bluuebunny/crossref_metadata_2025 huggingface dataset:
FASoft: A system for discrete channel frequency assignment
Authors: Hurley S. , Smith D. H. , Thiel S. U.
Published: February 2004

This paper describes a system, FASoft, for discrete channel frequency assignment. In practice, the assignment of frequencies in a network of compatible equipment is often done manually or by the use of a single computational technique. FASoft incorporates state‐of‐the‐art heuristics, sequential assignment algorithms, and a maximal clique algorithm to aid in the assignment process. Lower bounding procedures are included into the system to assess the performance of the assignment techniques and to provide an assessment of how close a particular assignment is to the optimal. The results show that FASoft produces optimal solutions to several practical examples.
Day‐to‐day variability in the occurrence of equatorial and low‐latitude scintillations in the Indian zone
Authors: Dabas R. S. , Lakshmi D. R. , Reddy B. M.
Published: February 2004

Nighttime ionospheric scintillation data at 4 GHz, recorded simultaneously (during September and October of 1989) from two satellites at Sikandarabad (dip 42.0°N) and Chenglepet (dip 10.5°N), along a common magnetic meridian (149.0°E), are analyzed. Scintillation occurrences on a daily basis at these two locations are examined in relation to presunset hour variations in h′F and their rate of rise, as well as with solar and magnetic activity conditions. The main objective of the study is to identify the ionospheric conditions over the magnetic equator necessary for observing intense gigahertz scintillation at 21°N magnetic latitude. The characteristics and occurrence pattern of scintillations at these two stations suggest that they are equatorial plasma bubble induced events. The scintillations and spread F at the equatorial location occur whenever h′F rises to levels of more than 400 km during evening hours. However, at 21°N magnetic latitude, scintillations were observed only on those nights when h′F rises to more than 500 km with dh′F/dt of 30 m/s or more. Also, whenever h′F was less than 400 km, no scintillations were observed at any of the locations. Scintillation activity was found to be inhibited during magnetic disturbances at both the locations except during postmidnight hours, where it is found to increase. With increasing magnetic activity, h′F values during evening hours decrease. The day‐to‐day variability in the occurrence of scintillations seems to be controlled mainly by the electric field, neutral winds, and magnetic activity. Scintillation intensity at low latitudes is found to be positively correlated with ionospheric electron content values observed during evening hours (2000 LT), as well as with their diurnal maximum values. In addition, scintillation intensity is also found to be dependent on the geometries of the ray paths to the respective locations and their intersections with the magnetic field lines.
A combined natural orthogonal functions/neural network technique for the radiometric estimation of atmospheric profiles
Authors: Frate Fabio Del , Schiavon Giovanni
Published: February 2004

An inversion technique is presented for retrieving vertical profiles of atmospheric temperature and vapor from the brightness temperatures measured by a ground‐based multichannel microwave radiometer and the surface measurements of temperature and relative humidity. It combines a profile expansion over a complete set of natural orthogonal functions with a neural network which performs the estimate of the coefficients of the expansion itself. A simulation study has been carried out, and the algorithm has been tested by comparing its retrievals with those obtained by means of linear statistical inversion applied on the same data sets. The analysis has been limited to the case of profiles with clouds in order to test the ability of the neural network to face nonlinear problems. The technique has proven to be flexible, showing a good capability of exploiting information provided by other instruments, such as a laser ceilometer. A fault tolerance evaluation has also been considered, which showed interesting properties of robustness of the algorithm.
A novel impedance‐tuned monopole antenna
Authors: Wagner Keely A. , Gearhart Steven S.
Published: February 2004

The insertion of coplanar stubs within printed strip monopole antennas allows for tuning of resonant frequencies and corresponding impedances. Manipulation of stub and antenna dimensions allows the creation of antennas with a single impedance‐matched resonance or with two matched resonances with a specified frequency ratio.
Randomization of alternating codes: Improving incoherent scatter measurements by reducing correlations of gated autocorrelation function estimates
Authors: Lehtinen M. S. , Huuskonen A. , Markkanen M.
Published: February 2004

Incoherent scatter radar autocorrelation function estimates produced by alternating codes are found to contain significant correlations between different lags and different heights. While no correlations are caused by the background thermal noise, the special structure of the alternating code sequences causes clutter or the self‐noise contribution of the codes themselves to introduce maximal positive correlations between the different lag estimates. Because of this, postintegration of adjacent heights does not improve the results as much as could be expected. For a high signal‐to‐noise ratio, alternating code results are worse than estimates produced by similar random codes. In this paper we show that we can correct the situation by randomizing the alternating codes. This is accomplished by multiplying each alternating code sequence in the alternating code cycle by a fixed random‐looking sequence. This multiplying sequence can be changed and randomly chosen at the end of each alternating code cycle. The multiplying sequence can also be kept constant with almost equally good results. If this is done, the special structure of the alternating code sequences actually causes the correlations to become less than the correlations produced by random codes. The improvement in accuracy is discussed in various situations. The reasons for the appearance of maximal positive correlations with alternating codes are explained in a mathematical appendix.
Development of a high‐stability water vapor radiometer
Authors: Tanner Alan B.
Published: February 2004

