backscatter. For example, the ocean and smoother lava flows have polarization signatures which are similar to those predicted by a slightly rough dielectric surface model; thus the model likely approximates the physical mechanisms responsible for the reflected energy from these surfaces. Urban areas, on the other hand, exhibit polarization signatures which resemble those predicted by dihedral corner reflector geometries. The coefficient of variation, a parameter derived from the polarization signature, is a measure of resolution scale variation of a surface and indicates the degree to which polarization filtering can be used to enhance or suppress the return from a collection of scatterers. Our observations show that the ocean has a low coefficient of variation; thus the return from the ocean is highly polarized, and polarization effects can be used successfully to suppress or enhance the return from the ocean. Parks and other vegetated areas exhibit a large coefficient of variation, suggesting that the return from these areas contains a considerable component that is randomly polarized; varying the transmit and receive polarizations will not change the return from the vegetated areas appreciably.
A new approach to the problem of wave scattering by many particles
Authors: Tateiba Mitsuo
Published: February 2008

A new approach to wave problem in many scatterers is presented. The coherent wave is analyzed generally in the case of random dislocation of periodically distributed scatterers and is discussed in detail in the slightly and strongly random dislocations. Some reasonable results are obtained.
High‐frequency scattering by a thin material half plane and strip
Authors: Volakis John L.
Published: February 2008

Diffraction coefficients are derived for a thin dielectric half plane and strip having arbitrary permittivity and permeability. This is accomplished by modeling the thin material layer by a pair of modified resistive and conductive sheets. By means of this model the dielectric half plane is first treated via the dual integral equation approach. By employing the half plane solution, up to third‐order multiply diffracted fields are then derived for the case of a strip. These are obtained via the extended spectral ray method and include the surface wave diffraction effects in a uniform manner. Numerical results are also presented which validate the accuracy of the model and that of the derived diffraction coefficients.
Influence of wind and temperature on the height limit of a radio acoustic sounding system
Authors: Masuda Yoshihisa
Published: February 2008

Influences of the atmospheric wind and temperature profiles upon the maximum height in temperature measurement by using a radio acoustic sounding system (RASS) were studied. The RASS uses radar to receive echoes (RASS echoes) backscattered from periodic perturbations in the atmospheric refractive index produced by an incident acoustic pulse and to measure the atmospheric temperature from the local speed of sound which is derived from the Doppler frequency shift of the RASS echo signal. One of the important conditions for the RASS echo to be efficiently backscattered (for monostatic radar) is that the radar beam is incident normal to the wave surface of the perturbations in the refractive index, i.e., to the acoustic wave front. This paper gives the results from numerical calculations to simulate the portion of the acoustic wave front where the above condition is satisfied, under a fixed configuration of the radar and acoustic antennas, and under changing shapes of the propagating acoustic pulse wave front influenced by height‐varying background atmospheric wind and temperature. Comparisons between the calculations and RASS experiments were made by using the middle and upper atmosphere (MU) radar with steerable beam under different atmospheric conditions. The numerical estimations of the height range for effective reception of RASS echo agree quite well with actual RASS observations carried out by using the MU radar. RASS echoes were obtained at altitudes up to 8.4 km under strong wind conditions in January 1988 and up to 22 km under calm wind conditions in July 1986.
Simultaneous observations of reflection echoes and refractive index gradient in the troposphere and lower stratosphere
Authors: Tsuda T. , May P. T. , Sato T. , Kato S. , Fukao S.
Published: February 2008

We have studied some characteristics of clear air echoes in the lower stratosphere and troposphere from simultaneous observations of vertical echo power and temperature profiles. The vertical echo power has been oversampled every 75 m with a height resolution of 150 m by the middle and upper atmosphere (MU) radar (35°N, 136°E). During the radar observations a radiosonde was launched at the MU radar site in order to measure temperature, humidity, and pressure with a height resolution of a few tens of meters, from which the mean gradient of generalized potential refractive index, M, was determined. In the lower troposphere (below 10 km altitude), M is enhanced owing to humidity by about 10–20 dB, and its fine structure is mainly determined by the vertical gradient of humidity. The relatively large time‐height variation of tropospheric echo power seems to be attributed to rapid changes in the humidity profile. On the other hand, in the upper troposphere (above 10 km altitude) and stratosphere the vertical structure of M is mainly determined by the Brunt‐Väisälä frequency and air density, where the former determines fine vertical structure of M and the latter the gradual decrease in M with a scale height of about 7 km. The measured M2 profile agrees well with the vertical echo power profile down to the radar height resolution of 150 m. That is, the vertical structure of the reflection coefficient is mainly determined by M2, and therefore the energy density of 3‐m scale fluctuations E(2k) seems to be distributed uniformly with height. The vertical spacing of intense reflection layers usually ranges from 500 m to a few kilometers, which corresponds to the dominant vertical scale of fluctuations in the Brunt‐Väisälä frequency profile. The vertical distribution of intense reflection layers seems to be explained by a predominance of a saturated vertical wave number spectrum of gravity waves with a slope of −3 and a dominant vertical scale of a few kilometers.
A comparison between the automatic ionogram scaling system ARTIST and the standard manual method
Authors: Gilbert John D. , Smith Richard W.
Published: February 2008

