bluuebunny/crossref_metadata_2025 huggingface dataset:
Does choice of multicriteria method matter? An experiment in water resources planning
Authors: Hobbs Benjamin F. , Chankong Vira , Hamadeh Wael , Stakhiv Eugene Z.
Published: February 2004

Many multiple criteria decision making methods have been proposed and applied to water planning. Their purpose is to provide information on tradeoffs among objectives and to help users articulate value judgments in a systematic, coherent, and documentable manner. The wide variety of available techniques confuses potential users, causing inappropriate matching of methods with problems. Experiments in which water planners apply more than one multicriteria procedure to realistic problems can help dispel this confusion by testing method appropriateness, ease of use, and validity. We summarize one such experiment where U.S. Army Corps of Engineers personnel used several methods to screen urban water supply plans. The methods evaluated include goal programming, ELECTRE I, additive value functions, multiplicative utility functions, and three techniques for choosing weights (direct rating, indifference tradeoff, and the analytical hierarchy process). Among the conclusions we reach are the following. First, experienced planners generally prefer simpler, more transparent methods. Additive value functions are favored. Yet none of the methods are endorsed by a majority of the participants; many preferred to use no formal method at all. Second, there is strong evidence that rating, the most commonly applied weight selection method, is likely to lead to weights that fail to represent the trade‐offs that users are willing to make among criteria. Finally, we show that decisions can be as or more sensitive to the method used as to which person applies it. Therefore, if who chooses is important, then so too is how a choice is made.
A partial contributing area model for linking rainfall simulation data with hydrographs of a small arid watershed
Authors: Ben‐Asher J. , Humborg G.
Published: February 2004

Four years of runoff measurement (29 events) in Kangussano, Mali, were analyzed on the basis of the partial area contribution concept. The study region is semiarid and the use of runoff water to satisfy crop consumption.is of high importance. A first‐order basin which included two flow channels draining an area of 1.14 106 ha (1.14 km2) was used for this purpose. The objective of this study was to develop and test a conceptual model to predict runoff on natural catchments of about this size. The model assumes that a basin is composed of a large number of pixels (satellite picture elements). Each pixel covers an area of 900 m2. The hydraulic properties of a representative pixel are determined by runoff simulation experiments. The model calculates the number of runoff generating pixels at a given time and rain depth. The areal runoff is a product of these two factors. Analysis of satellite images from LANDSAT and SPOT indicated similarities of soil cover complexes between the study area and an experimental area in Upper Volta. Results of runoff simulation from this area were adapted for the study area and used for the calculations. A good agreement between predicted and measured contributing area was obtained when the number of runoff generating pixels was 80 pixels/ram effective rain. Predicted and measured hydrographs were also in good agreement. It was therefore concluded that the model can satisfactorily predict actual hydrographs from data generated by rainfall‐runoff simulators. Dividing the watershed to surface elements of pixel's size makes the model capable of linking remote sensing information with simulation data in order to predict areal runoff.
Near‐bed sediment concentration in gravel‐bedded streams
Authors: Alonso Carlos V. , Mendoza Cesar
Published: February 2004

In this paper we present an analytical model for the concentration of suspended sediments in the proximity of the bed of gravel rivers. The model is applicable to high‐gradient streams carrying sands and finer sediment particles in suspension over poorly sorted gravel beds. The analysis is carried out in terms of equations which realistically describe the velocity profile of the carrying stream and the dispersion of heavy particles in turbulent shear flows over stable gravel beds. To test our hypotheses we verified the equations using available flume and river data and evaluated their response for various combinations of bed roughness and suspended load characteristics. Our results indicate that characterization of the near‐bed concentration can be formulated in terms of a velocity defect representation of the mean turbulent velocity profile and a sediment eddy diffusivity distribution developed for sand bed rivers. The near‐bed concentration is shown to be rather sensitive to variations in the gravel bed relative roughness, the depth at which the concentration is evaluated above the virtual bed surface, and the ratio between the settling velocity of the suspended sediment and the bed shear velocity.
Seasonal river runoff calculated from a global atmospheric model
Authors: Kuhl Stephan C. , Miller James R.
Published: February 2004

A global atmospheric general circulation model is used to examine seasonal river runoff for the world's largest rivers. The model's river runoff is not directly comparable to observed runoff at the mouth of a river basin because the model assumes that all runoff within a river's drainage basin reaches the river mouth instantaneously. It is useful, however, to examine the model's monthly runoff to determine the extent to which it does agree with runoff as understood by hydrologists, The runoff and precipitation for the river drainage basins are compared with observations. For most river basins the model produces too much precipitation and runoff. However, for the world's largest river, the Amazon, the mean annual runoff is less than half the observed. A common characteristic of high‐latitude rivers is a large runoff peak in the spring, primarily due to melting snow. The model reproduces these peaks but generally leads the observed runoff by one month. This arises because the model does not allow runoff to move between grid boxes but calculates only the total monthly runoff into the entire drainage basin. The runoff in dry river basins is poorly simulated by the model, in part because the precipitation is too large but also because the model's surface parameterizations do not accurately apportion the water lost between evapotranspiration and runoff. The present version of the atmospheric model contains two soil layers and specifies the grid box runoff at each time step as a linear function of the soil moisture storage and the precipitation. A more physically based model should improve the model's simulation of river runoff. A model's ability to simulate monthly river runoff is a good test of its hydrologic cycle and surface parameterizations in different climatic regions and provides a useful diagnostic for climate modelers.
Fingered flow in two dimensions: 1. Measurement of matric potential
Authors: Selker J. , Leclerq P. , Parlange J.‐Y. , Steenhuis T.
Published: February 2004

