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991.
A three-dimensional (3D) density model, approximated by two regional layers—the sedimentary cover and the crystalline crust (offshore, a sea-water layer was added), has been constructed in 1° averaging for the whole European continent. The crustal model is based on simplified velocity model represented by structure maps for main seismic horizons—the “seismic” basement and the Moho boundary. Laterally varying average density is assumed inside the model layers. Residual gravity anomalies, obtained by subtraction of the crustal gravity effect from the observed field, characterize the density heterogeneities in the upper mantle. Mantle anomalies are shown to correlate with the upper mantle velocity inhomogeneities revealed from seismic tomography data and geothermal data. Considering the type of mantle anomaly, specific features of the evolution and type of isostatic compensation, the sedimentary basins in Europe may be related into some groups: deep sedimentary basins located in the East European Platform and its northern and eastern margins (Peri-Caspian, Dnieper–Donets, Barents Sea Basins, Fore–Ural Trough) with no significant mantle anomalies; basins located on the activated thin crust of Variscan Western Europe and Mediterranean area with negative mantle anomalies of −150 to −200×10−5 ms−2 amplitude and the basins associated with suture zones at the western and southern margins of the East European Platform (Polish Trough, South Caspian Basin) characterized by positive mantle anomalies of 50–150×10−5 ms−2 magnitude. An analysis of the main features of the lithosphere structure of the basins in Europe and type of the compensation has been carried out. 相似文献
992.
Aeromagnetic signatures over the Edward VII Peninsula (E7) provide new insight into the largely ice-covered and unexplored eastern flank of the Ross Sea Rift (RSR). Positive anomalies, 10–40 km in wavelength and with amplitudes ranging from 50 to 500 nT could reveal buried Late Devonian(?)–Early Carboniferous Ford Granodiorite plutons. This is suggested by similar magnetic signature over exposed, coeval Admiralty Intrusives of the Transantarctic Mountains (TAM). Geochemical data from mid-Cretaceous Byrd Coast Granite, contact metamorphic effects on Swanson Formation and hornblende-bearing granitoid dredge samples strengthen this magnetic interpretation, making alternative explanations less probable. These magnetic anomalies over formerly adjacent TAM and western Marie Byrd Land (wMBL) terranes resemble signatures typically observed over magnetite-rich magmatic arc plutons. Shorter wavelength (5 km) 150 nT anomalies could speculatively mark mid-Cretaceous mafic dikes of the E7, similar to those exposed over the adjacent Ford Ranges. Anomalies with amplitudes of 100–360 nT over the Sulzberger Bay and at the margin of the Sulzberger Ice Shelf likely reveal mafic Late Cenozoic(?) volcanic rocks emplaced along linear rift fabric trends. Buried volcanic rock at the margin of the interpreted half-graben-like “Sulzberger Ice Shelf Block” is modelled in the Kizer Island area. The volcanic rock is marked by a coincident positive Bouguer gravity anomaly. Late Cenozoic volcanic rocks over the TAM, in the RSR, and beneath the West Antarctic Ice Sheet exhibit comparable magnetic anomaly signature reflecting regional West Antarctic Rift fabric. Interpreted mafic magmatism of the E7 is likely related to mid-Cretaceous and Late Cenozoic regional crustal extension and possible mantle plume activity over wMBL. Magnetic lineaments of the E7 are enhanced in maximum horizontal gradient of pseudo-gravity, vertical derivative and 3D Euler Deconvolution maps. Apparent vertical offsets in magnetic basement at the location of the lineaments and spatially associated mafic dikes and volcanic rocks result from 2.5D magnetic modelling. A rift-related fault origin for the magnetic lineaments, segmenting the E7 region into horst and graben blocks, is proposed by comparison with offshore seismic reflection, marine gravity, on-land gravity, radio-echo sounding, apatite fission track data and structural geology. The NNW magnetic lineament, which we interpret to mark the eastern RSR shoulder, forms the western margin of the “Alexandra Mountains horst”. This fundamental aeromagnetic feature lies on strike with the Colbeck Trough, a prominent NNW half-graben linked to Late Cretaceous(?) and Cenozoic(?) faulting in the eastern RSR. East–west and north–north–east to NE magnetic trends are also imaged. Magnetic trends, if interpreted as reflecting the signature of rift-related normal faults, would imply N–S to NE crustal extension followed by later northwest–southeast directed extension. NW–SE extension would be compatible with Cenozoic(?) oblique RSR rifting. Previous structural data from the Ford Ranges have, however, been interpreted to indicate that both Cretaceous and Cenozoic extensions were N–S to NE–SW directed. 相似文献
993.
