Human Losses Expected in Himalayan Earthquakes   总被引：1，自引：1，他引：0  

Max?WyssEmail author 《Natural Hazards》2005,34(3):305-314

Quantitative estimates of potential losses that may be caused by future great earthquakes along the Himalaya suggest that as many as 150,000 people may die, 300,000 may be injured and typically 3,000 settlements will be affected in a single event. Scenario results used here vary and are based on ruptures of 150 km segments of the plate boundary at seven positions, where sufficient elastic energy is believed to be stored for magnitude eight earthquakes. The method of calculating these results was calibrated, using the 17 disastrous Indian earthquakes, which have occurred since 1980. About 50 settlements in the region are considered most at risk because in each more than 2000 fatalities may occur.  相似文献   

Regional　Tectonic　Deformation　Background　and　Medium-　and　Short-Term　Precursors　to　the　Minle-Shandan　Earthquakes     

Zhang Xi 《中国地震研究》2005,19(1):12-21

INTRODUCTIONOnOctober 2 5,2 0 0 3,twoearthquakesofMS6 .1andMS5.8hitMinleandShandanofGansuProvinceinsuccession (at 38.4°N ,1 0 1 .2°E ;and 38.4°N ,1 0 1 .1°E) .Theseismicfaultisthrustandleft lateraltheMinle DamayingfaultwhichstrikesEWandisaffiliatedtot…  相似文献   

Deformation-enhanced metamorphic reactions and the rheology of high-pressure shear zones, Western Gneiss Region, Norway   总被引：4，自引：1，他引：4  

M. P. TERRY  F. HEIDELBACH 《Journal of Metamorphic Geology》2006,24(1):3-18

Microstructural and petrological analysis of samples with increasing strain in high‐pressure (HP) shear zones from the Haram garnet corona gabbro give insights into the deformation mechanisms of minerals, rheological properties of the shear zone and the role of deformation in enhancing metamorphic reactions. Scanning electron microscopy with electron backscattering diffraction (SEM–EBSD), compositional mapping and petrographic analysis were used to evaluate the nature of deformation in both reactants and products associated with eclogitization. Plagioclase with a shape‐preferred orientation that occurs in the interior part of layers in the mylonitic sample deformed by intracrystalline glide on the (0 0 1)[1 0 0] slip system. In omphacite, crystallographic preferred orientations indicate slip on (1 0 0)[0 0 1] and (1 1 0)[0 0 1] during deformation. Fine‐grained garnet deformed by diffusion creep and grain‐boundary sliding. Ilmenite deformed by dislocation glide on the basal and, at higher strains, prism planes in the a direction. Relationships among the minerals present and petrological analysis indicate that deformation and metamorphism in the shear zones began at 500–650 °C and 0.5–1.4 GPa and continued during prograde metamorphism to ultra‐high‐pressure (UHP) conditions. Both products and reactants show evidence of syn‐ and post‐kinematic growth indicating that prograde reactions continued after strain was partitioned away. The restriction of post‐kinematic growth to narrow regions at the interface of garnet and plagioclase and preservation of earlier syn‐kinematic microstructures in older parts layers that were involved in reactions during deformation show that diffusion distances were significantly shortened when strain was partitioned away, demonstrating that deformation played an important role in enhancing metamorphic reactions. Two important consequences of deformation observed in these shear zones are: (i) the homogenization of chemical composition gradients occurred by mixing and grain‐boundary migration and (ii) composition changes in zoned metamorphic garnet by lengthening diffusion distances. The application of experimental flow laws to the main phases present in nearly monomineralic layers yield upper limits for stresses of 100–150 MPa and lower limits for strain rates of 10^?12 to 10^?13 s^?1 as deformation conditions for the shear zones in the Haram gabbro that were produced during subduction of the Baltica craton and resulted in the production of HP and UHP metamorphic rocks.  相似文献   

On the resolving power of tomographic images in the Aegean area   总被引：2，自引：0，他引：2  

C. N. Ligdas  I. G. Main 《Geophysical Journal International》1991,107(1):197-203

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The imaging of upper mantle heterogeneity by seismic tomography is strongly limited by the uneven global distribution both of seismic recording stations and earthquake sources. This can result in a loss of resolution and significance in the final image, particularly when a sparse data set contains few ray paths which intersect at sufficiently high angles in the volume of interest. In order to investigate the theoretical resolving power of a previously published tomographic image of the Aegean area, synthetic tests of the inversion procedure using a ray-path matrix obtained in this previous study for local and teleseismic P -waves were carried out. The aim was to examine the extent to which the shape of a synthetic lithospheric slab penetrating to different depths is inherently distorted by the tomographic imaging procedure, and to compare the synthetic tomographic images with the results from the actual inversion. The distortion is found to take the form of an artificial stretching of the lithospheric slab. The maximum 'stretching factor', as indicated by the downdip displacement of the peak amplitude of the synthetic high-velocity anomaly, is found to be a factor of 2 or so, though the distortion is usually less than this. The peak amplitude of the tomographic image of a lithospheric slab is found from the inversion of traveltime data to be at depths at or below 400 km. This indicates that the high-velocity lithospheric slab in the Aegean penetrates deeper than the Benioff zone seismicity of about 200 km. However, no constraints of the maximum depth of penetration could be established with the data set used in the present work.  相似文献   

