Optimal Model for Geoid Determination from Airborne Gravity   总被引：2，自引：0，他引：2  

Novák  Pavel 《Studia Geophysica et Geodaetica》2003,47(1):1-36

Two different approaches for transformation of airborne gravity disturbances, derived from gravity observations at low-elevation flying platforms, into geoidal undulations are formulated, tested and discussed in this contribution. Their mathematical models are based on Green's integral equations. They are in these two approaches defined at two different levels and also applied in a mutually reversed order. While one of these approaches corresponds to the classical method commonly applied in processing of ground gravity data, the other approach represents a new method for processing of gravity data in geoid determination that is unique to airborne gravimetry. Although theoretically equivalent in the continuous sense, both approaches are tested numerically for possible numerical advantages, especially due to the inverse of discretized Fredholm's integral equation of the first kind applied on different data. High-frequency synthetic gravity data burdened by the 2-mGal random noise, that are expected from current airborne gravity systems, are used for numerical testing. The results show that both approaches can deliver for the given data a comparable cm-level accuracy of the geoidal undulations. The new approach has, however, significantly higher computational efficiency. It would be thus recommended for real life geoid computations. Additional errors related to regularization of gravity data and the geoid, and to accuracy of the reference field, that would further deteriorate the quality of estimated geoidal undulations, are not considered in this study.  相似文献   

Extracting flow structures from tracer data     

Judit Schneider  Tamás Tél 《Ocean Dynamics》2003,53(2):64-72

A method of visualizing structures in closed chaotic flows out of homogenous particle distributions is presented in the example of models of a meandering jet. To this end, the system will be leaked or opened up by defining a region of the flow, so that a particle is considered to be escaped if it leaves this region. By applying this method to an ensemble of nonescaped tracers, we are able to characterize mixing processes by visualizing the converging and stretching filamentations (stable and unstable manifolds) in the flow without using additional mathematical tools. The possibility of applying the algorithm to analyze buoy data, and a comparison with the finite time manifolds are discussed.  相似文献   

An experimental study of nominally symmetric and asymmetric structures isolated with the FPS     

Juan C. de la Llera  Jos L. Almazn 《地震工程与结构动力学》2003,32(6):891-918

This experimental investigation deals with the earthquake behaviour of a nominally symmetric and a mass‐asymmetric three‐storey structural model isolated with the frictional pendulum system (FPS). Both accidental and natural torsion are evaluated in the structure by using recorded accelerations in all building floors and measured deformations at the isolation level. A 3D‐shaking table was used to subject the model to five different ground motions, including impulsive as well as far‐field subduction‐zone type earthquakes. Results show that the analytical predictions of the earthquake behaviour of the isolated structure, as obtained from a physical model of the FPS, are in close agreement with the true complex inelastic measured behaviour of the FPS. Besides, experimental results also validate previous observations about the importance of accounting for the variability of the normal loads in modelling the earthquake behaviour of FPS isolators. Measured torsional deformation amplifications at the base of the building vary, in the mean, from 2.5% to 6% for the symmetric and asymmetric structural configurations, respectively. In relation to the fixed base structure, the reduction factors for the base shear of the isolated structure are, in the mean, about 3.9 for both configurations. Finally, it is concluded that the FPS is capable of controlling the lateral–torsional motions of mass‐asymmetric structures quite effectively by aligning the centre of mass of the superstructure with the centre of pendular and frictional resistance of the isolation system. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Physical model for dynamic analysis of structures with FPS isolators     

