共查询到20条相似文献,搜索用时 156 毫秒
1.
本文以东大别构造带内六安—英山地磁剖面磁异常数据为基础,结合研究区域地质学和地震学研究成果,反演给出研究区域居里面埋深及地下介质磁性结构模型.通过对磁异常变化特征曲线、介质磁性结构模型分析发现:东大别构造带北部磁异常较强且波动较大、地下磁性结构特征相对复杂,北淮阳地区磁异常较弱、地下介质结构成叠瓦状形态分布,合肥盆地磁异常曲线变化平缓、埋深较深,为连续均匀的磁性基底,结果较好地反应了合肥盆地、北淮阳、东大别构造带北部之间的差异;"霍山地震窗"地壳下方6~12km处存在显著地磁性差异,结合东大别构造带内70年代以来地震和历史强震,对"霍山地震窗"地震活动性与地下构造、场源关系进行了研究,初步探讨了其动力学成因. 相似文献
2.
3.
湖南省重磁异常特征与地震活动关系 总被引:1,自引:0,他引:1
重力场的梯级带与地震的分布是有对应关系的。在湖南省布格重力异常资料的基础上,结合航磁资料,对湖南省的重磁异常特征进行了分析,并据此推断出湖南省内的深部构造,探讨了它们与地震活动的关系。这些分析研究将对湖南省的地震监测预报提供参考。 相似文献
4.
5.
本文依据深部地球物理场、区域大地构造、地表活动断裂、地震活动等,划分了中国大陆的地震构造带,同时分析了地震构造带的活动特征和孕震构造条件,在此基础上,具体地把地震构造带的概念应用于地震危险区分析之中,探讨了地震危险区及地震前兆异常与地震构造带的关系,本文提出以地震构造带研究作为地震监测和预报工作的基础,将地震构造带作为系统性的活动构造条件应用于地震危险区划分之中。 相似文献
6.
7.
8.
9.
10.
11.
Pearlyn C. Manalo Carla B. Dimalanta Noelynna T. Ramos Decibel V. Faustino-Eslava Karlo L. Queaño Graciano P. YumulJr. 《Surveys in Geophysics》2016,37(3):557-578
Ground and aeromagnetic data are combined to characterize the onshore and offshore magnetic properties of the central Philippines, whose tectonic setting is complicated by opposing subduction zones, large-scale strike-slip faulting and arc–continent collision. The striking difference between the magnetic signatures of the islands with established continental affinity and those of the islands belonging to the island arc terrane is observed. Negative magnetic anomalies are registered over the continental terrane, while positive magnetic anomalies are observed over the Philippine Mobile Belt. Several linear features in the magnetic anomaly map coincide with the trace of the Philippine Fault and its splays. Power spectral analysis of the magnetic data reveals that the Curie depth across the central Philippines varies. The deepest point of the magnetic crust is beneath Mindoro Island at 32 km. The Curie surface shallows toward the east: the Curie surface is 21 km deep between the islands of Sibuyan and Masbate, and 18 km deep at the junction of Buruanga Peninsula and Panay Island. The shallowest Curie surface (18 km) coincides with the boundary of the arc–continent collision, signifying the obduction of mantle rocks over the continental basement. Comparison of the calculated Curie depth with recent crustal thickness models reveals the same eastwards thinning trend and range of depths. The coincidence of the magnetic boundary and the density boundary may support the existence of a compositional boundary that reflects the crust–mantle interface. 相似文献
12.
普里兹湾位于南极洲东部大陆边缘,其深部地壳结构特征对认识白垩纪冈瓦纳古陆裂解和新生代大陆边缘形成具有重要意义.本文利用重磁、多道反射地震、声纳浮标折射地震和ODP钻井数据对普里兹湾海域的深部地壳结构进行了研究.研究结果显示,普里兹凹陷表现为典型的盆地负重力异常特征,其沉积基底较深,而在四夫人浅滩为高幅重力正异常,其沉积基底普遍抬升.在大陆架中部存在SW-NE向条带状基底的抬升,且呈朝NE向逐渐变深的趋势.在中大陆架外侧,均衡残余重力异常呈V字形负异常条带状分布,其两翼分别与四夫人浅滩和弗拉姆浅滩外的大陆坡相连.该异常带在大陆架中部向陆的偏移可能是由于古大陆架边缘的地形影响,推测其与普里兹冲积扇同属于洋陆过渡带向陆的部分,在重力模拟剖面表现为地壳向海逐渐减薄.普里兹冲积扇的地壳厚度较薄,平均为6 km,最薄处可达4.6 km,并且根据洋陆过渡带向海端的位置,推测可能属于接近洋壳厚度的过渡壳.重力异常分区的走向与兰伯特地堑在普里兹湾的构造走向基本一致,可能主要反映了二叠纪-三叠纪超级地幔柱对普里兹湾的裂谷作用的影响.该区域的自由空间重力异常和均衡残余异常均表现为超过100×10-5m/s2的高幅正异常特征,可能由位于大陆架边缘的巨厚沉积体负载在高强度岩石圈之上的区域挠曲均衡作用所导致,可能与该区域第二期裂谷期之后的沉积间断以及快速进积加厚的演化过程有关.普里兹湾磁力异常的走向与重力异常明显不同,大致可分为东北高幅正异常区和西南低幅异常区.重磁异常在走向上的差异反映高磁异常主要来源于岩浆作用形成的铁镁质火成岩的影响,并且岩浆作用的时代不同于基底隆升的时代,而可能形成于前寒武纪或者南极洲和印度板块裂谷期间(白垩纪). 相似文献
13.