Preliminary design details and laboratory test results of a prototype microwave radiometer operating near 20 GHz are presented. Radiometric stability to 10 millikelvin on time scales from 100 to 10,000 s is the goal for the final system. The use of noise diodes as receiver gain calibrators is examined, and test results showing 30 parts per million stability per day in the intercomparison of noise diodes are presented. Temperature control of the radiometer is also examined, and the design of a solid state temperature control system capable of 1 mK stability near room temperature is presented. A new design for a mechanically actuated Dicke switch is also presented. The results of these laboratory developments are applied to a prototype radiometer. Early indications are that design goals are being met in the prototype. Future confirmation of the system's theoretical performance will only be possible with the completion of the final radiometer units.
A combined radiative transfer model for sea ice, open ocean, and atmosphere
Authors: Fuhrhop Rolf , Grenfell Thomas C. , Heygster Georg , Johnsen Klaus‐Peter , Schlüssel Peter , Schrader Meeno , Simmer Clemens
Published: February 2004

A radiative transfer model to compute brightness temperatures in the microwave frequency range for polar regions including sea ice, open ocean, and atmosphere has been developed and applied to sensitivity studies and retrieval algorithm development. The radiative transfer within sea ice is incorporated according to the “many layer strong fluctuation theory” ofStogryn[1986, 1987] and T. Grenfell [Winebrenner et al., 1992]. The reflectivity of the open water is computed with the three‐scale model ofSchrader[1995]. Both surface models supply the bistatic scattering coefficients, which define the lower boundary for the atmospheric model. The atmospheric model computes the gaseous absorption by theLiebe et al.[1993] model. Scattering by hydrometeors is determined by Mie or Rayleigh theory. Simulated brightness temperatures have been compared with special sensor microwave imager (SSM/I) observations. The comparison exhibits shortcomings of the ice model for 37 GHz. Applying a simple ad hoc correction at this frequency gives consistent comparison results within the range of observational accuracy. The simulated brightness temperatures show the strong influence of clouds and variations of wind speed over the open ocean, which will affect the sea ice retrieval even for an ice‐covered ocean. Simulated brightness temperatures have been used to train a neural network algorithm for the total sea ice concentration, which accounts for these effects. Sea ice concentrations sensed from the SSM/I data using the network and the NASA sea ice algorithm show systematic differences in dependence on cloudiness.
Stratosphere‐troposphere ozone exchange observed with the Indian MST radar and a simultaneous balloon‐borne ozonesonde
Authors: Mandal T. K. , Cho J. Y. N. , Rao P. B. , Jain A. R. , Peshin S. K. , Srivastava S. K. , Bohra A. K. , Mitra A. P.
Published: February 2004

The stratosphere‐troposphere (ST) mode operation of the Indian mesosphere‐stratosphere‐troposphere (MST) radar provided evidence of multiple stable layer structures near the tropopause and also of its “weakening” during late night hours on several occasions. Mass exchange can take place between the troposphere and the stratosphere during periods of such weakening. To examine whether there is any transport of ozone from the stratosphere to the troposphere at the time of tropopause weakening at tropical latitudes, simultaneous observations were carried out using the Indian MST radar located at Gadanki (13.5°N, 79.2°E), now fully operational in MST mode, and ozonesonde flights from Trivandrum (8.9°N, 76.6°E). Four campaigns of simultaneous observations were conducted during January 3–8, November 9–16, and December 5–10, 1994, and June 7–24, 1995. The results show occurrence of the tropopause weakening several times during January 3–8, November 9–16, and December 5–10, 1994. Simultaneous observations of ozone profiles, particularly on January 7–8, November 10 and 16, and December 7–8, 1994, the days of tropopause weakening, show evidence of a decrease in stratospheric ozone and a corresponding increase in tropospheric ozone after this event, the total ozone remaining essentially constant on these days with respect to other days. Tropopause weakening on January 4–5, 1994, however, does not show any considerable change in the ozone profiles. The results are presented here relating the degree of tropopause weakening to the extent of vertical mass exchange between the troposphere and the stratosphere. An effort has been made to examine the role of horizontal advection of ozone in increasing tropospheric ozone at the region of interest; the geographical distribution of tropospheric ozone residual (TOR) has been analyzed by the two data sets obtained independently from Meteor 3 total ozone mapping spectrometers (Meteor 3 TOMS) and the Upper Air Research Satellite (UARS). Simultaneously, the possibility of horizontal transport of ozone from the areas surrounding Tirupati and Trivandrum in increasing tropospheric ozone due to synoptic scale circulation has also been verified by close inspection of synoptic weather charts at 1000, 700, 500, and 300 hPa obtained from the National Center for Medium‐Range Weather Forecasting general circulation model at 0000 and 1200 UTC on January 7 and 0000 and 1200 UTC on January 8, 1994.
Radiometric profiling of temperature, water vapor and cloud liquid water using various inversion methods
Authors: Solheim Fredrick , Godwin John R. , Westwater E. R. , Han Yong , Keihm Stephen J. , Marsh Kenneth , Ware Randolph
Published: February 2004

