首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献，搜索用时 187 毫秒
1.
金光炎 《水文》1997,(2):1-5
回归计算中，由于资料和计算上的误差，使结果也产生一定的误差，通常，采用最小二乘法或最小一乘法来估计回归模型中的参数，即是取目标函数为最小来实现的，如果使目标函数在允许的误差范围内变化，则参数会有相应的变幅，本文探讨了两变数回归时参数估计的灵敏度，在相关关系不甚密切时，误差对结果的影响是较大的。  相似文献   

2.
Rock samples from the Kanin Peninsula and the Timan Ridge were analysed for in situ cosmogenic 10Be for exposure age dating purposes. Crystalline rocks were sampled at four sites on the Kanin Peninsula, either from bedrock outcrops or from glacial erratics, giving overall similar 10Be ages. Outcropping sandstone and crystalline erratics were available from three sites at the Timan Ridge. The highly weathered sandstone gives substantially younger 10Be ages than the adjacent erratics. The exposure ages from the Kanin Peninsula suggest that the last deglaciation of this area took place between 55 and 37 10Be kyr ago, in agreement with a preceding Kara Sea glaciation (55-45 kyr BP). The northwest coast of the peninsula was probably just outside the maximum limit of the last Scandinavian glaciation (20-17 kyr BP). Glacial erratic exposure ages from the Timan Ridge suggest that the 55-45 kyr BP Kara Sea glaciation reached the northern part of the ridge. The exposure dates do not show conclusive evidence regarding the existence of a Timan Ridge ice cap.  相似文献   

3.
Tholeiite basalts from 60° N to 65° N on the Mid-Atlantic Ridge were melted and recrystallized at atmospheric pressure in a CO2-H2 gas mixture. Seven basalts are from the Langjokull-Thingvellir volcanic zone and the Reykjanes Peninsula of Iceland and nine are from the Reykjanes Ridge. The crystallization sequence in both Iceland and Reykjanes Ridge basalts with (Total Fe as FeO)/(Total Fe as FeO+ MgO) [F/F + M] less than 0.6 is olivine, plagioclase, clinopyroxene. Chromian spinel crystallizes before plagioclase in one Iceland and one Reykjanes Ridge basalt with F/F+M less than 0.57. Chemical differences of the two groups of basalts (lower SiO2 and higher alkalis in Iceland basalts) can not simply be a result of low pressure fractional crystallization. Liquidus temperatures of the seven Iceland basalts decreases from 1,230° C to 1,170° C as the F/F+M of the rock increases from 0.52 to 0.70. The liquidus temperatures of the Reykjanes Ridge basalts are about 10° C lower than those of the Iceland basalts for the same F/F+M value. The profile of measured liquidus temperatures from 65° N on Iceland to 60° N on the Reykjanes Ridge has a minimum value at 63.2° N on the Reykjanes Ridge just south of Iceland. Model calculations of the pressure of phenocryst crystallization indicate that olivine and plagioclase in Langjokull basalts could have equilibrated between 2.0 and 6.2 kb (200 to 620 MPa). Phenocryst assemblages in Reykjanes Ridge basalts at 60° N could have crystallized together at greater than 2 kb (200 MPa) and probably less than 8 kb (800 MPa). A minimum in the equilibrium pressure of phenocryst crystallization occurs between 62.9° and 64° N and coincides with the minimum in the experimentally determined liquidus temperatures. The more extensive fractionation at low pressure in this area could be related to the shift of the Mid-Atlantic Ridge axis along the leaky transform fault from the Reykjanes Ridge to the Thingvellir volcanic zone.  相似文献   

4.
加权支持向量回归机及其在水质预测中的应用   总被引：1，自引：0，他引：1  
支持向量机是一种基于结构风险最小化原理的学习技术，也是一种新的具有很好泛化性能的回归方法。本文对用于回归估计的标准支持向量机加以改进，提出了一种新的用于回归估计的支持向量机学习算法，针对各样本重要性的差异，给各个样本的惩罚系数和误差要求赋予不同权重，并利用加权支持向量回归机的理论及其算法构建水质预测模型。实验结果表明，该方法对水质具有较好的预测效果。  相似文献   

