Tectonothermal evolution of a foreland fold and thrust belt: the Cantabrian Zone (Iberian Variscan belt,NW Spain)

Analysis of the conodont colour alteration index and the Kübler index of illite allowed us the characterization of four types of very low‐ or low‐grade metamorphism in the Cantabrian Zone (CZ) and determination of their regional and temporal distribution. These types are: (1) an orogenic Variscan metamorphism present only in restricted areas of the western and north‐western parts of the CZ where epizonal conditions are reached; (2) a burial metamorphism that appears in the basal part of some nappes, where anchizonal conditions are sometimes achieved; the thermal peak preceded emplacement of the nappes; (3) a late‐Variscan metamorphism in the southern and south‐eastern parts of the CZ; a cleavage, cutting most of the Variscan folds, is associated with this metamorphism, which has been related to an extensional episode; (4) a contact metamorphism and hydrothermal activity associated with minor intrusive bodies. The extension continued after the Variscan deformation giving rise to hydrothermal activity during Permian times.     

Fractionation of oxygen isotopes between mammalian bone-phosphate and environmental drinking water

The δ¹⁸O of mammalian bone-phosphate varies linearly with δ¹⁸O of environmental water, but is not in isotopic equilibrium with that water. This situation is explained by a model of δ¹⁸O in body water in which the important fluxes of exchangeable oxygen through the body are taken into account. Fractionation of oxygen isotopes between body and environmental drinking water is dependent on the rates of drinking and respiration. Isotopic fractionation can be estimated from physiological data and the estimates correlate very well with observed fractionation. Species whose water consumption is large relatively to its energy expenditure is sensitive to isotopic ratio changes in environmental water.     

Oxygen isotope variations in phosphate of biogenic apatites,II. Phosphorite rocks

Phosphorites from sedimentary sequences ranging in age from Archaean to Recent were analysed for δ¹⁸O in both the PO₄ (δ¹⁸O_p) and CO₃ (δ¹⁸O_c) in the apatite lattice. The oxygen isotope record is considerably better preserved in phosphates than in either carbonates or cherts. The use of the Longinelli and Nuti [8] temperature equation yields temperatures for Recent phosphorites that are in good agreement with those measured in the field. The δ¹⁸O_p values of ancient phosphorites decrease with increasing age. These changes with time are not likely to be due to post-depositional exchange. Changes in δ¹⁸O values of seawater and variations of temperature with time can account for the δ¹⁸O_p time trend, but the latter explanation is preferred. In Ancient phosphorites δ¹⁸O_c in structurally bound carbonate in apatite is not a reliable geochemical indicator.     

Simulating strong ground motion with the `k -2 ' kinematic source model: An application to the seismic hazard in the Erzincan basin, Turkey

We present a seismic hazard application of a kinematic broad-bandrupture model. This model is based on the k-square dislocation distribution concept (Herrero and Bernard, 1994).Synthetic seismograms are calculated in the far-field approximation with alayered velocity medium for the 13 March 1992 Erzincan earthquake.With a parametrization of the source constrained by other studies,the far-field contribution correctly fits the recorded strong ground motion, which presents a 0.5 to 2 Hz dominant frequency range.As the k-square model is particularly well adapted to synthetize realistic strong-motion at short distances from the fault,it is a reliable tool for calculating seismic hazard maps around active faults. We thus present a synthetic peak ground acceleration map associatedwith the 13 March 1992 activated fault, for a 60 km × 60 km regionaround the epicenter taking into account a smoothed velocity structure ofthe basin in agreement with the absence of significant site effects related to1D resonance deduced from the aftershock records study.This map is compared with several post seismic reports: macroseismicintensities, detailed distribution of damage, and soil cracking andliquefaction. Our model shows that the values of the peak acceleration andvelocity can explain the dominant spatial distributionof these effects, which concentrates in a narrow band along theactivated segment fault, and in particular at its southernextremity. These results enable us to present such maps forhypothetical future earthquake ruptures, located on the major visible orinferred active fault segments in and around the basin. The effects ofthese potential sources are analyzed in relation to the 1992 eventeffects in order to eliminate unknown site responses. We show that thesouthern part of the basin is particularly exposed because of thepresence of strike-slip faults,and that the western part of the basin would suffer a significantlyhigher strong motion levelthan during the 1992 event with the activation of moderate sizednormal faults evidenced on thesouthwestern edge of the basin.     

