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1.
R.B. Whitmarsh J.J. Langford J.S. Buckley R.J. Bailey D.J. Blundell 《Earth and Planetary Science Letters》1974,22(3):197-204
A 200 km long reversed seismic refraction line shot over Porcupine Ridge, a shoal area in the northeast Atlantic jutting out from the continental margin off Ireland, shows that the ridge has a crustal thickness of about 28 km. This result confirms the continental nature of this feature. The seismic data can be interpreted in two ways, one of which suggests the presence of a 6.7-km/sec refractor within the main crustal layer. 相似文献
2.
In this study, an updated distribution of Lophelia pertusa between the Porcupine Seabight and Norwegian shelf is presented. It seems unlikely that enigmatic mound structures observed at water depths of more than 570 m during acoustic seabed surveys, particularly to the west of the Shetland Islands, are related to the occurrence of L. pertusa. At these depths in the Faroe-Shetland Channel, the predominant influence of cold Arctic water precludes its growth. Iceberg dumpsites are also considered unlikely explanations for the origin of these mounds, and they are interpreted as most likely to be related to the release of fluids at the seabed. When mound structures were investigated, no scleractinian corals were recovered at water depths >500 m. This study shows the importance of seabed temperature as an environmental control on cold-water coral distribution. The significance of cold-water coral habitats in sustaining high levels of local-scale biodiversity is now becoming apparent in parallel with increased hydrocarbon extraction and fishing activity beyond the shelf edge. There is growing evidence that these areas have been marked by the passage of deep-water trawls. It seems likely that trawling activity has already reduced the extent of cold-water coral distribution in this region of the north-east Atlantic. 相似文献
3.
Systematic genetic analyses of fish populations allow the testing of temporal stability in their genetic structures and better understanding their pattern of connectivity. In this study the pattern of gene flow between the two Atlantic stocks of the European hake has been examined for the period 2000-2002. Present analyses indicate that a large genetic homogeneity existed among all Atlantic populations in that period, and that a systematic grouping occurred between Porcupine Bank samples and Cantabric ones. This scenario is congruent with an inter-annual gene flow from central grounds of the northern stock (Porcupine and Great Sole) to Iberian grounds inhabited by the southern stock. Additionally, estimated migration figures were in agreement with the good recruitments observed in the southern stock after 2003 despite the spawning biomass was at its historical minimum. Altogether these results highlight the central role of Porcupine bank and Great Sole in making sustainable both stocks and advocate the integrative management of this hake fishery by means of a multidisciplinary assessment. 相似文献
4.
It has been suggested that Porcupine Ridge, west of Ireland, represents a continental fragment displaced westwards relative to Europe at an early stage in the opening of the North Atlantic. This hypothesis presents difficulties, particularly in relation to the magnetic evidence for the onset of seafloor spreading at these latitudes. However, the structure of the Irish continental margin, so far as it is known, appears consistent with a westward rotation of Porcupine Ridge by some 23°; and there are still grounds for supposing that the adjacent Rockall Trough may represent a locus of Mesozoic seafloor spreading with which the rotation could have been associated. 相似文献
5.
Saeid Cheraghi Mostafa Naghizadeh David Snyder Rasmus Haugaard Thomas Gemmell 《Geophysical Prospecting》2020,68(1):62-81
In 2017, the Metal Earth multi-disciplinary exploration project acquired a total of 921 km of regional deep seismic reflection profiles and 184 km of high-resolution seismic reflection profiles in the Abitibi and Wabigoon greenstone belts of the Superior province of Canada. The Abitibi belt hosts several world-class mineral deposits, whereas the Wabigoon has sparse economic mineral deposits. Two high-resolution surveys in the Swayze area, a poorly endowed part of the western Abitibi greenstone belt, served as pioneer surveys with which to better understand subsurface geology and design a strategy to process other surveys in the near future. Swayze seismic data were acquired with crooked survey geometries along roads. Designing an effective seismic processing flow to address these geometries and complex geology required straight common midpoint lines along which both two-dimensional prestack dip-moveout correction and poststack migration processing were applied. The resulting seismic sections revealed steeply dipping and subhorizontal reflections; some correlate with folded surface rocks. An interpreted fault/deformation zone imaged in Swayze north would be a target for metal endowment if it extends the Porcupine–Destor structure. Because of the crooked line geometry of the surveys, two-dimensional /three-dimensional prestack time migration and swath three-dimensional processing were tested. The prestack time migration algorithm confirmed reflections at the interpreted base of the Abitibi greenstone belt. The swath three-dimensional images provided additional spatial details about the geometries of some reflections, but also had less resolution and did not detect many reflectors observed in two dimensions. Geological contacts between felsic, mafic and ultramafic greenstone rock layers are thought the main cause of reflectivity in the Swayze area. 相似文献
6.