We have developed a tunable temperature profiler based on a highly stable synthesizer that can observe at multiple frequencies on the shoulder of the 60‐GHz atmospheric oxygen feature. We are developing a similar radiometer to obtain the vertical distribution of water vapor by making observations on the pressure‐broadened water vapor line from 22 to 29 GHz. Information on cloud liquid water profiles is also contained in these two wave bands. Various mathematical retrieval methods for temperature, water vapor, and cloud liquid water profiles were tested based on these radiometer designs. These include neural networking, Newtonian iteration of statistically retrieved profiles, and Bayesian “most probable” retrievals. On the basis of realistic radiometer errors and performance, very good retrieval capability is demonstrated. The performance of the various retrieval methods are presented and compared. Examples of profile retrievals are also presented. Data were not binned into seasons to reduce computer time; better retrieval results for all methods would be expected with binning.
Canada Basin, Arctic Ocean: Evidence against a rotational origin
Authors: Lane Larry S.
Published: February 2004

The most widely accepted model for the opening of Canada Basin invokes 66° of counterclockwise rotation of Arctic Alaska and Chukotka away from the Canadian Arctic in Early Cretaceous time. Late Paleozoic structural trends and paleogeography have been used in support of the rotation hypothesis. Recent refinements in the ages of Paleozoic tectonic events in Arctic Alaska, Yukon, and the Canadian Arctic Islands provide new controls on correlations of late Paleozoic paleogeography and raise doubts about whether the Paleozoic tectonics of the Arctic Alaska‐Yukon region necessitate a rotational reconstruction of Arctic Alaska against the Canadian Arctic Islands. A rotational restoration of Arctic Alaska requires the Alaskan and Canadian margins to be conjugates of comparable age and evolution. The rift‐drift transition age for the Alaskan margin is most likely Hauterivian (Early Cretaceous), but for the Canadian Arctic margin it is most likely post‐Albian (mid‐Cretaceous). Crustal structure data from the Beaufort Sea continental margin in Canada define a rifted margin segmented by fracture zones which constrain the kinematics of ocean spreading to be northwestward, perpendicular to that required by the rotation hypothesis but subparallel to that suggested by seismic velocity anisotropy in the upper mantle. The Alaska‐Chukotka rotation hypothesis also fails to account for up to 600 km of continental overlap upon restoration of 66° of rotation and the absence of any accommodating contractional structures in northern Yukon and adjacent Northwest Territories. Because the Alaska‐Chukotka rotation hypothesis fails to account for much of the available data, senous doubt is cast on its viability. An existing multistage tectonic model for the evolution of Canada and Makarov basins is summarized as an example of a model which can account for the existing data.
Paleomagnetic evidence for rapid vertical‐axis rotations during thrusting in an active collision zone, northeastern Papua New Guinea
Authors: Weiler Peter D. , Coe Robert S.
Published: February 2004

A paleomagnetic study of three thrust sheets of the fold and thrust belt north of the Ramu‐Markham Fault Zone (RMFZ) indicates very rapid vertical‐axis rotations, with differential declination anomalies related to tectonic transport of thrust units. Data from this investigation indicate depositional ages straddling the Brunhes‐Matuyama reversal (780 ka) for the Leron Formation in Erap Valley. Net counterclockwise, vertical‐axis rotations as great as 90° since 1 Ma have occurred locally in the Erap Valley area. These rotations appear to be kinematically related to shear across a tear fault within the foreland fold and thrust belt of the colliding Finisterre Arc, which in turn is aligned with and may be structurally controlled by a major fault in the lower plate. These data indicate that vertical‐axis rotations occurred during thrusting; consequently, the actual rotation rate is likely several times higher than the calculated minimum rate. Such very rapid rotations during thrust sheet emplacement may be more common in fold and thrust belts than is presently recognized. Anisotropy of magnetic susceptibility data yields foliated fabrics with subordinate, well‐grouped lineations that differ markedly in azimuth in the three thrust sheets. The susceptibility lineations are rendered parallel by the same bedding‐perpendicular rotations used to restore the paleomagnetic remanence to N‐S thus independently confirming the rapid rotations. The restored lineations are perpendicular to the direction of tectonic transport, and the minimum susceptibility axes are streaked perpendicular to the lineation. We interpret these anisotropy of magnetic susceptibility data as primary sedimentary fabrics modified by weak strain accompanying foreland thrusting.
Contrasting styles of superposed deformation in the southernmost Andes
Authors: Klepeis Keith A. , Austin James A.
Published: February 2004