Precise management of the changing matric potential during infiltration into unsaturated soil required the development of miniature, high‐speed, planar tensiometers. A novel design was developed, with response time of less than 1 s. The applicability of the devices is shown through measurements of the matric potential in growing instabilities, both in the induction zone and along the vertical finger profile. Tensiometry is demonstrated to be a practical method of obtaining data with high temporal and spatial resolution for the study of dynamic flow fields and facilitates testing of theoretical results for unstable flow fields.
A space‐time accurate method for solving solute transport problems
Authors: Li Shu‐Guang , Ruan Feng , McLaughlin Dennis
Published: February 2004

Solute transport studies frequently rely on numerical solutions of the classical advection‐diffusion equation. Unfortunately, solutions obtained with traditional finite difference and finite element techniques typically exhibit spurious damping or oscillation when advection dominates. Recently developed variants of these techniques such as the finite analytic method (Chen and Li, 1979; Chen and Chen, 1984) and the optimal test function method (Celia et al., 1989a, b, c) perform well for steady state problems. Extensions of these methods to the transient case have, however, not been successful, primarily because of inadequate approximations of the temporal derivative. The new numerical method proposed in this paper avoids this difficulty by taking the Laplace transform of the transient equation. The transformed expression behaves like a steady state advection‐diffusion equation with a first‐order decay term. This expression can be solved with either the finite analytic or optimal test function method and the time dependence recovered with an efficient inverse Laplace transform algorithm. The result is an accurate and robust transient solution which performs well over a very wide range of Peclet numbers. We demonstrate this approach by applying the finite analytic method to a Laplace transformed one‐dimensional model problem. A comparison with other competing techniques shows that good approximations are required in both space and time in order to obtain accurate solutions to advection‐dominated problems. A good space approximation combined with a poor temporal approximation (or vice versa) does not give satisfactory results. The method we propose provides a balanced space‐time approximation which works very well for one‐dimensional problems. Extensions to multiple dimensions are conceptually straightforward and briefly discussed.
Analysis of the relationships between flood peaks and flood volumes based on crossing properties of river flow processes
Authors: Bacchi Baldassare , Brath Armando , Kottegoda Nath T.
Published: February 2004

A stochastic approach is developed for the determination of the reduction ratio between the annual maximum flow averaged over a consecutiveDhour period and the annual maximum of peak instantaneous flow with the same frequency of occurrence. Initially, crossing properties of the integrated flow process are related to those of the instantaneous flows, using a Gaussian hypothesis. The scale of fluctuation of the river flow process is the key parameter which governs the theoretical reduction function. Application is made to numerous historical series from Italy. To facilitate the applicability of the model, a method of calibration based on currently available hydrometric information is proposed. Quantiles of flood volumes are obtained from the theoretical reduction function. It is verified that the reduction ratio is independent of the return period and appears to be insensitive to the underlying distributions of the component processes. The non‐Gaussian case and scaling properties are discussed.
Fractal structure and properties of stream networks
Authors: Liu Tanzhuo
Published: February 2004

This paper studies the fractal structure and properties of stream networks through a comparison between stream networks and loopless random aggregate trees. Five fractal dimensions are recognized for stream networks, namely, topological dimension (dt), minimum path dimension (dm), fractal dimension of stream networks as a whole (df), diffusion dimension (dw), and spectral dimension (ds). Mathematical definitions and derivations of the fractal dimensions are proposed, which provide a theoretical basis for some recognized empirical relationships in drainage basin geomorphology. Relationships among the fractal dimensions are examined, and the average values of the fractal dimensions for natural stream networks are estimated. The hydrological implications of the fractal dimensions of stream networks are also discussed.
Eulerian‐Lagrangian solution of the vertically averaged groundwater transport equation
Authors: Bentley L. R. , Pinder G. F.
Published: February 2004

