bluuebunny/crossref_metadata_2025 huggingface dataset:
Global calibration of Gephyrocapsa coccolith abundance in Holocene sediments for paleotemperature assessment
Authors: Bollmann Jörg , Henderiks Jorijntje , Brabec Bernhard
Published: October 2002

A global sea surface temperature calibration based on the relative abundance of different morphotypes within the coccolithophore genus Gephyrocapsa in Holocene deep‐sea sediments is presented. There is evidence suggesting that absolute sea surface temperature for a given location can be calculated from the relative abundance of Gephyrocapsa morphotypes in sediment samples, with a standard error comparable to temperature estimates derived from other temperature proxies such as planktic foraminifera transfer functions. A total of 110 Holocene sediment samples were selected from the Pacific, Indian, and Atlantic Oceans covering a mean sea surface temperature gradient from 13.6° to 29.3°C. Standard multiple linear regression analyses were applied to this data set, linking the relative abundance of Gephyrocapsa morphotypes to sea surface temperature. The best model revealed an r2 of 0.83 with a standard residual error of 1.78°C for the estimation of mean sea surface temperature. This new proxy provides a unique opportunity for the reconstruction of paleotemperatures with a very small amount of sample material due to the minute size of coccoliths, permitting examination of thinly laminated sediments (e.g., a pinhead of material from laminated sediments for the reconstruction of annual sea surface temperature variations). Such fine‐scale resolution is currently not possible with any other proxy. Application of this new paleotemperature proxy may allow new paleoenvironmental interpretations in the late Quaternary period and discrepancies between the different currently used paleotemperature proxies might be resolved.
MODELING VEGETATION AS A DYNAMIC COMPONENT IN SOIL‐VEGETATION‐ATMOSPHERE TRANSFER SCHEMES AND HYDROLOGICAL MODELS
Authors: Arora Vivek
Published: October 2002

Vegetation affects the climate by modifying the energy, momentum, and hydrologic balance of the land surface. Soil‐vegetation‐atmosphere transfer (SVAT) schemes explicitly consider the role of vegetation in affecting water and energy balance by taking into account its physiological properties, in particular, leaf area index (LAI) and stomatal conductance. These two physiological properties are also the basis of evapotranspiration parameterizations in physically based hydrological models. However, most current SVAT schemes and hydrological models do not parameterize vegetation as a dynamic component. The seasonal evolution of LAI is prescribed, and monthly LAI values are kept constant year after year. The effect of CO2 on the structure and physiological properties of vegetation is also neglected, which is likely to be important in transient climate simulations with increasing CO2 concentration and for hydrological models that are used to study climate change impact. The net carbon uptake by vegetation, which is the difference between photosynthesis and respiration, is allocated to leaves, stems, and roots. Carbon allocation to leaves determines their biomass and LAI. The timing of bud burst, leaf senescence, and leaf abscission (i.e., the phenology) determines the length of the growing season. Together, photosynthesis, respiration, allocation, and phenology, which are all strongly dependent on environmental conditions, make vegetation a dynamic component. This paper (1) familiarizes the reader with the basic physical processes associated with the functioning of the terrestrial biosphere using simple nonbiogeochemical terminology, (2) summarizes the range of parameterizations used to model these processes in the current generation of process‐based vegetation and plant growth models and discusses their suitability for inclusion in SVAT schemes and hydrological models, and (3) illustrates the manner in which the coupling of vegetation models and SVAT schemes/hydrological models may be accomplished.
Closed form solution for three‐dimensional reflection of an arbitrary Gaussian beam by a smooth surface
Authors: Anastassiu Hristos T. , Pathak Prabhakar H.
Published: October 2002

A high‐frequency analysis of the reflection of an electromagnetic Gaussian beam (GB) from a metallic parabolic surface is presented for the three‐dimensional case. The reflected field is evaluated analytically by use of the physical optics approximation and is expressed in closed form in terms of the incident GB parameters. Similarities with the two‐dimensional case and also with ray tracing theory are pointed out. Although the same problem has been investigated in the past by several researchers, this paper presents a physically appealing and intuitive closed form expression for the reflected field in the paraxial zone that does not appear to be available in the literature.
A fast technique based on perfectly matched layers to model electromagnetic scattering from wires embedded in substrates
Authors: Rogier Hendrik , De Zutter Daniël
Published: October 2002

A two‐dimensional integral equation formulation is used to model electromagnetic scattering from metallic structures embedded in substrates. The new method involves a fast evaluation scheme for the Green's function of the substrate by using perfectly matched layers to obtain closed‐form expressions as a series of leaky and Berenger modes. Efficient summation of these series is performed by means of the Shanks transform. The modal series can be applied to calculate all interactions, except for the self‐patch contribution. The latter can be approximated with good accuracy by using the closed‐form quasi‐static part of the Green's function. The new technique is illustrated by studying scattering from wires embedded in a microstrip substrate.
Improved Fourier transform methods for solving the parabolic wave equation
Authors: Kuttler James R. , Janaswamy Ramakrishna
Published: October 2002