Brittle fault arrays, regional structural patterns, and marine multichannel seismic reflection profiles across the Magallanes basin near 53°S latitude show contrasting styles of superposed extensional, contractional, and transtensional deformation. Below the northeastern end of a NE‐SW transect of the basin, seismic reflection profiles show deepening levels of pre‐Late Jurassic basement and Upper Jurassic to Lower Cretaceous volcanic horizons toward the southwest. This trend is associated with apparent normal fault offsets that may be attributed to a widespread Late Jurassic‐Early Cretaceous extensional event. Contrastingly, below the southwestern end of Magallanes basin subsurface depths of basement and volcanic horizons shallow to the southwest. Integration of seismic reflection data with published seismic refraction data, geologic mapping, and satellite gravity anomaly data suggest that this shallowing trend is controlled structurally by craton‐vergent, basement‐involved contractional deformation. This style of shortening contrasts with thin‐skinned styles of thrusting in the northern and central parts of the basin on Tierra del Fuego. Structural relationships, stratigraphic data, and previously published metamorphic data indicate that basement‐involved contraction occurred during latest Cretaceous to early Tertiary time. Overprinting all contractional structures, steep Tertiary strike‐slip and oblique‐slip faults in the central and southern parts of the Magallanes basin display oblique‐normal (mostly down‐to‐the‐southwest) offsets across WNW‐ESE trending segments of the South American‐Scotia transform plate boundary on the South American continent. Newly discovered features along the plate boundary segment include sediment‐filled grabens and half grabens up to 7 km wide that occur between subparallel fault splays in the Magallanes fault zone. Kinematic analyses of fault‐slip data indicate that sinistral transtensional motion occurred within this fault zone between the eastern arm of the Straits of Magellan and central Tierra del Fuego. Together these data indicate that (1) the southernmost Andes were under compression during rapid cooling and exhumation of unique high‐pressure (∼8 kbars) basement rocks now exposed in the Darwin Metamorphic Complex (DMC) near 55°S latitude and (2) final exhumation of basement rocks in the DMC occurred during a shift away from compression toward transtension during late Tertiary crustal relaxation. We suggest that preexisting structural anisotropies formed during basement‐involved contractional deformation and the initiation of seafloor spreading south of South America during the Oligocene controlled late Tertiary sinistral transtensional patterns in the Magallanes fault zone.
Controls of erosional denudation in the orogen on foreland basin evolution: The Oligocene central Swiss Molasse Basin as an example
Authors: Schlunegger Fritz , Jordan Teresa E. , Klaper Eva Maria
Published: February 2004

A high‐resolution three‐dimensional reconstruction of the 25‐m.y.‐old central Swiss Molasse Basin reveals two sedimentary domains separated by a ∼5‐km‐wide flood‐plain. The proximal domain of the basin attained a width of 20 km, and its basement is steeply flexed (6°‐7° dip). Petrographic data indicate that it was filled by sediment from the Rigi dispersal system derived from the central Alps of eastern Switzerland and by locally sourced bajadas. In contrast, the distal sedimentary domain, located farther north, was gently dipping (<2°) and was filled by the meandering Lac Léman and Honegg dispersal systems. Chronological data reveal that sedimentation in the northern proximal part of the basin started at ∼27 Ma, when sediment supply to the basin started to increase. Deflection of the foreland plate at ∼25 Ma is successfully simulated by flexural modeling of the thrust load and the sediment load. The model reveals that the Lac Léman and Honegg dispersal systems are located on a buried flexural bulge. Furthermore, it shows that burial and suppression of the flexural bulge at ∼27 Ma as well as an increase of the basin wavelength were controlled by the contemporaneous increase in the sediment supply rate of the Rigi system. The model presented suggests that the tectonic subsidence of the Molasse Basin was mainly controlled by tectonic events in the northern part of the orogen, within ∼70 km distance from the tip of the orogenic wedge. Crustal thickening in this part of the orogen is reflected in the proximal Molasse by sedimentary cycles characterized by an increase in the sediment accumulation rates up section and by the presence of locally sourced bajada fans at the top of each cycle. Although south vergent back thrusting along the Insubric Line ∼150 km south of the foreland basin contributed little to flexure, it resulted in an increase of the sediment supply to the foreland basin. This is reflected in the Molasse by coarsening and thickening upward trends, an increase of the basin wavelength, basinward shifts of the depocenters of the dispersal systems, and uplift and erosion of the proximal basin border.
Extensional styles and gravity anomalies at rifted continental margins: Some North Atlantic examples
Authors: Keen C. E. , Dehler S. A.
Published: February 2004

Regional isostatic adjustment of the buoyancy forces created by lithospheric stretching during rifting is used to predict the crustal structure and gravity anomalies across rifted continental margins. Following earlier studies, we assume that stretching and necking of the lithosphere occurs around a “depth of necking,” which is the level of no vertical motion in the absence of gravitational forces. Differences in the depth of necking, coupled with lateral variation in flexural rigidity, can account for many of the variations in tectonic style observed across rifted continental margins and associated rifted basins. We investigate here seven transects crossing the rifted margin around the North Atlantic which display considerable variations in subsidence, crustal thickness variations, and gravity signatures. These are located where high‐quality seismic data are available as a constraint. Two conjugate margin segments are included to test for asymmetry in depth of necking which might be evidence of a simple shear mode of extension. Results suggest that both shallow (3 to 10 km) and deep (20 to 25 km) depths of necking occur. The depth of necking appears to be related to the intrinsic strength maximum within the lithosphere, rather than to the depth of preexisting structure. Shallower depths of necking may result from heating of the lithosphere during extension which decreases the depth of maximum strength. Deeper depths of necking may occur when the rates of extension are low and significant heating of the lithosphere does not occur. The depth of necking on at least one margin transect gives results very similar to a locally (Airy) compensated model, even though the lithosphere exhibits finite strength. Both conjugate margin segments display shallow depths of necking and favor a pure shear rather than a simple shear mode of extension.
Three‐dimensional elastic wave velocity structure of the Hualien region of Taiwan: Evidence of active crustal exhumation
Authors: Lin Cheng‐Horng , Yeh Yih‐Hsiung , Yen Horng‐Yuan , Chen Kou‐Cheng , Huang Bor‐Shouh , Roecker Steven W. , Chiu Jer‐Ming
Published: February 2004