Eulerian‐Lagrangian methods (ELMs) have been developed to reduce smearing and oscillations in numerically generated advection‐dominated transport solutions. Improvements in front propagation characteristics are gained, but new sources of errors are introduced in the tracking step of ELMs. The Eulerian‐Lagrangian least squares collocation method (ELLESCO) is applied to the vertically averaged transport equation, and the ELLESCO method is used to demonstrate how different types of discretization errors affect ELM solutions. The accuracy of ELMs is partially dependent on the accuracy of a tracking step. The tracking integration can be made as accurate as desired by dynamically adjusting the number of second‐order Runge‐Kutta integretion steps per finite difference transport step. However, the accuracy of the final position is dependent on accurate velocities. Inaccurate velocities can lead to poorly located concentration fronts and mass balance errors. Although ELLESCO can extend the spatial and temporal discretization limits of classical methods, concentration fronts must be spread over one and a half elements to avoid oscillations in the solution. Time truncation errors associated with concentration dependent source terms lead to mass balance errors, and source terms should be computed with the Crank‐Nicolson approximation to avoid excessive truncation error. The size of the finite difference transport time step and the magnitude of the local velocity determine the distance between the head and foot of the particle back tracks. This distance, referred to as the Lagrangian spatial resolution, must be less than the characteristic length of areal sources, or distortions will occur in the concentration front. The limit on the Lagrangian spatial resolution is an effective limit on the transport finite difference time step size.
Waste load allocation for whole effluent toxicity to protect aquatic organisms
Authors: Hutcheson M. R.
Published: February 2004

A process is developed to determine a waste load allocation that will implement the narrative criteria for fish and wildlife propagation found in states' water quality standards. The waste load allocation to implement the narrative chronic criterion is determined to be percent effluent at a location in the receiving stream, as opposed to an effluent concentration derived from the numerical waste load allocation process. A typical narrative chronic criterion is “receiving streams shall not exhibit chronic toxicity outside the mixing zone,” while a typical numerical chronic criterion is “receiving stream concentration shall not exceed 0.005 μg/L of chlordane outside the mixing zone.” Toxicity tests are used to implement narrative criteria, while compliance with numerical criteria involves concentration measurements. It is shown that the appropriate percent effluent is inversely proportional to the dilution factor for chronic toxicity. An appropriate waste load allocation to implement the narrative acute criterion is 100% effluent. Waste load allocation for whole effluent toxicity is feasible. The required independent variables are available to regulatory agencies, and toxicity testing has become routine.
Estimating an optimal distribution of water entitlements
Authors: Tisdell J. G. , Harrison S. R.
Published: February 2004

This paper is concerned with the distributive consequences of alternative methods of allocating transferable water licenses in Queensland, Australia. The equilibrium of a number of different cooperative games will be used to judge which method of initial allocation of water entitlements potentially produces the most equitable distribution of the income derived from regulated water.
Watershed modeling using land classifications
Authors: Kite G. W. , Kouwen N.
Published: February 2004

A comparison was made between using a lumped hydrological model and using a version of the same model applied successively to different land uses within subbasins. A watershed in the Rocky Mountains of British Columbia was divided into three contributing subbasins, and each of these was further subdivided by land cover classification using Landsat images. A hydrological model was applied separately to each land cover class in each subbasin, and the resulting hydrographs were routed to the subbasin outlet and then through lower subbasins. The final hydrographs were compared to those obtained using the model on the basin as a whole. It was found that using a semidistributed model gives goodness of fit statistics that are better than the lumped basin approach. The land class dependent parameter values found through optimization confirm the physical variations in storages and infiltration rates that would be expected in a mountain basin. The advantage of the semidistributed model is that relating the parameter values to land cover characteristics provides a method of investigating land use changes and allows the model to be more easily transferred to other basins.
El Niño‐Southern Oscillation related fluctuations of the marine carbon cycle
Authors: Winguth A. M. E. , Heinmann M. , Kurz K. D. , Maier‐Reimer E. , Mikolajewicz U. , Segschneider J.
Published: February 2004

We investigate the response of a three‐dimensional ocean circulation model (Hamburg LSG) coupled on‐line with an oceanic carbon cycle model (HAMOCC‐3) to El Niño‐Southern Oscillation (ENSO) induced fluctuations of the wind field. During El Niño 1982/1983, when upwelling and biological productivity in the equatorial Pacific were strongly reduced and sea surface temperatures were increased, the oceanic CO2 partial pressure in this region decreased significantly. Consequently, in 1982/1983 the CO2 flux from the tropical ocean into the atmosphere was reduced. However, in 1983 the interannual deviations from the long‐term trend in atmospheric CO2 showed in January low and in December high values with a total shift by more then 1.4 GtC. The model simulation supports the oceanic measurements and predicts a temporary uptake of 0.6 GtC during the ENSO year 1983. We conclude that the concurrent release of CO2 from the land biosphere must have been about 2 GtC.
The stratospheric winter of 1991/92 at Sodankylä in the European Arctic as compared with 1965–92 meteorological and 1988–91 ozone sounding statistics
Authors: Taalas Petteri , Kyrö Esko
Published: February 2004

The meteorological sounding record of 1965–92 and the ozone sounding record of 1988–92 at Sodankylä have been studied. In early 1992 the stratospheric temperatures and geopotential heights were lower than the 1965‐92 mean, especially in January. The occurrence of 50 hPa level temperatures below 195 K in January has increased considerably starting from the early 1980's up to a maximum in 1992. The partial pressures of stratospheric ozone in January–March 1992 were 17% lower than the 1988–91 averages with the largest relative monthly mean deviations up to −33% between the 13–17 km levels.
Stratospheric water vapor content evolution during EASOE
Authors: Ovarlez Joëlle , Ovarlez Henri
Published: February 2004

