由卫星和航空磁测成果推断中国岩石圈的磁性特征   总被引：11，自引：2，他引：11  

张昌达 《地球物理学进展》2003,18(1):103-110

根据前人所得卫星和航磁异常解释结果，作者的综合研究表明：(1)在塔里木、四川和松辽盒地，地壳呈强磁性，至少可分为两层，上层磁化强度为1A／m，下层为2A／m或更强一些。在上述盆地中央，地幔顶部约10km厚，也是强磁性的，此外，在南中国海，地壳和地幔顶部也是强磁性的，卫星磁异常的源位于上述部位。(2)西藏高原，中国东南沿海一带以及其他一些褶皱带之下，地壳是弱磁性的，磁性层在地表以下30km以内，磁化强度约0.66A/m。特别要指出的是，在东南沿海一带，磁性层底面和莫霍面重合，而居里等温面恰在莫霍面之下，因此这个带可能是Wasilewsky PJ等提出的“莫霍面是一个磁性界面”的一例。  相似文献   

On the Incorporation of the Effect of Crustal Structure into Empirical Strong Ground Motion Estimation     

J. Douglas  P. Suhadolc  G. Costa 《Bulletin of Earthquake Engineering》2004,2(1):75-99

This article has two purposes. Firstly, a validation exercise of the modal summation technique for the computation of synthetic strong-motion records is performed for two regions of Europe (Umbria-Marche and south Iceland), using a variety of region specific crustal structure models, by comparing the predicted ground motion amplitudes with observed motions. It is found that the rate of decay of ground motions is well predicted by the theoretical decay curves but that the absolute size of the ground motions is underpredicted by the synthetic time-histories. This is thought to be due to the presence of low-velocity surface layers that amplify the ground motions but are not included in the crustal structure models used to compute the synthetic time-histories. Secondly, a new distance metric based on the computed theoretical decay curves is introduced which should have the ability to model the complex decay of strong ground motions. The ability of this new distance metric to reduce the associated scatter in empirically derived equations for the estimation of strong ground motions is tested. It is found that it does not lead to a reduction in the scatter but this is thought to be due to the use of crustal structure models that are not accurate or detailed enough for the regions studied. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Modélisation morphodynamique cross-shore d'un estran vaseux     

Benoı̂t Waeles  Pierre Le Hir  Ricardo Silva Jacinto 《Comptes Rendus Geoscience》2004,336(11):1025-1033

Numerical experiments were performed to simulate the profile evolution of an intertidal mudflat with a 1D cross-shore morphodynamical model. First, the hydrodynamical forcing is a cross-shore tidal current due to semi-diurnal variations of the free surface elevation at the open boundary. Further, considering the conservation of the action density of surface gravity waves, a wave height (and resulting bottom shear stress) calculation is added to the morphodynamical model. Results of the numerical experiments show that the shape of the profile reaches equilibrium. The mudflat progrades continually when the forcing is tide only, whereas it can be steady under the simultaneous action of tide and waves. To cite this article: B. Waeles et al., C. R. Geoscience 336 (2004).  相似文献   

Archaeoseismic record at the ancient Roman City of Baelo Claudia (Cádiz, south Spain)     

P.G. Silva  F. Borja  C. Zazo  J.L. Goy  T. Bardají  L. De Luque  J. Lario  C.J. Dabrio 《Tectonophysics》2005,408(1-4):129

This study represents the first paleoseismic approach in Spain in which archaeological remains are considered. The ancient Roman city of Baelo Claudia (1st–4th centuries AD), located at the axial zone of the Gibraltar Strait (Cadiz, south Spain), contains abundant disrupted architectural relics and ground collapses (i.e. landsliding, liquefacion) probably related to historic earthquake damage of intensity IX–X MSK. The archaeological stratigraphy of the city evidence two major episodes of abrupt city destruction bracketed in AD 40–60 and AD 350–395 separated by an intervening horizon of demolition for city rebuilding, otherwise characteristic for many earthquake-damaged archaeological sites in the Mediterranean. The second episode led the eventual city abandonment, and it is evidenced by good examples of column collapse, distortion, failure and breakdown of house and city walls, and pavement warping and disruptions documented during different archaeological excavations, which can be catalogued as secondary coseismic effects. Main damaged relicts observable today are the set of pop-up like arrays and warping developed in the ancient Roman pavement. Their analysis indicate an anomalous westwards ground displacement oblique to the main gentle southward slope of the topography, as also evidence failures, collapses and breakdown of walls and columns, suggesting that stress acted in a broad SW–NE/WSW–ENE orientation consistent whit the expectable motion along the largest NE–SW strike-slip faults of the zone, which in turn can be catalogued as seismic sources of moderate events (ca. 5 mb). Major disruptions and city abandonment were hesitantly related to relatively far strong earthquakes occurred during the late 4th century AD in the Mediterranean or western coast of Iberia by Menanteau et al. [Menanteau, L., Vanney, J.R., Zazo, C., 1983. Belo II : Belo et son environment (Detroit de Gibraltar), Etude physique d'un site antique. Pub. Casa de Velazquez, Serie Archeologie 4., Ed. Broccard, París.]. However, this study indicates that the occurrence of close moderate earthquakes jointly with the unstable character of the ground at the zone (site effect) is a more reliable hypothesis to explain the observed deformations.  相似文献   