Jos L. Almazn  Juan C. De la Llera 《地震工程与结构动力学》2003,32(8):1157-1184

This article presents a physical model for frictional pendulum isolators (FPS) that is ready to be implemented in most commercial software. The model is capable of accounting for effects such as large deformations, sticking, and uplift and impact by sensing the normal loads in the isolators through a gap element. Sticking has been incorporated into the model by extending the Park–Wen hysteretic model to the case of large deformations. The proposed model has been tested against a theoretically ‘exact’ formulation leading to essentially identical results. To facilitate its use, the physical FPS model has been cast into a typical non‐linear structural element format, i.e. with deformation as input and restoring force as output. Examples of a building and a bridge have been chosen to show the potential of the element and to provide further insight into the earthquake response of structures with FPS isolators; in particular, in aspects such as the orientation in placement of the isolator, sticking, P? Δ, and other large deformation effects. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Pre-Caving, Drilling and Blasting in the Esmeralda Sector of the El Teniente Mine     

E. Leiva  L. Dur  n 《Fragblast: International Journal for Blasting and Fragmentation》2003,7(2):87-104

El Teniente Mine has developed the method of panel caving as an innovative pre-conditioning caving alternative for traditional mining of sectors located in primary rock. In applying this method, caving speed and area incorporation are the most relevant parameters to establish a desired production level in a specified sector. This is the context in which continuous improvements to several design alternatives have been developed and applied to optimize mine caving. Mine caving, by drilling and blasting, results in a narrow base cut of ore columns not larger than the height of the caving galleries, which usually measure 3.6 m. These confined blasting operations require drilling parallel blastholes that extend from the floor to the roof of the caving gallery. Panel caving aims at mitigating subvertical field stress transmission to the lower levels of the caving gallery. This improves the stability and helps maintain the advancement of the caved zone at the caving level, with respect to the development, preparation and ore mining activities in the production level. This paper analyzes and evaluates different panel caving alternatives. The result is the identification of the most adequate panel caving alternative for conditions in the Esmeralda Mine given safety, technical, operational and economic considerations.  相似文献   

Lower crustal granulite xenoliths from the Pannonian Basin,Hungary, Part 2: Sr–Nd–Pb–Hf and O isotope evidence for formation of continental lower crust by tectonic emplacement of oceanic crust   总被引：3，自引：0，他引：3  

Gábor Dobosi  Pamela D. Kempton  Hilary Downes  Antal Embey-Isztin  Matthew Thirlwall  Peter Greenwood 《Contributions to Mineralogy and Petrology》2003,144(6):671-683

Mafic granulite xenoliths from the lower crust of the Pannonian Basin are dominated by LREE-depleted bulk-rock compositions. Many of these have MORB-like ¹⁴³Nd/¹⁴⁴Nd but ⁸⁷Sr/⁸⁶Sr is elevated relative to most MORBs. Their '¹⁸O values cover a wide range from +3.8 to +9.5‰. A group of LREE-enriched mafic granulites have higher ⁸⁷Sr/⁸⁶Sr (0.704-0.708) and lower ¹⁴³Nd/¹⁴⁴Nd (0.5128-0.5124), with higher '¹⁸O values on average (+7.8 to +10.6‰) than the LREE-depleted granulites. The LREE-enriched granulites are, however, isotopically similar to newly discovered metasedimentary granulite xenoliths. A sublinear correlation in )Hf-)Nd isotope space has a shallower slope than the crust-mantle array, with the metasedimentary rocks forming the low )Hf end member; the radiogenic end is restricted to the LREE-depleted granulites and these overlap the field of MORB. Pb isotopes for the LREE-depleted samples are less radiogenic on average than those of the LREE-enriched and metasedimentary xenoliths, and metasedimentary granulites have consistently higher ²⁰⁸Pb/²⁰⁴Pb. The wide range in '¹⁸O over a restricted range in Nd and Sr isotope values, in combination with the predominance of LREE-depleted trace-element compositions, is consistent with an origin as a package of hydrothermally altered oceanic crust. The existence of '¹⁸O values lower than average MORB and/or mantle peridotite requires that at least some of these rocks were hydrothermally altered at high temperature, presumably in the oceanic lower crust. The low ¹⁴³Nd/¹⁴⁴Nd of the LREE-enriched mafic granulites cannot be explained by simple mixing between a LREE-depleted melt and an enriched component, represented by the recovered metasediments. Instead, we interpret these rocks as the metamorphic equivalent of the shallowest levels of the ocean crust where pillow basalts are intimately intercalated with oceanic sediments. A possible model is accretion of oceanic crustal slices during subduction and convergence, followed by high-grade metamorphism during the Alpine orogeny.  相似文献   