For the first time, data from mid‐latitude ionograms as scaled by the computer system ARTIST and by the standard manual method have been compared comprehensively. Differences between these scaled values for f0 F2 and M(3000)F2, are presented for five periods between 1984 and 1986, a time of low sunspot activity. These two parameters were studied, as they are most important for high‐frequency radio communications. The comparisons reveal that, on average, ARTIST provides acceptable data for about 93% of the time. ARTIST is shown to perform less well during the summer, mainly because of the presence of blanketing‐type Es and the proximity of f0F2 to f0F1. Severe broadcast station interference is another source of major error. On the basis of these comparisons, ARTIST provides a most valuable service in producing real‐time data which can be made available to the radio community by means of a dial‐in facility. The other parameters scaled by ARTIST have also been studied, but in far less detail, and no statistics were undertaken. However, these limited comparisons seem sufficient to show serious limitations in ARTIST performance, due mainly to the absence of any accuracy qualification. Such limitations are likely to preclude, in the foreseeable future, ARTIST replacement of manual scaling for the data published in monthly bulletins by Slough, United Kingdom ionospheric observatory.
Phase sensitive methods to determine the wavelength of electromagnetic waves in lossy nonuniform media: The case of surface waves along plasma columns
Authors: Margot‐Chaker Joëlle , Moisan Michel , Zakrzewski Zenon , Glaude Vital M. , Sauvé Gaston
Published: February 2008

Determining the wavelength of a wave propagating in a medium nonuniform along the wave path implies using a measurement technique that provides enough spatial resolution to permit following up the wavelength variation resulting from such a nonuniformity. This paper presents a theoretical analysis of the respective merits of two phase sensitive methods used for that purpose, under both weak and strong wave attenuation conditions. Modifications to these methods are recommended which assure both accuracy and spatial resolution of the wavelength measurements. These conclusions are substantiated by numerical simulations of phase measurements along surface wave‐sustained plasma columns used as an example of axially nonuniform and lossy media.
Intercomparison of radar measurements of rain by single‐ and dual‐wavelength techniques
Authors: Fujita Masaharu , Nakamura Kenji , Inomata Hideyuki , Okamoto Ken'ichi
Published: February 2008

We are experimenting with three different techniques of rain rate estimation to assess their appropriateness by analyzing the data on simultaneous rain measurements with a C band weather radar and a dual‐wavelength (3‐ and 0.86‐cm) radar scatterometer. These techniques are (1) a conventional single‐wavelength technique based on an empirical relation between a reflectivity factor and a rain rate; (2) a dual‐wavelength technique based on radar wave attenuation at one wavelength, where it is assumed that the raindrops sampled are Rayleigh scatterers at both wavelengths; and (3) an alternative dual‐wavelength technique using the method of least squares to minimize the difference between measurement‐derived quantities and their corresponding quantities derived from a radar equation. The rain rate estimates from the above three techniques are compared with each other, and the causes of their differences are discussed. The rain rate estimates obtained with each technique and gauge rain rates measured near the radar site are also compared to evaluate their absolute accuracy. The advantages and disadvantages of each rain rate estimation technique are discussed for specific situations and applications. As a result of investigation the following conclusions are obtained: The single‐wavelength technique gives fairly good rain rate estimates if an external radar calibration is made accurately. The dual‐wavelength technique based on radar wave attenuation needs verification of the estimates by auxiliary means to avoid unrealistic estimates, and the dual‐wavelength technique by means of a least squares method is useful for an airborne or a spaceborne application where an external calibration is difficult to perform.
Aspect sensitivity measurements of VHF backscatter made with the Chung‐Li radar: Plausible mechanisms
Authors: Woodman Ronald F. , Chu Yen‐Hsyang
Published: February 2008

A new technique, using beam broadening effects, has been developed to measure the aspect sensitivity of atmospheric clear air VHF radar echoes. It uses the relatively broad antenna beam of the vertical‐pointing antenna of the new Chung‐Li stratospheric‐tropospheric radar (25°N, 120°E). The aspect sensitivity measurement using this method is straightforward and free from convolution effects introduced by the finite width of the antenna beam pattern. The observed results agree very well with other measurements. The authors propose a turbulent layer model to explain the aspect sensitivity of the echoes. In this model, anisotropic turbulence is confined to a very thin (few meters) region at the boundary of a turbulent layer. This region is responsible for the aspect sensitivity of the echoes obtained from the vertical direction. The isotropic echoes obtained from the oblique beam arise from the isotropic turbulence embedded in the center of the layer, with 30–300 m in vertical extent. We show in an appendix that the magnitude of the partial reflection coefficient is much more sensitive to the shape, length scale, and smoothness, than to the slope of the refractive index profile. Therefore the functional shape of the refractive index profile is very important for estimating the reflection coefficient. Large errors can be made when assuming, for simplicity, nonphysical profiles. For partial reflecting mechanisms to be important, steplike discontinuities, confined within length scales of the order of a meter, would be required.
Scattering by a conducting strip over a lossy half‐space
Authors: Baertlein Brian A. , Wait James R. , Dudley Donald G.
Published: February 2008

