bluuebunny/crossref_metadata_2025 huggingface dataset:
Auroral Lyman α and H2 bands from the giant planets: 3. Lyman α spectral profile including charge exchange and radiative transfer effects and H2 color ratios
Authors: Rego D. , Prangé R. , Ben Jaffel L.
Published: September 2002

In this paper, third of a series of three dealing with a model of auroral H and H2 emission in the giant planets, we focus on the characteristics of the emergent emission, the only one which can be compared with observations. As the Jovian atmosphere is optically thick at 1215.67 Å, modeling of emergent auroral Lyman α line profiles requires the use of a radiative transfer code to model the transport of photons from the auroral source to the top of the atmosphere. Here, radiative transfer effects are modeled using the “doubling and adding” method. This radiative transfer code is self‐consistently coupled with the energy degradation code used in the first two papers to compute the excitation rate along the path of precipitating particles as a function of wavelength. Input parameters are the identity and the energy of the incoming particles. We find that the auroral Lyman α line profile shows a central reversal due to the atmospheric H overlying the emitting layer. The shape of the emergent line is almost only sensitive to the column of H in the line of sight to the emission, related, via the atmospheric model used, to the the particle penetration depth (i.e. their energy). In addition, in the case of proton precipitation, charge exchange produces fast H atoms (Hf) which precipitate with the protons. Hf can also be excited and radiate Lyman α photons. This produces a second, Doppler shifted, component, of the Lyman α profile. This component may represent as much as 77.4% of the total Lyman α intensity for 10 keV protons, and it decreases with incident proton energy. It also extends over a broad wavelength range (up to 56 Å for 1 MeV proton). Detection of this component would unambiguously identify protons as the particles responsible for the Jovian aurorae. However, for high proton energies, the escaping flux may be too weak to be detected. Finally, following earlier analyses of IUE auroral spectra, we compute the color ratio C between the fluxes escaping in two particular wavelength ranges of the H2 Werner and Lyman bands, 1230–1300 Å and 1557–1619 Å. We also compute the ratio CLyα between the H2 short‐wavelength range and the line integrated Lyman α flux. C and CLyα are sensitive to the CH4 and the H column densities, respectively, overlying the auroral source along the line of sight. Once an atmospheric model is assumed, energies of the precipitating particles can be derived. Each of these ratios shows a specific variation with the energy of the particles. In addition, CLyα is sensitive to the identity of precipitating particles as well, so that, combined together, they can, in principle, provide a unique diagnostic of the Jovian aurorae.
A Mössbauer investigation of iron‐rich terrestrial hydrothermal vent systems: Lessons for Mars exploration
Authors: Wade Manson L. , Agresti David G. , Wdowiak Thomas J. , Armendarez Lawrence P. , Farmer Jack D.
Published: September 2002

Hydrothermal spring systems may well have been present on early Mars and could have served as a habitat for primitive life. The integrated instrument suite of the Athena Rover has, as a component on the robotic arm, a Mössbauer spectrometer. In the context of future Mars exploration we present results of Mössbauer analysis of a suite of samples from an iron‐rich thermal spring in the Chocolate Pots area of Yellowstone National Park (YNP) and from Obsidian Pool (YNP) and Manitou Springs, Colorado. We have found that Mössbauer spectroscopy can discriminate among the iron‐bearing minerals in our samples. Those near the vent and on the surface are identified as ferrihydrite, an amorphous ferric mineraloid. Subsurface samples, collected from cores, which are likely to have undergone inorganic and/or biologically mediated alteration (diagenesis), exhibit spectral signatures that include nontronite (a smectite clay), hematite (α‐Fe2O3), small‐particle/nanophase goethite (α‐FeOOH), and siderite (FeCO3). We find for iron minerals that Mössbauer spectroscopy is at least as efficient in identification as X‐ray diffraction. This observation is important from an exploration standpoint. As a planetary surface instrument, Mössbauer spectroscopy can yield high‐quality spectral data without sample preparation (backscatter mode). We have also used field emission scanning electron microscopy (FESEM), in conjunction with energy‐dispersive X ray (EDX) fluorescence spectroscopy, to characterize the microbiological component of surface sinters and the relation between the microbiological and the mineralogical framework. Evidence is presented that the minerals found in these deposits can have multi‐billion‐year residence times and thus may have survived their possible production in a putative early Martian hot spring up to the present day. Examples include the nanophase property and the Mössbauer signature for siderite, which has been identified in a 2.09‐billion‐year old hematite‐rich chert stromatolite. Our research demonstrates that in situ Mössbauer spectroscopy can help determine whether hydrothermal mineral deposits exist on Mars, which is significant for exobiology because of the issue of whether that world ever had conditions conducive to the origin of life. As a useful tool for selection of samples suitable for transport to Earth, Mössbauer spectroscopy will not only serve geological interests but will also have potential for exopaleontology.
Hydrodynamic flow of N2 from Pluto
Authors: Krasnopolsky Vladimir A.
Published: September 2002

