南通地区新构造运动特征

从盆地沉积及其演变特征入手，总结了该区新构造运动特征；运用新构造运动理论对海岸线的变迁、长江的迁移及旋扭变形现象进行了探讨，并提出建立第四系各年代的地层沉降速率数学模型、用升降运动速率划分和对比第四纪地层的见解。     

The June 4th 1999 severe weather episode in San Quirino, Italy: a tornado event?

On the morning of June 4th 1999, a severe weather event took place in San Quirino, a small village of Friuli-Venezia Giulia in the northeast of Italy. This village is located near the piedmont of the Alps, 40 km west from Udine and 60 km north from Venice.Around 0900 UTC (1100 local time), a thunderstorm with an intense hail fall affected the area of San Quirino. A few minutes later (around 0920 UTC, source: a farmer), a funnel cloud from a cumulonimbus touched the ground, producing damages to houses, trees and sheds. The damaged area was quite narrow (about 300 m) and short (less than 10 km). No injuries to people were reported.In spite of the smallness of the area interested by the phenomenon, this storm is studied here starting from the synoptic scale, moving to the mesoscale and finishing with the storm scale, trying to underline its characteristics. These analyses, especially those coming from the Doppler radar images, bring us to the conclusion that the San Quirino episode was produced by a supercell storm.     

Fall vs flow activity during the 1991 climactic eruption of Pinatubo Volcano (Philippines)

Six years after the 1991 Mt. Pinatubo eruption, deep erosion incisions into the pyroclastic deposits accumulated around the volcano enabled us to investigate the stratigraphy of the climactic deposits both in valley bottoms and on contiguous ridges. Stratigraphic relationships between fall, flow, and surge deposits in the Marella drainage system indicate that during the climactic eruption a progressive shift occurred from an early convective regime, to a transitional regime feeding both the plinian convective column and mostly dilute density currents, to a fully collapsing regime producing mostly dense pyroclastic flows. Syn-plinian dilute density currents (surges) propagated up to ~10 km from the crater, both along valley bottoms and on contiguous ridges of the Marella Valley, whereas post-plinian pyroclastic flows had greater runout (~13 km), were confined to valleys and were not associated with significant surges. Stratigraphic study and grain-size analyses allow the identification of three types of intra-plinian deposits: (a) lower and often coarse-grained surge deposits, emplaced during the accumulation of the coarsest portion of the fallout bed at time intervals of ~16-24 min; (b) upper fine-grained surge deposits, interstratified with the fine-grained portion of the fall bed and emplaced at shorter time intervals of ~3-13 min; and (c) small-volume, channel-confined, massive pumiceous flow deposits interbedded with the upper surges in the upper fine-grained fall bed. Maximum clast size isopleths of 1.6 and 0.8 cm for lithics (ML) and 2.0 and 4.0 cm for pumices (MP) show almost symmetrical distribution around the vent, indicating that the passing of the typhoon Yunya during the climactic eruption had little effect on trajectories of high-Reynold-number clasts. Significant distortion was, however, observed for the 3.2-cm ML and 6.0-cm MP proximal isopleths, whose patterns were probably influenced by the interaction of the clasts falling from column margins with the uprising co-ignimbrite ash plumes. Application of the Carey and Sparks (1986) model to the undisturbed isopleths generated by the umbrella cloud yields a maximum column height of ~42 km, in good agreement with satellite measurements. Systematic stratigraphic and vertical grain-size studies of the plinian fall deposit in the Marella Valley, combined with satellite data and eyewitness accounts, reveal that the carrying capacity of the convective column and related fallout activity peaked in the early phase of the eruption, beginning slightly before 13:41 and gradually declined until its cessation 3 h later. Most of the pumiceous pyroclastic flow deposits were emplaced after the end of the fallout activity at ~16:30 but before the summit caldera collapse at approximately 19:11. Only a small volume of pumiceous flow deposits accumulated after the final caldera collapse. In contrast to the previous reconstruction of Holasek et al. (1996), which interpreted the progressive lowering of the column, documented by satellite data, as due to a decreasing mass eruption rate, we suggest that a progressive shift from a plinian column to a large co-ignimbrite column could also account for such a variation.     

MAPGIS下重磁数据直接成图的实现及意义

作者在文中介绍了通过编制QBASIC小程序实现两种常见格式重磁数据直接生成MAPGIS图形文件的方法，为其它类似格式数据在MAPGIS下成图及建库提供可借鉴的思路和途径。     

Modelling of ground motion in the vicinity of massive structures

A two-dimensional elastic Chebyshev spectral element method (SPEM) is used to model the seismic wavefield within a massive structure and in its vicinity. We consider 2-D models where a linear elastic structure, with quadrangular cross-section, resting on an elastic homogeneous half-space, is impinged upon by the waves generated by a surface impulse at some distance. The scattering of Rayleigh waves and the response of the structure are extensively analysed in a parametric way, varying size, mechanical parameters and shape of the load. Some of the models considered are representative of embankments and earth dams. The simulation shows that some models resonate, storing part of the incoming energy. With realistic parameters, the lowest resonance frequency is due to pure shear deformation and is controlled by the shear velocity and height of the load. Flexural modes are excited only at higher frequencies. The acceleration at the top of the structure may be five/seven times higher than at the base, depending on the mass of the structure. The gradual release of trapped energy produces a ground roll lasting several seconds after the wave front has passed. The ground-roll amplitude depends on the sturcture's mass and can be as large as 30% of the peak acceleration. Outside resonance conditions, the ground motion is almost unaffected by the presence of the artefact; the horizontal motion on top of it is nearly twice the motion at ground level. Similar results should be expected when the incident field is an upcoming shear wave. A qualitative discussion shows that the presence of anelastic attenuation in the embankment does not significantly alter the preceding conclusions, unless it is of very low values (e.g. Q < 15).The modelling results that we discuss indicate that the soil-structure interaction may substantially alter the ‘free-field’ ground motion. From a practical point of view, the main conclusions are: (1) careful analysis is necessary when interpreting seismic records collected in the vicinity of large artefacts; (2) seismic hazard at a site may depend on the presence of man-made structures such as embankments, dams, tall and massive buildings.     