Monthly composites of multi-year sea surface temperature (SST) and chlorophyll-a (Chl-a) have been used in combination with ocean model simulations to study bio-physical distribution patterns at Porcupine and Rockall Bank, two large submarine banks in the Northeast Atlantic in close proximity to the European shelf edge. Seven years (January 1998–December 2004) of remotely sensed data have been collated to create monthly climatological fields and to analyse principal spatio-temporal characteristics. At both banks, a region of cooler SST is found over the summit region compared to warmer waters of the surrounding ocean, less apparent in summer when capped by the seasonal thermocline. Enhanced Chl-a levels are found over both banks with a lifetime partly exceeding the bloom period. At Rockall Bank, both SST and Chl-a signals are more pronounced and persistent showing a 30% increase in annual Chl-a levels over the summit area with an even higher ratio in spring and autumn. A combination of physical processes appears to promote the enhanced productivity over both banks through the generation of a quasi-steady dome of cold, dense water during winter convection and upwelling events. This cold dome is associated with the presence of a retentive circulation based on Taylor cap dynamics and tidal rectification processes. The larger and more persistent enhancement of Chl-a levels over Rockall Bank would appear due to its isolated nature as well as its size. In contrast, Porcupine Bank is partly attached to the Irish shelf edge and exposed to the poleward flowing shelf edge current which may strip passive particles from the central bank region. Satellite derived Chl-a spring/summer distributions over the banks have been used to initialise model simulations of passive tracer dispersion. Timescales for the observed lifetime of the remotely sensed Chl-a patches are consistent with model derived retention timescales and simple scaling for the dispersion of passive biological material over the banks. Surface particle residence times over Rockall Bank are estimated to exceed Porcupine Bank values by a factor of two. Finally, the tidal contribution to individual particle motion is found to be large in some Rockall Bank areas, but less important at Porcupine Bank. 相似文献
7.
Katrin Heindel Jürgen Titschack Boris Dorschel Veerle A.I. Huvenne André Freiwald 《Continental Shelf Research》2010
Here we provide a detailed qualitative and quantitative insight on recent sediment composition and facies distribution of a cold-water coral (CWC) mound using the example of the Propeller Mound on the Irish continental margin (Hovland Mound Province, Porcupine Seabight). Five facies types on Propeller Mound are defined: (1) living coral framework, (2) coral rubble, (3) dropstone, (4) hardground, representing the on-mound facies, and (5) hemipelagic sediment facies, which describes the off-mound area. This facies definition is based on already published video-data recorded by Remotely Operated Vehicle (ROV), photo-data of gravity cores, box cores, and dredges from sediment surfaces as well as on the composition of the sediment fraction coarser than 125 μm, which has been analyzed on five selected box cores. Sediment compositions of the living coral framework and coral rubble facies are rather similar. Both sediment types are mainly produced by corals (34 and 35 wt%, respectively), planktonic foraminifers (22 and 29 wt%, respectively), benthic foraminifers (both 7 wt%), and molluscs (21 and 10 wt%, respectively), whereas the living coral framework characteristically features additional brachiopods (6 wt%). Hardgrounds are well-lithified coral rudstones rich in coral fragments (>30 surf%), foraminifers, echinoderms, and bivalves. The dropstone facies and the hemipelagic sediment typically carry high amounts of lithoclasts (36 and 53 wt%, respectively) and planktonic foraminifers (35 and 32 wt%, respectively); however, their faunal diversity is low compared with the coral-dominated facies (12 and <2 wt% coral fragments, 7 and 6 wt% benthic foraminifers, and 4 and 0 wt% balanids). Using the maximum likelihood algorithm within ArcGIS 9.2, spatial prediction maps of the previously described mound facies are calculated over Propeller Mound and are based on mound morphology parameters, ground-truthed with the sedimentary and faunal information from box cores, photographs, and video-data. This method is tested for the first time for CWC ecosystems and provides areal estimates of the predicted facies, as well as suggests further occurrences of living coral frameworks, coral rubble, and dropstones, which are not discovered in the area yet. Thus, sediment composition analysis combined with facies prediction mapping might provide a potential new tool to estimate living CWC occurrences and sediment/facies distributions on CWC mounds, which is an important prerequisite for budget calculations and definition of marine protected areas, and which will improve our understanding of CWC mound formation. 相似文献
8.