The integral equation for the current induced on a thin, perfectly conducting strip of infinite length above a homogeneous conducting half‐space is examined for an incident field with E parallel to the strip axis. A closed form quasi‐static solution is obtained for the case when the width and elevation of the strip are small compared to the skin depth (or wavelength for a lossless medium) in the lower region. Results are presented which compare the quasi‐static solution with a numerical solution of the exact integral equation.
Input admittance of a horizontal antenna over a two‐layered lossy half‐space
Authors: Ridd P. V. , Nicol J. L.
Published: February 2008

Calculations of the input admittance of a thin cylindrical horizontal dipole antenna over a two‐layered lossy half‐space have been carried out. This has allowed an evaluation to be made of the sensitivity of admittance measurements to variations in the electrical characteristics of the Earth below a conducting overburden and hence to determine the potential of such measurements in geophysical surveying. The results show that maximum sensitivity to changes in the complex permittivity of the lower half‐space is obtained by the use of a band of frequencies about the first antenna resonance. The maximum depth of sensitivity of the observations was found to be approximately one quarter of the resonance wavelength or 8 m for an antenna of length 15 m, indicating that admittance measurements provide a potentially useful and simple geological surveying technique.
Mean square slopes of the wind‐disturbed water surface, their magnitude, directionality, and composition
Authors: Wu Jin
Published: February 2008

Available laboratory and field data on fine structures of the wind‐disturbed water surface are reviewed and analyzed to deduce the quantitative variation of directional mean square slopes with the wind condition. The mean square slope is associated with the wind‐friction velocity, with its maximum component in the upwind‐downwind direction and minimum component in the crosswind direction. Its angular distribution is suggested to follow an elliptical function. Spectral compositions of fine surface structures are estimated; in the field, gravity wave components contribute the most at low winds (U10 < 7 m s−1 or u* < 20 cm s−1) and capillary components at high winds; in laboratory tanks, gravity components are relatively much more important. These along with the other features are used to explain discrepancies between laboratory and field results as well as those within each group.
Bispectrum of radar signatures and application to target classification
Authors: Walton Eric K. , Jouny Ismail
Published: February 2008

The scattering characteristics of a radar target can be specified by its impulse response. The impulse response can be computed using Fourier spectral estimation techniques on samples of the radar scattering obtained at a number of equally spaced frequencies. Usually, there is a clear relationship between the location of specific scattering mechanisms and the time such mechanisms appear in the impulse response. One of the difficulties in this type of analysis, however, is that complex targets often have multiple scattering interactions. Many of the terms in the impulse response are due to these interactions rather than specular subcomponent scattering. The bispectrum displays the specifics of the interactions of both single‐ and multiple‐reflection mechanisms. In addition, the suppression of Gaussian noise makes the bispectrum a source of robust features for classification of radar targets. Identification of multiple interaction terms as well as noise suppression are demonstrated in this paper. Finally, classification of scale models of commercial aircraft based on their bispectral signatures is performed.
Implementation of an ELF array of ionospheric dipoles using the high‐power auroral simulation facility
Authors: Werner D. H. , Albert A. M. , Ferraro A. J.
Published: February 2008

The feasibility of using the High‐Power Auroral Simulation (HIPAS) facility for the creation of a linear array of ionospheric Hertzian dipole sources is investigated and presented as a possible ELF/VLF communication system, as well as an ionospheric diagnostic technique. Linear ELF arrays consisting of at least two elements can theoretically be used to monitor, in real time, the ionospheric conditions in the vicinity of the HIPAS facility. This provides a means of studying irregularities due to turbulence or wave structures within the D region. Several experiments have been proposed for far‐field confirmation of ELF beam steering within the Earth‐ionosphere waveguide, including varying the progressive phase and interelement spacing of an ELF array in a precise temporal sequence. The successful creation of two‐element ELF ionospheric arrays using HIPAS is reported.
Limits of stresses in continental crusts and their relation to the depth‐frequency distribution of shallow earthquakes
Authors: Meissner R. , Strehlau J.
Published: February 2008