A standard method for modeling electromagnetic propagation in the troposphere is the Fourier split‐step algorithm for solving the parabolic wave equation. An important advance in this technique was the introduction of the mixed Fourier transform, which permitted the extension of the method from propagation over only smooth perfectly conducting surfaces to quite general surfaces with impedance boundary conditions. This paper describes improvements in the implementation of the mixed Fourier transform, which make the method more robust and efficient and avoid potential numerical instabilities, which occasionally caused problems in the previous implementation. Some examples are also presented.
Study of the effect of host loss on the chirality of composite chiral materials
Authors: Hui Hon Tat , Yung Edward K. N. , Jin Jian‐Ming
Published: October 2002

The effect of the host loss on the chirality of composite chiral materials is investigated. A modified single scattering theory is used to calculate the chirality parameters of composite chiral materials with different host losses. Results show that when the host loss is decreased, both the imaginary and the real parts of the chirality parameter increase very rapidly at frequencies near the resonant frequency of the embedded helixes and become narrower in bandwidth. However, only a small effect is observed for frequencies away from the resonant frequency. The effect of the host loss on the propagation constants of the two circularly polarized eigenwaves is also investigated. It is found that the host loss gives rise to rather significant imaginary parts of the propagation constants of the two eigenwaves and these imaginary parts increase with frequency. The effect of the host loss on the real parts of the propagation constant of the two eigenwaves is only observable near the resonant frequency of the embedded helixes. This study is limited to chiral materials with a dilute concentration of chiral inclusions.
A radio wave scattering algorithm and irregularity model for scintillation predictions
Authors: Costa Emanoel , Basu Santimay
Published: October 2002

An algorithm for calculations of phase and amplitude scintillation of satellite signals in the equatorial region will be described in detail. The algorithm will be developed by initially transforming the discrete version of the Huygens‐Fresnel integral into a convolution involving a series of coefficients with decreasing amplitudes. Next, the Fourier transform of the corresponding series of coefficients is stored for all the frequencies of interest, and the fast Fourier transform algorithm is used to evaluate discrete convolutions. Two phase screen models will be described. The first assumes that the phase fluctuations of the wave front emerging from the bottom of the irregularity layer are proportional to electron density fluctuations directly obtained from satellite in situ measurements. The second assumes that the same phase fluctuations can be obtained from their power spectral densities and phase spectra, represented by analytical functions with parameters provided by physics‐based or morphological models of ionospheric irregularities. The propagation algorithm will be applied to both phase screen models, assuming five frequencies in the high‐VHF to low‐SHF band (suffering strong to weak scattering), to display its potential in the prediction of phase and amplitude scintillation of satellite signals.
Syntectonic remagnetization in the southern Methow block: Resolving large displacements in the southern Canadian Cordillera
Authors: Enkin Randolph J. , Mahoney J. B. , Baker Judith , Kiessling Mark , Haugerud Ralph A.
Published: October 2002

The Upper Cretaceous Ventura Member of the Goat Wall unit in the southern Methow block of southern British Columbia and northern Washington State holds a syntectonic magnetization. Eight new sites from Manning Park in British Columbia give a mean direction of D = 27.5°, I = 60.1°, k = 304.7, α95 = 3.2° after optimal partial tilt correction. Of five groups of bedded sites from farther south in the basin reported by Bazard et al. [1990], four have a syntectonic remanence with a direction similar to what we observe. The exception is one group which has optimal concentration of remanence directions on >100% untilting and an abherent direction which must be rejected. Combining the accepted sites, the optimal differential syntilting direction is D = 11.8°, I = 61.5°, k = 39.3, α95 = 3.4° (N = 47), giving a mean pole of 79.8°N, 359.2°E, K = 19.5, and A95 = 4.8°. The age of the remagnetization is constrained to be between 88 and 80 Ma. Compared to cratonic North America, this result indicates that the southern Methow block was displaced from the south by 1800 ± 500 km, meaning it lay south of the Sierra Nevada subduction zone but well north of other paleomagnetically constrained Cretaceous rock units from the Insular superterrane, including correlative strata of the Mount Tatlow area in the northern Methow block. Among several possibilities to reconcile this discrepancy, the most plausible has the whole Methow block translated coherently but with the southern Methow block strata remagnetized during transit.
Structural evolution of the middle Archean coastal Pilbara terrane, Western Australia
Authors: Kiyokawa Shoichi , Taira Asahiko , Byrne Tim , Bowring Sam , Sano Yuji
Published: October 2002