During EASOE, 7 in situ stratospheric water vapor content measurements were performed, in the polar region, with a balloon‐borne frost‐point hygrometer, from November 1991 until March 1992. The comparison between the frost‐point and the air temperature profiles shows on 11 December the occurrence of PSC formation conditions when a PSC was observed by lidars. Outside the vortex the mean water vapor content seems to be very stable, 4 to 5 ppmv from 16 to 25 km. But is very changeable below 16 km, due to the variability in the origin of the air masses where the measurements occur, as these air parcels come sometimes from the tropics, then bringing dry air. Inside the vortex, a vertical descent of the air masses is observed, and is estimated to be 4 km around 25 km at the end of March, before the vortex breakdown. The rehydration of the vortex induced by this descent, from February to March, is shown.
Introduction to the Special Section on the Lithoprobe Sudbury Project
Authors: Boerner D. E. , Milkereit B. , Naldrett A. J.
Published: February 2004

Integrated geophysical and rock property studies of the Sudbury Structure have revealed it is highly deformed with substantial NS shortening in the Sudbury Igneous Complex. Understanding the nature and extent of deformation is essential to determining the original shape of the structure and the results of these studies are sufficient to discount many of the objections to an impact origin.
The lifetime of leewave‐induced ice particles in the Arctic stratosphere: II. Stabilization due to NAT‐coating
Authors: Peter Thomas , Müller Rolf , Crutzen Paul J. , Deshler Terry
Published: February 2004

Large ice particles with radii of 1–5 µm and particle number densities up to 1 cm−3 were observed by balloonborne particle counters at altitudes 20–24 km about 250 km SE of Kiruna (northern Sweden). The particles were probably formed during strong adiabatic cooling in leewaves over the Norwegian mountains. At the time of measurement, temperatures were 5‒10 K above the frost‐point. Pure ice particles of this size would evaporate within a few minutes; however, these particles somehow survived the passage of 2‐3 hours from the Norwegian mountains to the Gulf of Bothnia. The slow evaporation could be explained if at some point the particles had acquired a coating of nitric acid trihydrate (NAT). In air cooling slowly the condensation of NAT will precede the condensation of ice. However, if the air cools very rapidly then nitric acid and ice could condense simultaneously, with the nitric acid embedded in the ice crystal in the form of NAT clusters. In particular large HNO3/H2O ratios in the solid phase would be reached if the formation of pure NAT during initial cooling is suppressed, e.g. when solid NAT nuclei are absent. During warming the preferential evaporation of water would expose the clusters, leaving eventually an almost complete surface layer of NAT. Model calculations suggest that for particles undergoing vertical movement in leewaves this could happen several times in succession, greatly prolonging their lifetime. Thus leewave cloud particles may persist much further downstream than has been previously thought.
The longwave emission signature of urban pollution: Radiometric FTIR measurement
Authors: Lubin Dan , Simpson A. Sabrina
Published: February 2004

Air pollutants trapped beneath frequent temperature inversions in the Los Angeles basin bring about surface radiance enhancements of up to fifty percent in the middle‐infrared window (8–12 microns). This constitutes an anthropogenic modification to the downwelling longwave flux which can be as large as 9 W/m². A Fourier Transform Infrared (FTIR) spectroradiometer has been used to measure middle‐infrared atmospheric emission spectra under Los Angeles smog, and these 1 cm−1 resolution spectra demonstrate that both anthropogenic aerosols and increased tropospheric ozone abundance contribute to enhancements in surface longwave radiation.
The kinetic response of a stochastic plasma to low frequency perturbations
Authors: Hurricane Omar A. , Pellat René , Coroniti Ferdinand V.
Published: February 2004

Following suggestion that substorm breakup might be caused by an interchange or ballooning instability, several MHD and gyro‐kinetic stability analysis have been performed for plasma sheet magnetic field geometries. However, the stochastic ion dynamics in the highly stressed, thin high‐ß near earth plasma sheet violate the locality requirements of MHD and the invarience of the magnetic moment, μ, required by gyro‐kinetic theories. In this paper we develop a new linear Vlasov kinetic theory (for low frequency modes ω <ωb, ωb being the bounce frequency) which includes the dynamics of stochastic ions.
An explanation for the double seismic layers north of the Mendocino Triple Junction
Authors: Wang Kelin , Rogers Garry C.
Published: February 2004