Clustering and visualization of earthquake data in a grid environment     

Dave A.Yuen  Benjamin J. Kadlec  Evan F. Bollig  Witold Dzwinel  Zachary A. Garbow  Cesar R. S. da Silva 《Visual Geosciences》2005,10(1):1-12

We present a web client-server service WEB-IS, which we have developed for remote analysis and visualization of seismic data consisting of both small magnitude events and large earthquakes. We show that the problem-solving environment (PSE) intended for prediction of large magnitude earthquakes can be based on this WEB-IS idea. The clustering schemes, feature generation, feature extraction techniques and rendering algorithms form a computational framework of this environment. On the other hand, easy and fast access both to the seismic data distributed among distant computing resources and to computational and visualization resources can be realized in a GRID framework. We discuss the usefulness of NaradaBrokering (iNtegrated Asynchronous Real-time Adaptive Distributed Architecture) as a middleware, allowing for flexibility and high throughput for remote visualization of geophysical data. The WEB-IS functionality was tested both on synthetic and the actual earthquake catalogs. We consider the application of similar methodology for tsunami alerts.  相似文献   

Long-term deforestation in NW Spain: linking the Holocene fire history to vegetation change and human activities     

Joeri Kaal  Yolanda Carrión Marco  Eleni Asouti  Maria Martín Seijo  Antonio Martínez Cortizas  Manuela Costa Casáis  Felipe Criado Boado 《Quaternary Science Reviews》2011,30(1-2):161-175

The Holocene fire regime is thought to have had a key role in deforestation and shrubland expansion in Galicia (NW Spain) but the contribution of past societies to vegetation burning remains poorly understood. This may be, in part, due to the fact that detailed fire records from areas in close proximity to archaeological sites are scarce. To fill this gap, we performed charcoal analysis in five colluvial soils from an archaeological area (Campo Lameiro) and compared the results to earlier studies from this area and palaeo-ecological literature from NW Spain. This analysis allowed for the reconstruction of the vegetation and fire dynamics in the area during the last ca 11 000 yrs. In the Early Holocene, Fabaceae and Betula sp. were dominant in the charcoal record. Quercus sp. started to replace these species around 10 000 cal BP, forming a deciduous forest that prevailed during the Holocene Thermal Maximum until ～5500 cal BP. Following that, several cycles of potentially fire-induced forest regression with subsequent incomplete recovery eventually led to the formation of an open landscape dominated by shrubs (Erica sp. and Fabaceae). Major episodes of forest regression were (1) ～5500–5000 cal BP, which marks the mid-Holocene cooling after the Holocene Thermal Maximum, but also the period during which agropastoral activities in NW Spain became widespread, and (2) ～2000–1500 cal BP, which corresponds roughly to the end of the Roman Warm Period and the transition from the Roman to the Germanic period. The low degree of chronological precision, which is inherent in fire history reconstructions from colluvial soils, made it impossible to distinguish climatic from human-induced fires. Nonetheless, the abundance of synanthropic pollen indicators (e.g. Plantago lanceolata and Urtica dioica) since at least ～6000 cal BP strongly suggests that humans used fire to generate and maintain pasture.  相似文献   

Shallow necking depth and differential denudation linked to post‐rift continental reactivation: The origin of the Cenozoic basins in southeastern Brazil     

Rafael M. Silva  Victor Sacek 《地学学报》2019,31(6):527-533

The southeastern Brazilian margin presents post‐breakup Cenozoic tectonism that created a series of grabens and small sedimentary basins, known as the Continental Rift of Southeastern Brazil. The formation of this rift occurred long after the South Atlantic ocean opening and has been attributed to different mechanisms like regional uplift induced by hotspot activity, pulses of Andean orogeny and reactivation of pre‐existing faults. However, the proposed models lack an analytical or numerical verification from a geodynamic point of view. Based on finite element modelling of the lithospheric stress field evolution we conclude that a shallow necking depth, consistent with the hyperextended southeastern Brazilian margin, combined with differential denudation of the continent, resulted in an extensional stress field in the upper crust that induced the observed Cenozoic tectonism.  相似文献   