W. Nienaber H.W. Dosso L.K. Law F.W. Jones V. Ramaswamy 《Physics of the Earth and Planetary Interiors》1977,15(1):69-76
Using an electromagnetic analogue model, the behavior of time-varying electromagnetic fields for an island near a continental coastline is examined for the H-polarization case, in which the electric field of the inducing source is perpendicular to the continental coastline. A study of the effect of the shape of the island, using square- and circular-island models, indicates that over the island, anomalies in the field components are confined to a smaller area for the circular island than for the square island. A study of the effect of ocean-channel width between the island and continent shows that, as the channel width decreases, anomalies in the magnetic field components over the island decrease. The anomaly in the electric field at the continental coastline first increases and then decreases with decreasing channel width. 相似文献
14.
南海经历了中生代主动大陆边缘到新生代被动大陆边缘的转换,其岩石层地球物理场具有明显的块、带特征.本文通过综合分析南海地区深地震探测、面波层析成像、重磁异常以及地热与岩石层流变学等各种地质地球物理资料,对南海地壳及岩石层的综合地球物理特征进行了深入总结,发现深地震探测剖面所确定的洋、陆壳转换位置与空间重力异常梯级带位置较为一致,据此拟定了南海洋、陆壳的转换边界;依据多条地壳结构剖面中拉张减薄的程度确定了正常减薄陆壳、洋陆壳过渡带及洋壳等属性特征,并初步圈定了南海下地壳高速层的分布范围.对比分析了南、北陆缘地壳结构及其拉张减薄的变化特征,从综合地球物理特征的相似性上推测了北部陆缘的中西沙陆块与南部陆缘的南沙礼乐滩陆块具有共轭对称性.依据S波速度梯度变化确定了南海岩石层厚度分布情况,揭示出南海北部陆缘存在一条岩石层厚度的减薄带,且该减薄带与高热流带具有较好的一致性.在综合分析的基础上,以深地震探测剖面与重、磁异常变化的对应性为基础,划定了南海边界构造的位置. 相似文献
15.
J.R. Weber 《Journal of Geodynamics》1986,6(1-4)
Gravity and bathymetric results from the 1983 Canadian Expedition to Study the Alpha Ridge (CESAR) have outlined positive free-air anomalies centred on the continental break off Ellesmere Island characteristic of normal Atlantic-type passive margins. These data confirm implications derived from depth-to-magnetic basement calculations that the ridge may not be structurally connected to the continent. Across the Alpha Ridge magnetic and gravity anomalies mimic the bathymetry. The magnetic anomalies apparently are not caused, to any great extent, by internal structures or magnetic reversals, but rather seem to result simply from variations in depths to a homogenous magnetic structure. The gravity anomalies across a 500 km wide section of the Alpha Ridge can be almost completely accounted for by topography, shallow sedimentary fill and a simple two-tier crustal model. This implies an extraordinary lateral density homogeneity unknown in continental structures of comparable size. Gravity models show the crustal thickness to increase gradually from 20 km at the Marvin Spur to 38 km at the ridge crest. A comparison of this model with a gravity model of the continental-type Lomonosov Ridge, which has a thickness of about 25 km, indicates that, at the same thickness of 25 km, the average crustal density of the Alpha Ridge is 0.08 Mg/m3 greater. These gravity constraints, the unusually homogenous seismic velocity structure revealed by the CESAR studies, the homogeneous magnetic structure, and the extraordinary high intensity satellite magnetic anomaly associated with the Alpha Ridge, indicate that the ridge may be composed of a large pile of mafic rock, possibly unique on this planet. 相似文献
16.