The middle Archean coastal Pilbara terrane is composed of two lithotectonic units: the Karratha and Cleaverville‐Roebourne supercomplexes. The Karratha supercomplex lies tectonically beneath the Cleaverville‐Roebourne supercomplex and consists of 3270 ∼ 3250 Ma granitic batholiths and metamorphosed terrigenous sediments. It is identified as a juvenile continental crust with tonalite‐trondhjemite‐granodiorite type granites. The Cleaverville‐Roebourne supercomplex is interpreted as a dismembered immature island arc which has a restored crustal thickness of ∼20 km. This supercomplex consists of 3195 Ma bimodal volcanic‐chemical sedimentary sequences, metabasite, low‐K granitic gneiss and peridotite. Regionally distributed granite‐porphyries (circa 3020 ∼ 3000 Ma) have intruded all of the coastal Pilbara terrane. Detailed structural analyses and zircon U/Pb dating suggest that the coastal Pilbara terrane records two phases of deformation. The first phase is an immature island arc and micro‐continental crust collision and is represented by top to the northwest thrusting (D1, circa 3100–3020 Ma). This phase of deformation (an arc‐continent collision) appears to represent an important transition in the formation of continental crust. The 3020 Ma granite‐porphyry event may be related to syn‐post collision igneous activity and may reflect a second crustal thickening associated with magmatic underplating. The second phase of deformation is characterized by regional‐scale left‐lateral strike‐slip faulting (D2, circa 3020–2925 Ma) and by more localized right‐lateral strike‐slip faulting (D3, circa 2925–2770 Ma). This phase of craton‐scale strike‐slip faulting may represent stabilization of the newly formed continental crust.
Stable isotopic evidence for a Pre‐Middle Miocene rain shadow in the western Basin and Range: Implications for the paleotopography of the Sierra Nevada
Authors: Poage M. A. , Chamberlain C. P.
Published: October 2002

A recently proposed method for approximating the paleorelief of mountain belts makes use of the predictable relationship between the isotopic depletion of precipitation and the net elevation of an orographic barrier over which an air mass rises. This rain shadow effect often creates desert regions on the lee side of mountain belts in which precipitation is isotopically light. Changes in the isotopic composition of precipitation can be estimated from the isotopic composition of authigenic or pedogenic minerals, which can then be used to infer both the development of relief during orogenesis as well as the stability of a rain shadow formed by developing mountains. The δ18O of smectites formed from the weathering of Middle Miocene to Late Pliocene volcanic ashes currently exposed in the rain shadow of the modern Sierra Nevada of California show no indication of large‐scale Late Cenozoic surface uplift of the Sierra and corresponding regional rain shadow development. Rather smectite isotope data tentatively suggest that elevations may have decreased over this time by as much as 2000 m toward the southern end of the range and 700 m in regions farther north. This suggests that the modern rain shadow cast over the western Basin and Range has been in existence since pre‐Middle Miocene and that the Sierra Nevada have been a prominent orographic barrier since before this time. These interpretations are in accord with several recent studies also suggesting a possible Cenozoic elevation loss of an already developed Sierra Nevada mountain range.
Reappraisal of hypothetical Franciscan thrust wedging at Coalinga: Implications for tectonic relations along the Great Valley flank of the California Coast Ranges
Authors: Dickinson William R.
Published: October 2002

Correlation of the character and orientation of seismic reflectors imaged on profiles across the Coalinga anticline with known surface geology indicates that local Franciscan thrust wedging, favored for past geodynamic interpretations of the 1983 Coalinga earthquake, is an untenable hypothesis. The inference that a subhorizontal detachment surface of simple shear is present beneath the anticline is consequently unnecessary, and unlikely in view of the coherent areal pattern of wrench folding within the southern Diablo Range. Elsewhere along the structural front of the California Coast Ranges at the western flank of the Great Valley, interpretations of similar thrust wedging based in part on analogy with supposed structural relations at Coalinga are equally questionable. In a wider context, the seismogenic behavior of blind thrust and reverse faults in California cannot be interpreted with the invalid concept of thrust wedging at Coalinga as a guiding template for geotectonic interpretations.
A reinterpretation of the Balakot Formation: Implications for the tectonics of the NW Himalaya, Pakistan
Authors: Najman Yani , Pringle Malcolm , Godin Laurent , Oliver Grahame
Published: October 2002

The Balakot Formation of the Himalayan foreland basin in Pakistan was originally described as a >8 km thick clastic red bed succession within which are stratigraphically intercalated four gray marl bands containing fossils dated at 55–50 Ma. On this basis, and the reported conformable contact with the underlying Paleocene Patala Formation, the Balakot Formation red beds were interpreted as tidal facies dated at 55–50 Ma, by >20 Myr the oldest foreland basin sediments eroded from the metamorphic orogen. However, our new detailed structural mapping shows the Balakot Formation to be in tectonic contact with the underlying Patala Formation, and the marl bands to be structurally intercalated with the red beds. Hence neither the nature of the Balakot Formation lower contact nor the intercalated marl bands can be used to date the red beds. Our Ar/Ar dating of 257 individual detrital white micas from the Balakot Formation red bed sandstones shows that the red bed succession must be younger than 37 Ma, and we thus conclude that the first exposed foreland basin continental sediments eroded from the metamorphic mountain belt were deposited after 37 Ma, at least 15 Myr later than previously believed. These new structural, stratigraphic, and isotopic data from the Balakot Formation provide new constraints to the early tectonic evolution of the mountain belt, result in reassessment of the facies and provenance of the Balakot Formation, and force reconsideration of models of orogenesis, basin evolution, and the timing and diachroneity of India‐Asia collision that are based on the original documentation of the Balakot Formation.
Along‐depth stress rotations and active faults: An example in a 5‐km deep well of southern Italy
Authors: Mariucci Maria Teresa , Amato Alessandro , Gambini Roberto , Giorgioni Maurizio , Montone Paola
Published: October 2002

