辽宁西部地区地震前后重力异常反映     

吴云成  李子涛 《东北地震研究》1997,13(2):13-19

采用高精度拉科斯特重力仪在辽宁西部地区进行多期重力重复测量，获得了较为丰富的基础资料，通过对资料的分析与研究，进一步加深了辽宁西部地区重力场变化的认识。特别是１９９４年１０月和１９９６年７月，在测区内及其附近相继发生ＭＬ４．９级和ＭＬ５．０级地震。而这两次地震为１９８８年以来在辽宁西部地区发生的最大地震。通过对该区流动重力资料空间上和时间上的研究分析，从中获得了震前重力变化的某些前兆信息。通过对该  相似文献   

永登5.8级地震前后的重力变化   总被引：2，自引：1，他引：2  

祝意青 《地震》1997,17(2):205-211

着重分析了１９９５年７月２２日永登５．８级地震前后的重力异常变化及其与地震的对应关系，对这次地震的探讨性分析，进一步说明流动重力测量对一些较大地震作出一定的预报是可行的。  相似文献   

石油重磁资料处理解释系统在微机上的实现     

吴健生  王家林 《物探化探计算技术》1996,18(1):35-46

微机技术的发展和石油重磁勘探的需要促使了石油重磁资料微机处理和解释系统的建立。系统由输入、输出辅助子系统、重磁场分离和转换子系统及五个反演解释子系统八部分组成。五个反演解释子系统针对重磁力方法在油气勘探中所能解决的地质问题的类型不同而设计。计算模块的选择注意到方法的有效和适应，地球物理综合解释的需要及平面与剖面、定量正演与反演相结合的重要性。实际应用例子说明系统建立的成功和有效  相似文献   

中国重力勘探的发展与展望   总被引：4，自引：0，他引：4       下载免费PDF全文

王懋基  蔡鑫  涂承林 《地球物理学报》1997,40(Z1):292-298

回顾了重力勘探半个世纪的发展概况，尤其是自80年代以来在技术方法上的进步对重力勘探发展的影响；概述重力勘探在区域重力调查、区域构造研究、油气勘探和固体矿产勘探等方面取得的成就；最后对重力勘探的发展方向，提出进一步发展的意见．  相似文献   

赣中(崇仁-东乡)重力场特征及其对温泉热源的控制     

曹俊昌  龚育龄徐方 《华东地质学院学报》2004,27(2):166-169

断裂构造能够引起重力场的异常分布，温泉热源的形成和空间展布主要受深大断裂、基底构造等地质因素控制。基于这一思路，根据该区重力资料，结合地质及其它地球物理资料对深部地质结构做了一些探讨。对重力资料进行了一些处理，挖掘深部地质信息，根据所得信息推断出了一些基底断裂，有一些是本次重力结果新发现的断裂。此外，还证实了前人已圈定的断裂构造，这些构造在控热、导热作用方面起着重要作用，深大断裂、基底构造它们交汇部位附近是寻找温泉热源的有利地区。  相似文献   

Long term variations in the mesospheric mean flow observed at Grahamstown (South Africa) and Adelaide (Australia)     

S.B. Malinga  L.M.G. Poole  R.A. Vincent 《Journal of Atmospheric and Solar》2004,66(18):1745

The seasonal and interannual behaviour of monthly mean winds at a height of 90 km recorded at Grahamstown (33.3°S, 26.5°E) and Adelaide (34.5°S, 138.5°E) between 1987 and 1994 are compared. The zonal wind is found to be consistently stronger at Grahamstown and is always eastward, whereas at Adelaide it sometimes reverses. Maxima tend to occur near the solstices, the primary maximum during summer at Grahamstown, in agreement with satellite results, and during winter at Adelaide. The meridional wind also tends to be stronger at Grahamstown, but at both stations is predominantly northward with a maximum in summer and generally not as strong as the zonal component. This seasonal behaviour is reasonably well understood in terms of the interaction of the mean flow with gravity waves propagating up from below, with coriolis forces also playing an important role in the case of the meridional wind. Satellite observations do not generally support the idea that longitudinal differences between the stations could be attributed to the presence of a tropospheric/stratospheric stationary wave. It is suggested that these differences are more probably associated with local effects. Interannual zonal wind patterns at the two sites are similar over the summer months but are less well correlated during the rest of the year. The underlying causes of this variability are not well understood but are most probably global in nature, at least during the summer.  相似文献   

Gravity anomalies and associated tectonic features over the Indian Peninsular Shield and adjoining ocean basins     

D.C. Mishra  K. Arora  V.M. Tiwari 《Tectonophysics》2004,379(1-4):61-76

A combined gravity map over the Indian Peninsular Shield (IPS) and adjoining oceans brings out well the inter-relationships between the older tectonic features of the continent and the adjoining younger oceanic features. The NW–SE, NE–SW and N–S Precambrian trends of the IPS are reflected in the structural trends of the Arabian Sea and the Bay of Bengal suggesting their probable reactivation. The Simple Bouguer anomaly map shows consistent increase in gravity value from the continent to the deep ocean basins, which is attributed to isostatic compensation due to variations in the crustal thickness. A crustal density model computed along a profile across this region suggests a thick crust of 35–40 km under the continent, which reduces to 22/20–24 km under the Bay of Bengal with thick sediments of 8–10 km underlain by crustal layers of density 2720 and 2900/2840 kg/m³. Large crustal thickness and trends of the gravity anomalies may suggest a transitional crust in the Bay of Bengal up to 150–200 km from the east coast. The crustal thickness under the Laxmi ridge and east of it in the Arabian Sea is 20 and 14 km, respectively, with 5–6 km thick Tertiary and Mesozoic sediments separated by a thin layer of Deccan Trap. Crustal layers of densities 2750 and 2950 kg/m³ underlie sediments. The crustal density model in this part of the Arabian Sea (east of Laxmi ridge) and the structural trends similar to the Indian Peninsular Shield suggest a continent–ocean transitional crust (COTC). The COTC may represent down dropped and submerged parts of the Indian crust evolved at the time of break-up along the west coast of India and passage of Reunion hotspot over India during late Cretaceous. The crustal model under this part also shows an underplated lower crust and a low density upper mantle, extending over the continent across the west coast of India, which appears to be related to the Deccan volcanism. The crustal thickness under the western Arabian Sea (west of the Laxmi ridge) reduces to 8–9 km with crustal layers of densities 2650 and 2870 kg/m³ representing an oceanic crust.  相似文献   