《Journal of Geodynamics》1999,27(4-5):567-583
Upper mantle P and S wave velocities in the western South America region are obtained at depths of foci from an analysis of travel time data of deep earthquakes. The inferred velocity models for the Chile–Peru–Ecuador region reveal an increase of P velocity from 8.04 km/s at 40 km to 8.28 km/s at 250 km depth, while the S velocity remains almost constant at 4.62 km/s from 40 to 210 km depth. A velocity discontinuity (probably corresponding to the L discontinuity in the continental upper mantle) at 220–250 km depth for P and 200–220 km depth for S waves, with a 3–4% velocity increase, is inferred from the velocity–depth data. Below this discontinuity, P velocity increases from 8.54 km/s at 250 km to 8.62 km/s at 320 km depth and S velocity increases from 4.81 km/s at 210 km to 4.99 km/s at 290 km depth. Travel time data from deep earthquakes at depths greater than 500 km in the Bolivia–Peru region, reveal P velocities of about 9.65 km/s from 500 to 570 km depth. P velocity–depth data further reveal a velocity discontinuity, either as a sharp boundary at 570 km depth with 8–10% velocity increase or as a broad transition zone with velocity rapidly increasing from 560 to 610 km depth. P velocity increases to 10.75 km/s at 650 km depth. A comparison with the latest global average depth estimates of the 660 km discontinuity reveals that this discontinuity is at a relatively shallow depth in the study region. Further, a velocity discontinuity at about 400 km depth with a 10% velocity increase seems to be consistent with travel time observations from deep earthquakes in this region. 相似文献
9.
本文利用30个基准台所记录的238条长周期面波资料,经过适配滤波和分格频散反演,得到中国大陆及邻区147个分格10-105s的纯路径频散,进而反演出青藏高原及邻近地区深至170km的剪切波三维速度结构.研究表明,青藏高原中西部地区和东部地区的地壳平均厚度分别为70±7km和65±7km,地壳平均剪切波速度分别为3.55和3.62km/s,上地幔顶盖平均速度分别为4.63和4.61km/s; 岩石层厚度均为120±10km;东部地区下地壳内30-40km深度处普遍存在低速层;青藏高原及其东侧的上地幔低速层内有横贯东西且明显向上隆起的低速腔.滇西缅北地区的地壳厚45±5km,上地壳及下地壳内都有低速层;上地幔顶盖的速度为4.42km/s,比青藏高原本体及恒河平原都低.恒河平原地壳厚34±2km,速度平均为3.45km/s;上地幔顶盖厚86±10km,速度平均为4.63km/s,顶盖内55-83km深处有一个低速夹层. 相似文献
10.
利用中国大陆以及最近与俄罗斯拼接的中亚地区的布格重力和地形数据，采用响应函数和互相关函数技术，结合弹性板挠曲理论，研究了中国大陆及其邻近地区（２５°Ｎ－７０°Ｎ，５０°Ｅ－１４０°Ｅ）的岩石层强度，用现代均衡的观点探讨了研究区的均衡补偿机制．研究结果表明，整个中国大陆及其邻近地区的有效弹性厚度Ｔｅ值为３５ｋｍ．其中，青藏地区Ｔｅ值为８５ｋｍ．西伯利亚西部至乌拉尔Ｔｅ值为７５ｋｍ，天山、塔里木盆地Ｔｅ值为４０ｋｍ，帕米尔高原Ｔｅ值为２５ｋｍ左右，西伯利亚中部、蒙古以及中国东北北部Ｔｅ值为４０ｋｍ，华北Ｔｅ值为２５ｋｍ，华南Ｔｅ值为４０ｋｍ．均衡补偿对于波长大于几千米的地形负荷为局部补偿，对几百公里到１１００ｋｍ的地形负荷为局部补偿和岩石层强度所支持，短波长地形负荷基本上由岩石层强度所支持． 相似文献
11.