High frequency strong ground motion modelling in the Catania area associated with the Ibleo-Maltese fault system

A hybrid statistical-deterministic approach has been applied to estimate strong ground motion parameters (PGA, spectral ordinates) in South-Eastern Sicily for a M = 7 earthquake. A number of 100 different rupture processes have been simulated along a composite fault system representing two segments of the Ibleo-Maltese fault scarp. Map at regional scale of mean PGA in the 0.5–20 Hz frequency band shows highest values (0.4–0.5 g) nearby and North of Catania, due to a dominant directivity effect. The COV parameter, which expresses the variability of PGA values as a function of source complexity, is higher in the region nearby and South of the town of Augusta, where, depending on the rupture history, rather large PGA values can be observed (>0.4 g). PGA attenuation curves suggest that an azimuthal variation could be related to the source extent and directivity. The response and pseudo acceleration spectra are computed for different sites in the town of Catania including an approximate 1D site response. Ground motion amplification effects at high frequency (5–20 Hz) are produced by thin shallow layer of soft clay, loose pyroclastites and fill. We observe small amplification effects, in the frequency ranges 2–3 Hz and 5–10 Hz, in sites where recent alluvia reach a thickness of some tens of meters. Otherwise, sites located on outcrops of massive lavas show moderate attenuation.     

NLTE analysis of massive ob stars in open clusters

We present a new method for deriving stellar masses and distances using the theory of radiatively driven winds as presented by Kudritzkiet al. (1989) and the stellar parameters derived from NLTE spectroscopic analysis. We illustrate the procedure with five stars observed in three open clusters and show that the method can be advantageous against the more usual of using the expression for the gravity. The comparison with evolutionary tracks indicates a possible discrepancy between the masses and helium abundances (when enhanced) derived from these tracks and those obtained by the other methods.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

The water balance of an Amazonian micro‐catchment: the effect of interannual variability of rainfall on hydrological behaviour

In humid tropical systems, the large intraseasonal and interannual variability of rainfall can significantly affect all components of the water balance. This variability and the lack of detailed hydrological and meteorological data in both temporal and spatial scales have created uncertainties regarding the closure of the water balance for the Amazon basin. Previous studies in Amazonian micro‐catchments suggested that both the unsaturated and groundwater system, which are not taken into consideration in basin‐wide water budgets published in the literature, play an important role in controlling the timing of runoff generation. In this paper, the components of the water balance and the variations in different storages within the system were examined using 3 years' data from a 6·58 km² micro‐catchment in central Amazonia. The role and relative importance of the various stores were examined. The results show a strong memory effect in the groundwater system that carries over seasonal climate anomalies from one year to the next and affects the hydrological response well beyond the time span of the anomaly. In addition, the deep unsaturated zone was found to play a key role in reducing most of the intraseasonal variability and also affected the groundwater recharge. This memory effect is crucial for sustaining streamflow and evaporation in years with rainfall deficiency. The memory effect caused by storage in the groundwater and unsaturated systems may also prevent the closure of annual large‐scale water balances, which assume that storage returns to a standard state each year. Copyright © 2007 John Wiley & Sons, Ltd.     

New applications of the Poisson distribution in micropalaeontology: relationships between environmental variables and the Ammonia tepida distribution in the south‐western Spanish estuaries

The application of the Poisson regression to the populations of the benthic foraminifer Ammonia tepida collected in three south‐western Spanish estuaries permits to obtain a quantitative approach between some environmental variables and the number of individuals of this species. Although the three general models are unsatisfactory to predict the observed abundance of this micro‐organism, a partial statistical analysis permits to detect quantitatively the impact of each variable. This analysis indicates an increasing abundance from the high‐salt marshes to the subtidal channels and higher densities in those samples subjected to very euryhaline conditions. Increasing sand percentages show negative effects on the A. tepida abundance, whereas the silt contents do not affect significantly to this species and increasing organic carbon percentages have a small positive effect on the A. tepida densities.