Based on published results of experiments on low‐temperature, low‐pressure frictional sliding and creep at higher temperature and pressure, theoretical curves of yield strength versus depth corresponding to maximum crustal stresses (STRESSMAX) are calculated. These curves are compared to the frequency‐depth distribution of earthquakes (DEFREQ) in several tectonic areas. Both sets of curves have a very similar form and show a prominent peak. From the similarity it is concluded that it is basically the temperature and the water content of the entire crust, not the properties of a particular layer, which determine the shape of maxima of the DEFREQ curves. The peaks of DEFREQ curves are generally at 5‐ to l0‐km depth and agree with STRESSMAX peaks of wet upper crust only. At this depth range the high stresses provide an increased ‘cracking potential’, resulting in an increased number and an increased stress drop of earthquakes. More and stronger barriers/asperities seem to exist at these depths, causing large earthquakes to nucleate in this high‐strength region. The stresses required to overcome the strength maximum are built up from below by ductile creep. The lower crust is considered to be a stress and viscosity minimum; in orogenic zones, strong interaction with plumes from the mantle may take place, and lateral movements are probable.
A new global crustal thickness map
Authors: Soller David R. , Ray Richard D. , Brown Richard D.
Published: February 2008

An up‐to‐date global compilation of crustal thickness and Pn velocity values from published seismic refraction and surface wave data has been created. From 297 referenced sources, a total of 2508 crustal thickness and 1806 Pn velocity values have been selected. This represents a significant expansion of previous compilations. The inclusion of surface wave data results in a more uniform coverage of the earth's surface than is possible by using only published refraction data. The crustal thickness data are contoured on a global Van der Grinten projection. This compilation currently resides in a computer data base and is available on computer compatible tape. Recommendations for improvement in form and content will be welcomed, as periodic updates are anticipated.
Propagating rifts and continental breakup
Authors: Courtillot Vincent
Published: February 2008

A simple quantitative model is proposed whereby continental breakup starts with a phase of continental rifting and continues with the propagation of rifts toward locked zones. These zones are deformed in the rifting process while oceanic crust is generated in the wake of the rift tip. The deformed zones will cause overlaps when a continental reassembly is attempted. The model accounts for the shape and distribution of magnetic quiet zones at ocean‐continent boundaries and for the detailed geometry of some V‐shaped zones of oceanic magnetic anomalies. The former provide an estimate of the scale at which the hypothesis of rigid plates fails, and the latter are used to measure the velocity of rift propagation. Illustrations are provided for present rifting in the Red Sea and Gulf of Aden and for early rifting of the South Atlantic and breakup of Pangea.
New methods for estimating displacements of thrust faults affecting Atlantic‐type shelf sequences: With an application to the Champlain Thrust, Vermont
Authors: Rowley David B.
Published: February 2008

Large thrust‐related displacements occur in many orogenic belts. Existing methods for estimating the displacements across such faults require knowledge of the sub‐surface geometry of the fault. Where appropriate well and seismic reflection data are not available, standard structural techniques of projecting stratigraphic separations down the dip of the fault yield only minimum estimates of displacement. Since many fold‐thrust belts involve sedimentary sequences developed along ancient Atlantic‐type margin continental shelves, the prethrusting cross‐sectional shape of such sequences may be used to estimate displacements across large thrust faults affecting these sequences. The characteristic shape of such shelf sequences is that of a triangular, seaward thickening wedge. Simple trigonometric relationships utilizing various data, including stratigraphic thickness for a given time‐stratigraphic interval in transported and untransported sections, the position of the prethrusting depositional hinge line, the time span in millions of years of the chosen time‐stratigraphic interval, or assumed dimensions and rates of an average Atlantic‐type margin, are used to derive estimates of displacements. Some limitations of these methods are discussed qualitatively; a rigorous test is not, however, attempted now. Two of the methods are applied to the Champlain Thrust of Vermont. Previous estimates suggest much less the 30 km of east‐west displacement of this fault. The displacement across this thrust estimated by using methods proposed here suggest somewhat greater than 80 km of east‐west displacement. This amount of displacement requires that the entire Green Mountain Anticlinorium, including Grenville basement, is detached and constitutes a relatively thin basement‐cored thrust sheet geometrically similar to the Blue Ridge Thrust sheet of the Southern Appalachians.
Structural evolution of an A‐type subduction zone, lofoten‐Rombak Area, northern Scandinavian Caledonides
Authors: Hodges K. V. , Bartley J. M. , Burchfiel B. C.
Published: February 2008

The climactic phase of the Caledonian orogeny in Scandinavia involved collision of the Baltic and Greenland cratons in late Ordovician (?) to Silurian time. We infer that the collision resulted in large‐scale subduction of the leading edge of the Baltic craton beneath an ‘Andean‐type’ Greenland continental margin. Deep erosional levels in the Lofoten‐Rombak area, Norway‐Sweden (˜69°N) permit direct examination and evaluation of the structural evolution of a continental or A‐type subduction zone. The early stages of collision involved en bloc underthrusting of the continental margin to depths of at least 30 km. During this process, deformational effects in the lower plate were restricted to its upper few hundred meters. Ultimately, en bloc A‐type subduction should be limted by buoyancy effects. As convergence continued, the lower plate became involved in a series of imbricate thrusts with the same vergence as the intial subduction zone. The temporal and spatial relationships between these basement‐involved thrusts are similar to those observed in foreland fold and thrust terrains. Field and geophysical data bearing on lower plate behavior elsewhere in the Caledonldes and in other collisional orogens suggest that the structural features observed in the Lofoten‐Rombak area may be generally characteristic of A‐type subduction in continent‐continent collisional settings.
Paleogeography and Andean structural geometry, northwest Argentina
Authors: Allmendinger Richard W. , Ramos Victor A. , Jordan Teresa E. , Palma Miguel , Isacks Bryan L.
Published: February 2008