Summary The estimation of the theoretical short-period PKiKP/PKIKP magnitude calibrating curves for deep foci, based on the Earth model PREM and the zero approximation of the ray theory is presented. A set of calibration curves is given for periods 0.8 s, 1.2 s and 1.6 s, for depths 25 km, 200 km, 400 km and 600 km and the epicentral distance range of 12 200 km to 19 800 km. In the calculation we consider the mutual interference of PKiKP and PKIKP wave branches in the corresponding distance range of 13 000 km to 16 000 km for the chosen Gabor's signal. Calibrating curves reflect mainly the distribution of model parameters, the prevailing period and in the distance range of interference also the form of the chosen signal. 相似文献
12.
长320 km横跨鲁西地区的聊城－连云港宽角反射地震剖面揭示了鲁西地区的地壳结构，上地壳为二层结构，总厚18～20 km，速度5.4～6.2 km/s；下地壳也分为二层结构，总厚度13～15 km，速度6.4～6.7 km/s.Moho深度33～35 km.Pn 速度为7.9 km/s.地壳速度分布在横向上有较大变化，且平均速度为6.2～6.5 km/s，较正常值偏高.研究结果发现地壳内有两个近直立的高速体.从下地壳延伸到上地壳并直达沉积盆地的底部.可能是幔源岩浆大量侵入地壳，使得地壳的局部平均速度增高.近直立的高速体可能是幔源岩桨上涌的通道.鲁西地壳结构的研究对于探讨古地台的裂解与沉陷机制具有一定的意义. 相似文献
13.
利用布设在长白山地区的19个PASSCAL宽频带流动地震台站近一年的远震记录和布设在镜泊湖火山区14个宽频带轻便数字地震仪三个月的远震记录,共得到高质量的423个接收函数,通过对这些接收函数的共转换点叠加得到研究区的间断面的分布及形态.研究结果表明,研究区存在410、520km和660km间断面.410km和660km间断面较为连续且具有正相关性质,410km间断面在长白山天池火山下局部上隆,660km间断面具有复杂的多界面性质.410km和660km之间的过渡带厚约250km,接近全球平均水平.珲春深震区下660km界面下陷,其上还有多组震相,这些震相在珲春深震区东西两侧不连续,推测西太平洋板块至少已经俯冲到欧亚大陆下的上地幔过渡带中.410km间断面在长白山火山区下局部上隆,660km间断面具有的复杂结构和珲春深源地震的发生均与俯冲板块在过渡带中的活动有关. 俯冲板块在受到660km间断面的强大阻力后,在660km间断面之上变为近水平扩张.推测在欧亚大陆下西太平洋板块的最前端可能已经不是一个完整的整体,或许是由几个有一定联系的板块残片组成. 相似文献
14.
Field measurements of seismic P-wave velocities have been carried out by surface to surface refraction measurements for five different rock types. Subweathering velocities are surprisingly high and range from 5.0 km/sec in quartz monzonite to 6.2 km/sec in amphibolite in agreement with the proposal of Nur and Simmons for water-saturated low-porosity rocks. Maximum velocities found are 6.1 km/sec for quartz monzonite, 5.8 km/sec for granite gneiss, 6.4 km/sec for syenite, 6.4 km/sec for anorthosite, and 7.0 km/sec for amphibolite, and maximum depth for these velocities is 1.3 km. We conclude as follows: (1) field measurements correspond well with laboratory measurements but true velocity may be slightly higher than laboratory measurements, (2) shallow velocities are much higher than older laboratory measurements but agree well with recent laboratory measurements on water-saturated samples, (3) velocities much less than 6 km/sec seem unlikely in the crust unless in an area of extreme tectonic activity, (4) velocities of 6.5–6.7 km/sec commonly reported for the lower continental crust probably correspond to rocks less mafic than basalt or gabbro. 相似文献
15.
