Infrared and electron microprobe analysis of tourmalines

Infrared and electron microprobe analysis of natural tourmalines from the dravite-schorl and elbaite-schorl series were carried out. The infrared study differentiates between OH groups located at the centre of hexagonal rings and those which are placed between hexagonal pillars and are coordinated to two Al ions. The correlation of infrared spectra with chemical composition of tourmalines made possible the assignment of different OH stretching bands to the more frequent octahedral cation associations. The study of the thermal dehydroxylation of tourmalines in air indentified the IR bands corresponding to OH bonded to Fe⁺² ions in AlAlFe, AlFeLi or FeFeFe environments. The change in intensity of the OH absorption lines with the sample orientation has permitted the identification of several orientations of the OH bond axes. Electron microprobe analysis of zoned coloured samples has shown that the Fe, Mn distribution is partially ordered in some samples of the elbaite-schorl series.     

The transition from an active to a passive margin (SW end of the South Shetland Trench, Antarctic Peninsula)

The lateral ending of the South Shetland Trench is analysed on the basis of swath bathymetry and multichannel seismic profiles in order to establish the tectonic and stratigraphic features of the transition from an northeastward active to a southwestward passive margin style. This trench is associated with a lithospheric-scale thrust accommodating the internal deformation in the Antarctic Plate and its lateral end represents the tip-line of this thrust. The evolutionary model deduced from the structures and the stratigraphic record includes a first stage with a compressional deformation, predating the end of the subduction in the southwestern part of the study area that produced reverse faults in the oceanic crust during the Tortonian. The second stage occurred during the Messinian and includes distributed compressional deformation around the tip-line of the basal detachment, originating a high at the base of the slope and the collapse of the now inactive accretionary prism of the passive margin. The initial subduction of the high at the base of the slope induced the deformation of the accretionary prism and the formation of another high in the shelf—the Shelf Transition High. The third stage, from the Early Pliocene to the present-day, includes the active compressional deformation of the shelf and the base-of-slope around the tip-line of the basal detachment, while extensional deformations are active in the outer swell of the trench.     

Structure of the Padul-Nigüelas Basin (S Spain) from H/V Ratios of Ambient Noise: Application of the Method to Study Peat and Coarse Sediments

—?This paper presents the results of the application of a technique of geophysical surveying based on resonance frequency of materials, in a small basin within the Internal Zones of the Betic Cordillera (southern Spain). The frequencies determined have enabled the main features of the basin's structure to be delineated, clearly identifying its asymmetry due to variations in the position of the rigid basement in different sectors. The results show that this method does not guarantee a perfect identification of coarse sediments, unless these overlie substantial more rigid materials. On the other hand, the same method was very effective for studying very soft sediments (peat), and it was possible to establish a quantitative relationship for determining the thickness of these sediments based on their resonance frequency. This relationship was then used to map peat thickness in the basin. The results have been compared with gravity studies and mechanical drillings undertaken in the region.     

Improving the Abel transform inversion using bending angles from FORMOSAT-3/COSMIC

The FORMOSAT-3/COSMIC satellite constellation has become an important tool toward providing global remote sensing data for sounding of the atmosphere of the earth and the ionosphere in particular. In this study, the electron density profiles are derived using the Abel transform inversion. Some drawbacks of this transform in LEO GPS sounding can be overcome by considering the separability concept: horizontal gradients of vertical total electron content (VTEC) information are incorporated by the inversion method, providing more accurate electron density determinations. The novelty presented in this paper with respect to previous works is the use of the phase change between the GPS transmitter and the LEO receiver as the main observable instead of the ionospheric combination of carrier phase observables for the implementation of separability in the inversion process. Some of the characteristics of the method when applied to the excess phase are discussed. The results obtained show the equivalence of both approaches but the method exposed in this work has the potentiality to be applied to the neutral atmosphere. Recent FORMOSAT-3/COSMIC data have been processed with both the classical Abel inversion and the separability approach and evaluated versus colocated ionosonde data.     

Improving explicit time integration by modal truncation techniques

This paper describes a modal weighting technique that improves the stability characteristics of explicit time-integration schemes used in structural dynamics. The central difference method was chosen as the trial algorithm because of its simplicity, both in terms of formulation and ease of numerical stability and convergence analysis. It is shown how explicit algorithms may be reformulated in order to make them stable for any integration time by attenuating high-frequency oscillation modes that are generated by mesh geometry rather than generic dynamical features. We discuss results from trial calculations obtained from mathematical models that represent hysteretic restoring force elements and an application on a physical, four-degree-of-freedom, base-isolated structure using the pseudodynamic technique. © 1998 John Wiley & Sons, Ltd.     

Mechanical aspects of thrust faulting driven by far-field compression and their implications for fold geometry

In this paper we present a mechanical model that intends to captures the kinematical aspects of thrust fault related folds induced by regional-scale far-field contraction. Fold shapes may be the only surface evidence of the geometry of underlying faults, so complex fault interactions are assessed in terms of how they influence fold geometry. We use the finite element method to model the fold and finite deformation frictional contact to model the activation and evolution of slip throughout preexisting faults. From several simulated 2D fault patterns we infer how one may form an anticline similar to that observed at Sheep Mountain Anticline, Wyoming.     

Reevaluation of the earthquakes of 10 March and 19 May 1951 in southern Spain

Damage and parameters of the earthquakes of 10 March and 19 May 1951 in southern Spain have been reevaluated. Data available do not allow accurate depth determinations and previous estimates of larger depths are not confirmed, so depths have been fixed at 30 km for both shocks. Magnitudes (Ms) have been determined as 5.4 and 5.6, respectively. Intensities estimated at 22 and 29 sites from contemporary documentary sources give maximum values of VI–VII and VI (EMS Scale), lower than previous estimates. The focal mechanism for the May shock is right-lateral strike-slip with a normal component of motion, with planes with strikes 273° and 169°; seismic moment 1.9 × 10¹⁶ Nm and dimension 6 km (radius of circular fault). Shocks are located near the boundary between the Iberian plateau and the Guadalquivir Basin and may be related to faults connected with this boundary.     

W3(OH)区域H2O脉泽的快速时变

通过对 Ｗ３（ＯＨ）区域 ２２ ＧＨz Ｈ_(２)Ｏ脉泽源的短时间跟踪观测,探测到速度为-５２．８ ｋｍ／ｓ子谱的流量密度呈线性下降趋势,变化时标约为 １９天．同时也观测到了整个脉 泽源的谱线宽度与该子谱的强度之间的相关变化．这些现象可能是由脉泽云之间的相 互碰撞导致脉泽抽运率的变化所引起的。