D.C. Mishra 《Earth and Planetary Science Letters》1984,71(1):173-180
Magnetic anomalies over the continental shelf off the east coast of India (Orissa) suggest the presence of a highly magnetic rock type magnetized with an intensity of 900 nT in a direction, azimuth(A) = 150° and inclination(I) = +65°. This suggest the occurrence of igneous volcanic rocks which is confirmed from samples found below Tertiary sediments from a few boreholes in this region. The depth of this rock type as estimated from magnetic anomalies varies from approximately 1–2 km near the coast to 4–4.5 km towards the shelf margin. This direction of magnetization is the reverse of the reported direction of magnetization for the Rajmahal Traps of the Cretaceous period (100–110 m.y). A small strip of the body near the continental shelf margin appears, however, to possess normal magnetization suggesting the occurrence of normal and reversed polarities side by side, a characteristic typical for oceanic magnetic anomalies. The reversed polarity of the rocks on the continental shelf suggests that they correspond probably to the MO reversal (115 m.y.) on world magnetostratigraphic scale and provide a paleolatitude of 47°S for the land mass of India which agrees with the palaeoreconstruction of India and Antarctica. In this reconstruction, the Mahanadi Gondwana graben on the Indian subcontinent falls into line with the Lambert Rift in Antarctica, suggesting a probable common ancestry. The volcanic rocks on the continental shelf off the east coast of India might represent a missing link, that is, rocks formed between India and Antarctica at the time of the break-up of Gondwanaland. Satellite magnetic anomalies (MAGSAT) recorded over the Indian shield and interpreted in terms of variations in the Curie point geotherm provide a direction of magnetization which also places this continent close to Antarctica. As such MAGSAT anomalies recorded over eastern Antarctica are found compatible with those recorded over the Indian shield. 相似文献
17.
《Earth and Planetary Science Letters》2006,241(3-4):686-698
The SISMAR seismic survey on the Moroccan Atlantic Margin recorded deep penetration images of the continent–ocean boundary. This paper focuses on the 3D observation of a landward dipping reflector, overlaid by a layered unit. The deep part of the reflector plunges towards the continent beneath thinned continental crust whereas its upper part finishes at the top of the basement in a transition zone where likely volcanics dipping reflectors are visible and where a magnetic anomaly named S1 marks the continent–ocean boundary location. As the landward dipping reflector crosses the Moho, it is interpreted as a lithospheric detachment with associated volcanic material originating from the asthenospheric mantle. Observations are used (i) to build a 2D model to explain the mechanisms of the lithospheric breaking off between Moroccan margin and its conjugate Canadian margin, the landward dipping reflector allowing mantle exhumation; (ii) to propose an ENE–WNW trend for the initial rifting extension in this part of Atlantic during late Triassic, direction compatible with that of the southern Grand Banks transform margin. 相似文献
18.
The Pamir plateau, located north of the western syntaxis of the India-Eurasia collision system, is regarded as one of the most possible places of the ongoing continental deep subduction. Based on a N-S trending linear seismic array across the Pamir plateau, we use the methods of the harmonic analysis of receiver functions and the cubic spline interpolation of surface wave dispersions to coordinate their resolutions, and perform a joint inversion of these datasets to construct a 2-D S-wave velocity model of the crust and uppermost mantle there. A spatial configuration among the intermediate-depth seismicity, Moho topography, and low-velocity anomalies within the crust and upper mantle is revealed, which provides new seismological constraints on the geodynamic processes of the continental subduction. These results not only further confirm the deep subduction of the Asian continental lower crust beneath the Pamir plateau, but also indicate the importance of the metamorphic dehydration of the subducting continental crustal material in the genesis of the intermediate-depth seismicity and the crustal deformation. 相似文献
19.
20.
利用我国地震台站记录的瑞利波观测资料,通过适配滤波频时分析技术进行数据处理,获得了穿越我国东南及陆缘地区的瑞利波频散.使用随机反演理论取得了东南大陆及陆缘地带4°×4°网格的纯路径频散数据.在网格反演的基础上使用Harkrider的面波反演程序求得了该区剪切波的三维速度结构.结果表明:1.华南大陆Moho界面埋深为30-40km,并由西向东逐渐减薄,在陆缘与浅海地域为25-28km,具有明显的分区特征.2.上地幔低速层埋深为60-0km,变化幅度较大,这与深部断裂分布及深层过程有关,但NS向剖面上各界面的起伏变化均比EW向剖面平缓.3.东南陆缘是东亚大陆的海陆过渡带,在深部表现为Moho界面埋深和地壳平均速度降低的地带,地幔深部界面的起伏形态充分表明,深浅介质结构和物质耦合的不均匀性. 相似文献