Active tectonics of the north and central Aegean Sea   总被引：20，自引：0，他引：20  

Tuncay Taymaz  James Jackson  Dan McKenzie 《Geophysical Journal International》1991,106(2):433-490

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Deformation and stress regimes in the Hellenic subduction zone from focal Mechanisms     

Marco?BohnhoffEmail author  Hans-Peter?Harjes  Thomas?Meier 《Journal of Seismology》2005,9(3):341-366

Fault plane solutions for earthquakes in the central Hellenic arc are analysed to determine the deformation and stress regimes in the Hellenic subduction zone in the vicinity of Crete. Fault mechanisms for earthquakes recorded by various networks or contained in global catalogues are collected. In addition, 34 fault plane solutions are determined for events recorded by our own local temporary network on central Crete in 2000–2001. The entire data set of 264 source mechanisms is examined for types of faulting and spatial clustering of mechanisms. Eight regions with significantly varying characteristic types of faulting are identified of which the upper (Aegean) plate includes four. Three regions contain interplate seismicity along the Hellenic arc from west to east and all events below are identified to occur within the subducting African lithosphere. We perform stress tensor inversion to each of the subsets in order to determine the stress field. Results indicate a uniform N-NNE direction of relative plate motion between the Ionian Sea and Rhodes resulting in orthogonal convergence in the western forearc and oblique (40–50^∘) subduction in the eastern forearc. There, the plate boundary migrates towards the SE resulting in left-lateral strike-slip faulting that extends to onshore Eastern Crete. N110^∘E trending normal faulting in the Aegean plate at this part is in accordance with this model. Along-arc extension is observed on Western Crete. Fault plane solutions for earthquakes within the dipping African lithosphere indicate that slab pull is the dominant force within the subduction process and responsible for the roll-back of the Hellenic subduction zone.  相似文献   

A Melt Inclusion Record of Volatiles, Trace Elements and Li-B Isotope Variations in a Single Magma System from the Plat Pays Volcanic Complex, Dominica, Lesser Antilles   总被引：2，自引：0，他引：2  

GURENKO  ANDREY A.; TRUMBULL  ROBERT B.; THOMAS  RAINER; LINDSAY  JAN M. 《Journal of Petrology》2005,46(12):2495-2526

Glass inclusions in plagioclase and orthopyroxene from daciticpumice of the Cabrits Dome, Plat Pays Volcanic Complex in southernDominica reveal a complexity of element behavior and Li–Bisotope variations in a single volcanic center that would gounnoticed in a whole-rock study. Inclusions and matrix glassesare high-silica rhyolite with compositions consistent with about50% fractional crystallization of the observed phenocrysts.Estimated crystallization conditions are 760–880°C,200 MPa and oxygen fugacity of FMQ + 1 to +2 log units (whereFMQ is the fayalite–magnetite–quartz buffer). Manyinclusion glasses are volatile-rich (up to 6 wt % H₂O and 2900ppm Cl), but contents range down to 1 wt % H₂O and 2000 ppmCl as a result of shallow-level degassing. Sulfur contents arelow throughout, with <350 ppm S. The trace element compositionof inclusion glasses shows enrichment in light rare earth elements(LREE; (La/Sm)_n = 2·5–6·6) and elevatedBa, Th and K contents compared with whole rocks and similaror lower Nb and heavy REE (HREE; (Gd/Yb)_n = 0·5–1·0).Lithium and boron concentrations and isotope ratios in meltinclusions are highly variable (20–60 ppm Li with ⁷Li= +4 to +15 ± 2; 60–100 ppm B with ¹¹B = +6 to+13 ± 2) and imply trapping of isotopically heterogeneous,hybrid melts. Multiple sources and processes are required toexplain these features. The mid-ocean ridge basalt (MORB)-likeHREE, Nb and Y signature reflects the parental magma(s) derivedfrom the mantle wedge. Positive Ba/Nb, B/Nb and Th/Nb correlationsin inclusion glasses indicate coupled enrichment in stronglyfluid-mobile (Ba, B) and less-mobile (Th, Nb) trace elements,which can be explained by fractional crystallization of plagioclase,orthopyroxene and Fe–Ti oxides. The ⁷Li and ¹¹B valuesare at the high end of known ranges for other island arc magmas.We attribute the high values to a ¹¹B and ⁷Li-enriched slabcomponent derived from sea-floor-altered oceanic crust and possiblyfurther enriched in heavy isotopes by dehydration fractionation.The heterogeneity of isotope ratios in the evolved, trappedmelts is attributed to shallow-level assimilation of older volcanicrocks of the Plat Pays Volcanic Complex. KEY WORDS: subduction; volcanic arcs; igneous processes; melt inclusions; SIMS; trace elements; lithium and boron isotopes; diffusion  相似文献   

