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61.
Lithoprobe and industry seismic profiles have furnished evidence of major zones of easterly dipping Grenville deformed crust extending southwest from exposed Grenville rocks north of Lake Ontario. Additional constraints on subsurface structure limited to the postulated Clarendon–Linden fault system south of Lake Ontario are provided by five east–west reflection lines recorded in 1976. Spatial correlations between seismic structure and magnetic anomalies are described from both Lake Ontario and the newly reprocessed New York lines.In the Paleozoic to Precambrian upper crust, the New York seismic sections show: (1) An easterly thickening wedge of subhorizontal Paleozoic strata unconformably overlying a Precambrian basement whose surface has an apparent regional easterly dip of 1–2°. Minor apparent normal offsets, possibly on the order of tens of meters, occur within the Paleozoic section. The generally poorly reflective unconformity may be locally characterized by topographic relief on the order of 100 m; (2) Apparent local displacement on the order of 90 m at the level of the Black River Group diminishes upward to little or no apparent offset of Queenston Shale; (3) Within the limited seismic sections, there appears to be no evidence that the complete upper crustal section is vertically or subvertically offset; (4) Dipping structure in the Paleozoic strata (15° to 35°) resembles some underlying Precambrian basement elements; (5) The surface continuity of inferred faults constituting the Clarendon–Linden system is not strongly supported by the seismic data.Beneath the Paleozoic strata, the seismic sections show both linear and arcuate reflector geometry with easterly apparent dips of 15° to 35° similar to the deep structures imaged on seismic lines from nearby Lake Ontario and on Lithoprobe lines to the north. The similarity supports an extension of easterly dipping Central Metasedimentary Belt structures of the Grenville orogen from southern Ontario to beneath western New York State.From a comparison of the magnetic and gravity fields with the New York seismic sections, we suggest: (1) The largely nonmagnetic Paleozoic strata appear to contribute negligibly to magnetic anomalies. Seismically imaged fractures in the New York Paleozoic strata appear to lie mainly west of a positive gravity anomaly. The relationship between magnetic and gravity anomalies and the changes in the geometry of interpreted Precambrian structures remains enigmatic; (2) North to northeast trending curvilinear magnetic and gravity anomalies parallel, but are not restricted to the principal trend of the postulated Clarendon–Linden fault system. Paleozoic fractures of the Clarendon–Linden system may partly overlie a southward extension of the Composite Arc Belt boundary zone. 相似文献
62.
多次深地震探测结果表明南海北部陆缘地壳结构在走向和倾向上都有明显的变化.在一些相隔很近的测线上,探测的深部地壳结构却相差较大,为了分析这些探测结果中差异的原因和地壳结构变化的可靠性,本文以东沙东侧海域测线和东沙西侧海域测线为例,对采集的海底地震仪记录进行了时间、位置校正和初至波走时拾取,利用有限差分地震走时层析成像进行了走时反演,获得所在剖面的地壳速度结构,并分析了模型的横向分辨率,剔除模型中短波长的横向速度变化.分辨率检测结果表明,模型的横向分辨率随着深度快速下降,0~8 km深度范围可以分辨10 km的横向变化,8~17 km的范围能够分辨10~40 km,而17~33 km的范围只能分辨40~80 km.因此,折射波的横向分辨能力不高,在地壳深部难以分辨较小的横向速度变化,前人探测的南海北部6 km宽、延伸至莫霍面的滨外断裂带并不能清晰的识别. 相似文献
63.
M. Zhang H.-W. Meyer L. A. Groat U. Bismayer E. K. H. Salje G. Adiwidjaja 《Physics and Chemistry of Minerals》1999,26(7):546-553
Powder infrared spectroscopy and X-ray diffraction techniques on single crystals were used to study the thermal behaviour
of malayaite, CaSnSiO5. Infrared spectra show a discontinuity in the temperature evolution of phonon frequencies and absorbance near 500 K. However,
crystal structure data collected at 300, 450, 550, 670, and 750 K show no evidence of a symmetry-breaking phase transition
and no split positions. The most obvious change with heating is a tumbling motion of the SnO6 octahedra and an increase of the anisotropic displacement factors of Ca. The thermal evolution of the mean-square vibrational
amplitude of the Ca atom shows a pronounced change in slope near 500 K. The evidence suggests that the 500 K anomaly in malayaite
is more similar in character to the 825 K (β-γ) transition as opposed to the 496 K (α-β) transition in synthetic titanite.
Received: 26 March 1998 / Revised, accepted: 23 December 1998 相似文献
64.