Neogene tectonic segmentation of the Andean Cordillera in northwestern Argentina is a function of both the dip of the subducted plate and of major paleogeographic structures and sedimentary basins. Vergence, fault dip, and lateral continuity of Neogene structures can be related to the character and pre‐existing geometries and structures of the materials in which they form. South of 27°S the thick‐skinned Sierras Pampeanas, which occur mostly over a flat segment of the subducted Nazca Plate, formed where little sedimentary cover overlay crystalline basement. North of 24°S, the thin‐skinned Subandean belt, overlying an inclined slab segment, formed within a thick, elongate, eastward‐tapering trough of Paleozoic and Mesozoic sediments that may represent a complex of pre‐Andean foreland basin deposits. The transitional region between 24°–27°S (the Santa Barbara System and Cordillera Oriental) is characterized paleogeographically by complex cross‐trending structures and irregular basin geometries, and the Neogene structures are equally complex and variable. The paleogeographic features of NW Argentina are a product of compressional tectonism during much of the Paleozoic that resulted in an orogenic belt oriented obliquely to the modern Andes. This earlier orogen was disrupted by several zones of transverse structures and by Cretaceous extensional or pull‐apart basins. These features clearly influence the geometry of the superposed Andean structures. More intriguing, however, is the possibility that preexisting structures of the continental lithosphere may in some way help to modify the geometry of the subducted plate.
Structural analysis and interpretation of the surface deformations of the El Asnam Earthquake of October 10, 1980
Authors: Philip H. , Meghraoui M.
Published: February 2008

The El Asnam earthquake of October 10, 1980, represents the major seismotectonic event of these last decades in the West Mediterranean area. It has induced a large amount of surface breaks. This earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of North Africa. The tectonic analysis of surface rupture shows the complexity of the deformation mechanism. The principal mechanism consists of the activation of a NW‐SE trending thrust fault, accompanied with a left‐lateral motion and with an intense deformation of the northwestern overthrusting block. An accurate description of these deformations shows that, for a large part, the breaks geometry depends closely on the substratum structure. Finally, the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation.
Speculations on the Mesozoic Plate tectonic evolution of eastern China
Authors: Klimetz Michael P.
Published: February 2008

Several orogenic belts transecting eastern China are the sites of former convergent plate margins, although there have been varying views on the collisional framework of individual continental blocks, styles of convergence at these zones, and the timing of respective collisions. A tectonic study of eastern China, Mongolia and the southern Soviet Far East indicates the collision of the South China Block with a combined North China‐Northeast China Fold Zone Block in the Late Triassic‐Early Jurassic, their collective suturing to Eurasia in the Late Jurassic‐Early Cretaceous, followed by the Sikhote Alin‐Japan Block in the Mid to Late Cretaceous. The evidence is as follows: (1) A linear belt of Late Triassic‐Early Cretaceous granites and granodiorites trends east from the Qinlingshan through the Dabieshan to the Huaiyang massif. Ophiolites, flysch, subduction zone mélange, a paired metamorphic belt indicating north dipping subduction and marine strata of Carboniferous to Late Triassic age from the Qinlingshan define the suture between the North and South China Blocks, (2) A sinuous belt of ultramafics, blueschists, silicic to intermediate magmatism and west and north vergent folds and thrusts trend from the west margin of the Ordos Basin through central Inner Mongolia and along the east Great Khingan Range to the Amur River. Coupled with a Mid Jurassic‐Early Creataceous unconformity a suturing of eastern Chinese blocks to Eurasia along this zone is suggested, (3) A fold and thrust belt with ultramafics, flysch, blueschists and subduction zone mélange along the Ussuri River in northeast China indicates the suturing of the Sikhote Alin‐Japan Block to Eurasia along a west dipping subduction zone in the Mid to Late Cretaceous. Similarly, a tectonic study of southern China and Southeast Asia has revealed a complex regional mosaic of suture‐bounded terrains which nucleated about the eastern, western and southern margins of the Yangtze Craton during the Late Triassic and Early Jurassic. The evidence is as follows: (4) A north–south trending belt of ophiolites, blueschists, calc‐alkaline volcanics and subduction zone mélange, including granites, granodiorites and strongly deformed marine strata all of Late Triassic age exposed in the Longmenshan of Sichuan merge with the Kekexilishan ophiolite zone into the Ailaoshan‐Tengtiaohe ophiolite and blueschist belt in central Yunnan along which the Songban‐Ganzi Complex and the Shan‐Thai‐Malaya Block join the Craton, and (5) A southeastern prolongation of the Ailaoshan‐Tengtiaohe belt bifurcates into the southeast trending Konvoi zone of northern Vietnam and the north‐south trending Pak Lay‐Luang Prabang zone of Laos and eastern Thailand. Zones of ophiolite, calc‐alkaline volcanics and strong Late Triassic deformation, they separate the Indosinia and Shan‐Thai‐Malaya Blocks from the Craton respectively. These findings differ significantly from previous interpretations of a Late Paleozoic consolidation of South‐Eastern Asia as well as disputing the existence of a true Pangea.
Tectonic analysis of the Dead Sea Rift Region since the Late‐Cretaceous based on mesostructures
Authors: Eyal Yehuda , Reches Ze'ev
Published: February 2008