994.
对永胜6级地震的预报及依据 总被引:2,自引:1,他引:2
2001年10月27日在云南永胜发生6.0级地震,震前四川省地震局有较准确的中期和短临预报,加强了川滇交界地区的地震监测预报工作,并且向四川省政府作了汇报,取得了明显的社会效益。经验性地震预报重视川滇菱形地块西界断裂带动态活动图像的分析,尤其对历史强震破裂空段附近出现的中小震活动带或新活跃区段的研究;同时,重视4级前震群、川滇交界地区地下水位、水温、形变观测异常的跟踪分析和震情预测。 相似文献
995.
半无限空间中圆形孔洞周围SH波的散射 总被引:14,自引:5,他引:14
建立了求解在含有圆形孔洞的弹性半空间中SH波散射与圆形孔洞附近动应力集中问题的解析方法。利用SH波散射的对称性和多极坐标的方法,构造了一个可以预先满足半空间自由表面上应力自由边界条件的圆形孔洞对SH波散射的波函数。利用这一波函数,则可将该问题转化成对一个圆形孔洞散射的求解问题。该问题的解答最终又可归结为对一组无究代数方程组的求解问题,并可利用截断有限项的方法对其进行计算,最后给出了有关圆形也洞附近动应力集中问题的算例和数值结果,并讨论了波数与圆孔至自由边界距离变化对动应力集中的影响。 相似文献
996.
997.
小波变换在少震、弱震区地下水位数据分析中的应用 总被引:12,自引:2,他引:12
利用小波变换和多尺度分析原理,对位于少震弱震区的湖南的具有不同变化形态的6口典型井4年的水位日均值序列进行了分析。结果显示,通过多尺度分析可以很方便地将水位日均值序列中的高频部分与低频部分分开,而且对不同井孔的含水层系统而言,分离出去的频率成分的主模是不同的,这反应出不同井孔的含水层系统对同一频率的响应存在差异,主模的频率反映了正常背景下井孔-含水层系统的优势频率。Morlet小波分析的结果对时间序列的突然变化和周期结构都有很好的反映。 相似文献
998.
999.
本文对辽宁省防震减灾“九五”重点项目实施过程中采取的管理体制及管理措施进行了介绍。在管理体制上 ,建立了较为完善的组织机制构 ,按照全省地震系统一盘棋的指导思想 ,把市地震局作为一级管理机构 ,由市地震局负责本地区项目的实施与组织管理工作 ;在项目管理中 ,采取了跟踪检查、抓样板示范、抓项目施工质量、抓创新、抓技术培训等行之有效的措施 ,为“九五”重点项目的顺利完成并取得较好成绩提供了保证 相似文献
1000.
Introduction Bohai Bay, along with its adjacent areas, is one of the seismically active areas in North China. Understanding its crust/upper-mantle structural characteristics and lateral heterogeneity of the medium in this area is of great significance to the study of seismogenic environment, thus improvimg the level of earthquake prediction. For years, scientists have studied the area by gravity and magnetic methods (FENG, et al, 1989), geothermal field (WU, et al, 1988; TIAN, ZHANG, 19… 相似文献