The 1.80–1.74-Ga gabbro–anorthosite–rapakivi Korosten Pluton in the Ukrainian Shield: a 3-D geophysical reconstruction of deep structure     

S. V. Bogdanova  I. K. Pashkevich  V. B. Buryanov  I. B. Makarenko  M. I. Orlyuk  V. M. Skobelev  V. I. Starostenko  O. V. Legostaeva 《Tectonophysics》2004,381(1-4):5

The deep structure of the gabbro–anorthosite–rapakivi granite (“AMCG-type”) Korosten Pluton (KP) in the northwestern Ukrainian Shield was studied by 3-D modelling of the gravity and magnetic fields together with previous seismic data. The KP occupies an area of ca. 12,500 km² and comprises several layered gabbro-anorthositic intrusions enveloped by large volumes of rapakivi-type granitoids. Between 1.80 and 1.74 Ga, the emplacement of mafic and associated granitoid melts took place in several pulses. The 3-D geophysical reconstruction included: (a) modelling of the density distribution in the crust using the observed Bouguer anomaly field constrained by seismic data on Moho depth, and (b) modelling of the magnetic anomaly field in order to outline rock domains of various magnetisation, size and shape in the upper and lower crust. The density modelling was referred to three depth levels of 0 to 5, 5 to 18, and 18 km to Moho, respectively. The 3-D reconstruction demonstrates close links between the subsurface geology of the KP and the structure of the lower crust. The existence of a non-magnetic body with anomalously high seismic velocity and density is documented. Most plausibly, it represents a gabbroic stock (a parent magma chamber) with a vertical extent of ca. 20 km, penetrating the entire lower crust. This stock has a half-cylindrical shape and a diameter of ca. 90 km. It appears to be connected with a crust–mantle transitional lens previously discovered by EUROBRIDGE seismic profiling. The position of the stock relative to the subsurface outlines of the KP is somewhat asymmetric. This may be due to a connection between the magmatism and sets of opposite-dipping faults initially developed during late Palaeoproterozoic collisional deformation in the Sarmatian crustal segment. Continuing movements and disturbances of the upper mantle and the lower crust during post-collisional tectonic events between 1.80 and 1.74 Ga may account for the long-lived, recurrent AMCG magmatism.  相似文献   

Slab behaviour and its surface expression: new insights from gravity modelling in the SE-Carpathians   总被引：1，自引：0，他引：1  

Blanka Sperner  Dumitru Ioane  Robert J. Lillie 《Tectonophysics》2004,382(1-2):51-84

We use lithosphere-scale gravity models to calculate gravity anomalies resulting from oceanic subduction, continental collision, slab steepening, delamination, and break-off. Local isostasy was assumed for determining vertical movements caused by mass changes related to these tectonic processes. Our results show that subduction is accompanied by basin subsidence on the upper plate caused by the heavy lithospheric root of the subducting slab. The basin evolution goes parallel with the slab evolution and shows considerable modifications when the processes at depth change (slab steepening, delamination, break-off). Characteristic gravity anomaly curves were acquired for the different tectonic scenarios. These curves together with other data (e.g. basin evolution on the upper and the lower plate) were used for the reconstruction of the tectonic evolution of the SE-Carpathians which includes Tertiary subduction and collision followed by slab steepening and delamination.  相似文献   

Processing and interpretation of the gravity field of the East African Rift: implication for crustal extension     

A. Tessema  L.A.G. Antoine 《Tectonophysics》2004,394(1-2):87-110

Compilation of new and existing gravity data were undertaken to assess the nature of the crust beneath the East African Rift System. Using 3D gravity modeling code crustal model of gravity profiles across two sectors of the rift were computed. The results are discussed in light of the structure of the rift system.The results of the 3D modeling of gravity profiles across the two rift zones revealed northward thinning of the crust. The maximum crustal attenuation occurs beneath the Afar depression, indicating the Afar rift undergoes an intense fragmentation of the crust resulting from faulting and magmatic activity. However, our computed crustal thickness below the Afar depression falls within an upper bound compared to elsewhere below tectonically active rift zones. This can be explained in terms of crustal accretion resulting from an impact of the Afar mantle plume since 30 Ma ago.The residual gravity obtained using high-cut filtering techniques reveals significant density contrast between the northern and southern sectors of the rift. The northern part of the rift is characterized by regular patterns of positive gravity anomalies, which can be interpreted in terms of a zone of crustal thinning through which relatively dense materials have intruded the overlying crust. In contrast, south of the Main Ethiopian Rift, the anomalies are characterized by random patterns and low amplitudes. The along-rift-axis variation in gravity anomalies implies that the style of crustal deformation changed progressively, beginning with regionally distributed crustal deformation, such as the one we observe within the more juvenile and wider southern segment of the rift, to localized deformation within the active and narrow rift zones of the northern sector of the Ethiopian Rift. We suggest that the key parameters controlling along-rift-axis variation in gravity anomalies are the rate of crustal extension, faulting and magmatic activities.  相似文献