5.
Shikotan Island of the Lesser Kuril Ridge forms, together with the Vityaz Ridge, the outer arc of the Kuril island-arc system. Marine Pliocene sediments first registered on the island contain diatoms and palynomorphs, which allow their dating. The thin Pliocene semiconsolidated sediments constitute the upper part of sections in the coastal and central areas of the island. They rest with the erosional surface and stratigraphic hiatus upon the Upper Cretaceous-Lower Paleogene (Campanian-Danian) Malokuril’sk Formation. The Pliocene sediments were deposited in relatively shallow-water environments of open sea near the shore, with a forest-free landscape and freshwater basins. The occurrence of reworked marine Oligocene and Miocene diatoms in these sedimentary rocks indicates their development in the Lesser Kuril Ridge area and contribution of their eroded material to the formation of Pliocene sequences. Wide development of Pliocene Marine sediments on Shikotan Island is evidence for ascending movements in the region during the post-Pliocene period, which is also characteristic of the Greater Kuril Ridge islands. The composition and formation conditions of the Pliocene sediments in the outer arc of the Kuril island-arc system suggest that the southwestern (Lesser Kuril Ridge) and northeastern (Vityaz Ridge) segments of this single anticlinal structure evolved under different tectonic regimes through the Pliocene.  相似文献   

6.
The recent tectonics of the Arctic Basin and northeastern Asia are considered as a result of interaction between three lithospheric plates: North-America, Eurasia and Spitsbergen. Seismic zones (coinciding in the Norway-Greenland basin with the Kolbeinsey, Mohns and Knipovich ridges, and in the Arctic Ocean with the Gakkel Ridge) clearly mark the boundaries between them. In southernmost Svalbard (Spitsbergen), the secondary seismic belt deviates from the major seismic zone. This belt continues into the seismic zone of the Franz Josef Land and then merges into the seismic zone of the Gakkel Ridge at 70°–90°E. The smaller Spitsbergen plate is located between the major seismic zone and its secondary branch.Within northeastern Asia, earthquake epicenters with magnitude over 4.5 are concentrated within a 300-km wide belt crossing the Eurasian continent over a distance of 3000 km from the Lena estuary to the Komandorskye Islands. A single seismic belt crosses the northern sections of the Verkhoyansky Ridge and runs along the Chersky Ridge to the Kolymo-Okhotsk Divide.To compute the poles of relative rotation of the Eurasian, North-American and Spitsbergen plates we use 23 new determinations of focal-mechanism solutions for earthquakes, and 38 azimuths of slip vectors obtained by matching of symmetric mountain pairs on both sides of the Knipovich and Gakkel ridges; we also use 14 azimuths of strike-slip faults within the Chersky Ridge determined by satellite images. The following parameters of plate displacement were obtained: Eurasia/North America: 62.2°N, 140.2°E (from the Knipovich Ridge section south of the triple junction); 61.9°N, 143.1°E (from fault strikes in the Chersky Ridge); 60.42°N, 141.56°C (from the Knipovich section and from fault strikes in the Chersky Ridge); 59.48°N, 140.83°E, α = 1.89 · 10−7 deg/year (from the Knipovich section, from fault strikes in the Chersky Ridge and from the Gakkel Ridge section east of the triple junction). The rate was calculated by fitting the 2′ magnetic lineations within the Gakkel Ridge).North-America/Spitsbergen: 70.96°N, 121.18°E, α = −2.7 · 10−7 deg/year from the Knipovich Ridge section north of the triple junction, from earthquakes in the Spitsbergen fracture zone and from the Gakkel Ridge section west of the triple junction). Eurasia/Spitsbergen: 70.7°N, 25.49°E, α = −0.99 · 10−7 deg/year (from closure of vector triangles).  相似文献   