We have measured the orientations of small faults, slickensides, tectonic stylolites, vein with secondary mineralization, small folds and dikes in Israel and Sinai. These structures are indicators of paleo‐stress or strain and provide the pattern of tectonic deformation. Data were collected at 130 stations, most with tens of separate measurements; most stations showed consistent deformation. Stations were located on exposures ranging from Precambrian crystalline rocks to Pleistocene sediments. We have defined two tectonic stress fields, each relatively uniform in both time and space. One stress field, with dominating maximum horizontal compression trending W to WNW, in the Late Cretaceous to Eocene rocks in the folds and plateaus west of the Dead Sea rift. The second field, with dominating horizontal extension trending E to ENE, in all rocks inside the rift and proximal thereto. The first stress field is called the Syrian Arc stress, and the second is called the Dead Sea stress. A change in style of tectonic deformation, which corresponds to the two stress fields, is manifested also in the major structures in Israel. The Late Cretaceous to Neogene deformation is characterized by long wavelength folds and monoclines, whereas the Neogene to Recent deformation is characterized by normal and strike slip faults and volcanic activity.
A model for the crustal evolution of southern Scotland
Authors: Leggett J. K. , McKerrow W. S. , Soper N. J.
Published: February 2008

In the late Silurian, southern Scotland was a mature accretionary active margin of Sumatra‐type, on the southeastern edge of North America, while England was on a passive margin on the opposite side of the Iapetus Ocean. Southward subduction below England during the Middle Ordovician produced a magmatic arc which now lies close to the Iapetus suture, and thus argues for a missing forearc terrane. Tectonic erosion or strike‐slip removal may be responsible for some of this missing terrane to the north of the Lake District, but we now suggest that underthrusting below southern Scotland may also be an important cause. If the Ordovician forearc terrane of northern England is now below the Southern Uplands, we would have an explanation for the evidence for similar lower crustal foundations on either side of the surface trace of the Iapetus suture (velocity structure from the LISPB study, Sr/U‐Pb isotopic signatures and geophysical attributes of the c. 400 Ma granites). The under‐thrusting model still leaves room for considerable modification of both margins by large strike‐slip faults. Seismic refraction profiles of modern accretionary active margins (Sumatra, SW Japan) allow us to propose a likely velocity profile for late Silurian southern Scotland. We choose a Mesozoic forearc truncated by strike‐slip faulting, the Queen Charlotte Islands margin of the NE Pacific, as an analogue for the late Silurian southern Iapetus margin. Following previous suggestions of highly oblique and slow convergence during the final stages of closure of Iapetus, we combine the two profiles by under‐thrusting the southern margin to produce a model which involves minimal shortening in the collision zone. The crustal profile resulting from such a collision would be very similar to the modern southern Scotland profile, both in terms of the scale of the tectono‐stratigraphic terranes involved and of the resulting crustal velocity structure. The cessation of accretion after the mid‐Wenlock may be related to impingement of the English continental crust against the Scottish trench. Subsequent uplift of the Southern Uplands may be connected with the appearance of coarse detritus in the Lake District during the Silurian.
The Snake Range Décollement: An exhumed Mid‐Tertiary ductile‐brittle transition
Authors: Miller Elizabeth L. , Gans Phillip B. , Garing John
Published: February 2008

The Snake Range décollement (SRD) in east‐central Nevada separates supracrustal rocks extended by normal faulting from ductilely deformed igneous and metamorphic rocks. A well‐known stratigraphy unaffected by earlier faulting permits analysis of both upper and lower plate strain leading to a better understanding of how vastly different rock types and deformational styles are juxtaposed along low‐angle faults in metamorphic core complexes. Middle Cambrian to Permian upper plate rocks are cut by two generations of NE trending, east directed normal faults. Both generations were initiated as high‐angle (60°) planar faults that flattened abruptly into the SRD and rotated domino style to low angles, yielding a total rotation of bedding of about 80–90°. Faulting is Tertiary in age as 35‐m.y.‐old volcanic rocks are involved and resulted in about 450–500% extension in a N55W‐;S55E direction. The SRD developed as a subhorizontal surface 6–7 km deep at the top of the Cambrian Pioche Shale. Lower plate granitic rocks and their late Precambrian‐Cambrian metamorphic country rocks were involved in progressive ductile to brittle extension at low greenschist grade, forming a penetrative subhorizontal foliation and N55–70W lineation that increases in intensity eastward and upward toward the SRD. Stretching and thinning in the lower plate is coaxial and comparable in magnitude to upper plate extension, and is interpreted as synchronous. K‐Ar ages ranging from 20 to 40 m.y. in the lower plate suggests the N. Snake Range represents a Tertiary thermal anomaly. We conclude that the SRD developed as a ductile‐brittle transition zone at 6–7 km depth. Gravity data suggests that the gently domed SRD is cut by younger Basin and Range faults, but the geology of adjacent ranges suggests that the SRD does not continue more than 60 km in any given direction. The lack of stratigraphic omission across the SRD rules out large amounts of movement on a surface that originally cut downsection, and we suggest that extensional detachment faults such as the SRD can be developed locally as boundaries between brittlely extended rocks and underlying ductile extension and intrusion.
Cretaceous and Early Tertiary paleomagnetic results from the Antarctic Peninsula
Authors: Watts Doyle R. , Watts Gary C. , Bramall A. M.
Published: February 2008