We propose that the gently eastward dipping double planed seismic zone observed at 15–25 km depths in the southern Cascadia subduction zone, just north of the Mendocino triple junction, is a direct consequence of the thermally controlled rheology. As the oceanic lithosphere subducts to a depth of about 15 km, the temperature regime causes a brittle‐plastic transition to occur within the oceanic crust. Thus, a ductile layer forms in the lower oceanic crust, sandwiched between the brittle upper crust and brittle upper mantle. The very high strain rates near the triple junction caused by the northward push of the Pacific plate on the Gorda plate increase the seismicity and thus accentuate the double seismic zone in this region. This model explains the focal mechanisms observed in the seismic zone and their spatial change. The double seismic layers clearly define the position of the subducting Gorda plate, previously uncertain in the Cape Mendocino region.
Current deformation and the width of the seismogenic zone of the northern Cascadia subduction thrust
Authors: Dragert H. , Hyndman R. D. , Rogers G. C. , Wang K.
Published: February 2004

Evidence has been obtained for the accumulation of elastic strain across the northern Cascadia subduction zone that may be released in a future very large subduction thrust earthquake. Vertical and horizontal strain rates across the southern Vancouver Island region have been determined through (1) long‐term trends in tide gauge data, (2) changes in repeated accurate leveling surveys, (3) changes in repeated high‐accuracy gravity profiles, and (4) horizontal shortening observed in repeated precise positioning surveys. The outer coast is uplifting at a rate of a few millimeters per year decreasing landward, and shortening is occurring across the 100‐km‐wide coastal region at a rate of about 0.1 microstrain per year (mm km−1yr−1). The results are compared with the distribution of strain accumulation predicted from elastic dislocation and viscoelastic models for a subduction thrust fault. The location of the fault as used in the models is well defined by multichannel seismic reflection and other geophysical data. Most of the observed current deformation can be explained by interseismic strain accumulation associated with the subduction thrust of southern Vancouver Island and northern Washington, provided the locked portion is restricted to a 60‐km‐wide band offshore beneath the continental shelf and slope. This conclusion also results from modeling the coseismic subsidence on the outer coast of Vancouver Island about 300 years ago deduced from paleoseismicity data. The unusually narrow downdip extent of the subduction thrust seismogenic zone, that extends little if at all beneath the coast, is a consequence of high temperatures associated with the young age of the subducted oceanic lithosphere and the thick blanket of insulating sediments. The high temperatures limit brittle seismogenic behavior downdip to where the thrust fault is at a depth of less than 15 km. The distance from the seismic portion of the megathrust limits the estimated ground motion at the major centers of Vancouver and Victoria from this source. The narrow width may also limit the earthquake size; however, events of magnitude well over 8 are possible.
On the temporal evolution of high‐temperature hydrothermal systems at ocean ridge crests
Authors: Lowell Robert P. , Germanovich Leonid N.
Published: February 2004

The results of heat balance calculations for a single‐pass hydrothermal system overlying an axial magma body, based on a given rate of heat output of 102–103 MW at a time t0, predict that vent temperatures should decay rapidly for t > t0, as the magma freezes and the boundary layer between the hydrothermal system and liquid magma thickens. The model may describe a declining phase of high‐temperature, high‐heat‐output hydrothermal activity. The model shows that for systems with heat output ∼100 MW or greater, the boundary layer between the magma and hydrothermal system must remain thin, if vent temperatures remain relatively constant on a decadal timescale. A thin boundary layer can be maintained as a result of downward migration of the hydrothermal system into freshly frozen magma or by some mechanism that maintains high heat flux from liquid magma to the base of the boundary layer. Some combination of these factors is likely to operate. Downward migration of the hydrothermal system into freshly frozen magma may occur in conjunction with fracturing resulting from dike injection and the propagation of these cracks laterally away from the dike as a result of thermal stresses. High heat flux from liquid magma to the base of the hydrothermal system cannot be maintained simply by convection within the magma chamber. High heat flux might be maintained as a result of magma chamber replenishment or by latent heat transfer during the formation of a cumulate mush at the base of the magma chamber, however. A hydrothermal system, in which the permeability decreases with time, can maintain relatively constant vent temperatures even though the thermal output declines. Better time series data on thermal output of the vents, and not just on the vent temperature, could help distinguish whether the permeability is decreasing or whether heat flux as well as vent temperatures are relatively constant.
Behavior of the brittle crust in wide plate boundary zones
Authors: Lamb Simon H.
Published: February 2004

In wide and active continental plate boundary zones, ductile flow in the deeper and strong parts of the lithosphere may control crustal deformation. This is likely if average resistive shear stresses on faults in the brittle crust are much less than 108 Pa and the underlying bulk effective viscosity is much greater than 1021 Pa s. In this case, a simple model of distributed deformation, referred to as the floating block model, may be useful. This treats the crust as an array of rotating and translating rigid blocks, which are floating on an underlying continuous flow with a constant rheology. The model is analyzed in detail in this paper because it has the potential to link detailed observations of crustal deformation with the large‐scale flow. Crustal blocks are defined by at least two sets of faults. The kinematics of crustal deformation can be described in terms of the motions of these blocks. Both the relative motion on block boundaries (faults) and block tilting about a horizontal axis can be described in terms of the underlying flow and block rotation about a vertical axis. However, rotations about a vertical axis, which are an important component of the crustal deformation, will depend not only on the underlying flow but also on the shape, orientation and arrangement of the crustal blocks. The average rotation rate about a vertical axis, over finite rotations, will be significantly different from that predicted at any instant. Also, the rotation history is considerably complicated if, as is likely, the underlying flow field, or block shape, has changed with time. These aspects of crustal deformation are discussed with reference to real zones of active deformation in New Zealand, Greece and western North America.
Comparison of magnetic hysteresis parameters of unremagnetized and remagnetized limestones
Authors: Channell J. E. T. , McCabe C.
Published: February 2004