A new method of analytic solution for the equation of hydrodynamic flow from an atmosphere has been developed. This method conserves a term neglected in the equation for the McNutt [1989] approximation and significantly improves uncertainty of the solution. Structure of Pluto's upper atmosphere near perihelion was calculated by this method at various solar activity and at various methane mixing ratios. Both the UV absorption by CH4 at 1000–1400 Å and the EUV absorption by N2 heat the upper atmosphere with the global‐mean rates of 1.4 × 10−3 and 2.9 × 10−4 ergs cm−2 s−1, respectively, at mean solar activity. Hydrodynamic outflow of N2 from Pluto at perihelion is equal to (2.0–2.6)×1027 s−1 at mean solar activity and varies by a factor of 3–4 from solar minimum to solar maximum. The exobase lies below the sonic level. Pluto's atmosphere does not completely fit both the conditions of static and hydrodynamically escaping atmospheres and is an intermediate case of a slow hydrodynamic escape. The total loss for the age of the solar system corresponds to an ice layer that is 500 m thick and 5 × 10−4 of Pluto's mass. Pluto's atmosphere is restricted to 3000–4500 km, which makes possible a close flyby of future spacecraft.
High‐resolution UK37 temperature reconstructions in the South China Sea over the past 220 kyr
Authors: Pelejero Carles , Grimalt Joan O. , Heilig Stephanie , Kienast Markus , Wang Luejiang
Published: September 2002

Past sea surface temperatures (SST) in the northern and southern areas of the South China Sea have been reconstructed for the past 220 kyr using the UK37 alkenone index. The SST profiles follow the glacial/interglacial pattern exhibiting differences between Last Glacial Maximum and Holocene that are 1°–3°C larger than those observed at the same latitudes in the Atlantic and Pacific Oceans. In Termination I both planktonic foraminiferal δ18O and SST exhibit well‐defined Bølling‐Allerød and Younger Dryas events with temperature differences between both periods of 0.8° and 0.4°C in north and south, respectively. SSTs record a constant north‐south difference of 1°C in the interglacials and nearly 2.5°C in the glacial stages. These differences define two distinct climatic and water circulation patterns that correspond with glacial/interglacial sea level oscillations which opened and closed water exchange with the tropical Indo‐Pacific Ocean through the present Sunda Shelf.
Tectonic forcings of Maastrichtian ocean‐climate evolution
Authors: Frank Tracy D. , Arthur Michael A.
Published: September 2002

A global compilation of deep‐sea isotopic records suggests that Maastrichtian ocean‐climate evolution was technically driven. During the early Maastrichtian the Atlantic intermediate‐deep ocean was isolated from the Pacific, Indian, and Southern Oceans; deep water formed in the high‐latitude North Atlantic and North Pacific. At the early/late Maastrichtian boundary a major reorganization of oceanic circulation patterns occurred, resulting in the development of a thermohaline circulation system similar to that of the modern oceans. A combination of isotopic and plate kinematic data suggests that this event was triggered by the final breaching of tectonic sills in the South Atlantic and the initiation of north‐south flow of intermediate and deep water in the Atlantic. The onset of Laramide tectonism during the mid Maastrichtian led to the concurrent draining of major epicontinental seaways. Together, these events caused cooling, increased latitudinal temperature gradients, increased ventilation of the deep ocean, and affected a range of marine biota.
Mid‐Wisconsin Laurentide ice sheet growth and decay: Implications for Heinrich events 3 and 4
Authors: Kirby Matthew E. , Andrews John T.
Published: September 2002

A close look at the sedimentology of Heinrich event 4 from the northwest Labrador Sea indicates that an extended ice margin, perhaps greater than before Heinrich events 1 or 2 (H‐1 and H‐2), existed in the Hudson Strait region pre‐Heinrich event 4 (H‐4) and, that on the basis of characteristics of the sediment unit, Heinrich event‐4 was different than Heinrich events 1 or 2 (i.e., larger ice sheet collapse(?), longer duration(?), “dirtier” icebergs(?)). Other data from across the southern and eastern margin of the Laurentide Ice Sheet, as well as Greenland and the North Atlantic, support this interpretation, possibly indicating a relative mid‐Wisconsin glacial maximum pre‐Heinrich event 4. Many of these data also indicate that Heinrich event 4 (35 ka) resulted in serious climatic and oceanographic reorganizations. We suggest that Heinrich event 4 gutted the Hudson Strait, leaving it devoid of ice for Heinrich event 3. We further hypothesize that Heinrich event 3 did not originate from axial ice transport along the Hudson Strait; thus Heinrich event 3 may be more analogous to the proposed northward advancing ice from Ungava Bay during Heinrich event 0 than to the more typical down‐the‐strait flow during H‐1, H‐2, and H‐4. Consequently, the climatic and oceanographic impacts resulting from Heinrich events are highly susceptible to the type, origin, and magnitude of ice sheet collapse, something which varied per Heinrich event during the last glacial period.
Late Quaternary variations in sea surface temperatures and their relationship to orbital forcing recorded in the Southern Ocean (Atlantic sector)
Authors: Brathauer Uta , Abelmann Andrea
Published: September 2002