We have analyzed a 1500 m section at 3.9 to 5.4 km depth in a well of the southern Apennines, in order to better characterize the local active stress field and its correlation with tectonic structures. In this paper we present and discuss the results obtained from the comparison between breakouts and structural analysis from dipmeter data. We have found that the mean breakout direction is in agreement with the regional stress field that in this area is characterized by normal faulting (σ1 = σv) with NE‐SW trending extension (horizontal σ3). Since the regional stress field is relatively well known in this region, we could detect and study some anomalous horizontal stress directions along the well, which we interpret as due to faults crosscutting the borehole. A detailed comparison between the breakout‐inferred stress variations along depth and the faults identified by the dipmeter analysis reveals that some of these faults are associated with stress rotations, whereas others do not show any variation. The former can be interpreted either as “open” fractures or as faults that slipped recently with a near‐complete stress drop, and the latter can be interpreted as “sealed” faults. In particular, we found that the main thrust faults of the area, mainly active in Pliocene times, appear to be sealed, whereas ∼E‐W trending high‐angle (normal?) faults determine strong stress rotations, suggesting that they are the main active structures of the region. This suggests that the study area is located in a transfer zone between the two main “Apenninic” (NW‐SE trending) fault systems which ruptured in the last 150 years. This study has shown that a detailed analysis of the structural and geometrical characteristics of deep wells can be used for the reconnaissance of active structures. This approach can contribute to seismic hazard studies and, if carried out in an oil‐bearing section, can help to maximize the hydrocarbon production.
Modeling the evolution of the Guadalquivir foreland basin (southern Spain)
Authors: Garcia‐Castellanos D. , Fernàndez M. , Torne M.
Published: October 2002

Previous quantitative studies dealing with the origin of foreland basins have focused primarily either on the rheological basis of the lithosphere mechanical response or on the relationship between orogenic loading and sediment geometry. To link the evolution of the Guadalquivir foreland basin (South Iberia) with the thermomechanical stratification of the Iberian lithosphere, we combine quantitative approaches to deep and shallow processes: thrust loading, lithospheric flexure, thickness changes of the crust and the lithospheric mantle, and surface mass transport. A planform flexural analysis of the present‐day load distribution shows that basement subsidence is related not only to upper crustal thrusting but also to a deep‐seated additional load. On the basis of the observed gravity and geoid fields, we propose this additional load to be related to a lithospheric mantle thickening larger than the coeval crustal thickening. Further modeling of the evolution of a basin cross section reveals that the architecture of the sedimentary basin is additionally related to the lithosphere rheological response. The quantitative study of the evolution of basement faulting and the forebulge uplift of Sierra Morena leads us to conclude that viscous stress relaxation and/or plastic yielding within the lithosphere are key processes to explain the flexural evolution of the basin.
Upper Rhine Graben: Role of preexisting structures during rift evolution
Authors: Schumacher Markus E.
Published: October 2002

The evolution of the Cenozoic Upper Rhine Graben was controlled by a repeatedly changing stress field and the reactivation of a complex set of crustal discontinuities that had come into evidence during Permo‐Carboniferous times. A comparison of the spatial and temporal thickness distribution of synrift deposits with preexisting fault patterns permits to infer a sequence of distinct basin subsidence phases that can be related to changes in the ambient stress field. Reactivation of a system of late Palaeozoic fault systems, outlining troughs and highs, controlled the nucleation of initially separated middle and late Eocene basins, the depocenters of which coincided with a preexisting WSW‐ENE trend. During Oligocene crustal extension the individual basins coalesced, resulting in the development of the SSW‐NNE striking Upper Rhine Graben. During the late Oligocene (Chattian) change in stress field, the Upper Rhine Graben was probably reactivated as a dextral strike‐slip system with the central graben segment forming a releasing bend. During the early Miocene (Aquitanian), a major reorientation of the regional stress field is held responsible for the main subsidence phase of the northern parts of the Upper Rhine Graben. This is reflected by a counterclockwise rotation and northeastward shift of the depocenter axis and later by the middle Miocene uplift and erosion of the southern parts of the Upper Rhine Graben. During the Plio‐Quaternary, the Upper Rhine Graben was reactivated as a sinistral strike‐slip system with the central graben segment forming a restraining bend.
The Transylvanian basin, transfer zone between coeval extending and contracting regions: Inferences on the relative importance of slab pull and rift push in arc–back arc systems
Authors: Huismans Ritske S. , Bertotti Giovanni
Published: October 2002