The Hualien region of Taiwan is located at a complex transition of the boundary between the Eurasian and Philippine Sea Plates. To the southwest, the mountains of Taiwan are uplifting rapidly as a consequence of an ongoing arc‐continent collision, while to the east the oceanic Philippine Sea Plate is subducting northward beneath Eurasia. We investigated the structure and dynamics of this region by analyzing seismograms of local earthquakes recorded during a deployment of the Portable Array for Numerical Data Acquisition II network. P and S wave velocity structures deduced from travel time tomography analysis show that the collisional suture to the south of Hualien is characterized by a narrow (< 10 km width), near vertically dipping zone of low velocities that extends to depths in excess of 20 km. Velocities in the Eastern Central Range west of the suture zone are significantly higher and define a feature 10–15 km wide that appears to be continuous from the near surface to depths as great as 40 km. Farther to the west beneath the Western Central Range, the velocities again decrease. Focal mechanisms of local earthquakes show that while thrust faulting is the predominate mode of deformation throughout the region, normal faulting occurs as well beneath the Eastern Central Range. Thus the rapid uplift of the mountains of Taiwan may be a result not only of compressional shortening but also of an excess of positive buoyancy. We suggest that the higher velocities and extensional mechanisms in the Eastern Central Range are caused by the ongoing exhumation of previously subducted continental crust, while the lower velocities to the west reflect continued underthrusting of the crust beneath the Eastern Central Range.
On uplift and exhumation during convergence
Authors: Stüwe Kurt , Barr Terence D.
Published: February 2004

A simple kinematic model is used to illustrate the vertical motions of rocks during convergent deformation and erosion at the surface. It is shown that rocks may move upward or downward in the crust, depending on the relative rates of erosion and thickening and depending on their initial depth in the crust. Exhumation during thickening can only occur if rapid denudation accompanies the thickening process. During homogeneous thickening with erosion that is elevation dependent, the initial depth from which rocks can be exhumed is only determined by the density distribution in the column and is independent of erosion or thickening rates. The maximum initial depth, from which rocks can be exhumed, is of the order of 30 km or less. There is therefore no conflict in the observation of synchronous exhumation and convergent deformation if the peak pressure of rocks is equivalent to no more than 30 km of burial. It is also shown that uplift (defined as vertical motion of the surface with respect to a reference level, for example the geoid) and exhumation (defined as vertical motion of rocks with respect to the surface) may follow different patterns in time and that the difference between the two evolutions may be a useful indicator of the exhumation process. The model serves to emphasize the important differences between uplift and exhumation which are often not distinguished in the literature.
Paleomagnetic evidence that the central block of Salinia (California) is not a far‐traveled terrane
Authors: Whidden Katherine J. , Lund Steve P. , Bottjer David J. , Champion Duane , Howell David G.
Published: February 2004

New paleomagnetic results from Late Cretaceous (75–85 m.y.) red beds on the central block of Salinia indicate that Salinia was located within 6° (in latitude) of its current cratonal North American position during the Late Cretaceous (after correction for Neogene San Andreas Fault transport). The red beds formed as alluvial‐fan overbank deposits with hematite cement deposited directly on Salinian granites in the La Panza Range. Paleomagnetic analysis shows two components of magnetization in the red beds, a low‐blocking‐temperature present‐day overprint residing in goethite and a high‐blocking‐temperature (>600°) component residing in hematite. The hematite magnetization is a chemical remanent magnetization which formed soon after deposition during pedogenesis. The bedding‐corrected hematite remanence contains a magnetic polarity stratigraphy with antipodal normal and reversed directions. Twenty‐three Class I sites (α95 < 20°) have an average hematite direction with inclination =54.4° and declination = 18.2° (α95 = 6.1°) after structural correction. These paleomagnetic data suggest that Salinia resided at about 35°N latitude during the Late Cretaceous, within 6° of its current location adjacent to cratonal North America. By contrast, a summary of paleomagnetic data from the Peninsular Ranges terrane and the Sur‐Obispo terrane, which are currently outboard of Salinia, shows northward transport of these terranes of 12° to 22° relative to their current locations in North America since the Cretaceous. The offsets increase systematically away from the craton with the most outboard Sur‐Obispo terrane (which is composed of accretionary prism and distal forearc material) showing the largest degree of northward translation.
Deep structure of the continental lithosphere in an unextended orogen: An explosive‐source seismic reflection profile in the Urals (Urals Seismic Experiment and Integrated Studies (URSEIS 1995))
Authors: Steer David N. , Knapp James H. , Brown Larry D. , Echtler Helmut P. , Brown Dennis L. , Berzin Robert
Published: February 2004