Paleomagnetic results are presented for early Tertiary and Cretaceous igneous and volcanic units from the northern Antarctic Peninsula. When combined with previously published data, they permit the construction of a polar wander path that is very similar to one derived for the East Antarctic craton by rotating Tertiary and Cretaceous poles from India and Australia into the Antarctic frame of reference. When considered in this context, the paleomagnetic data from the Orville Coast, which was previously interpreted as evidence in favor of oroclinal bending or relative rotation of the southern Antarctic Peninsula with respect to the northern part, may be considered as an in situ resulte The implications of the new data are as follows: (1) The Antarctic Peninsula down to the Orville Coast has been a part of the Antarctic plate since 100 m.y. ago. (2) Movement of the Antarctic Peninsula required to avoid overlap in reconstructions of Gondwanaland must have occurred before 100 m.y. ago.
Timing and tectonic setting of Tertiary low‐angle normal faulting and associated magmatism in the southwestern United States
Authors: Glazner Allen F. , Bartley John M.
Published: February 2008

Major episodes of Tertiary low‐angle normal faulting in the southwestern United States south of latitude 37°N moved northward with time, occurring about 25 million years ago in southern Arizona, 20 million years ago in the Mojave Desert region, and 10 to 15 million years ago in the Las Vegas area. In most areas, faulting and associated volcanism occurred when the Mendocino triple junction lay to the west. This correspondence probably resulted from the unstable configuration of the triple junction. East‐west to northeast‐southwest horizontal stretching, as plates pulled apart at the triple junction, prevented development of a hole in the lithosphere at the triple junction. The regional strain history predicted by this model is consistent with observed Tertiary low‐angle faults, strike‐slip faults, and folds.
Kinematics of the Philippine Sea Plate
Authors: Ranken B. , Cardwell R. K. , Karig D. E.
Published: February 2008

In this study new instantaneous rotation vectors describing the motion of the Philippine Sea plate relative to surrounding plates are determined that most nearly satisfy all available geological, geophysical and seismological observations along the plate margins. Pacific‐Philippine and Caroline‐Pacific, poles are generated from a set of trial Eurasia‐Philippine poles of rotation, using published determinations of the Eurasia‐Pacific and Caroline‐Philippine poles. The Pacific‐Philippine, Caroline‐Pacific, and Eurasia‐Philippine poles are then checked for agreement with: (1) slip vectors determined from focal mechanisms of earthquakes along the Ryukyu trench and the Nankai trough, (2) convergence at the Sagami trough, (3) extension in the Mariana trough, (4) extension behind the Bonin trench, (5) extension in the western Sorol trough, and (6) convergence at the Mussau trench. Trial Eurasia‐Philippine poles are eliminated if predicted plate motions do not match observed plate motions. The locations and rotation rates of the three best fitting poles are Eurasia‐Philippine: 37.0°N, 141.0°E, 1.60°/Ma; Pacific‐Philippine: 3.8°N, 130.4°E, 1.68°/Ma; Caroline‐Pacific: 16.9°N, 141.4°E, 0.54°/Ma. The plate motions predicted by these new poles are compared with the spatial distribution of earthquakes and new focal mechanism solutions in the complex region where the Philippine, Pacific, and Caroline plates intersect. Intermediate and deep focus earthquake hypocenters along the southern Mariana arc show a southward decrease in the length of the seismic zone which qualitatively agrees with the predicted convergence rate as the pole of rotation is approached and as the effect of back arc spreading in the Mariana trough disappears. The absence of volcanism and intermediate‐depth seismicity along the southernmost Mariana, Yap, and Palau sections of the plate boundary is attributed to very low convergence rates. A new focal mechanism solution along the trench south of Guam is the first clear underthrusting solution found along the Mariana trench and agrees with the convergence direction implied by the Pacific‐Philippine pole of rotation. No clear underthrusting focal mechanism solutions were found along the Yap and Palau trenches, although three high‐angle thrust solutions demonstrate that compression is occurring in the upper plate, perpendicular to the plate boundary.
Displacement and strain patterns of extensional orogens
Authors: Kligfield Roy , Crespi Jean , Naruk S. , Davis G. H.
Published: February 2008