Structural analysis and paleostress fault slip inversion of the Transylvanian basin and its border regions with the surrounding East and South Carpathians and the Pannonian basin (e.g., the Apuseni Mountains) reveal at least two distinct tectonic phases for the Neogene evolution for the eastern part of the Pannonian basin system. Our main focus is on the role of the Transylvanian basin and its border regions in the Neogene as a transition zone between the extending Pannonian basin and the converging East and South Carpathians. The results provide constraints on the mechanisms responsible for as well the formation of the Transylvanian basin itself as on the relation between the basin‐formational processes operating in the Pannonian basin and the contractional history of the East and South Carpathian mountain belt. In the middle Miocene (17–14/12 Myr) the Transylvanian basin underwent E‐W extension coeval with the first and major phase of overall E‐W extension affecting the Pannonian basin and with submarine accretionary wedge tectonics in the East Carpathian arc. In the late Miocene to early Pliocene (12–8/6 Myr) the Transylvanian basin experienced a strong pulse of E‐W oriented shortening coeval with the climax of compression in the East Carpathians and a second rift phase affecting the Pannonian basin. Continued contractional deformation affected the Transylvanian basin during the Pliocene and Pleistocene with compression directions shifting to ESE‐WNW directions.
Counterclockwise rotation of the western Alps since the Oligocene: New insights from paleomagnetic data
Authors: Collombet M. , Thomas J. C. , Chauvin A. , Tricart P. , Bouillin J. P. , Gratier J. P.
Published: October 2002

A paleomagnetic study of Penninic units in the southern part of the Alpine arc has been carried out. More than 200 samples (23 sites) were collected in Briançonnais Ammonitico rosso limestones of the high Ubaye valley and the Ligurian Alps. A characteristic component of magnetization of reverse polarity was isolated on most of the sites. This component does not pass the fold test and is interpreted as a Tertiary overprint related to Alpine metamorphism. Mean directions in geographic coordinates are D = 121°, I = −52°, α95 = 11°, and D = 72°, I = −48°, α95 = 15° for the Ubaye and the Liguria localities, respectively, indicating large counterclockwise rotations about vertical axis of 68° and 117° relative to stable Europe. These rotations, in agreement with a previous study conducted in the Briançon area, together with other paleomagnetic data from the western Alps, show that the internal Alps suffered a large but nonhomogeneous counterclockwise rotation since the Oligocene. The rotations are in agreement with the combination of earlier separately proposed processes: the rotation of the Adriatic plate accounts for about 25° of rotation, remaining rotation and southward gradient would be related to left‐lateral shear accommodating the displacement between Adria and Europe at the southern border of the western Alps. Furthermore, the southward extrusion of the western Alps south of the Simplon fault zone may account for up to 10° of rotation. Rotations appear therefore as a major process accommodating deformation in the western Alps since the Oligocene.
Seismic anisotropy of the French Massif Central and predisposition of Cenozoic rifting and volcanism by Variscan suture hidden in the mantle lithosphere
Authors: Babuška Vladislav , Plomerová Jaroslava , Vecsey Luděk , Granet Michel , Achauer Ulrich
Published: October 2002

We model the structure of the lithosphere, its thickness, and seismic anisotropy caused mainly by systematic orientation of olivine crystals, from spatial variations of P wave delay times and the shear wave splitting observed at a dense network of mobile and permanent stations within the French Massif Central (MC). Three major lithosphere domains with different seismic anisotropy are distinguished. A suture in the deep lithosphere limits the thick lithosphere of the Limousin (western MC) characterized by a consistent anisotropic pattern with high velocities dipping to the west. The eastern MC, comprising two different domains with a weakened mantle fabric in the south, shows the high velocities dipping systematically to the east. The suture between the western and eastern MC parallels the major crustal boundary, the late Variscan Sillon Houiller transfer fault in the south and the Tauve‐Aigueperse fault in the north, with an offset of 10–20 km to the east. The offset of the crustal and mantle parts of the same suture indicates that the rigid upper crust might be detached from the mantle lithosphere. We suggest that the mantle suture, hidden beneath an allochthonous crust, was reactivated during the Cenozoic extension of the weakened and thinned lithosphere in the south of the eastern MC and predestined a space for the major volcanism (Mont Dore, Cantal). The rigid northern domain, characterized by a thicker lithosphere with a well‐preserved mantle fabric, reacted to the extension predominantly by rifting (e.g., Limagne and Roanne Grabens).
Fault structure and related basins of the North Aegean Sea and its surroundings
Authors: Koukouvelas Ioannis K. , Aydin Atilla
Published: October 2002

