The complete SRSS modal combination rule

The complete Square‐Root‐of‐Sum‐of‐Squares (c‐SRSS) modal combination rule is presented. It expresses the structural response in terms of uncoupled SDOF modal responses, yet accounting fully for modal response variances and cross‐covariances. Thus, it is an improvement over the classical SRSS rule which neglects contributions from modal cross‐covariances. In the c‐SRSS rule the spectral moments of the structural response are expressed rigorously in terms of the spectral moments of uncoupled modal responses and of some coefficients that can be computed straightforwardly as a function of modal frequencies and damping, without involving the computation of cross‐correlation coefficients between modal responses. An example shows an application of the c‐SRSS rule for structural systems with well separated and closely spaced modal frequencies, subjected to wide‐band and narrow‐band excitations. Comparisons with response calculations using the SRSS and the Complete Quadratic Combination rules are given and discussed in detail. Based on the c‐SRSS rule a response spectrum formulation is introduced to estimate the maximum structural response. An example considering a narrow‐band excitation from the great Mexico earthquake of September 19, 1985, is given and the accuracy of the response spectrum formulation is examined. Copyright © 2010 John Wiley & Sons, Ltd.     

An Analytical Model for Hydraulic Fracturing in Shallow Bedrock Formations

A theoretical method is proposed to estimate post‐fracturing fracture size and transmissivity, and as a test of the methodology, data collected from two wells were used for verification. This method can be employed before hydrofracturing in order to obtain estimates of the potential hydraulic benefits of hydraulic fracturing. Five different pumping test analysis methods were used to evaluate the well hydraulic data. The most effective methods were the Papadopulos‐Cooper model (1967), which includes wellbore storage effects, and the Gringarten‐Ramey model (1974), known as the single horizontal fracture model. The hydraulic parameters resulting from fitting these models to the field data revealed that as a result of hydraulic fracturing, the transmissivity increased more than 46 times in one well and increased 285 times in the other well. The model developed by dos Santos (2008) , which considers horizontal radial fracture propagation from the hydraulically fractured well, was used to estimate potential fracture geometry after hydrofracturing. For the two studied wells, their fractures could have propagated to distances of almost 175 m or more and developed maximum apertures of about 2.20 mm and hydraulic apertures close to 0.30 mm. Fracturing at this site appears to have expanded and propagated existing fractures and not created new fractures. Hydraulic apertures calculated from pumping test analyses closely matched the results obtained from the hydraulic fracturing model. As a result of this model, post‐fracturing geometry and resulting post‐fracturing well yield can be estimated before the actual hydrofracturing.     

Strong-motion accelerograph array in Santiago,Chile, and preliminary evaluation of site effects

A strong-motion accelerograph array in Santiago, Chile has been installed. One of the sites is located on rock and the other six sites are on soil ground with different surface geology, so that local site effects on ground motions can be studied. As a preliminary evaluation of the site effects, the spectral ratios of weak-motion records at soil sites with respect to the rock site are calculated. The spectral ratios show that the amplification of ground motions with respect to the rock site is approximately 1.25 on dense gravel deposits, 2.5 on stiff pumice ground and 3.5 on soft silt ground.     

The use of predictive modeling techniques for optimal exploitation of spatial databases: a case study in landslide hazard mapping with expert system-like methods

. A case study is presented in which different probabilistic prediction models (Bayesian probability, fuzzy logic "and", "or", "sum", "product", "gamma" operations, and certainty factors) are used to produce landslide hazard maps for a hilly and mountainous region in the northern Apennines, Italy. Seven data layers are exploited to detect most vulnerable areas: lithology, distance from the geological lineaments, annual rainfall amount, land cover type, topographic slope and aspect, and the distance from hydrographic network segments. The results of the different predictions are compared using the prediction rate index and critically discussed, to evaluate the possibility of using readily available databases for land planning.     

On the Dynamics and Topology of the Elliptic Rectilinear Restricted 3-Body Problem

We study a symmetric collinear restricted 3-body problem, where the equal mass primaries perform elliptic collisions, while a third massless body moves in the line between the primaries, during the time between two consecutive elliptic collisions. After desingularizing binary and triple collisions, we prove the existence of a transversal heteroclinic orbit beginning and ending in triple collision. This orbit is the unique homothetic orbit that the problem possess. Finally, we describe the topology of the compact extended phase space. This revised version was published online in July 2006 with corrections to the Cover Date.     

Palaeomagnetic study of Permocarboniferous glacial varves from the Itarare Subgroup, southern Brazil

Summary. A sequence of 167 glacial varves from Itu, State of São Paulo (Brazil), has been sampled for palaeomagnetic analysis. Since the varve thicknesses permit individual measurements, an attempt was made to compare annual palaeomagnetic results with recent observatory data. Inclination and declination plots show larger variations than those displayed by the present geomagnetic field. This could, however, be due to sedimentation factors since it may be assumed that the pattern of the present geomagnetic field variations is not greatly different from that of the Permocarboniferous field. In the next paper (Ernesto & Pacca) the experimental data are submitted to spectral analysis and the results support some of the hypotheses raised in this work.     