沿乌鲁木齐－库尔勒３５０余公里长的测线上完成了穿越天山的地震转换波野外观测，得出天山造山带的深部构造剖面图和壳内Ｐ，Ｓ波速度结构模型．天山的结晶地壳可分为４层，各层的速度分别是：Ｖｐ值为５．９，６．３，６．６，６．９ｋｍ／ｓ；Ｖｓ值为３．２，３．５，３．７，３．９ｋｍ／ｓ。上地幔顶部的波速：Ｖｐ值为８．１０ｋｍ／ｓ。Ｖｓ值为４．６ｋｍ／ｓ。天山地区的地壳厚度为４２－５６ｋｍ，中天山最厚，达到５０－５６ｋｍ。地壳中部存在低速透镜体。探测结果表明，天山大地构造可分为北天山、中天山和南天山３个区，其地壳深部构造特征各不相同。用颤动构造理论来解释天山造山带的形成机制和演化较板块构造理论更为合理。 相似文献
16.
1982—1983年在甘肃永登地区进行了系列人工大爆破,本文分析研究了甘宁青地震台网的观测记录,求得各种波的平均速度为:V_(?)=6.00公里/秒,V_(?)=3.56公里/秒,V_(pn)=8.16公里/秒,V_(?)=4.54公里/秒。表层直达纵波速度V_o=4.82公里/秒。莫霍界面上的反射波P_M在140—180公里范围比P_g波强10—7倍。並获得该地区的地壳厚度为:(1)甘肃北山的河西堡—高台一带为48.3公里。古浪—张掖—嘉峪关的河西走廊一带为50.2公里。祁连山南麓为53.6公里。(2)青海中南部为54.4公里。(3)甘肃东部的礼县—武都地压为48.7公里。定西—岷县—通谓地区为50.5公里。(4)宁夏六盘山区为51.6公里。六盘山西侧的甘肃静宁为48.6公里,东侧的平凉为47.5公里,东南端的陕西宝鸡为46.1公里。以上的地壳厚度分布显示了青藏高原地壳在东北边缘的递减,以及甘肃东部地区地壳的某些起伏。 相似文献
17.
沿乌鲁木齐－库尔勒３５０余公里长的测线上完成了穿越天山的地震转换波野外观测，得出天山造山带的深部构造剖面图和壳内Ｐ，Ｓ波速度结构模型．天山的结晶地壳可分为４层，各层的速度分别是：Ｖｐ值为５．９，６．３，６．６，６．９ｋｍ／ｓ；Ｖｓ值为３．２，３．５，３．７，３．９ｋｍ／ｓ。上地幔顶部的波速：Ｖｐ值为８．１０ｋｍ／ｓ。Ｖｓ值为４．６ｋｍ／ｓ。天山地区的地壳厚度为４２－５６ｋｍ，中天山最厚，达到５０－５６ｋｍ。地壳中部存在低速透镜体。探测结果表明，天山大地构造可分为北天山、中天山和南天山３个区，其地壳深部构造特征各不相同。用颤动构造理论来解释天山造山带的形成机制和演化较板块构造理论更为合理。 相似文献
18.
According to the actual observation conditions of the Yangtze River valley from Anqing city to Maanshan city, we designed the 3D acquisition geometry, and applied the multi-scale checkerboard semblance analysis to assess the preliminary resolution of the designed observation. The checkerboard semblance tests use the refraction and reflection travel-time simultaneous inversion algorithm to quantitatively provide both resolution assessment of velocity structure and Moho topography. The multi-scale checkerboard semblance recovery results show that while the checkerboard semblance threshold value is 0.5, the preliminary resolution of the designed acquisition geometry is better than 10 km in the upper crust (the depth is less than 10 km), around 15 km in the mid-crust (the depth is 10?25 km), and better than 20 km in the lower crust (the depth is 25?33 km). The preliminary tomographic resolution for the Moho topography is about 20 km in the ray-path coverage area beneath the acquisition geometry. While the checkerboard semblance threshold value is 0.75, the preliminary resolution is 20 km in the upper crust, around 20?25 km in the mid-crust and 25 km in the lower crust. And the preliminary tomographic resolution for the Moho topography is better than 30 km in the ray-path coverage area beneath the acquisition geometry. These non-linear checkerboard tests reveal that the designed acquisition geometry is suitable to image the crustal velocity structure of the Yangtze River valley in the Anhui province. 相似文献
19.
利用湖南省棋梓桥万罗山定向爆破观测资料,使用迭代法对棋梓桥至酃县剖面进行了二维构造反演,得到4层地壳结构模型:界面1埋深1.8—4km,v<6.0km/s;界面2埋深10.5—15km,6.0km/s相似文献