Rock fabrics that result from displacement in extensional orogens provide a means of identifying geometric models responsible for extension of continental crust. Strain compatibility arguments indicate that a finite extension can be accommodated by displacements across (1) planar, nonrotating faults or ductile shear zones, (2) shear zones which rotate above a horizontal detachment (the domino model), or (3) shear zones which rotate as a result of a horizontally oriented, pure shear stretching component (the plastic model). Listric, normal shear zone geometries may develop as the result of a depth dependent change in the pure shear component (in the plastic model) or the area loss component (in the planar shear zone model). Within the geometric framework of these various models, the effects of superposed simple shear, pure shear extension, and area change on the rock fabric are investigated. These displacement components, which may be superposed sequentially or simultaneously, determine the state of finite strain associated with a given magnitude of tectonic extension. The relationships between displacement and strain are expressed as graphs of foliation dip (or strain ratio) versus shear strain and as graphs of foliation dip (or strain ratio) versus tectonic extension. The shear strain graphs illustrate the effects of the different displacement components on the rock fabric in a single shear zone, whereas the tectonic extension graphs better illustrate these effects on the regional scale. The shear strain and tectonic extension graphs can be used by field geologists (1) to determine tectonic extension across a region from measurements of strain ratio or orientation and fluctuation of foliation, (2) to distinguish between possible extension models from field data, and (3) to evaluate the influence of shear zone attitude and thickness upon the amount of displacement. Applications of these methods are illustrated for field areas in metamorphic core complexes of Arizona and in the Basin and Range province of the North America Cordillera.
The Snake Range Décollement interpreted as a major extensional shear zone
Authors: Bartley John M. , Wernicke Brian P.
Published: February 2008

Geological and geophysical constraints suggest that the Snake Range décollement of east‐central Nevada is a major Tertiary low‐angle normal fault zone. This interpretation is consistent with all existing data, and alleviates problems that result if large displacement across the décollement is excluded [Miller et al., 1983]. Based on published surface geology and COCORP seismic reflection profiling, we have constructed cross sections that suggest approximately 60 km of normal displacement on the décollement. Advantages of this interpretation over models that exclude large displacement are that it provides for overburden consistent with kyanite‐grade metamorphism of footwall rocks, predicts reasonable crustal thicknesses before and after extension without invoking unexposed mantle‐derived Tertiary intrusions at depth, and explains contrasting metamorphism and structural styles of hanging wall and footwall without requiring an extreme geothermal gradient during regional metamorphism and extensional strain. The present domal shape of the décollement is interpreted to result at least partly from reverse drag above an underlying, younger detachment related to much of the extension in ranges to the west of the Snake Range.
Late Mesozoic and Cenozoic tectonic history of south central California
Authors: Engel A. E. J. , Schultejann P. A.
Published: February 2008

The late Mesozoic‐Cenozoic history of south central California is punctuated by at least five major tectonic events. The oldest of these involves Late Cretaceous drag folding and thrusting of epizonal shelf sediments westward over and to the north along the rising eastern margin of the Peninsular Ranges Batholith. These overthrusts, with associated drag folds and nappes, form imbricate stacks of metasediments, slices of plutons, and mylonites which overlie a regional core of Cretaceous granitic plutons of the Peninsular Ranges Batholith. A second, distinct kind of epizonal, low‐temperature crustal displacement includes an episode of mid‐Tertiary detachment faulting and folding. This represents the westerly extension of the detachment terrane of eastern California and western Arizona and Utah, superimposed upon the Cretaceous structural features, The mid‐Tertiary motions involve major E‐W extension and N‐S compressive strain, with formation of east‐trending antiformal “core complexes,” remarkably parallel to a pervasive set of fold axes and B‐lineations formed in the Cretaceous thrusting and folding. All of these features are repeatedly segmented and displaced by step‐faulting as sial in the Salton Trough is fragmented and depressed 5 to 10 km below sea level at intervals throughout the Cenozoic. The irregular step‐faulted interface of the Peninsular Ranges Batholith and Salton Trough is accentuated by a series of NE to SE striking left‐lateral and dipslip faults with displacements of several to 10 kilometers. These appear to both predate and occur during movements along the San Andreas system. Pliocene‐Pleistocene right‐lateral faulting, a younger extension of the San Andreas displacements north of the Transverse Ranges, has broken and displaced all older structural features, with total net slip in south central California of perhaps 300 km. Total right‐lateral slip along the several strands of the San Andreas system are measurable via reconstruction of the mosaic of numerous older, predominantly E‐W trending linear elements, mid‐Tertiary antiforms, and Cretaceous and older rocks. Right‐lateral strain on the San Andreas appears to either alternate with or to be a byproduct of N‐S compressional strain from the Pleistocene to the present. A resultant effect is a large family of E‐W trending folds and fault scarps in Plio‐Pleistocene sediments.