U–Pb SHRIMP data constraints on calc-alkaline granitoids with 1.3–1.6 Ga Nd TDM model ages from the central domain of the Borborema province,NE Brazil     

I.P. Guimarães  A.F. Silva Filho  C.N. Almeida  M.B. Macambira  R. Armstrong 《Journal of South American Earth Sciences》2011,31(4):383-396

The Tabira, Itapetim and Timbaúba granitoids are intruded into metasedimentary sequences and Cariris Velhos (Tonian) orthogneisses from the Central Domain of the Borborema Province, NE Brazil. They have U–Pb SHRIMP ages of 593 ± 7 Ma; 615 ± 9 Ma and 616 ± 5 Ma respectively. The studied granitoids have zircon cores inherited from the protholith, with a large number of analyses showing ²⁰⁶Pb/²³⁸U ages ranging from 950 to 1200 Ma. Oscillatory zoning typical of magmatic zircon is common, although it is faint in some inherited cores.The studied granitoids are calc-alkaline and show Nd T_DM model ages ranging from 1.30 to 1.56 Ga and ?Nd (600 Ma) ranging from ?2.40 to ?5.34. These values are similar to those recorded in the country rocks. The lowest values of ?Nd (600 Ma) were recorded in enclaves of dioritic composition. Nd and U–Pb SHRIMP data suggest a significant participation of the metasedimentary rocks in the protholith of these granitoids. The Mesoproterozoic Nd T_DM model ages recorded in the studied granitoids are interpreted as the result of a hybrid source involving melting of metagraywackes, metamafic rocks of Tonian ages and/or biotite – bearing orthogneisses (Cariris Velhos Orthogneisses). The resulted melting was modified by mingling with juvenile Brasiliano melts, diorite in composition.The Timbaúba granitoids intrusions are coeval with high-T metamorphism and flat-lying foliation forming event in an intracontinental setting, during the Brasiliano convergence and contractional deformation. The Itapetim Pluton was emplaced in the convergence - lateral escape setting and the Tabira granitoids were intruded after the flat-lying foliation event, representing sin transcurrent intrusions.Our data show that within the Central Domain of the Borborema Province, granitoids with similar petrographic and geochemical compositions can have distinct ages and be intruded in distinct tectonic regimes.  相似文献   

Throughfall patterns in sugarcane and riparian forest: understanding the effect of sugarcane age and land use conversion          下载免费PDF全文

Robson Willians da Costa Silva  Luiz Felippe Salemi  Rafael Pires Fernandes  Tatiana Morgan Berteli de Andrade  Jorge Marcos de Moraes  Plínio Barbosa de Camargo  Luiz Antonio Martinelli 《水文研究》2016,30(15):2579-2589

Sugarcane is an annual crop with a dynamic canopy that changes over time mainly because of genetic adaptation. There is uncertainty about the temporal trends of throughfall (TF) in this important commercial crop. In the present paper, we used troughs to measure TF in a third and fourth ratoon and subsequently in a fourth and fifth ratoon. Additional measurements were carried out in an adjacent riparian forest. There were no significant differences between cycles of sugarcane, growth phases and riparian forest. The TF results for ratoon crop and riparian forest in 2011/2012 were 76% and 79.5% of gross rainfall, respectively, while in 2012/2013, they were 79% and 78%, respectively. However, TF was remarkably lower in the riparian forest relative to ratoon from the second half of the culm formation and elongation phase (280 days after harvest) until harvest. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Numerical modelling of desiccation cracking     

Aruna L. Amarasiri  Jayantha K. Kodikara  Susanga Costa 《国际地质力学数值与分析法杂志》2011,35(1):82-96

The ability to model and predict the formation of desiccation cracks is potentially beneficial in many applications such as clay liner design, earth dam construction, and crop science, etc. However, most studies have focused on statistical analysis of crack patterns and qualitative study of contributing factors to crack development rather than prediction. Because it is exceedingly difficult to capture the nonlinear processes during desiccation in analytical modelling, most such models handle crack formation without considering variation of material properties with time, and are unattractive to use in realistic modelling. The data obtained from laboratory experiments on clay soil desiccating in moulds were used as a basis to develop a more refined model of desiccation cracking. In this study, the properties, such as matric suction, stiffness and tensile strength of soil, and base adhesion, could be expressed approximately as functions of moisture content. The initial conditions and the development of suction due to desiccation and the varying material properties were inputted to UDEC, a distinct element code, using its internal programming language FISH. The model was able to capture some essential physical aspects of crack evolution in soil contained in moulds with varying lengths, heights, and materials of construction. Extension of this methodology is potentially beneficial not only for modelling desiccation cracking in clay, but also in other systems with evolving material properties such as concrete structures and road pavements. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献