Scaling properties and spatial organization of snow depth fields in sub‐alpine forest and alpine tundra

This paper reports on a study analysing the spatial distribution functions, the correlation structures, and the power spectral densities of high‐resolution LIDAR snow depths (～1 m) in two adjacent 500 m × 500 m areas in the Colorado Rocky Mountains, one a sub‐alpine forest the other an alpine tundra. It is shown how and why differences in the controlling physical processes induced by variations in vegetation cover and wind patterns lead to the observed differences in spatial organization between the snow depth fields of these environments. In the sub‐alpine forest area, the mean of snow depth increases with elevation, while its standard deviation remains uniform. In the tundra subarea, the mean of snow depth decreases with elevation, while its standard deviation varies over a wide range. The two‐dimensional correlations of snow depth in the forested area indicate little spatial memory and isotropic conditions, while in the tundra they indicate a marked directional bias that is consistent with the predominant wind directions and the location of topographic ridges and depressions. The power spectral densities exhibit a power law behaviour in two frequency intervals separated by a break located at a scale of around 12 m in the forested subarea, and 65 m in the tundra subarea. The spectral exponents obtained indicate that the snow depth fields are highly variable over scales larger than the scale break, while highly correlated below. Based on the observations and on synthetic snow depth fields generated with one‐ and two‐dimensional spectral techniques, it is shown that the scale at which the break occurs increases with the separation distance between snow depth maxima. In addition, the breaks in the forested area coincide with those of the corresponding vegetation height field, while in the tundra subarea they are displaced towards larger scales than those observed in the corresponding vegetation height field. Copyright © 2009 John Wiley & Sons, Ltd.     

Diatom assemblages from surface sediments of the Río de la Plata estuary,Uruguay

The Río de la Plata estuary (RdlP) exhibits environmental gradients associated with the freshwater input and oceanic water intrusion. The aim of this study was to assess diatom species distribution in surface sediment samples related to such environmental gradients. The internal section of RdlP was dominated by Aulacoseira spp., Eunotia spp., Staurosirella martyi, Actinocyclus normanii and Thalassiosira baltica, indicatives of low salinity levels and high trophic conditions, associated with the riverine and estuarine regimes. The external section was dominated by Coscinodiscus radiatus, Thalassiosira spp., Paralia sulcata, Cyclotella striata, among other marine taxa, indicatives of high salinity and low trophic conditions, associated with the influence of the Southwestern Atlantic Ocean. Furthermore, the intermediate section presents a mixture of both diatom groups representing mixing conditions. The observed diatom species groups capture fairly well the RdlP environmental variability and can be reliably used for paleoenvironmental studies in this and other similar estuarine systems.     

Central mass-to-light ratios and dark matter fractions in early-type galaxies

Dynamical studies of local elliptical galaxies and the Fundamental Plane point to a strong dependence of the total mass-to-light ratio ( M / L ) on luminosity with a relation of the form   M / L ∝ L ^γ  . The 'tilt'γ may be caused by various factors, including stellar population properties (metallicity, age and star formation history), initial mass function, rotational support, luminosity profile non-homology and dark matter (DM) fraction. We evaluate the impact of all these factors using a large uniform data set of local early-type galaxies from Prugniel & Simien. We take particular care in estimating the stellar masses, using a general star formation history, and comparing different population synthesis models. We find that the stellar M / L contributes little to the tilt. We estimate the total M / L using simple Jeans dynamical models, and find that adopting accurate luminosity profiles is important but does not remove the need for an additional tilt component, which we ascribe to DM. We survey trends of the DM fraction within one effective radius, finding it to be roughly constant for galaxies fainter than   M _B∼−20.5  , and increasing with luminosity for the brighter galaxies; we detect no significant differences between S0s and fast- and slow-rotating ellipticals. We construct simplified cosmological mass models and find general consistency, where the DM transition point is caused by a change in the relation between luminosity and effective radius. A more refined model with varying galaxy star formation efficiency suggests a transition from total mass profiles (including DM) of faint galaxies distributed similarly to the light to near-isothermal profiles for the bright galaxies. These conclusions are sensitive to various systematic uncertainties which we investigate in detail, but are consistent with the results of dynamical studies at larger radii.     

Anomalous Diffuse CO2 Emissions at the Masaya Volcano (Nicaragua) Related to Seismic-Volcanic Unrest

Anomalous changes in the diffuse emission of carbon dioxide within the Masaya caldera have been observed before two seismic events that occurred at 10 and 30 km from the observation site. Their epicenters are located, respectively, south of Managua in Las Colinas (4.3 magnitude) and the Xiloa caldera (3.6 magnitude), in 2002 and 2003, recorded by the geochemical station located at El Comalito, Masaya volcano (Nicaragua). Anomalous increases were observed, which occurred around 50 and 8 days before the main seismic event that took place in Las Colinas, and 4 days before the seismic swarm at the Xiloa caldera, with a maximum CO₂ efflux of 9.3 and 10.7 kg m^?2 day^?1, respectively. The anomalous CO₂ efflux increases remained after filtering with multiple regression analysis was applied to the CO₂ efflux time series, which indicated that atmospheric variables, during the first 4 months, explained 23 % CO₂ variability, whereas, during the rest of the time series, CO₂ efflux values are poorly controlled with only 6 %. The observed anomalies of the diffuse CO₂ emission rate might be related to pressure changes within the volcanic–hydrothermal system and/or to geostructural changes in the crust due to stress/strain changes caused before and during the earthquakes’ formation, and seem not to be related to the activity of the main crater of Masaya volcano.