7.
A thorough examination of geophysical data from the Greenland-Norwegian Sea, Eurasia Basin and southern Labrador Sea shows significant asymmetry of several parameters (basement topography adjusted for sediment loading, free-air gravity anomaly, spreading half-rate and seismicity) with respect to crustal age:
1. (1) Average zero-age depth (0–57 m.y. B.P.), depth of highest rift mountain summits, and depth to magnetic basement (10–30 km from axis of Mohns and Knipovich ridges) is less on the North American plate flanks. The zero-age depth asymmetry is 400–500 m for the Eurasia Basin (0–57 m.y. B.P.) and for Mohns Ridge (57-22 m.y. B.P.), and 150–200 m for younger Mohns Ridge crust (22-0 m.y. B.P.) and for the extinct Aegir Ridge (57-27 m.y. B.P.). There is little or no asymmetry in the Labrador Sea except near the extinct rift valley, where the east flank is 150–300 m shallower. Magnetic depth-to-source computations provide an independent confirmation of basement asymmetry: The belts 10–30 km from the axis of Mohns and Knipovich ridges are 100–150 m shallower on the west flank of these ridges. The shallower ridge flank is topographically rougher, so that average rift mountain summits are 300 m shallower on the west flanks of the Mohns-Knipovich ridges, a larger asymmetry than for average zero-age depth. The amount of topographic asymmetry is greatest near the Mohns-Knipovich bend. Asymmetry appears to be greatest for ridges oriented normal to the spreading direction, and less for oblique spreading.
2. (2) Free-air gravity anomaly asymmetries of +5 to +20 mGal ( + sign indicates west flank is more positive) are associated with topographic asymmetry at least within 10–15 m.y. of the axis of Mohns and Knipovich ridges. Gravity is reduced on the older flanks west of the extinct Mid-Labrador Ridge and east of Mohns Ridge; asymmetric crustal layer thicknesses or densities provide one possible explanation, although deep-seated sources (e.g., mantle convection), unrelated to the crust, cannot be excluded.
3. (3) Spreading half-rate was about 5–15% lower on the North American plate flanks of Mohns Ridge (57-35 m.y.) and in the Eurasia Basin (0–57 m.y.); thus the fast-spreading flank tends to produce deeper, smoother crust. However, topographic asymmetry cannot relate only to spreading-rate asymmetry, since for the young Mohns Ridge crust (<9 m.y. B.P.) faster spreading and higher topography are both associated with the west flank.
4. (4) Mid-plate seismicity is higher on the Eurasia (eastern) flank of Mohns and Knipovich ridge, but this effect may be unrelated to the other three.
The fluid-dynamical model of Stein et al. correctly explains the sense of spreading-rate asymmetry (the North American plate, moving faster over mantle, is growing more slowly). However, the other asymmetries and their causal relationships remain theoretically unexplained.  相似文献   