Late Quaternary summer sea surface temperatures (SSTs) have been derived from radiolarian assemblages in the East Atlantic sector of the Southern Ocean. In the subantarctic and the polar frontal zone, glacial SSTs (oxygen isotope stages 2, 4, 6, and 8) were 3°–5°C cooler than today, indicating northward displacements of the isotherms about 2°–4° of latitudes. During interglacials, SSTs almost reached modern levels (oxygen isotope stages 7 and 9) or exceeded them by 2°–3°C (oxygen isotope stages 1 and 5.5). In the subantarctic Atlantic Ocean, changes in SST and calcium carbonate content of the sediment precede variations in global ice volume in the range of the main Milankovitch frequencies. Comparisons with the timing of North Atlantic Deep Water (NADW) proxy records suggests that this early response in the subantarctic Atlantic Ocean is not triggered by the flux of NADW to the Southern Ocean.
Similar glacial and Holocene deep water circulation inferred from southeast Pacific benthic foraminiferal carbon isotope composition
Authors: Matsumoto Katsumi , Lynch‐Stieglitz Jean
Published: September 2002

We present Holocene and last glacial maximum (LGM) oxygen and carbon isotope measurements on Planulina wuellerstorfi in six southeast Pacific cores. Sedimentation rates are low in this part of the ocean, and measurements were made on individual foraminiferal shells in order to identify the Holocene and glacial individuals on the basis of their extreme δ18O. The new δ13C data were combined with previous P. wuellerstorfi data for interpretation of global thermohaline circulation. Data from the Southern Ocean were examined closely for regional coherency and a few anomalous δ13C values suspected of having productivity overprint were removed. The resulting global δ13C distributions and gradients indicate that the deep water circulation was similar during the Holocene and LGM. This interpretation brings δ13C data to a better agreement with Cd/Ca data and marks a sharp contrast with a widely held view based on δ13C measurements that the glacial Southern Ocean was the terminus of the thermohaline circulation. The proposed presence of glacial North Atlantic Deep Water does not necessarily contradict the postulated presence of Glacial North Atlantic Intermediate Water.
Molecular environmental geochemistry
Authors: O'Day Peggy A.
Published: September 2002

The chemistry, mobility, and bioavailability of contaminant species in the natural environment are controlled by reactions that occur in and among solid, aqueous, and gas phases. These reactions are varied and complex, involving changes in chemical form and mass transfer among inorganic, organic, and biochemical species. The field of molecular environmental geochemistry seeks to apply spectroscopic and microscopic probes to the mechanistic understanding of environmentally relevant chemical processes, particularly those involving contaminants and Earth materials. In general, empirical geochemical models have been shown to lack uniqueness and adequate predictive capability, even in relatively simple systems. Molecular geochemical tools, when coupled with macroscopic measurements, can provide the level of chemical detail required for the credible extrapolation of contaminant reactivity and bioavailability over ranges of temperature, pressure, and composition. This review focuses on recent advances in the understanding of molecular chemistry and reaction mechanisms at mineral surfaces and mineral‐fluid interfaces spurred by the application of new spectroscopies and microscopies. These methods, such as synchrotron X‐ray absorption and scattering techniques, vibrational and resonance spectroscopies, and scanning probe microscopies, provide direct chemical information that can elucidate molecular mechanisms, including element speciation, ligand coordination and oxidation state, structural arrangement and crystallinity on different scales, and physical morphology and topography of surfaces. Nonvacuum techniques that allow examination of reactions in situ (i.e., with water or fluids present) and in real time provide direct links between molecular structure and reactivity and measurements of kinetic rates or thermodynamic properties. Applications of these diverse probes to laboratory model systems have provided fundamental insight into inorganic and organic reactions at mineral surfaces and mineral‐water interfaces. A review of recent studies employing molecular characterizations of soils, sediments, and biological samples from contaminated sites exemplifies the utility and benefits, as well as the challenge, of applying molecular probes to complicated natural materials. New techniques, technological advances, and the crossover of methods from other disciplines such as biochemistry and materials science promise better examination of environmental chemical processes in real time and at higher resolution, and will further the integration of molecular information into field‐scale chemical and hydrologic models.
State‐space formulation of two‐dimensional electromagnetic scattering from dielectric cylinders
Authors: Abu Zaid Naser A. , Niazi Abdullah Y. , Tosun Haluk
Published: September 2002

A numerical method is presented for the problem of transverse magnetic or transverse electric scattering from infinitely long, lossy dielectric cylinders of arbitrary cross section. The method is based on the solution of a system of linear ordinary differential equations in the state‐space form. The solution is achieved by finding the state transition‐matrix and the zero‐state response of the respective system. Numerical results are presented for cylinders of various cross sections, and they are compared with the results obtained by either exact or approximate numerical methods.
Autocorrelation method for temporal interpolation and short‐term prediction of ionospheric data
Authors: Muhtarov Plamen , Kutiev Ivan
Published: September 2002