评述“前陆盆地”名词在中国中西部含油气盆地中的引用——反思中国石油构造学的发展   总被引：22，自引：5，他引：17  

罗志立  刘树根 《地质论评》2002,48(4):398-407

“前陆盆地”一词,在中国中西部含油气盆地研究中被许多学者广泛引用,在空间上有“泛前陆盆地化”,在地史演化中有“扩大化”,名词术语引用上有“复杂化”的倾向,因而引起同行的关注。本文从文献中追踪前陆盆地原命名者的涵义和沿革,正确理解国外学者提出前陆盆地的特及模式,再根据中国的实际地质特征与国外典型前陆盆地对比,结果发现我国中西部前陆盆地的特殊在于大国外所称的前陆盆地的共同性。因而认为在中国中西部直接引用“前陆盆地”一词不当。建议采用“陆内俯冲型前陆盆地”（Intracontinental subduction foreland basin）一(间称－C型前陆盆地）,以示有中国地质特色的前陆盆地,为今后建立油气成藏模式和指导油气勘探理论依据。最后,还讨论了中国石油学发展中,值得反思的3个问题。  相似文献   

A site effect study in the Verchiano valley during the 1997 Umbria-Marche (Central Italy) earthquakes     

Stéphane Gaffet  Giovanna Cultrera  Michel Dietrich  Françoise Courboulex  Fabrizio Marra  Michel Bouchon  Arrigo Caserta  Cécile Cornou  Anne Deschamps  Jean-Paul Glot  Robert Guiguet 《Journal of Seismology》2000,4(4):525-541

Strong site effects were observed during the two M _W 5.7 and M _W 6.0 main shocks of the Colfiorito seismic crisis which occured on September 26, 1997 in Umbria-Marche (Central Italy).The most obvious indications of these effects are the dramatic differences in damage shown by buildings of similar construction in neighboring villages.Such observations were specifically made in the Verchiano valley in the fault area, 15 km south of Colfiorito where the Verchiano village and the Colle and Camino hamlets were heavily damaged (MCS intensity IX-X) since the first main shock of 1997/09/26,while in contrast, the Curasci village located 2 km eastwards remains almost intact.In order to study the anomalous ground motion amplifications in this area, an array of 11, 3-components seismo- and accelero-meters was set up during the 1997/10/20-24 period, extending from the western side of the valley, up to the top of Mount San Salvatore, going accross the Colle and Curasci hamlets.During the experiment, 67 aftershocks enlightened the valley from the Colfiorito (10 km north) and the Sellano (6 km south) active swarms.Seismic refraction experiments were conducted at the same time in the 500 m wide, 1500 m long Verchiano valley in order to determine the thickness and main characteristics of the alluvial infilling.The main results are: (i) compared to the valley side ground motion, and for all the events, recordings in the central part of the valley (piana di Verchiano) show relative amplification of 10 with a clear lengthening of the seismogram duration by a factor of 2 – (ii) broad band relative amplification of 6–8 is also clearly identified at the top of the Mount San Salvatore overhanging the valley – (iii) any of the site effect measurements done explains by itself the strongly contrasted damage observed at Colle and Curasci: i.e. the modification of the near-field radiation pattern by interaction with the free heterogeneous surface may have induced local shadow zones that saved Curasci.  相似文献   

大陆深俯冲的最大深度——来自数值模拟实验的结果   总被引：1，自引：0，他引：1  

张可丰  方之楚徐备 何金有 《岩石学报》2005,21(4):1311-1315

采用粘弹性材料8块体有限元模型并设定温度场后进行的大陆深俯冲二维数值模拟表明,在组合载荷(负浮力、洋中脊推力从上到下10～30MPa 和地幔对流拖曳力100MPa)作用下,陆壳俯冲实际垂向位移可达117km,最终俯冲深度达到147km,而洋壳实际垂向位移约162km,最终俯冲深度达到231km;在洋壳、陆壳俯冲到一定深度以前,它们的俯冲速度基本保持不变,表现为洋壳、陆壳底端的位移-时间曲线近似为直线;当俯冲时间超过9Ma,洋壳、陆壳分别达到167km、96km 深度后,俯冲速度会越来越慢。  相似文献