Fault structure and basin evolution in the northern Aegean Sea and its surroundings have been investigated using bathymetry, available onshore and offshore seismic profiles, onshore fault patterns from NE Greece, NW Turkey, three islands in the Aegean Sea, surface ruptures associated with the, 1978 Thessaloniki earthquakes, GPS measurements from North Aegean Islands and a number of earthquake focal plane solutions, and historic seismicity. Bathymetric and isopach data show that the North Aegean Trough can be divided into the Sporades basin and the Saros Trough. Post‐Miocene sediment thickness differences in these basins, offset of distinct horizons, and frequent seismicity along basin‐bounding faults indicate that sediment accumulation in the area is fault controlled. Offshore seismic profiles show that the basin‐bounding faults are dominantly characterized by apparent normal components as well as strike‐slip components inferred from typical fault zone profiles. Additional evidence for existence of strike‐slip faulting comes from earthquake focal plane solutions. We refined the pattern and kinematics of the faults controlling the basins and classified them into two major groups. The faults in the first group trend NE‐SW and ENE‐WSW and are here interpreted to be dominantly right‐lateral strike slip with normal or reverse components. These faults accommodate a similar amount of deformation like the Ganos fault and thus represent the westernmost extension of the North Anatolian fault zone. The faults in the second group trend NW‐SE and are dominantly normal faults with an occasional left‐lateral component. These faults are believed to manifest the termination of the North Anatolian fault zone. Because of the segmentation of the right‐lateral strike‐slip faults and the preexisting NE trending tectonic grain, the basins are compartmentalized into smaller depocenters. Basins are orientated with their long axes either parallel to the NE‐SW to ENE‐WSW trending echelon strike‐slip faults, or, in the zone north of the strike‐slip faults parallel to the NW‐SE trending normal faults. The interpretations regarding the kinematics of the faults are consistent with the data compiled from the islands near the faults and from the land in NE Greece and NW Turkey. The northern Aegean basins and their spatial relationships to the fault architecture representing the diffused termination of the North Anatolian fault system are consistent with the mechanical principles of the strike‐slip tectonics.
Flood frequency analysis: Evidence and implications of secular climate variability, New South Wales
Authors: Franks Stewart W. , Kuczera George
Published: October 2002

One of the assumptions of flood frequency analysis is that annual maximum flood peaks are independently and identically distributed. Recent work has shown there exist persistent climate modes that modulate regional climates over multiyear timescales around the globe. Such persistence raises the question whether annual maximum floods are indeed independently and identically distributed. This study revisits this assumption. Noting that a significant shift in Pacific and Indian Ocean sea surface temperatures and other atmospheric variables occurred in the mid‐1940s, 41 flood records in New South Wales, Australia, were stratified into pre‐1945 and post‐1945 records. It was found that the two‐parameter lognormal distribution adequately fitted the stratified samples, and in many cases the stratified distributions were significantly different. In fact, the ratio of the post‐1945 to the pre‐1945 20‐year flood exceeded one for 37 of the 41 sites. The evidence that the flood probability model is climate dependent for the case study region is strong. This has implications for flood risk assessment requiring inter alia the need to distinguish between short‐ and long‐term flood risk. In the presence of long‐term climate persistence, traditional flood frequency analysis can at best only provide estimates of long‐term or unconditional flood risk. The estimation of short‐term flood risks will require improved mechanistic understanding of multidecadal climate variability and the development of stochastic models that explicitly recognize such secular variations.
Evaluating a single‐class net deposition equation in overland flow conditions
Authors: Beuselinck Laurent , Hairsine Peter B. , Govers Gerard , Poesen Jean
Published: October 2002

The quantitative description of sediment transport across areas of net deposition is an essential part of assessing the off‐site effects of soil erosion on hillslopes. A new approach to describing sediment deposition across areas of net deposition, the single‐class Hairsine and Rose [1992a, 1992b] sediment deposition equation, is evaluated here using a series of controlled laboratory experiments. Hydraulic and sediment transport input parameters, sensitivity analysis, calibration using half the experimental data, and evaluation using the remaining data are presented. Simulations of overland flow hydraulics are evaluated using measured flow velocities. This evaluation shows that the Manning's equation gives a good estimate of flow velocities. Calibration is conducted by adjusting the fraction of stream power available for sediment (re)entrainment (F), and the threshold stream power below which no reentrainment occurs (Ωcr), to minimize the error between the simulated and the measured outflow sediment concentrations. The calibration runs show that the single‐class Hairsine et al. equation is very sensitive to the characteristic settling velocity adopted. The evaluation found that good simulations are obtained if appropriate threshold values are used. Incorporation of the reentrainment term significantly improves sediment outflow simulations above the threshold value.
Relative influence of natural watershed properties and human disturbance on stream solute concentrations in the southwestern Brazilian Amazon basin
Authors: Biggs Trent Wade , Dunne Thomas , Domingues Tomas Ferreira , Martinelli Luiz Antonio
Published: October 2002