An autocorrelation method is developed for temporal interpolation and short‐term prediction of ionospheric characteristics. The ionospheric data are considered as a realization of a periodic process with randomly dispersed measured values superimposed on it. The autocorrelation function or its nonnalized autocorrelation coefficients are determined from the measured data over a period of 20–30 days, and on that basis an autocorrelation model is obtained. This model is then used to interpolate the missing values in the monthly tables of ionospheric characteristics, here called “gaps.” The interpolation at a given hour is performed by calculating weighting coefficients for the neighboring measured values. The procedure selects those measurement values around the gap which have the highest autocorrelation coefficients. The model can be used to extrapolate (predict) the data, treating the prediction period (usually 24 hours) as a gap placed at the end of the available data. The method also calculates the so‐called prediction error, which is found to be close to the standard deviation of the measured data. The interpolation and prediction error are estimated to be less than 12% in the case of ƒoF2.
The Esrange MST radar: A brief introduction and procedure for range validation using balloons
Authors: Chilson Phillip B. , Kirkwood Sheila , Nilsson Annika
Published: September 2002

The Esrange VHF radar (ESRAD) is a relatively new mesosphere‐stratosphere‐troposphere (MST) class radar located in northern Sweden (67.88°N, 21.10°E), about 30 km east of Kiruna. The radar operates continuously and has already been included in several campaigns in which multiple profiling instruments have been used, for example, lidars, radiosondes, and scientific balloons. To intercompare the different measurements, it is essential to have precise height estimates. In this paper we begin by presenting a short technical overview of the radar. Then we describe a radar validation conducted in 1997 during a period when numerous scientific balloons were launched from Esrange. All of these balloons were tracked using one or more of the following techniques: Omega navigational system, Global Positioning System (GPS), or the Esrange C‐band tracking radar (ESR). A number of these balloons passed close enough to the ESRAD beam that they could be detected by the MST radar. This unique data set has been used to check the range estimation of ESRAD. Furthermore, the data have been used to make a rough check of the geometry of the formed beam.
What are the mechanisms for non‐Bragg scattering from water wave surfaces?
Authors: Lee P. H. Y. , Barter J. D. , Beach K. L. , Lake B. M. , Rungaldier H. , Thompson H. R. , Wang L. , Yee R.
Published: September 2002

Experimental data obtained in the past several years have provided conclusive evidence that non‐Bragg scattering plays a major role in X‐band microwave backscatter from water wave surfaces, and non‐Bragg scattering events are especially noticeable at small grazing angles, for wind‐roughened surfaces, in the presence of breaking waves. We have conducted scattering experiments under a variety of wind wave conditions in an attempt to determine the different mechanisms which contribute to non‐Bragg scattering. At small grazing angles we find that non‐Bragg scattering is due to fast scatterers generated by the wave breaking, and with increasing wave steepness and surface roughness, mechanisms of multiple scattering and multipath interference become increasingly important.
An investigation of tilted aspect‐sensitive scatterers in the lower atmosphere using the MU and Aberystwyth VHF radars
Authors: Worthington Richard M. , Palmer Robert D. , Fukao Shoichiro
Published: September 2002

This study investigates subtle variations of the zenith and azimuth dependence of VHF‐radar echo power in the troposphere and lower stratosphere. Using the middle and upper atmosphere (MU) and Aberystwyth radars, we reanalyze data from two areas of the literature on tilted aspect‐sensitive scatterers, linking results from the spatial interferometry (SI) and Doppler beam‐swinging (DBS) techniques. Whereas wind profilers commonly use three or five radar beams, we examine a MU radar data set with 64 beam positions, so that maps of echo power distribution can be plotted as far as 5° from zenith. The power distribution pattern is often skewed, with the azimuth of maximum power being closely related to the wind shear caused by, for example, inertia‐gravity waves in the lower stratosphere. The results imply that inertia‐gravity wave motions are closely coupled to the smaller‐scale wind field, causing patches of Kelvin‐Helmholtz instability and/or steepening of other shorter‐period gravity waves. These effects can alter the distribution of the tilts of aspect‐sensitive scatterers and explain the skewed echo power patterns. The deviations of vertical‐beam incidence angle measured by SI are found to be inappropriate for off‐vertical beams, and it also appears impossible for basic DBS systems to be used for measuring vertical‐beam incidence angles. Further tests of mountain wave data are consistent with the tilted layer model and help to confirm that the azimuth of gravity waves may be calculated using radar echo‐power imbalances.
Transient analysis of multielement wire antennas mounted on arbitrarily shaped perfectly conducting bodies
Authors: Aygün Kemal , Fisher Stephen E. , Ergin A. Arif , Shanker Balasubramaniam , Michielssen Eric
Published: September 2002

This paper presents a novel algorithm for analyzing transient radiation from multielement wire systems mounted on arbitrarily shaped, three‐dimensional, perfectly conducting bodies. The algorithm simultaneously characterizes the transient radiation properties of the antenna and the performance of the feed network via a hybrid integral‐equation/finite difference scheme. Numerical examples that validate and demonstrate the efficacy of the proposed scheme are presented.
Modeling of raindrop size distributions from multiwavelength rain attenuation measurements
Authors: Maitra A. , Gibbins C. J.
Published: September 2002