For white magnetite‐bearing Mesozoic pelagic limestones from Italy which carry a “primary” magnetization, the values of Mrs/Ms and Hcr/Hc generally lie in the pseudo‐single domain (PSD) field of the Day et al. (1977) plot. The logarithmic plot of Mrs/Ms against Hcr/Hc gives a straight line (R = 0.814) with slope and intercept close to the empirical mixing line of Parry (1982) for single domain (SD) and multidomain (MD) magnetite. For one of the white pelagic limestone formations (Maiolica Formation), samples with hysteresis ratios closer to the MD field display increased paramagnetic susceptibility and are from the upper part of the formation characterized by increased detrital clay. We therefore associate the increased MD magnetite with increased detrital influx. For pinkish and reddish varieties of the Italian pelagic limestones, the presence of hematite is manifest by high saturation fields, a wide range of Hcr/Hc, and “wasp‐waisted” hysteresis loops attributed to the mixing of magnetite and high‐coercivity authigenic hematite. The hysteresis ratios for a collection of Paleozoic and Mesozoic remagnetized magnetite‐bearing limestones from Britain, Nevada, Alaska and the Appalachians lie mainly outside the PSD field and appear to follow a power law trend. Following Jackson et al. (1993), the high values of Hcr/Hc and the characteristically “wasp‐waisted” hysteresis loops can be interpreted in terms of a fine‐grained subspherical high‐coercivity SD magnetite mixed with a high proportion of superparamagnetic magnetite. The slope and intercept of the power law relationship for Mrs/Ms and Hcr/Hc in the remagnetized limestones are distinct from those observed for the Italian limestones, and may provide a means of fingerprinting magnetite of “primary” as opposed to diagenetic origin.
Some theoretical predictions on the relationships among spreading rate, mantle temperature, and crustal thickness
Authors: Su Wusi , Mutter Carolyn Z. , Mutter John C. , Buck W. Roger
Published: February 2004

A series of numerical experiments on mantle flow and melting predict a positive relation between mantle temperature and crustal thickness. The models also demonstrate that crust formed at slow spreading rates is more sensitive to variations in mantle temperature than crust formed at fast rates so that the range of calculated thicknesses is much greater for crust formed at slower rates. An instantaneous mantle temperature increase results in a transient pulse of melt production that is also more pronounced at slower spreading rates. The predicted behavior is caused by the interplay between mantle flow driven by plate separation and that driven by thermal, compositional, and melt‐related buoyancy. A temperature increase results in a decrease in mantle viscosity and an increase in the depth at which melting begins. A lower viscosity leads to stronger buoyancy‐driven flow that carries more mantle to shallow depths below the ridge. Thermal buoyancy effects, which may result in cooling and mixing of depleted and undepleted material under the ridge, appear to be of greater importance at slower spreading rates. The steady state results are broadly consistent with global compilations of oceanic crustal thickness that show larger variations in crustal thickness at slower spreading rates than at faster rates. Thicknesses estimated from seismic refraction data from crust formed within a single segment of the Mid‐Atlantic Ridge but at different spreading rates (1.0 to 1.9 cm/yr) are consistent with (but do not prove) the model results. The transient pulse of melt production associated with a rapid increase in mantle temperature might occur when a ridge becomes proximal to a hot spot.
Prediction of large events on a dynamical model of a fault
Authors: Pepke S. L. , Carlson J. M. , Shaw B. E.
Published: February 2004

We present results for long‐term and intermediate‐term prediction algorithms applied to a simple mechanical model of a fault. The long‐term techniques we consider include the slip‐predictable and time‐predictable methods and prediction based upon the distribution of repeat times between large events. Neither the slip‐predictable nor time‐predictable method works well on our model. In comparison, the time interval method is much more effective and is used here to establish a benchmark for predictability. We consider intermediate‐term prediction techniques which employ pattern recognition to identify seismic precursors. These methods are found to be significantly more effective at predicting coming large events than methods based on recurrence intervals. The performances of four specific precursors are compared using a quality function Q, which is similar to functions used in linear cost‐benefit analysis. When the quality function equally weights (1) the benefit of a successful prediction, (2) the cost of maintaining alerts, and (3) the cost of false alarms, we find that Q is optimized in algorithms based on the most conventional precursors when alarms occupy 10–20% of the mean recurrence interval and approximately 90% of the events are successfully predicted. The measure Q is further used to explore optimization questions such as variation in the space, time, and magnitude windows used in the pattern recognition algorithms. Finally, we study the intrinsic uncertainties associated with seismicity catalogs of restricted lengths. In particular, we test the hypothesis that many shorter catalogs are as effective as one long catalog in determining algorithm parameters, and we find that the hypothesis is valid for the model when the catalogs are of the order of the mean recurrence interval.
Velocity and inferred porosity model of the Oregon accretionary prism from multichannel seismic reflection data: Implications on sediment dewatering and overpressure
Authors: Cochrane G. R. , Moore J. C. , MacKay M. E. , Moore G. F.
Published: February 2004