8.
The results of analysis of the anomalous magnetic field of the Reykjanes Ridge and the adjacent basins are presented, including a new series of detailed reconstructions for magnetic anomalies 1–6 in combination with a summary of the previous geological and geophysical investigations. We furnish evidence for three stages of evolution of the Reykjanes Ridge, each characterized by a special regime of crustal accretion related to the effect of the Iceland hotspot. The time interval of each stage and the causes of the variation in the accretion regime are considered. During the first, Eocene stage (54–40 Ma) and the third, Miocene-Holocene stage (24 Ma-present time at the northern Reykjanes Ridge north of 59° N and 17–11 Ma-present time at the southern Reykjanes Ridge south of 59° N), the spreading axis of the Reykjanes Ridge resembled the present-day configuration, without segmentation, with oblique orientation relative to the direction of ocean floor opening (at the third stage), and directed toward the hotspot. These attributes are consistent with a model that assumes asthenospheric flow from the hotspot toward the ridge axis. Decompression beneath the spreading axis facilitates this flow. Thus, the crustal accretion during the first and the third stages was markedly affected by interaction of the spreading axis with the hotspot. During the second, late Eocene-Oligocene to early Miocene stage (40–24 Ma at the northern Reykjanes Ridge and 40 to 17–11 Ma at the southern Reykjanes Ridge), the ridge axis was broken by numerous transform fracture zones and nontransform offsets into segments 30–80 km long, which were oriented orthogonal to the direction of ocean floor opening, as is typical of many slow-spreading ridges. The plate-tectonic reconstructions of the oceanic floor accommodating magnetic anomalies of the second stage testify to recurrent rearrangements of the ridge axis geometry related to changing kinematics of the adjacent plates. The obvious contrast in the mode of crustal accretion during the second stage in comparison with the first and the third stages is interpreted as evidence for the decreasing effect of the Iceland hotspot on the Reykjanes Ridge, or the complete cessation of this effect. The detailed geochronology of magnetic anomalies 1–6 (from 20 Ma to present) has allowed us to depict with a high accuracy the isochrons of the oceanic bottom spaced at 1 Ma. The variable effect of the hotspot on the accretion of oceanic crust along the axes of the Reykjanes Ridge and the Kolbeinsey and Mid-Atlantic ridges adjoining the former in the north and the south was estimated from the changing obliquity of spreading. The spreading rate tends to increase with reinforcing of the effect of the Iceland hotspot on the Reykjanes Ridge.  相似文献   

9.
ABSTRACT

New analysis of the geophysical data of the ultraslow-spreading Mohns Ridge and its off-axis structure reveals a distinctive asymmetric structure. We calculate residual bathymetry (RB) and residual mantle Bouguer gravity anomaly (RMBA) and decompose the anomalies into symmetric and asymmetric components between the ridge conjugates. The western flank of the Mohns Ridge at crustal age of ~50–15 Ma is characterized by a broad zone of elevated RB and more negative RMBA, which we term the Vesteris Plateau (VP). The VP anomaly has a surface area of ~1.12 × 105 km2 and an excess crust volume of ~2.33 × 105 km3, making it a significant anomaly comparable to other anomalies such as the Bermuda Rise. Extending north of the Kolbeinsey Ridge for more than 500 km, the VP lies above an anomalous upper mantle region of low shear-wave seismic velocity, indicating that the VP might represent the northernmost reach of the Iceland-Jan Mayen mantle anomaly. In addition, the western ridge flank of the Mohns Ridge at crustal age of 6–0 Ma is associated with higher RB and more positive RMBA relative to the eastern conjugate, indicating tectonic uplift and associated exposure of lower crust and upper mantle near the ridge axis.  相似文献   

10.
The plate margin features defining the Arabian Sea Triple Junction (ASTJ) are: the Aden Ridge (AR), Sheba Ridge (SR) with their intervening Alula-Fartak Transform (AFT), Carlsberg Ridge (CR) and Owen Fracture Zone (OFZ). Exact nature of ASTJ is presently debated: whether it is RRF (ridge-ridge-fault) or RRR (ridge-ridge-ridge) type. A revised seismicity map for ASTJ is given here using data for a period little more than a century. “Point density spatial statistical criterion” is applied to short-listed 742 earthquakes (mb ≥ 4.3), 10 numbers of spatio-temporal seismic clusters are identified for ASTJ and its arms. Relocated hypocentres help better constraining the cluster identification wherever such data exist. Seismic clusters actually diagnose the most intense zones of strain accumulation due to far field as well as the local stress operating at ASTJ. An earthquake swarm emanating from a prominent seismic cluster below SR provides an opportunity to investigate the pore pressure diffusion process (due to the active source) by means of “r-t plot”. Stress and faulting pattern in the active zones are deduced from 43 CMT solutions. While normal or lateral faulting is characteristic for these arms, an anomalous thrust earthquake occurs in the triangular ‘Wheatley Deep’ deformation zone proximal to ASTJ. The latter appears to have formed due to a shift of the deformational front from OFZ towards a transform that offsets SR. Though ASTJ is still in the process of evolution, available data favour that this RRF triple junction may eventually be converted to a more stable RRR type.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号