Techniques for modeling the distribution of raindrop sizes, in terms of the lognormal and modified gamma distribution, from multiwavelength rain attenuation measurements at millimeter and infrared wave bands have been demonstrated. In order to obtain the three‐parameter lognormal distribution, three experimental measurements are required, which can be attenuations at two frequencies and rain rate. Three measurements are used to form three equations, which are treated as nonlinear and are solved using a numerical technique to obtain the distribution parameters. The gamma distribution is treated as a two‐parameter distribution, taking a fixed value of 2 for the index. The two parameters of the gamma distribution are obtained from measurements of rain rate and infrared attenuation following the technique described by Maitra and Gibbins [1995]. From an analysis of two rain events it is found that the measured attenuations at millimeter wavelengths show somewhat better agreement with the calculated attenuations obtained from the lognormal distribution than from the modified gamma distribution. The gamma model gives higher number densities for small drops than those given by the lognormal model.
Trench‐parallel stretching and folding of forearc basins and lateral migration of the accretionary wedge in the southern Ryukyus: A case of strain partition caused by oblique convergence
Authors: Lallemand Serge , Liu Char‐Shine , Dominguez Stéphane , Schnürle Philippe , Malavieille Jacques
Published: September 2002

Detailed seafloor mapping in the area east of Taiwan revealed trench‐parallel stretching and folding of the Ryukyu forearc and lateral motion of the accretionary wedge under oblique convergence. East of 122°40′E, a steep accretionary wedge is elongated in an E–W direction. A major transcurrent right‐lateral strike‐slip fault accommodates the strain partitioning caused by an oblique convergence of 40°. A spectacular out‐of‐sequence thrust may be related to the subduction of a structural high lying in the axis of the N–S trending Gagua Ridge. This asperity is likely responsible for the uplift of the accretionary wedge and forearc basement and may have augmented strain partitioning by increasing the coupling between the two plates. West of 122°40′E, the low‐taper accretionary wedge is sheared in a direction subparallel to the convergence vector with respect to the Ryukyu Arc. The bayonet shape of the southern Ryukyu Arc slope partly results from the recent (re)opening of the southern Okinawa Trough at a rate of about 2 to 4 cm/yr. Right‐lateral shearing of the sedimentary forearc with respect to the nonlinear Ryukyu backstop generates trench‐parallel extension in the forearc sediment sequence at dilational jogs and trench‐parallel folding at compressive jogs. The Hoping Basin lies above a diffuse trench/trench/fault (TTF) or TFF unstable triple junction moving toward the south along a N–S transform zone which accommodates the southward drift of the Ryukyu Arc with respect to Eurasia.
Inversion tectonics and the evolution of the High Atlas Mountains, Morocco, based on a geological‐geophysical transect
Authors: Beauchamp Weldon , Allmendinger Richard W. , Barazangi Muawia , Demnati Ahmed , El Alji Mohamed , Dahmani Mohammed
Published: September 2002

The High Atlas Mountains of North Africa were formed over a major intracontinental rift system that had extended from what is now the Atlantic margin of Morocco to the Mediterranean coast of Tunisia. The Atlas rift system began in the Triassic and was active through the Jurassic. The inversion phase of the Atlas rift system began in the Early Cretaceous and extended into the present. The major uplift phase occurred between 30 and 20 Ma (Oligocene‐Miocene) and corresponds to the Alpine orogenic event. The uplift and inversion of the Atlas rift system resulted in a shortening of the rift basin by a minimum of 36 km. A restoration of the deformed cross section indicates the original Atlas rift basin was approximately 113 km wide, comparable to the width of the present‐day Red Sea. Synrift and postrift sedimentary rocks were uplifted by the reactivation of synrift normal faults, with further shortening along newly formed thin‐skinned thrust faults. Structures formed by the reactivation of synrift faults resulted in structures with different geometries than those created by newly formed fault‐bend and fault‐propagation faults. Shortening across the High Atlas Mountains involved a partitioning of strain, with the greatest magnitude of shortening occurring along the margins of the High Atlas Mountains.
Balancing cross sections with kinematic constraints: The Dolomites (northern Italy)
Authors: Schönborn Gregor
Published: September 2002