Explosive‐source near‐vertical seismic reflection data from the Urals Seismic Experiment and Integrated Studies (URSEIS) profile displays an image of orogenic lithosphere to depths of 225 km. The reflective crustal section is characterized by dipping, crustal‐scale shear zones, and a pronounced crustal root that show no evidence of overprinting by extension and are preserved since late Paleozoic collision. Toward the east, the Uralian crustal root is composed of a partially subducted volcanic arc, while to the west it has affinity with the East European platform. The reflection character of the Moho varies across tectonic strike and implies that the Moho (1) acted as a structural detachment beneath the Trans‐Uralian Zone, (2) forms a tectonic boundary between terranes beneath the East Uralian Zone, (3) consists of a transitional zone from eclogitized lower crust to peridotitic upper mantle in the crustal root, (4) is a 3–9 km thick reflective zone beneath the fold and thrust belt, and (5) is a boundary <200 m thick in the west. Mantle reflections at 80–100 km depth (22–24 s) may represent a continuation of the Main Uralian fault into the subcrustal lithosphere. Alternatively, these reflectors may signify Paleozoic or younger mantle shear zones or the top of a zone of partial melting in the upper mantle. Deeper mantle reflections at 140–160 km (35–45 s) and 225 km (55 s) may image mafic intrusions at the base of the lithosphere or along localized shear zones in the upper mantle.
Collisional melange development: Geologic associations of active melange‐forming processes with exhumed melange facies in the western Banda orogen, Indonesia
Authors: Harris R. A. , Sawyer R. K. , Audley‐Charles M. G.
Published: February 2004

Analysis of block assemblages, matrix clay mineral composition and microfauna, and offshore seismic reflection profiles reveal that the Bobonaro melange in the Timor region is sourced from mud‐rich Australian continental margin sequences that are remobilized during accretion and form various facies depending on the structural conditions of emplacement. Melange facies include broken formation, matrix‐rich mud injections, and classic mixed block‐in‐clay facies. Each of these are distinguished by varying degrees of remobilization, mixing, and dispersion at different structural positions across the orogenic wedge. The most important structural control is whether melange was generated beneath or in front of upper plate Banda forearc basement (Banda Terrane). At the present collisional deformation front in the Timor trough, seismic reflection profiles show that melange forms mostly by stratal detachment and fluid‐assisted remobilization above a basal decollement propagating laterally along overpressured Jurassic to Cretaceous clay‐rich sequences of the distal Australian continental margin. The broken, clay‐rich material injects upward through faults to form intrusive bodies at the base of slope cover sediment to form mud ridges at the surface. Similar patterns of stratal disruption are exposed onshore in the Pliocene Kolbano fold and thrust wedge of southern Timor, which is structurally contiguous with the Timor trough deformation front. Melange in the Kolbano Mountains is mostly broken formation and matrix‐rich injections of mud from Jurassic and Cretaceous units. Deformation mechanisms include intense layer‐parallel extension associated with emplacement by mud diapirs that rise from near the decollement upward to the surface along fault conduits. In the hinterland of the orogenic wedge (East Timor and northern West Timor), melange is dominantly of mixed block‐in‐clay facies with large blocks derived from roof thrust sheets of intermixed Banda Terrane and Maubisse Formation units. At the structural base of these thrust sheets is the Sonnebait Disruption Zone (SDZ), which formed the initial suture between the Banda Terrane and structurally underthrust Australian continental margin sequences during the late Miocene to early Pliocene. The thickest accumulations of mixed block‐in‐clay melange in the Timor region are found at the southern edge (outlet) of the SDZ, near the Central and Viqueque synorogenic basins. The extent of block dispersion and mixing in the SDZ is indicative of intense shear strains perhaps induced by an oversupply of accretable material when the suture zone was clogged by underthrusting of the Australian continental margin.
Seven million years of strike‐slip and related off‐fault deformation, northeastern Marlborough fault system, South Island, New Zealand
Authors: Little Timothy A. , Jones Andrew
Published: February 2004

The Marlborough fault system (MFS), South Island, New Zealand is remarkable for the oblique‐slip nature of its active faulting and can be placed in a framework of Pacific‐Australian (Pac‐Aus) plate motions and geodetic strain. New Zealand illustrates changing degrees of upper plate slip partitioning in an obliquely convergent margin that varies along strike in crustal type and subduction geometry. In this paper, we focus on the NE part of this transcurrent fault system, especially the Awatere fault, which is the only Marlborough fault to offset a major Neogene basin. Strike slip on an ancestral eastern strand of this fault began after ∼7.4–6.4 Ma; later vertical axis rotation may have caused it to be abandoned in favor of the currently active strand. Since ∼7 Ma, at least 34±10 km of dextral slip has accrued on the Awatere fault, <6 km of slip has accrued on two nearby strands, and <4 km has accrued on the currently active coastal strand. Comparison of Miocene with late Quaternary offsets suggests that rates of strike slip on the fault have been nearly constant or have possibly decelerated. We interpret spatial and temporal patterns of strike slip in the MFS to reflect southward migration of transform motion resulting from increased Pac‐Aus plate convergence. Late Neogene to present‐day shortening directions in NE South Island are indicative of a partially slip‐partitioned margin. Slip partitioning diminishes southward as the underlying subduction interface becomes strongly coupled, suggesting a simple mechanical relationship between these processes.
Intrinsic biodegradation of MTBE and BTEX in a gasoline‐contaminated aquifer
Authors: Borden Robert C. , Daniel Robert A. , LeBrun Louis E. , Davis Charles W.
Published: February 2004