We use a synoptic sampling of stream water to quantify the effect of soil type, rock type, deforestation extent determined by Landsat TM imagery, and urban population density on stream solute concentrations for 60 different watersheds in the dry season and 49 in the wet season in the southwestern Brazilian Amazon basin. Catchment areas range between 18 and 12,500 km2. Soil exchangeable cation content explains most of the variance in stream concentrations of cations, dissolved silicon (Si), and acid neutralizing capacity (ANC) in both forested and deforested basins based on regression analysis (R2 range 0.61–0.81), though the mechanism underlying the relationship is unknown. We use the relationship between soil exchangeable cation content and stream solute concentrations in forested catchments to estimate the predisturbance and postdisturbance signal concentrations of stream solutes for deforested watersheds. Signal concentrations of potassium (K), sodium (Na), and chloride (Cl) increase with deforestation extent for streams on gneiss, granite, and sedimentary rock in both the dry and wet seasons after the effect of soil type has been statistically removed. Sulfate (SO4) signal concentrations increase with deforestation extent in the dry season only. For catchments >40% deforested but with no urban populations, the ratios of disturbed to predisturbance stream concentrations range from 1.2 to 3.1 (K), 0.8 to 2.2 (Na), 0.7 to 2.7 (SO4), and 2.4 to 14.6 (Cl) in the dry season and 1.2 to 2.2 (K) and 0.6 to 3.4 (Cl) in the wet season. Urban population density strongly affects Cl and SO4 concentrations in both seasons and Na concentrations in the dry season; the urban signal comprises 40–58% of the dry season Cl signal and 83–89% of the wet season Cl signal for watersheds with >250 persons per km2. Streams on mica‐schist, mafic rock and carbonate shale have higher concentrations of Ca, Mg, Si, and ANC than watersheds on gneiss, granite, tertiary sediments or sandstone for a given soil exchangeable cation content in both seasons. Simple mass balance calculations suggest that supplemental cattle salts could comprise a significant fraction of the Na and Cl signals in the wet season but would not significantly impact wet season concentrations of Ca, Mg, or K.
Fluvial fan deltas: Linking channel processes with large‐scale morphodynamics
Authors: Sun Tao , Paola Chris , Parker Gary , Meakin Paul
Published: October 2002

Alluvial fan deltas are built by aggrading and avulsing river channels. A numerical model of flow and sediment transport in channels is combined with a condition for channel avulsion to describe evolution of the fan surface. The model combines elements of two recent approaches: (1) diffusional models of depositional basin filling, which describe the evolution of overall morphology, and (2) cellular models of channel evolution, which provide simplified descriptions of channel dynamics. Here the cellular formulation is used simply as a template for discretizing a standard set of equations describing flow and sediment transport within channels. The basic formulation is thus grid‐invariant, and the results are in actual rather than arbitrary time and length scales. The model captures the interaction between microscale (channel) morphodynamics, including converging and diverging flow and avulsion, and morphodynamics at the macroscale (fan). It provides a starting point for the study of a wide range of topics, including the three‐dimensional stratigraphy of fan delta deposits and the response of fan deltas to engineering activities.
Evolving interface between clean and nonaqueous phase liquid (NAPL)‐contaminated regions in two‐dimensional porous media
Authors: Imhoff Paul T. , Farthing Matthew W. , Gleyzer Simon N. , Miller Cass T.
Published: October 2002

We studied the dissolution of nonaqueous phase liquids (NAPLs) at residual saturation in two‐dimensional systems using physical and numerical experiments. In all cases, preferential dissolution pathways developed in the NAPL‐contaminated regions. A permeability feedback mechanism led to the formation of centimeter‐scale dissolution fingers in homogeneous porous media, while fingers up to 1 order of magnitude wider formed in media with heterogeneous distributions of intrinsic permeability k, when σ2(lnk) was large. The structure of the interface between the NAPL‐contaminated and NAPL‐free regions was examined as dissolution progressed. In all cases the interface was a self‐affine fractal. The scaling relationship of Family and Vicsek [1985] fitted the interface data from the numerical simulations reasonably well.
Pathways for nitrate release from an alpine watershed: Determination using δ15N and δ18O
Authors: Campbell Donald H. , Kendall Carol , Chang Cecily C. Y. , Silva Steven R. , Tonnessen Kathy A.
Published: October 2002

Snowpack, snowmelt, precipitation, surface water, and groundwater samples from the Loch Vale watershed in Colorado were analyzed for δ15N and δ18O of nitrate to determine the processes controlling the release of atmospherically deposited nitrogen from alpine and subalpine ecosystems. Although overlap was found between the δ15N(NO3) values for all water types (−4 to +6‰), the δ18O(NO3) values for surface water and groundwater (+10 to +30‰) were usually distinct from snowpack, snowmelt, and rainfall values (+40 to +70‰). During snowmelt, δ18O(NO3) indicated that about half of the nitrate in stream water was the product of microbial nitrification; at other times that amount was greater than half. Springs emerging from talus deposits had high nitrate concentrations and a seasonal pattern in δ18O(NO3) that was similar to the pattern in the streams, indicating that shallow groundwater in talus deposits is a likely source of stream water nitrate. Only a few samples of surface water and groundwater collected during early snowmelt and large summer rain events had isotopic compositions that indicated most of the nitrate came directly from atmospheric deposition with no biological assimilation and release. This study demonstrates the value of the nitrate double‐isotope technique for determining nitrogen‐cycling processes and sources of nitrate in small, undisturbed watersheds that are enriched with inorganic nitrogen.
Laboratory observations and mathematical modeling of colloid‐facilitated contaminant transport in chemically heterogeneous systems
Authors: Saiers James E.
Published: October 2002