Balancing of structural cross sections is often hindered by a limited database or tectonic complications. In such cases, kinematic constraints may help to better constrain the construction of a cross section and its extrapolation to depth. The kinematic implications of a known structure (generally at the surface) have to be considered for the unknown structure and for the internal consistency of a cross section. A key point is the quantification of shortening of the known structure. The extrapolation of this parameter allows balancing in an approximate way, emphasizing major structures while minor structures are either neglected or treated in a simplified way. With this approach a quick overview can be achieved on how much leeway for interpretation exists, critical points for testing various working hypotheses become more evident, and the trial‐and‐error effort during the construction of a balanced section is considerably shortened. Still the implications the observed structures have on the deeper crustal levels can be assessed. This concept is applied to a section across the Italian Dolomites, a brittle fold‐and‐thrust belt lacking reflection seismic data so far and thus with a poorly known deep structure. Still active south vergent Alpine thrusting is oriented approximately perpendicular to previous Dinaric thrusting. The ramp flat style is dominant due to rheological constrasts within the stratigraphic sequence. Thanks to kinematic balancing based on surface data, three Alpine thrust systems could be identified, each defining a thrust sheet with its particular basement unit and its sedimentary part. Superposition of the two more external basement units led to the presently observed high elevation of the Triassic sequence in the Dolomites. Shortening since late Miocene times amounts to more than 50 km. Retrodeformation of Alpine thrusting is a key for better understanding the previous Dinaric structures and kinematics.
Accretion in the wake of terrane collision: The Neogene accretionary wedge off Kenai Peninsula, Alaska
Authors: Fruehn Juergen , von Huene Roland , Fisher Michael A.
Published: September 2002

Subduction accretion and repeated terrane collision shaped the Alaskan convergent margin. The Yakutat Terrane is currently colliding with the continental margin below the central Gulf of Alaska. During the Neogene the terrane's western part was subducted after which a sediment wedge accreted along the northeast Aleutian Trench. This wedge incorporates sediment eroded from the continental margin and marine sediments carried into the subduction zone on the Pacific plate. Prestack depth migration was performed on six seismic reflection lines to resolve the structure within this accretionary wedge and its backstop. The lateral extent of the structures is constrained by high‐resolution swath bathymetry and seismic lines collected along strike. Accretionary structure consists of variably sized thrust slices that were deformed against a backstop during frontal accretion and underplating. Toward the northeast the lower slope steepens, the wedge narrows, and the accreted volume decreases notwithstanding a doubling of sediment thickness in the trench. In the northeasternmost transect, near the area where the terrane's trailing edge subducts, no frontal accretion is observed and the slope is eroded. The structures imaged along the seismic lines discussed here most likely result from progressive evolution from erosion to accretion, as the trailing edge of the Yakutat Terrane is subducting.
Opposing gradients of permanent strain in the aseismic zone and elastic strain across the seismogenic zone of the Kodiak shelf and slope, Alaska
Authors: von Huene R. , Klaeschen D.
Published: September 2002

An industry‐acquired seismic reflection line from the Aleutian Arc to the Alaska Trench was prestack depth‐migrated and further constrained with wide‐angle ocean bottom hydrophone seismic velocity data and swath mapping. From the seismic reflection image, individual thrust slices, the backstop, and the forearc basin were resolved sufficiently well to balance the section. Tectonic shortening and age estimates provided rates of permanent contraction in five discrete segments over ∼150 km during the past 3 Myr. About 70% of the plate convergence is measured as contraction across the ∼40‐km‐wide Neogene accretionary prism which composes less than 10% of the forearc. Permanent contraction is minimal above the 1964 Alaska earthquake aftershock zone indicating dominently elastic strain. Since elastic strain is poorly recorded in the geological record, it was approximated from the historical record of the 1964 Alaska earthquake. The 1964 coseismic vertical deformation displays an inverse pattern to the permanent strain, consistent with the earthquake cycle concept. Elastic deformation is dominant beneath the shelf and upper slope, rapid permanent deformation is concentrated beneath the lower slope, and a transition between them occurs beneath the middle slope.
A possible middle Paleozoic suture in the Altyn Tagh, NW China
Authors: Sobel Edward R. , Arnaud Nicolas
Published: September 2002

Preliminary 40Ar/39Ar thermochronologic results from two transects across the Altyn Tagh (AT) range allow new interpretations for the genesis of the range and provide constraints for its subsequent displacement. Recent reports of Middle to Upper Ordovician pillow lavas in the NE portion of the range as well as the first reports of high‐pressure metamorphic rocks within the range are interpreted as the remnants of a lower Paleozoic ocean subducted within the AT. Muscovite and biotite ages from schist, gneiss, and granodiorite document a significant metamorphic and intrusive event throughout the range at 435±20 Ma. This fabric is crosscut by undeformed, postorogenic microgranite plutons dated at 383±7 Ma by muscovite. These data suggest that an ocean basin closed after the Early Silurian and prior to the Middle Devonian, forming the herein named Lapeiquan suture. The lack of similary aged plutons to the north and the suggestion of a synchronous arc to the south implies that subduction was south dipping (present geography). If the Altyn Tagh contains a middle Paleozoic suture, lateral continuations should be identifiable. Possibilities to the west include the Kudi suture in the western Kunlun Shan. Comparisons of lithologies and radiometric data reveal significant similarities between the Kudi suture and the Altyn Tagh, suggesting that the AT originated as part of the same middle Paleozoic orogenic belt. Reconstruction of the Paleozoic structure of northern Tibet is complicated by Cenozoic deformation, particularly along the Altyn Tagh fault. Although this could be used as a measure of the finite post‐Devonian deformation, a more thorough understanding of Paleozoic geodynamics is a prerequisite to unraveling subsequent displacements.
Quaternary transfer faulting and belt front deformation at Pakuashan (western Taiwan)
Authors: Mouthereau F. , Lacombe O. , Deffontaines B. , Angelier J. , Chu H. T. , Lee C. T.
Published: September 2002