Three‐dimensional field monitoring of a gasoline plume showed rapid decay of toluene and ethylbenzene during downgradient transport with slower decay of xylenes, benzene, and MTBE under mixed aerobic‐denitrifying conditions. Decay was most rapid near the source but slower farther downgradient. Effective first‐order decay coefficients varied from 0 to 0.0010 d−1 for MTBE, from 0.0006 to 0.0014 d−1 for benzene, from 0.0005 to 0.0063 d−1 for toluene, from 0.0008 to 0.0058 d−1for ethylbenzene, from 0.0012 to 0.0035 d−1 for m‐, p‐xylene, and from 0.0007 to 0.0017 d−1 for o‐xylene. Laboratory microcosm studies confirmed MTBE biodegradation under aerobic conditions; however, the extent of biodegradation was limited.
Pump‐and‐treat optimization using well locations and pumping rates as decision variables
Authors: Huang Changlin , Mayer Alex S.
Published: February 2004

A new optimization formulation for dynamic groundwater remediation management is developed by simultaneously using well locations and the corresponding pumping rates as the decision variables. The genetic algorithm is applied to search for optimal pumping rates and the discrete space of well locations. The optimization model is applied to hypothetical, three‐dimensional, contaminated aquifer systems with homogeneous and heterogeneous porous media properties. Optimal well locations and pumping rates obtained with the moving‐well model are less expensive than solutions obtained with a comparable fixed‐well model. Optimization with a linear objective function formulation identifies some of the optimal well locations obtained with a nonlinear formulation but results in higher pumping rates than the nonlinear formulation and ignores the higher drawdowns produced in low‐permeability areas. Optimal well locations are found along the mass centerline of the contaminant plumes and in high‐permeability areas in the heterogeneous system. Dynamic pumping rates and well locations produce more cost‐effective solutions relative to a static model. The well location search path and convergence behavior indicate that the genetic algorithm is an effective alternative solution scheme and that well location optimization is more important than pumping rate optimization.
Seasonal patterns in streamwater nutrient and dissolved organic carbon concentrations: Separating catchment flow path and in‐stream effects
Authors: Mulholland Patrick J. , Hill Walter R.
Published: February 2004

Distinct seasonal patterns in streamwater nutrient and dissolved organic carbon (DOC) concentrations are evident in the data record from 7 years of weekly sampling in the West Fork of Walker Branch (WB) and 4 years of weekly sampling in a nearby stream, upper White Oak Creek (WOC), both first‐order streams in the Ridge and Valley Province of eastern Tennessee. Concentrations of NO3 and soluble reactive phosphorus (SRP) in both streams showed a repeated pattern of annual maxima in summer and biannual minima in autumn and spring. Concentrations of DOC in WB exhibited distinct autumn maxima. To determine whether temporal variations in catchment hydrological processes could explain the seasonal nutrient and DOC variations in WB, we used an end‐member mixing analysis involving Ca and SO4 concentrations to separate stream discharge into three catchment flow paths of differing nutrient concentrations. Stream NO3, SRP, and DOC concentrations were predicted solely on the basis of temporal variation in the importance of these flow paths and measurements of nutrient concentrations for the different flow paths. Ratios of observed/predicted concentrations in stream water near 1.0 suggested that catchment effects alone explained streamwater concentrations, whereas ratios substantially different from 1.0 suggested that in‐stream processes were important determinants of streamwater concentrations. Observed/predicted NO3 and SRP concentration ratios showed repeated annual patterns with values closer to 1.0 during winter and summer (generally 0.8–1.2) and minima (<0.6) in spring and autumn, suggesting substantial in‐stream net uptake at these times. Observed/predicted DOC concentration ratios were more variable and generally ≥1 but did show consistent autumn maxima (>2.5), indicating substantial in‐stream DOC generation at this time. Observed/predicted ratios for all nutrients were generally less variable and were closer to 1.0 at high flow compared to low flow, suggesting that in‐stream controls on streamwater chemistry are less important at high discharge than at low discharge. Our results indicate two general modes of control of stream nutrient concentrations: (1) catchment control via seasonal variation in the dominant hydrologic pathway (greater proportion of deep groundwater in summer), which produces lower winter and higher summer concentrations, and (2) in‐stream control via high rates of net nutrient uptake during the spring (primarily by autotrophs) and autumn (primarily by heterotrophs).
Renormalization group analysis of macrodispersion in a directed random flow
Authors: Jaekel Uwe , Vereecken Harry
Published: February 2004