The NW-trending Bucaramanga fault links, at its southern termination, with the Soapaga and Boyacá faults, which by their NW trend define an ample horsetail structure. As a result of their Neogene reactivation as reverse faults, they bound fault-related anticlines that expose the sedimentary fill of two Early Jurassic rift basins. These sediments exhibit the wedge-like geometry of rift fills related to west-facing normal faults. Their structural setting was controlled further by segmentation of the bounding faults at approximately 10 km intervals, in which each segment is separated by a transverse basement high. Isopach contours and different facies associations suggest these transverse anticlines may have separated depocenters of their adjacent subbasins, which were shaped by a slightly different subsidence history and thereby decoupled. The basin fill of the relatively narrow basin associated with the Soapaga fault is dominated by fanglomeratic successions organized in two coarsening-upward cycles. In the larger basin linked to the Boyacá fault, the sedimentary fill consists of two coarsening-upward sequences that, when fully developed, vary from floodplain to alluvial fan deposits. These Early Jurassic rift fills temporally constrain the evolution of the Bucaramanga fault, which accommodated right-lateral displacement during the early Mesozoic rift event. 相似文献
65.
Ionosonde data from sixteen stations are used to study the semiannual and annual variations in the height of the ionospheric F2-peak, hmF2. The semiannual variation, which peaks shortly after equinox, has an amplitude of about 8 km at an average level of solar activity (10.7 cm flux = 140 units), both at noon and midnight. The annual variation has an amplitude of about 11 km at northern midlatitudes, peaking in early summer; and is larger at southern stations, where it peaks in late summer. Both annual and semiannual amplitudes increase with increasing solar activity by day, but not at night. The semiannual variation in hmF2 is unrelated to the semiannual variation of the peak electron density NmF2, and is not reproduced by the CTIP and TIME-GCM computational models of the quiet-day thermosphere and ionosphere. The semiannual variation in hmF2 is approximately isobaric, in that its amplitude corresponds quite well to the semiannual variation in the height of fixed pressure-levels in the thermosphere, as represented by the MSIS empirical model. The annual variation is not isobaric. The annual mean of hmF2 increases with solar 10.7 cm flux, both by night and by day, on average by about 0.45 km/flux unit, rather smaller than the corresponding increase of height of constant pressure-levels in the MSIS model. The discrepancy may be due to solar-cycle variations of thermospheric winds. Although geomagnetic activity, which affects thermospheric density and temperature and therefore hmF2 also, is greatest at the equinoxes, this seems to account for less than half the semiannual variation of hmF2. The rest may be due to a semiannual variation of tidal and wave energy transmitted to the thermosphere from lower levels in the atmosphere. 相似文献
66.
The dynamic identification of a historical masonry palace located in Benevento (Italy) has been carried out. The case study is representative of many buildings located in historic Italian centres. Since the building has been instrumented by the Department of Civil Protection with a permanent dynamic monitoring system, some of the recorded data, acquired in various operating conditions have been analysed with basic instruments of the Operational Modal Analysis in order to identify the main eingenfrequencies and vibration modes of the structure. The experimental results have been compared to the numerical outcomes provided by a detailed three-dimensional Finite Element (FE) model of the building where Soil–Structure Interaction (SSI) has been taken into account. The comparison of experimental vs. numerical frequencies and vibration modes of the palace evidenced the role exerted by the subsoil on the dynamic response of the building. 相似文献
67.
68.
双塔连体高层混合结构抗震性能研究 总被引:8,自引:4,他引:8
外钢框架-混凝土核心筒结构体系被认为是适合我国国情的高层建筑结构体系之一,我国已有多个采用这种结构体系的单塔楼工程实例,但对双塔连体高层混合结构的研究较少。本文针对上海国际设计中心不等高双塔连体混合结构,进行了7度多遇地震、基本烈度、罕遇地震和8度罕遇地震阶段的模拟地震振动台试验研究,得到了结构的破坏模式,并对模型结构和原型结构的动力反应进行了详细的分析,最后提出了此类结构设计的一些建议。研究表明,高位连体的竖向地震反应比较明显,设计中应适当考虑动力放大效应;在各水准地震作用下结构整体变形均呈现弯曲型;主塔楼核心筒在中震下可以保证"不坏",但结构小震下的层间位移略超过规范限值。 相似文献
69.
70.
探讨了金属矿物生物组构的分类体系,将金属矿物的生物组构分为:(1)金属矿物的生物有机胶体组构,由生物直接成矿作用形成;(2)交代作用成因的金属矿物生物组构,由生物间接成矿作用形成。组构又分为结构和构造两个亚类。以典型的实例资料叙述了各种金属矿物生物组构的特征。 相似文献