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71.
72.
Lodolo Emanuele Coren Franco Schreider Anatoly A. Ceccone Giulio 《Marine Geophysical Researches》1997,19(5):439-450
The southwestern part of the Scotia Sea, at the corner of the Shackleton Fracture Zone with the South Scotia Ridge has been investigated, combining marine magnetic profiles, multichannel seismic reflection data, and satellite-derived gravity anomaly data. From the integrated analysis of data, we identified the presence of the oldest part of the crust in this sector, which tentative age is older than anomaly C10 (28.7 Ma). The area is surrounded by structural features clearly imaged by seismic data, which correspond to gravity lows in the satellite-derived map, and presents a rhomboid-shaped geometry. Along its southern boundary, structural features related to convergence and possible incipient subduction beneath the continental South Scotia Ridge have been evidenced from the seismic profile. We interpret this area, now located at the edge of the south-western Scotia Sea, as a relict of ocean-like crust formed during an earlier, possibly diffuse and disorganized episode of spreading at the first onset of the Drake Passage opening. The successive episode of organized seafloor spreading responsible for the opening of the Drake Passage that definitively separated southern South America from the Antarctic Peninsula, instigated ridge-push forces that can account for the subduction-related structures found along the western part of the South Scotia Ridge. This seafloor accretion phase occurred from 27 to about 10 Ma, when spreading stopped in the western Scotia Sea Ridge, as resulted from the identification of the marine magnetic anomalies. 相似文献
73.
P. Cobo C. Ranz A. Fernández M. Cuesta D.K. Anthony M. Siguero 《Marine Geophysical Researches》2005,26(2-4):87-95
Vertical resolution is of fundamental importance in sonar exploration and is directly related to the duration of the acoustic
pulse generated by the transducer. The shorter the radiated pulse, the higher the vertical resolution. Many sub-bottom profiling
sonar systems use piezoelectric transducers because they are reversible and well understood. Piezoelectric projectors are
normally resonant transducers, which are intrinsically narrowband. A piezoelectric transducer is usually driven by a tone-burst.
However, it is possible to use Fourier techniques to find a pre-compensated electrical driving function so that the transducer
radiates a prescribed wider band acoustic waveform. This technique can be applied to synthesize zero-phase cosine-magnitude,
Gaussian, and bionic pulses, with a conventional sandwich transducer. Zero-phase cosine-magnitude waveforms provide minimum
length pulses (and therefore maximum resolution) within a prescribed frequency band.The aim of this paper is to illustrate
the synthesis of wideband acoustic pulses using an underwater piezoelectric projector. The conventional acoustic waveform
radiated when a Tonpiltz transducer is transiently excited using a “click” and allows its frequency response function to be
measured. This function is used to design the electrical signal which then drives the transducer so that it radiates the shortest
pulse compatible with its mechanical response. The significant resolution enhancement of the waveform shaping process is illustrated
by its application to a sediment wedge model. 相似文献
74.
Riccardo?Geletti Emanuele?LodoloEmail author Anatoly?A.?Schreider Alina?Polonia 《Marine Geophysical Researches》2005,26(1):17-28
The structural framework of the southern part of the Shackleton Fracture Zone has been investigated through the analysis of
a 130-km-long multichannel seismic reflection profile acquired orthogonally to the fracture zone near 60° S. The Shackleton
Fracture Zone is a 800-km-long, mostly rectilinear and pronounced bathymetric lineation joining the westernmost South Scotia
Ridge to southern South America south of Cape Horn, separating the western Scotia Sea plate from the Antarctic plate. Conventional
processing applied to the seismic data outlines the main structures of the Shackleton Fracture Zone, but only the use of enhanced
techniques, such as accurate velocity analyses and pre-stack depth migration, provides a good definition of the acoustic basement
and the architecture of the sedimentary sequences. In particular, a strong and mostly continuous reflector found at about
8.0 s two-way traveltime is very clear across the entire section and is interpreted as the Moho discontinuity. Data show a
complex system of troughs developed along the eastern flank of the crustal ridge, containing tilted and rotated blocks, and
the presence of a prominent listric normal fault developed within the oceanic crust. Positive flower structures developed
within the oceanic basement indicate strike-slip tectonism and partial reactivation of pre-existing faults. Present-day tectonic
activity is found mostly in correspondence to the relief, whereas fault-induced deformation is negligible across the entire
trough system. This indicates that the E–W-directed stress regime present in the Drake Passage region is mainly dissipated
along a narrow zone within the Shackleton Ridge axis. A reappraisal of all available magnetic anomaly identifications in the
western Scotia Sea and in the former Phoenix plate, in conjunction with new magnetic profiles acquired to the east of the
Shackleton Fracture Zone off the Tierra del Fuego continental margin, has allowed us to propose a simple reconstruction of
Shackleton Fracture Zone development in the general context of the Drake Passage opening. 相似文献
75.
76.
在20×10~9Pa和25×10~9Pa条件下,对石榴石橄榄岩进行的14次高温高压熔融实验研究表明,在1600℃时石榴石橄榄岩开始熔融(初熔),熔体中的SiO_2>70%,Na_2O+K_2O>8%,类似于A型花岗岩成分。本实验为地幔花岗岩的成因提供了证据。 相似文献
77.
本文以我国北黄海的烟威渔场为研究对象,采用优选因子场预报模式,对盐度的时空变化进行预报试验。文中对所采用的统计预报方法,作了简要介绍。对影响本海区盐度变化的显著因子及预报结果作了初步分析。预报试验表明:预报的总体平均绝对误差为0.27‰,预报相对误差在18%左右,预报误差小于0.5‰的站数占总站数的85%,预报趋势与实测资料基本一致。 相似文献
78.
姜效典 《中国海洋大学学报(自然科学版)》1992,(2)
由磁异常Z_α和重力异常g,利用样条函数的微、积分性质,从泊松方程出发,直接解得磁性体的磁化方向。该方法适用于任意形状磁性体的磁异常。 相似文献
79.
资料显示,在整个台湾以东海区内磁异常几乎全为负磁异常,磁异常分块现象明显。通过对本海区的磁力资料进行分析和研究,表明本海区的地磁异常表现为明显的条带状异常特征。由于受板块差异性运动的影响,以加瓜海脊为界,东西两侧具有不同的磁条带方向,在加瓜海脊以东,磁条带为NW-SE向(120°),而在加瓜海脊以西则为近东西向(80°)。加瓜脊以西地区的扩张时间为45~38Ma,相当于19~16号磁条带;而加瓜脊以东地区的扩张时间为40~35Ma,相当于17~13号磁条带。加瓜脊以西的磁条带相对于以东的磁条带要老,由此推断出加瓜脊以西相对于东侧发生了北向位移。 相似文献
80.
该文建立高效凝胶渗透色谱法 (HPGPC) ,明胶比浊法 ,氧瓶燃烧法三种分析方法考察海洋硫酸多糖药物几丁糖酯的稳定性 ,采用这三种方法分别考察几丁糖酯原料药在高温、高湿、强光照射及加速条件下分子量及分布宽度、样品中硫酸根含量及样品含量的变化情况。结果表明 :三种方法均适用于几丁糖酯的稳定性考察 ,几丁糖酯在上述影响因素条件下稳定性良好 相似文献