The arcuate Pakuashan anticline is located in the outermost front units of the Western Foothills of Taiwan. This oblique feature of the deformation front is investigated in terms of combined morphostructural analysis, based on imagery and digital elevation model as well as microtectonic analysis of fault slip data. A subsurface structural study based on available seismic and well data was also carried out, resulting in improved mapping of the Neogene series and associated structures. This mapping allowed construction of several along‐strike cross sections. Such combined analyses revealed that the transverse Pakuashan fold is located above a major transfer fault zone. This active fault zone accommodates differential westward propagation of thrust units; its kinematic evolution is principally controlled by the geometry of the foreland Peikang High, behaving as a buttress for the west verging thrust sheets. A preliminary analytical model of the oblique thrusting at Pakuashan is based on similar cases studied by Apotria et al. [1992]. It involves quaternary transfer faulting accommodating the motion of connected thrust sheets, moving over oblique ramps linked to a preexisting major basement boundary (the hinge fault of the Peikang High). This analytical modeling accounts for the occurrence of local extension at the intersection of oblique ramps in the southern Pakuashan. Numerous complementary structural and tectonic evidences led us to establish a complete deformation model, involving local rotation in southern Pakuashan which caused differential slips in northern Pakuashan, resulting in tear faulting. These evidences include large extension at the intersection of oblique ramps, distributed extension in the transverse zone, regional wrench deformation, absence of major reorientation of local stress inside the transverse zone, along‐strike variation of structural styles coupled with low to high uplift rate from the Northern to the Southern part of the Pakuashan fold. Thus a synthetic reconstruction of the Pakua Transfer Fault Zone evolution is proposed, as a typical example of active transfer faulting, evolving gradually from a primary tear fault with a slight curvature to the left‐lateral tear fault or transfer fault that offsets two distinct frontal thrust‐and‐fold sheets.
Large‐scale transpressive shear zone patterns and displacements within magmatic arcs: The Coast Plutonic Complex, British Columbia
Authors: Chardon Dominique , Andronicos Christopher L. , Hollister Lincoln S.
Published: September 2002

The Coast Plutonic Complex is the largest magmatic arc of the North American Cordillera, extending from northwestern Washington State to eastern Alaska. It forms the transition between two tectonic domains that are suspected to have undergone several phases of large (several thousands of kilometers) orogen‐parallel displacement during the Mesozoic and early Cenozoic. A compilation of fabric data, published isotopic ages, and new structural observations shows that the western Coast Plutonic Complex was affected by subvertical, orogen‐parallel, crustal‐scale shear zones. These shear zones mainly reflect sinistral transpression and were sequentially active from ∼110 to 87 Ma during the intrusion of voluminous batholiths. Sinistral shearing was roughly coeval with the development of the thrust belts flanking the Coast Plutonic Complex (between ∼101 and ∼85 Ma), suggesting plate‐scale transpression was a first‐order process in the construction of the Coast Mountains orogen. These shear zones separate panels with distinct plutonic and cooling histories, suggesting the sinistral displacements between crustal blocks were large (greater than tens to hundreds of kilometers). This transpressive shear system likely reflects the Jurassic to early Late Cretaceous migration of outboard Cordilleran terranes to the south suggested by paleomagnetic evidence and plate reconstruction models. This example from the Coast orogen shows how transpression is partitioned between a thermally weakened magmatic arc and outwardly vergent fold‐and‐thrust belts. Our analysis further shows that the ∼2000‐km‐long Late Cretaceous to early Tertiary Coast shear zone has a minimum extent toward the south to at least 51°30′N.
A numerical modeling study to investigate the assumptions used in the calculation of probable maximum precipitation
Authors: Abbs Deborah J.
Published: September 2002

A numerical model of the atmosphere has been employed to evaluate the assumptions used in the simple two‐parameter model that is utilized for many probable maximum precipitation (PMP) calculations. These assumptions are (1) the precipitation is linearly related to the precipitable water; (2) the precipitation efficiency of the storm does not change as the moisture available to the storm increases; and (3) terrain modulates the distribution of the precipitation but does not affect the synoptic‐scale dynamics of the storm. A single case study is used to illustrate the techniques employed and to describe the results that were common to four case studies. We show that long‐lived, moderate rainfall processes are important contributors to the total precipitation produced by the storm. Increases in the moisture availability result in the heavy rainfall beginning earlier, lasting longer, and being more continuous. As the moisture availability changes, the spatial distribution of the area over which more than 50% of the total rainfall falls as heavy rainfall changes. As the moisture availability is increased, the precipitation efficiency of the storm does not change significantly. Terrain effects are shown to have an effect on the amount of rainfall that occurs over the higher terrain as well as on the distribution of the rainfall due to the “convergence component” of the storm. Despite these deficiencies in the assumptions used to estimate PMP, improvements in the estimation of PMP may soon be possible if increased effort is placed on (amongst other things) the numerical modeling of extreme rainfall events. These improvements are only possible if the results of these efforts are communicated to the hydrological community.
An integrated global and local optimization approach for remediation system design
Authors: Zheng Chunmiao , Wang P. Patrick
Published: September 2002