基于计算机视觉的专题图读取系统

本文提出了一种基于计算机视觉的专题图读取系统方案。该系统用CCD相机获取专题图影象,通过线划跟踪、弧段矢量化、拓扑结构形成、数据压缩、几何纠正与拼接等步骤,实现专题图的自动读取,继而进行各种几何量算和统计,建立专题信息库     

A viscoelastic shear zone model of compressional and extensional plate boundaries

A model is proposed describing the mechanical evolution of a shear zone along compressional and extensional plate boundaries, subject to constant strain rate. The shear zones are assumed as viscoelastic with Maxwell rheology and with elastic and rheological parameters depending on temperature and petrology. Stress and strain are computed as functions of time and depth. For both kinds of boundaries the model reproduces the existence of a shallow seismogenic zone, characterized by a stress concentration. The thickness of the seismogenic layer is evaluated considering the variations of shear stress and frictional strength on faults embedded in the shear zone. Assuming that a fault dislocation takes place, the brittle-ductile transition is assumed to occur at the depth at which the time derivative of total shear stress changes from positive to negative values. The effects of different strain rates and geothermal gradients on the depth of the brittle-ductile transition are studied. The model predictions are consistent with values inferred from seismicity data of different boundary zones.     

Analysis of the vortivity and divergence of the thermal wind in pure geostrophic flow

By applying the horizontal del operator to the thermal wind equation in vectorial form and considering only horizontal geostrophic motion, expressions are found for the vorticity and divergence of thermal wind. It is shown that vorticity, in the case of pure geostrophic flow at all levels, depends upon four factors, namely: latitude, horizontal distribution of temperature, temperature lapse rate and divergence of horizontal temperature gradient. The divergence of the thermal wind, on the other hand, depends only upon the orientation of the mean isotherms of an isobaric layer relative to the parallel circles. These terms are evaluated and it is shown that the latitude term and the lapse rate term are far greater than the remaining terms of the vorticity equation for geostrophic flow. A criterion is then given which enables to determine the conditions for irrotational horizontal motion with vertical geostrophic wind shear.

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Zusammenfassung Durch Anwendung des horizontalenNabla-Operators auf die thermische Windgleichung in vektorieller Form und bei ausschließlicher Berücksichtigung der geostrophischen Horizontalbewegung lassen sich Ausdrücke für die vorticity und die Divergenz des thermischen Windes herleiten. Es wird gezeigt, daß die vorticity im Falle einer rein geostrophischen Strömung in allen Niveaus von folgenden vier Faktoren bedingt ist: Breite, horizontale Temperaturverteilung, vertikaler Temperaturgradient und Divergenz des horizontalen Temperaturgradienten. Andrerseits hängt die Divergenz des thermischen Windes nur von der Orientierung der mittleren Isothermen einer in Bezug auf die Parallelkreise isobaren Schicht ab. Diese vier Terme werden ausgewertet und es wird gezeigt, daß das Breitenglied und der Term für den Vertikalgradienten viel größer sind als die übrigen Terme der vorticity-Gleichung für geostrophische Strömung. Schließlich wird ein Kriterium entwickelt, das gestattet, die Bedingungen für rotorfreie Horizontalbewegung mit vertikaler geostrophischer Windscherung zu bestimmen.

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Résumé On peut déduire des équations sur la rotationelle et la divergence du vent thermique en appliquant l'opérateur nabla horizontal à l'équation du vent thermique sous une forme vectorielle et en ne considérant que le mouvement géostrophique horizontal. On démontre que la rotationelle, dans le cas d'un courant géostrophique pur, dépend dans tous les niveaux des quatre facteurs suivants: latitude, répartition horizontale de la température, gradient vertical de la température et divergence du gradient horizontal de température. D'autre part, la divergence du vent thermique ne dépend que de l'orientation des isothermes moyennes d'une couche isobare par rapport aux parallèles. En évaluant ces quatre termes, on montre que les termes relatifs à la latitude et au gradient vertical sont beaucoup plus grands que les autres termes de l'équation de la rotationelle pour un courant géostrophique. Pour terminer, l'auteur développe un critère qui permet de déterminer les conditions pour un mouvement horizontal irrotationel mais avec un cisaillement vertical géostrophique du vent.

     

Analysing Lava Risk for the Etnean Area: Simulation by Cellular Automata Methods

The model SCIARA, based on the Cellular Automata paradigm, is a versatile instrument whose scope is to analyse volcanic risk from lava flows.The possible fields of intervention are:[(a)] Long term forecasting of the flow direction at various eruption rates and points of emission by locating potential risk areas and permitting the creation of detailed maps of risk;[(b)] The possibility to follow the progress of an event and predict its evolution;[(c)] The verification of the possible effects of human intervention on real or simulated flows in stream deviation.A risk scenario has been developed for the Etnean territories of the towns of Nicolosi, Pedara and S. Alfio, simulating possible episodes with different vent locations along the fracture opened in the 1989 eruption and successively activated in the 1991–1993 eruption.The main characteristics of lava flows, that might be dangerous to the inhabited areas, have been analysed on the basis of the carried out Cellular Automata.