电阻率层析成像方法技术近年发展概况

本文对近年来电阻率层析成像在方法技术方面的进展作了简要介绍,并对几种具有代表性的方法,表述了它们各自的优缺点,提出了继续研究的方向。     

Bottom-current deposits in the Miocene–Pliocene Misaki Formation, Izu forearc area, Japan

Sedimentary structures in the middle–late Miocene to early Pliocene Misaki Formation, Miura Group, Miura Peninsula, Central Japan, were studied, and paleocurrent data were interpreted as the result of deep-sea bottom-current flow. These current data were further compared with present-day bottom currents in the northwestern Pacific region. The Misaki Formation is thought to be a forearc deposit within the Izu oceanic arc, and is composed of thick volcaniclastic beds interbedded with siliceous biogenic clayey sediments. Sedimentary structures showing paleocurrent directions are involved in the upper part of the volcaniclastic beds, in the pumiceous beds just above the volcaniclastic beds, and in the pelagic sediments. Based on paleomagnetic data suggesting considerable rotation of the beds, all the current directions were reconstructed to their original orientation. The paleocurrents are summarized into the following three groups. The first group in the volcaniclastic beds indicates southeast-directed paleocurrent directions. The second group in the upper parts of volcaniclastic beds and in some pumiceous beds exhibits a southwest- and northeast-directed paleoflow. The third group usually observed in the pumiceous beds with parallel lamination displays a northwest- or southeast-directed paleocurrent. The origin of each group's paleoflow direction is attributed to turbidity current, internal tidal current, and contour current influences, respectively. Present-day observations of the deep-sea northwest Pacific suggest that most of the bottom-current indicators in the Misaki Formation are related to North Pacific Deep Water, possibly Antarctic Bottom Water as well as a combination of tidal and local effects. It is concluded that the beds of the Misaki Formation were deposited in the proto-Sagami basin ca 9 Ma and were formed under weak bottom currents in a wide and flat basin during colder climatic conditions, whereas the beds dated at ca 6 Ma were deposited under strong bottom-current flow, and were then accreted to the Honshu arc.     

对计算土壤和岩石中氡浓度及其表面析出率表面边界条件的讨论

本文对求解土壤或岩石中氡浓度及其表面析出率的边界条件进行了探讨。以空气中无穷远处氡浓度为零（空气中无氡源）的自然边界条件代替空气与土壤或岩石交界面氡浓度为零的边界条件,给出了土壤和岩石中氡浓度及其表面析出率的具体表达式。与前人研究结果比较,该式中增加了一项,表面氡析出率缩小了一个倍数。通过对土壤、岩石的具体计算．表明两种边界条件的计算结果有相当的偏差。同时,文中还讨论了在两类边界条件下对流对土壤或岩石中氡浓度及其表面析出率计算的影响。     

极光区高空物理过程与磁层-电离层耦合

极区高空物理现象之观测具有悠久历史。对极区地磁、电离层和极光现象的深入考察将地球物理的研究领域扩展到了外层空间,并提出了太阳风－磁层－电离层－热层间耦合这一重要课题。耦合物理机制的证实不仅是火箭、卫星探测的重要贡献,而且也是基于对地面雷达和遍及全球大陆的地磁台站、电离层垂测站之长期观测成果。对流电场、一区和二区场向电流、电离层扰动电流系（包括极光区电集流）,以及电导率的分布和变化乃是一有机整体,对其每一环节的深入认识均与对整体的全面了解密不可分。有关的理论和模式研究则有助于人们深入理解各个耦合过程的相互关系,以及其各发展阶段中不同物理过程的相对重要性。     

电偶源电场的时间谱转换为频谱的误差探讨

基于层状导电和可极化大地表面,电偶源电场的时间谱在无随机干扰和有随机干扰时,进行频谱转换的计算结果,证明了时—频转换的误差传递问题严重。但是,采用窗口（圆滑）滤波可以有效压制随机干扰,使时—频转换达到必要的计算精度。     

基于K-Means算法的架空输电线路载流量计算

针对边界条件取值过于保守导致架空输电线路载流量过小而无法充分发挥输电线路的载流能力的问题,本文提出了一种基于K-Means算法的架空输电线路载流量计算方法.首先对历史气象数据进行统计分析,然后根据每月气象数据的相似性,使用K-Means算法划分时段,并选取各时段最为合适的边界条件,最后基于选定的边界条件使用摩根公式进行仿真计算.通过这种方法,可以在保证线路运行安全的条件下挖掘输电线路的隐性输送能力.     