A two‐dimensional model of seismic velocity derived from multichannel seismic data collected off Oregon in 1989 shows that as sediments are carried from Cascadia Basin into the accretionary prism, there are measurable changes in velocity‐depth profiles. In the seaward most area of the basin, where no thrust faults are observed, there is a landward (and downward) increase of velocity in the sedimentary section. We attribute the velocity increase in the basin to a reduction of porosity resulting from consolidation and cementation, accompanied by diffusive flow of pore water driven by lateral tectonic as well as gravitational stress. Near the base of the slope there is an area of incipient thrusting (the protothrust zone) where protothrusts sole out into a protodécollement. Synthetic seismogram modeling of the reverse‐polarity reflection from the protodécollement shows a 100‐m‐thick layer with a slightly lower velocity relative to the sediments above it. Above the protodécollement, velocity continues to increase landward. We suggest that in this area the diffusive flow of pore water out of the sediment is augmented above the protodécollement by fault‐focused flow. Below the protodécollement a reversal in velocity may be due to an increase in porosity resulting from overpressuring of pore fluid trapped by reduction of the permeability of the sediment above the protodécollement. Farther landward, where thrusting has formed a fault‐bend fold, velocity values are lower in the accreted section of sediments relative to the velocity at a comparable subbottom depth in the protothrust zone. The decrease in velocity is a result of microfracturing of the highly consolidated sediments accompanying uplift and folding and reflects the increasing role of fracturing and faulting in the control of dewatering of the sediments.
A spectral formalism for computing three‐dimensional deformations due to surface loads: 2. Present‐day glacial isostatic adjustment
Authors: Mitrovica J. X. , Davis J. L. , Shapiro I. I.
Published: February 2004

Using a spherically symmetric, self‐gravitating, linear viscoelastic Earth model, we predict present‐day three‐dimensional surface deformation rates and baseline evolutions arising as a consequence of the late Pleistocene glacial cycles. In general, we use realistic models for the space‐time geometry of the final late Pleistocene deglaciation event and incorporate a gravitationally self‐consistent ocean meltwater redistribution. The predictions of horizontal velocity presented herein differ significantly, in both their amplitude and their spatial variation, from those presented in an earlier analysis of others which adopted simplified models of both the late Pleistocene ice history and the Earth rheology. An important characteristic of our predicted velocity fields is that the melting of the Laurentide ice sheet over Canada is capable of contributing appreciably to the adjustment in Europe. The sensitivity of the predictions to variations in mantle rheology is investigated by considering a number of different Earth models, and by computing appropriate Frechet kernels. These calculations suggest that the sensitivity of the deformations to the Earth's rheology is significant and strongly dependent on the location of the site relative to the ancient ice sheet. The effects on the predictions of three‐dimensional deformation rates of altering the ice history or adopting approximate models for the ocean meltwater redistribution have also been considered and found to be important (the former especially so). Finally, for a suite of Earth models we provide predictions of the velocity of a number of baselines in North America and Europe. We find that, in general, both radial and tangential motions contribute significantly to baseline length changes, and that these contributions are a strong function of the Earth model. We have, furthermore, found a set of Earth models which, together with the ICE‐3G deglaciation chronology, produce predictions of baseline length changes that are consistent with very long baseline interferometry measurements of baselines within Europe.
The double seismic zone in Kuril‐Kamchatka: The tale of two overlapping single zones
Authors: Kao Honn , Chen Wang‐Ping
Published: February 2004