A global optimization (metaheuristic) method, tabu search, is integrated with linear programming to solve remediation design problems. This integrated approach takes advantage of the fact that the global optimization approach is most effective for optimizing discrete well location variables, while linear programming is much more efficient for optimizing continuous pumping rate variables. In addition, an efficient forward solution updating procedure is used to lessen the computational burden of the global optimization approach. With this procedure the new solution to a linear flow model perturbed by pumping is obtained as the sum of a nonperturbed base solution and the solution to the perturbed portion of the flow system, which can be derived directly without running the flow model. Numerical results, based on a two‐dimensional capture zone design problem, show that the computation time can be reduced to a small fraction of that required by the conventional approach, in which a forward simulation model is run each time the objective function needs to be evaluated. It is also demonstrated that the maximum number of wells allowed in a given design has a significant effect on the total remediation costs. (The total remediation costs are nearly doubled when only one well is allowed instead of the optimal number of six for the test problem.) A Monte Carlo analysis, based on 200 realizations of a lognormally distributed random hydraulic conductivity field (the variance of lnT = 1.0), further reveals that the total remediation costs determined for the heterogeneous aquifer have a large uncertainty (the ratio of standard derivation over mean is 0.4). The total remediation costs and associated uncertainty are also shown to increase with the uncertainty of the hydraulic conductivity field.
Determining water content and saturation from dielectric measurements in layered materials
Authors: Chan Christina Y. , Knight Rosemary J.
Published: September 2002

Measurements of the dielectric constant in regions of the subsurface are commonly made to determine water content and in turn to determine water saturation. The accuracy with which water content or saturation information can be obtained from dielectric data is very dependent upon the model used to relate dielectric constant to water content or saturation. Most models assume that the material can be described as a homogeneous mixture of solids and fluids. While this may be valid in the interpretation of laboratory data, we suggest that in the interpretation of field data, improved accuracy in water content and saturation estimates can be obtained by accounting for the presence of layering. We present three relationships for determining water content or saturation from dielectric constant for layered materials. These three layered averages take into account both the layer thickness and measurement direction. We numerically model the relationship between the dielectric constant and both the fine fraction and water content or saturation in sand‐fine systems. We calculate dielectric constant as a function of water content or saturation using these three relationships for layered systems and compare the results to those calculated using two relationships for homogeneous systems. There are considerable differences between the dielectric constants predicted from the relationships for layered and homogeneous media. There are also differences between the individual relationships for the layered media due to the geometries of the systems. The numerical results illustrate the inaccuracy that can result in water content and especially saturation estimates if an inappropriate relationship is used to interpret dielectric data from a layered system.
A conceptual model for infiltration and redistribution in crusted soils
Authors: Smith R. E. , Corradini C. , Melone F.
Published: September 2002

Treating the crust as a single layer, a simplified but accurate infiltration and redistribution model for a crust‐topped soil profile is developed. The method is an extension of an earlier infiltration and redistribution model for homogeneous soil profiles. The crust layer is conceptually subdivided into regions associated with surface water content and interface water content, respectively. The extension of the wetting front into the subsoil is described by the homogeneous soil method described earlier. Two ordinary differential equations are written which match pressure heads and fluxes at the soil interface and are solved by a Runge‐Kutta technique. The model is tested against the results of the Richards equation with variations in the key variables of capillary length scale and saturated hydraulic conductivity for both soil and crust and for cases where ponding occurs both in the crust region and after wetting has entered the subsoil region. In all cases the profile water contents and infiltration rates are very reasonably simulated.
Fluorescence intensity variations of speleothem‐forming groundwaters: Implications for paleoclimate reconstruction
Authors: Baker Andy , Mockler Natalie J. , Barnes William L.
Published: September 2002

Groundwater discharges onto 16 speleothems and surface climate parameters have been measured in an oolitic limestone site in England. Groundwater recharge is demonstrated to lag behind periods of hydrologically effective precipitation by 30–50 days. With the exception of short periods of high rainfall intensity or quantity, summer rainfall has no effect on groundwater discharge onto the speleothems because of the development of a soil moisture deficit. The first groundwater fluorescence intensity increase was demonstrated to lag the autumn increase in groundwater discharge by 10–20 days, suggesting that the first groundwater comprises “old” stored groundwater, whereas later water derives from the overlying soil and has a high organic acid concentration. Despite the lags, the structure of autumn and winter moisture availability is reflected within the annual fluorescence intensity variations, suggesting that fluorescent organic acids, when trapped within speleothem calcite, may provide a proxy for past winter moisture variations for temperate latitudes.