We apply “field theoretic” methods to the calculation of the effective diffusivity (macrodispersion coefficient) in a random flow. We show how this approach can be utilized to calculate a perturbation series for the effective diffusivity of conservative tracers in an incompressible velocity field with nonvanishing mean. The first‐order (i.e., “one‐loop”) approximation of this series coincides with classical results derived by Gelhar and Axness and Dagan. A renormalization group (RNG) approach is utilized, and the results are compared to the classical first‐order perturbation theory. For a moderate variability of the permeability the renormalized theory predicts only small corrections to the longitudinal dispersivity. However, the transverse dispersivity can be larger than that predicted by the first‐order perturbation theory by several orders of magnitude. We compare these values to the outcome of Monte Carlo simulations and find that the RNG predictions are in much better, though not perfect, accordance with the results of simulations. Moreover, the results are in good quantitative agreement with reported observations from the Borden Site field experiment.
Deep well injection of brine from Paradox Valley, Colorado: Potential major precipitation problems remediated by nanofiltration
Authors: Kharaka Yousif K. , Ambats Gil , Thordsen James J. , Davis Roy A.
Published: February 2004

Groundwater brine seepage into the Dolores River in Paradox Valley, Colorado, increases the dissolved solids load of the Colorado River annually by ∼2.0 × 108 kg. To abate this natural contamination, the Bureau of Reclamation plans to pump ∼3540 m3/d of brine from 12 shallow wells located along the Dolores River. The brine, with a salinity of 250,000 mg/L, will be piped to the deepest (4.9 km) disposal well in the world and injected mainly into the Mississippian Leadville Limestone. Geochemical modeling indicates, and water‐rock experiments confirm, that a huge mass of anhydrite (∼1.0 × 104 kg/d) likely will precipitate from the injected brine at downhole conditions of 120°C and 500 bars. Anhydrite precipitation could increase by up to 3 times if the injected brine is allowed to mix with the highly incompatible formation water of the Leadville Limestone and if the Mg in this brine dolomitizes the calcite of the aquifer. Laboratory experiments demonstrate that nanofiltration membranes, which are selective to divalent anions, provide a new technology that remediates the precipitation problem by removing ∼98% of dissolved SO4 from the hypersaline brine. The fluid pressure used (50 bars) is much lower than would be required for traditional reverse osmosis membranes because nanofiltration membranes have a low rejection efficiency (5–10%) for monovalent anions. Our results indicate that the proportion of treatable brine increases from ∼60% to >85% with the addition of trace concentrations of a precipitation inhibitor and by blending the raw brine with the effluent stream.
Regional streamflow regimes and hydroclimatology of the United States
Authors: Lins Harry F.
Published: February 2004

The dominant regions of interannual streamflow variability in the United States are defined, and their seasonality and persistence characteristics identified, using an orthogonally rotated principal components analysis (RPCA) of a climatically sensitive network of 559 stream gages for the period 1941–1988. This classification of streamflow regimes is comprehensive and unique in that separate analyses of the streamflow record, for each month of the year, are carried out to detail the month‐to‐month changes in the dominant streamflow patterns. Streamflow variations, or anomalies, in the Upper Mississippi, South Atlantic/Gulf, Far West, Ohio Valley, Northeast, and Eastern/Mid‐ Atlantic regions, as well as a pattern of opposing streamflow anomalies in the West, are observed in all seasons of the year. Anomalies in the Southern Plains and New England regions are observed in autumn, winter, and spring; those in the Rocky Mountains and Middle Mississippi regions occur in late spring and summer.
Diagnostic modeling of residence times in estuaries
Authors: Oliveira Anabela , Baptista António M.
Published: February 2004

The variability of estuarine residence times is elucidated through accurate, diagnostic numerical tracking of a large number of particles, complemented with statistical analysis. Residence times are shown to have strong spatial and temporal variability, which is accentuated by exchanges between the estuary and the coastal ocean due to chaotic stirring at the mouth. The concept of a single residence time per estuary, while convenient from both ecological and engineering viewpoints, is therefore shown to be an oversimplification. Maps of residence times and cumulative histograms are examined as alternatives. The former are attractive only for once‐through tracers, while the latter appear useful over a broader range of tracer characteristics.
Solution and scaling of one‐dimensional groundwater‐solute flow with large density variations
Authors: Johns R. T. , Resele G.
Published: February 2004

A scaling analysis and solution of one‐dimensional groundwater‐solute flow is presented for the steady state case when density is strongly dependent on the concentration. The solution is applicable to one‐dimensional vertical or sloping flow with constant head and solute concentrations at the inlet and outlet. The dependent dimensionless variables (density, concentration, equivalent freshwater head, and fluid velocity) are shown to be a function of four dimensionless groups: a Peclet number of diffusion, a Peclet number of dispersion, a buoyancy number, and a density number. In practice, however, the dependent variables are shown to be independent of the density number and only a function of the remaining three dimensionless groups. The results show that the velocity decreases quickly by several orders of magnitude as the Peclet and buoyancy numbers increase. The rapid decrease in velocity occurs when the buoyancy number (defined as the ratio of the buoyancy force to equivalent freshwater driving force) is greater than unity. We further show that aquifers can have substantial velocity reductions even when density variations are not large, whereas aquitards will exhibit relative small velocity reductions independent of density variations. Implications of the velocity reduction to hydrogeologic investigations of nuclear waste disposal sites are discussed.