The classic double seismic zone in the central portion of the Kuril‐Kamchatka arc seems to turn into a regular Wadati‐Benioff zone with downdip compression and extension in the northeastern and southwestern ends of the arc, respectively. To delineate this lateral changeover, we studied 33 large‐ to moderate‐sized (mb≥5.1) earthquakes that occurred at depths shallower than 200 km between 1963 and 1991. These events took place in two regions where the double seismic zone terminates and single seismic zones emerge. Precise earthquake source parameters, including focal depths and mechanisms, are determined from a careful analysis of a mixture of analog and digital P and SH waveforms recorded at teleseismic distances. Our results indicate that the double seismic zone is confined between approximately 46° and 53°N. Northeast of 53°N, intermediate‐depth earthquakes (∼70–200 km) show only downdip compressional focal mechanisms. Furthermore, the Wadati‐Benioff zone there seems to be a continuation of the upper, compressional layer of the double seismic zone. Thus the changeover from a double to a single seismic zone in this case is simply disappearing of the lower, extensional sheet of the double seismic zone. Similarly, southwest of 46°N, intermediate‐depth earthquakes show only downdip extensional mechanisms. The single seismic zone is unlikely to consist of two layers of extensional seismicity. In fact, nowhere along the entire arc did we observe two distinct seismogenic layers with a single state of strain. In other words, these extensional events did not occur in the same seismogenic structure as the upper (compressional) layer of the double seismic zone. However, we cannot ascertain whether the single seismic zone in extension is simply a southwestern extension of the lower (extensional) layer of the double seismic zone. Lateral variation from a single zone under extension in the southwest, to a double seismic zone, and finally to a single zone under compression cannot be accounted for by conventional models of a double seismic zone. On the other hand, the addition of a component of stress transmitted from depths greater than 250 km can explain the observed lateral variation in the state of strain at intermediate depths because the slab between depths of 250–450 km is under extension in the southwestern end of the arc, whereas the rest of the arc is under compression. Vanishing of the lower (extensional) layer of the double seismic zone toward the northeastern end of the arc is interpreted as a result of compression transmitted from below overshadowing extension caused by effects such as unbending. A similar reasoning applies to the southwestern termination of the double seismic zone.
Dynamics of the transition zone in coastal zone color scanner‐sensed ocean color in the North Pacific during oceanographic spring
Authors: Glover David M. , Wroblewski J. S. , McClain Charles R.
Published: February 2004

A transition zone in phytoplankton concentration running across the North Pacific basin at 30° to 40° north latitude corresponds to a basin‐wide front in surface chlorophyll observed in a composite of coastal zone color scanner (CZCS) images for May, June, and July 1979–1986. This transition zone with low chlorophyll to the south and higher chlorophyll to the north can be simulated by a simple model of the concentration of phytoplankton, zooplankton, and dissolved nutrient (nitrate) in the surface mixed layer of the ocean applied to the North Pacific basin for the climatological conditions during oceanographic springtime (May, June, and July). The model is initialized with a 1° × 1° gridded estimate of wintertime (February, March, and April) mixed layer nitrate concentrations calculated from an extensive nutrient database and a similarly gridded mixed layer depth data set. Comparison of model predictions with CZCS data provides a means of evaluating the dynamics of the transition zone. We conclude that in the North Pacific, away from major boundary currents and coastal upwelling zones, wintertime vertical mixing determines the total nutrient available to the plankton ecosystem in the spring. The transition zone seen in basin‐scale CZCS images is a reflection of the geographic variation in the wintertime mixed layer depth and the nitracline, leading to a latitudinal gradient in phytoplankton chlorophyll.
Annual and interannual variations of phytoplankton pigment concentration and upwelling along the Pacific equator
Authors: Halpern David , Feldman Gene C.
Published: February 2004

The following variables along the Pacific equator from 145°E to 95°W were employed: surface layer phytoplankton pigment concentrations derived from Nimbus 7 coastal zone color scanner (CZCS) measurements of ocean color radiances; vertical velocities simulated at the 90‐m bottom of the euphotic layer from a wind‐driven ocean general circulation model; and nitrate concentrations estimated from model‐simulated temperature. The upward flux of nitrate into the euphotic layer was calculated from the simulated vertical motion and nitrate concentration. The CZCS‐derived phytoplankton pigment concentration was uniform from 175° to 95°W. Longitudinal profiles of upwelling, phytoplankton biomass, and 90‐m nitrate flux were of different shapes. The small annual cycles of the phytoplankton pigment concentration and nitrate flux were in phase: increased phytoplankton biomass was associated with increased upward nitrate flux, but the phase was not consistent with the annual cycles of the easterly wind or of the upwelling intensity. Variation of phytoplankton pigment concentration was greater during El Niño than during the annual cycle. The substantially reduced phytoplankton pigment concentration observed during El Niño was associated with smaller upward nitrate flux. Phytoplankton biomass during non‐El Niño conditions was not related to nitrate flux into the euphotic layer.
Hydrographic conditions associated with the relaxation of an upwelling event off the Galician Coast (NW Spain)
Authors: Castro C. G. , Pérez F. F. , Alvarez‐Salgado X. A. , Rosón G. , Ríos A. F.
Published: February 2004

During the GALICIA‐XI cruise from May 10 to May 14, 1991, the relaxation of a previous strong upwelling event took place along the Galician coast caused by a shift in the position of the Azores High. The coldest temperatures and highest nitrate levels were found near the coast corresponding to the advection of subsurface waters, particularly of Eastern North Atlantic Water (ENAW). On the basis of thermohaline properties, ENAW of polar (ENAWp) and tropical (ENAWt) origin are distinguished. The highest salinity values found correspond to a saline wedge of ENAWt located off the west coast of Galicia. The relaxation of upwelling produced a shoreward migration of surface water from oceanic stations which came into contact with upwelled Eastern North Atlantic Water from the coastal stations to form a convergence front 28 km off the coast. Meanwhile, the saline wedge displaced towards both the north and the shore which is favored by the compression of the upwelling system to a narrow coastal strip outwardly limited by the convergence zone.