Estimates of subtidal volume flux in mid-Chesapeake Bay

Utilizing 20 days of current meter and sea level elevation records taken in two cross-sections in mid-Chesapeake Bay an objective interpolation procedure was devised to allow the computation of vertical profiles of the laterally integrated subtidal volume fluxes at each section, at 3-h intervals over the period of the experiment. The presence of a classical mean estuarine circulation was observed; however, departures from this gravitational circulation were revealed on a shorter time scale, reaching the value of 20 000 m³ s^?1 over a day, and featuring behaviors of reverse estuarine, storage and discharge modes.The volume flux computations through each cross-section based on the measured current velocities, the freshwater inflow and the calculated Stokes transport were in agreement with each other. A two-layered box model of the mean subtidal circulation in the segment of the estuary bound by the two cross-sections is offered.A comparison was made between the computations of net volume flux into and out of the Bay above these sections using two independent methods: (1) the accounting of volume continuity based upon direct measurements of volume flux through the sections; and (2) the direct calculation of the time rate of change of volume of the upper Bay obtained from tide gauge records. The agreement between the two results was found to be very good. Further evidence is provided for the upward phase propagation of the oscillations in the residual motion of estuarine waters.     

Rapid dome growth at Montagne Pelée during the early stages of the 1902–1905 eruption: a reconstruction from Lacroix’s data

Information obtained from various parts of the two books on Montagne Pelée by Lacroix enables an estimate to be made of the size of l’Etang Sec summit crater, the volume of the 1902–1905 lava dome and its growth rate at various stages of development. During the week preceding the 8 May nuée ardente, dome growth was between 28 and 38 m³ s^–1, leading to a volume of 17–23×10⁶ m³ on the morning of the catastrophe. Considering that significant parts of the dome (~1/3?) were removed by the 8 and 20 May climactic eruptions, a high magmatic flux could have continued until at least 27 May, when the total remaining volume was estimated to 53×10⁶ m³. After moderate activity in June–July (of order 10 m³ s^–1), vigorous dome growth resumed dramatically, leading to the third climactic eruption of 30 August (a true calculation for this period being not feasible because of poor quality of the data). From November 1902 to July 1903 most of the effusive activity was concentrated in the great spine (erupted volume ~15×10⁶ m³, magma flux 1.2 m³ s^–1), which was eventually destroyed by collapse and minor nuées ardentes. The end of the eruption was characterized by a very low effusion rate, <1 m³ s^–1 in average from August 1903 to October 1905.     

Complex proximal deposition during the Plinian eruptions of 1912 at Novarupta,Alaska

Proximal (<3 km) deposits from episodes II and III of the 60-h-long Novarupta 1912 eruption exhibit a very complex stratigraphy, the result of at least four transport regimes and diverse depositional mechanisms. They contrast with the relatively simple stratigraphy (and inferred emplacement mechanisms) for the previously documented, better known, medial–distal fall deposits and the Valley of Ten Thousand Smokes ignimbrite. The proximal products include alternations and mixtures of both locally and regionally dispersed fall ejecta, and numerous thin complex deposits of pyroclastic density currents (PDCs) with no regional analogs. The locally dispersed component of the fall deposits forms sector-confined wedges of material whose thicknesses halve radially from and concentrically about the vent over distances of 100–300 m (cf. several kilometers for the medial–distal fall deposits). This locally dispersed fall material (and many of the associated PDC deposits) is rich in andesitic and banded pumices and richer in shallow-derived wall-rock lithics in comparison with the coeval medial fall units of almost entirely dacitic composition. There are no marked contrasts in grain size in the near-vent deposits, however, between locally and widely dispersed beds, and all samples of the proximal fall deposits plot as a simple continuation of grain size trends for medial–distal samples. Associated PDC deposits form a spectrum of facies from fines-poor, avalanched beds through thin-bedded, landscape-mantling beds to channelized lobes of pumice-block-rich ignimbrite. The origins of the Novarupta near-vent deposits are considered within a spectrum of four transport regimes: (1) sustained buoyant plume, (2) fountaining with co-current flow, (3) fountaining with counter-current flow, and (4) direct lateral ejection. The Novarupta deposits suggest a model where buoyant, stable, regime-1 plumes characterized most of episodes II and III, but were accompanied by transient and variable partitioning of clasts into the other three regimes. Only one short period of vent blockage and cessation of the Plinian plume occurred, separating episodes II and III, which was followed by a single PDC interpreted as an overpressured "blast" involving direct lateral ejection. In contrast, regimes 2 and 3 were reflected by spasmodic sedimentation from the margins of the jet and perhaps lower plume, which were being strongly affected by short-lived instabilities. These instabilities in turn are inferred to be associated with heterogeneities in the mixture of gas and pyroclasts emerging from the vent. Of the parameters that control explosive eruptive behavior, only such sudden and asymmetrical changes in the particle concentration could operate on time scales sufficiently short to explain the rapid changes in the proximal 1912 products.Editorial responsibility: R. Cioni     

矿井直流电法三维正演计算的若干问题

介绍了用于矿井直流电法三维正演模拟不同数值计算方法的特点及其适用范围,提出了用对数等间距和算术等间距相结合的网格剖分方式,说明了电极互换原理所满足的地质条件。针对合成系数矩阵为非对角占优的特点,采用了大数处理方法,使其线性方程组适用于现有的求解方法。最后通过对具体问题的探讨,阐述了地质模型的计算精度和计算时间之间的相互关系,为模型参数的选择提供了一定的理论基础。