Preliminary Rock-Slope-Susceptibility Assessment Using GIS and the SMR Classification   总被引：1，自引：1，他引：1  

Irigaray  C.  Fernández  T.  Chacón  J. 《Natural Hazards》2003,30(3):309-324

This paper aims to examine the impact of large-scale structuraladjustments (like the Greater Dhaka Flood Protection Project, GDFPP) on local living environment.It focuses the importance of environmental factors in flood hazard mitigation, and examines theenvironmental attitudes of the floodplain residents arising from the large-scale structural adjustments.Based on `perceived natural hazard research perspectives', this paper examines: (i) the reasons for persistentfloodplain occupation, and (ii) the importance of environmental factors in the choice, motivations and decision-makingof floodplain residents.This research used data collected from 300 households situated inthe eastern part of Dhaka. The face-to-face household survey data provided individuals' responses to a structuredquestionnaire on hazards and environment. Survey concerned urban floodplains, and looked fordata on housing, household characteristics, and residents' attitudes. Results of interview surveys wereused to: (i) explore the reasons of floodplain occupation, and (ii) residents' attitudes to tolerable levelof flood risk and willingness to accept environmental change resulting from the proposed structural embankments inthe eastern perimeter of Dhaka City, Bangladesh.Findings revealed that floodplain occupation (by theindividuals' decision-making) was a result of overall reaction to the Government's structuraladjustment policies that resulted from institutional, locational and socio-economic factors. The attitude survey results provided residents' perception to hazards and environment to be dependenton the socio-economic factors – but in a complex manner, many factors are interrelated.In addition to support for structural embankments, the study sample displayed a common concernand widespread environmental awareness. In terms of any `trade-off' between thebenefits (resources) from the embankments and costs (hazards) due to the detrimental impact on environment, the residents of Dhaka, despite some concern forsacrificing embankments for environment, tended to show a generalconsensus for embankments.  相似文献   

Surface-water quality for the Salí River watershed in NW Argentina     

J. Fernández-Turiel  C. Pérez-Miranda  G. Almada  M. Medina  C. Riviere  M. Gordillo 《Environmental Geology》2003,43(8):941-949

Spatial and temporal variations of Na, Mg, Si, K, Ca, SO₄^2-, Cl^-, HCO₃^-, Ag, Al, As, Au, B, Ba, Be, Bi, Br, Ce, Cd, Co, Cr, Cs, Cu, Dy, Er, Eu, F, Fe, Ga, Ge, Gd, Hf, Hg, Ho, I, La, Li, Mn, Mo, Nb, Nd, Ni, P, Pb, Pr, Rb, Sb, Sm, Sn, Sr, Ta, Tb, Te, Th, Ti, Tl, U, V, W, Y, Yb, Zn, and Zr were monitored through 37 sampling stations to determine the main aspects influencing the surface-water quality in the Salí River watershed (Tucumán Province, NW Argentina). The influence of the regional geological setting on water chemistry allows to distinguish three sub-basins. The interaction with sedimentary rocks was found to be dominant in the northern and central-eastern sub-basin as well as in the southern sub-basin, whereas the metamorphic-granitic basement of the Pampean Ranges was noted in the central sub-basin. In addition, anthropogenic activities affect the spatial variation of K, P, Mn, Rb, and Pb as well as dissolved oxygen concentrations and Eh. Temporal water-quality variation is related to the spatial distribution of precipitation and to the seasonal character of the main local industries (sugar cane, alcohol, citrus), increasing P and K concentrations and decreasing dissolved oxygen concentration and Eh in winter. Cl^-, Na, SO₄^2-, Al, As, B, Fe, Mn, Se and U concentrations exceed the regulated drinking-water thresholds at several sampling stations.  相似文献   