In the work reported here, I examine colloid‐facilitated solute transport through a natural porous medium that exhibits grain‐scale heterogeneity in chemical composition. I conducted six column experiments using the contaminant hydroxyatrazine (HA) and either homogeneous clay‐colloid suspensions or mixtures of clay colloids and dissolved organic matter. The transport of colloids composed of illite and montmorillonite, although not conservative, is only slightly affected by rate‐limited mass transfer reactions with the oxide‐coated aquifer material. Coinjection of HA with monomineralogic suspensions of illite colloids produces modest increases in effluent concentrations of HA relative to experiments performed with colloid‐free influent solutions. Montmorillonite colloids have a much higher capacity to bind HA than illite colloids and substantially increase the transport rate of HA in the column experiments. Suwannee River humic acid (SRHA) does not strongly complex aqueous phase HA, but its addition to column influent mixtures that contain HA and montmorillonite suppresses HA adsorption to the clay colloids and promotes a decline in HA mobility. A model for colloid‐facilitated transport, formulated to account for nonuniformity in the kinetics of colloid deposition and HA adsorption, closely describes HA transport in experiments performed with monomineralogic clay‐colloid suspensions, heterogeneous suspensions made of both illite and montmorillonite, and mixtures of montmorillonite and SRHA.
Modes of response of a gravel bed river to meander straightening: The case of the Sainte‐Marguerite River, Saguenay Region, Quebec, Canada
Authors: Talbot Tracey , Lapointe Michel
Published: October 2002

In the 1960s, extensive meander straightening (rectification) was conducted along 8 km of the Sainte‐Marguerite River to facilitate highway construction along the valley bottom. Comparison of long profiles and data on bed pavement caliber from the current river channel and the man‐made oxbows sheds light on the multifaceted responses to this anthropogenic perturbation of the river over the last 4 decades: (1) reprofiling consisting of 1 m of bed incision in the upper 4 km coupled with 2 m of bed aggradation in the lower 2 km of the straightened reach; (2) a doubling of the caliber of bed pavement in the zone of maximum degradation; (3) regrowth of three meanders within the reach, increasing its length by 7% (400 m); and (4) net input of 4 × 104 m3 of valley‐side sediment from channel erosion into three terraces. Hydraulic and sediment transport reconstructions indicate that reprofiling and pavement coarsening over nearly 4 decades equally contributed to transport reequilibration along the reach, while meander regrowth and lateral sediment inputs from terraces played minor roles.
Using chemical, hydrologic, and age dating analysis to delineate redox processes and flow paths in the riparian zone of a glacial outwash aquifer‐stream system
Authors: Puckett Larry J. , Cowdery Timothy K. , McMahon Peter B. , Tornes Lan H. , Stoner Jeffrey D.
Published: October 2002

A combination of chemical and dissolved gas analyses, chlorofluorocarbon age dating, and hydrologic measurements were used to determine the degree to which biogeochemical processes in a riparian wetland were responsible for removing NO3−from groundwaters discharging to the Otter Tail River in west central Minnesota. An analysis of river chemistry and flow data revealed that NO3−concentrations in the river increased in the lower half of the 8.3 km study reach as the result of groundwater discharge to the river. Groundwater head measurements along a study transect through the riparian wetland revealed a zone of groundwater discharge extending out under the river. On the basis of combined chemical, dissolved gas, age date, and hydrologic results, it was determined that water chemistry under the riparian wetland was controlled largely by upgradient groundwaters that followed flow paths up to 16 m deep and discharged under the wetland, creating a pattern of progressively older, more chemically reduced, low NO3−water the farther one progressed from the edge of the wetland toward the river. These findings pose challenges for researchers investigating biogeochemical processes in riparian buffer zones because the progressively older groundwaters entered the aquifer in earlier years when less NO3−fertilizer was being used. NO3−concentrations originally present in the groundwater had also decreased in the upgradient aquifer as a result of denitrification and progressively stronger reducing conditions there. The resulting pattern of decreasing NO3−concentrations across the riparian zone may be incorrectly interpreted as evidence of denitrification losses there instead of in the upgradient aquifer. Consequently, it is important to understand the hydrogeologic setting and age structure of the groundwaters being sampled in order to avoid misinterpreting biogeochemical processes in riparian zones.
Groundwater flow to a horizontal or slanted well in an unconfined aquifer
Authors: Zhan Hongbin , Zlotnik Vitaly A.
Published: October 2002

New semianalytical solutions for evaluation of the drawdown near horizontal and slanted wells with finite length screens in unconfined aquifers are presented. These fully three‐dimensional solutions consider instantaneous drainage or delayed yield and aquifer anisotropy. As a basis, solution for the drawdown created by a point source in a uniform anisotropic unconfined aquifer is derived in Laplace domain. Using superposition, the point source solution is extended to the cases of the horizontal and slanted wells. The previous solutions for vertical wells can be described as a special case of the new solutions. Numerical Laplace inversion allows effective evaluation of the drawdown in real time. Examples illustrate the effects of well geometry and the aquifer parameters on drawdown. Results can be used to generate type curves from observations in piezometers and partially or fully penetrating observation wells. The proposed solutions and software are useful for the parameter identification, design of remediation systems, drainage, and mine dewatering.