Predictive GIS-Based Model of Rockfall Activity in Mountain Cliffs   总被引：6，自引：1，他引：6  

Marquínez  J.  Menéndez Duarte  R.  Farias  P.  JiméNez Sánchez  M. 《Natural Hazards》2003,30(3):341-360

Rockfall susceptibility has been analysed in mountain cliffs of the Cantabrian Range, North Spain. The main aim of this analysis has been to build a predictive model of rockfall activity from a low number of environmental and geological variables. The rockfall activity has been quantified in a GIS. The cartographic information used shows the spatial distribution of all the recent talus screes as well as their associated source areas in the rock-slopes. The area relation At/Ar (recent talus scree polygon/source basins) in the rock slopes has been used as the rockfall activity indicator. This relation has been validated in 50 pilot rock-slopes and compared with the relation number of recent rock fragments/source basin, obtained from field work. The environmental factors causing rockfall depend on the rock slope situation, and these are: altitude and sun radiation on the rock cliff. The geological factors considered are: lithology, relative position of the main discontinuities with respect to the topographic surface and two morphologic parameters: the roughness and slope gradient. A logistic regression analysis has been applied to a population of 442 limestone and quartzite rock cliffs. The dependent variable is the rockfall activity indicator, which allows the definition of two classes of rock cliff units: low and high activity. The independent variables are altitude, sun radiation (equinox radiation, summer solstice radiation, winter solstice radiation), slope roughness, slope gradient,anisotropy and lithology. Results suggest that it is possible tobuild a valid cartographic predictive model for rockfall activity in mountain rock cliffs from a limited number of easily obtainable variables. The method is especially applicable in massive rock slopes or in regions with uniform rock mass characteristics.  相似文献   

Architecture of fault zones determined from outcrop, cores, 3-D seismic tomography and geostatistical modeling: example from the Albalá Granitic Pluton, SW Iberian Variscan Massif     

J. Escuder Viruete  R. Carbonell  D. Martí  M. J. Jurado  A. Prez-Estaún 《Tectonophysics》2003,361(1-2):97-120

The 3-D seismic tomographic data are used together with field, core and well log structural information to determine the detailed 3-D architecture of fault zones in a granitic massif of volume 500×575×168 m at Mina Ratones area in the Albalá Granitic Pluton. To facilitate the integration of the different data, geostatistical simulation algorithms are applied to interpolate the relatively sparse structural (hard) control data conditioned to abundant but indirect 3-D (soft) seismic tomographic data. To effectively integrate geologic and tomographic data, 3-D migration of the velocity model from the time domain into the depth domain was essential. The resulting 3-D model constitutes an image of the fault zone architecture within the granitic massif that honours hard and soft data and provides an evaluation of the spatial variability of structural heterogeneities based on the computation of 3-D experimental variograms of Fracture Index (fault intensity) data. This probabilistic quantitative 3-D model of spatially heterogeneous fault zones is suitable for subsequent fluid flow simulations. The modeled image of the 3-D fault distribution is consistent with the fault architecture in the Mina Ratones area, which basically consists of two families of subvertical structures with NNE–SSW and ENE–WSW trends that displaces the surfaces of low-angle faults (North Fault) and follows their seismically detected staircase geometry. These brittle structures cut two subvertical dykes (27 and 27′ Dykes) with a NNE–SSW to N–S trend. The faults present high FI (FI>12) adjacent bands of irregular geometry in detail that intersect in space delimiting rhombohedral blocks of relatively less fractured granite (FI<6). Both structural domains likely correspond with the protolith and the damaged zone/fault core in the widely accepted model for fault zone architecture. Therefore, the construction of 3-D grids of the FI in granitic areas affected by brittle tectonics permits the quantitative structural characterization of the rock massif.  相似文献