民乐、山丹6.1级地震异常及台站实现短临预报的思考

在综合分析了民乐-山丹6.1级地震前张掖中心台范围内震兆异常特征的基础上,总结了本次地震前该台的短临预报过程及存在的问题,对今后台站如何搞好地震短临预报工作进行了探讨.     

Green''''s functions for uniformly distributed loads acting on an inclined line in a poroelastic layered site

Based on one type of practical Biot's equation and the dynamic-stiffness matrices of a poroelastic soil layer and half-space, Green's functions were derived for uniformly distributed loads acting on an inclined line in a poroelastic layered site. This analysis overcomes significant problems in wave scattering due to local soil conditions and dynamic soil-structure interaction. The Green's functions can be reduced to the case of an elastic layered site developed by Wolf in 1985. Parametric studies are then carried out through two example problems.     

一种利用机载激光点云的河流横纵断面自动提取方法

传统的河流断面测量方法具有周期长、成本高、外业多等不足,为此提出一种基于机载激光点云的河流横纵断面自动提取方法.首先,使用渐进三角网滤波器从机载点云中分离出地面点,用以构建三角网模型,并将其转化成数字高程模型数据.接着,利用洼地填充、流向分析、流量分析、河流栅格提取、矢量化等水文分析模块,从数字高程模型数据中自动提取出...     

一次自上向下发展的高原涡的多尺度动力学分析

高原涡作为经常给我国带来暴雨等灾害的天气系统,其形成一般认为是通过感热和潜热自下而上激发的,然而,2013年5月下旬发生的一次引发其下游灾害性强降水的高原涡却是由对流层高层天气尺度低涡诱发的.为此,基于新发展的多尺度子空间变换和多尺度能量涡度方法以及ERA5再分析资料对其动力学过程进行了详尽的探讨,先将原始场重构到三个...     

Sound velocity in carbonate sediments from the Whiting Basin,Puerto Rico

A series of sediment cores were obtained from the Whiting Basin southeast of Puerto Rico to investigate the factors affecting the velocity of sound in marine carbonate deposits. The cores indicated that the deposits in the Whiting Basin are similar to abyssal-plain deposits with lenticular turbidite sequences alternating with pelagic sediments. The sediment, comprised of highly porous sands and silts, averaged 80% calcium carbonate consisting of aragonite, low-Mg calcite and high-Mg calcite.Normal methods for predicting sound velocity from the physical properties of the deposits were found to be inaccurate for these samples. The established relationships of grain size and porosity to sound velocity were invalid because the sands found in the cores consisted of hollow-foram tests, causing high porosity independent of grain size. The rigidity of the deposit was the most significant factor determining sediment sound velocity and was itself controlled by the sediment source, transportation effects and the packing of the deposit. Future work is needed to accurately measure the effect of these factors on the rigidity modulus.     

Sediment waves on the Moroccan continental rise

A nearly continuous zone of sediment waves is present on the lower continental rise off western Morocco which parallels the regional bathymetric trends. The individual sediment waves within the zone migrate upslope with time and, in general, also trend parallel to the regional bathymetric contours. These observations suggest that geostrophic contour currents are responsible for the formation of sediment waves. Physical oceanographic measurements and sea-floor photographs indicate only a very weak bottom circulation in this region. This suggests either that strong bottom currents are not essential for the formation of sediment waves or that relatively stronger bottom currents flowed along the continental margin of Morocco in the recent past. Turbidity flows may also influence the distribution of these sediment waves.     

An analytical and experimental study of zoning in plagioclase

A detailed electron microprobe study has been conducted on natural and experimentally grown zoned plagioclase feldspars. Discontinuous, sector, and oscillatory chemical zoning are observed superimposed on continuous normal or reverse zoning trends. The relative accuracy of 3 element (Na, Ca, K) microprobe traverses was found statistically to be 2 mole percent. Comparison of microprobe data on natural zoned plagioclase with zoned plagioclase grown in controlled experiments has shown that it may be possible to distinguish zonal development resulting from physio-chemical changes to the bulk magma from zoning related to local kinetic control on the growth of individual crystals.     

The age,origin, and volcanological significance of the Y-5 ash layer in the Mediterranean

The Y-5 ash is the most widespread layer in deep-sea sediments from the eastern Mediterranean. This ash layer was previously correlated with the Citara-Serrara tuff on Ischia Island and dated at approximately 25,000 yr B.P. New data on the glass chemistry of the Y-5 ash and pyroclastic deposits from the Neopolitan volcanic province suggest that the layer is correlative with the large-volume Campanian ignimbrite and not with the deposit from Ischia Island. The volume of the Y-5 ash is approximately 65 km³ which is comparable in magnitude to the volume of the Campanian ignimbrite. An interpolated age of approximately 38,000 yr B.P. is estimated based on sedimentation rates derived from δ¹⁸O stratigraphy. There is a discrepancy between this estimate and previously reported radiocarbon ages which range from 24,000 to 35,000 yr B.P. We propose that the “Campanian tuff ash layer” should be adopted as the full stratigraphic name for the Y-5 ash. The deep-sea ash layer is divisible into two units in proximal localities, probably correlating with two major phases of the eruption: plinian and ignimbrite.     

Possible implications of modal mineralogy for melting in mantle lherzolites

The melting reaction at the solidus of mantle peridotite is commonly peritectic in nature, with liquid and one or more solid phases produced upon melting. In some situations, one of the phases participating on the reactant side of the reaction is present in low abundance. This article explores the possible effects of the low abundance of a reactant phase on the melting behavior of mantle peridotite.For example, spinel lherzolite begins to melt via the peritectic reaction, clinopyroxene + orthopyroxene + spinel = olivine + liquid in the ∼1- to 2-GPa pressure range. In natural spinel lherzolites, spinel is a modally minor mineral and may be infrequently in contact with both clinopyroxene and orthopyroxene. If these mutual contacts are insufficient to generate an interconnected melt, then significant melting may not occur until a combination of minerals that are modally abundant and in contact begin to melt. This scenario could have implications for the physical process of melting and for the timing of formation of an interconnected melt network and separation of the melt from the residue.To begin to investigate this possibility, the spatial relationships between the constituent minerals in two fertile spinel lherzolites were determined by elemental mapping with the electron microprobe. Olivine, orthopyroxene, and clinopyroxene are of similar size, whereas the spinel was smaller and interstitial. Spinel and clinopyroxene are frequently in contact, but mutual contacts of spinel, clinopyroxene, and orthopyroxene are rare. Because of the changes in modal mineralogy anticipated for these lherzolites with increasing temperature, these mutual contacts will be even less common at the solidus. Therefore, an interconnected, potentially extractable, melt may not occur by the solidus spinel + orthopyroxene + clinopyroxene melting reaction.     

基于粗糙集理论与遗传规划的地表下沉系数预测研究

利用粗糙集理论处理大数据量.消除冗余信息等方面的优势,计算出下沉系数各影响因素的属性重要性,约简了遗传规划训练样本集,建立了基于粗糙集和遗传规划的地表下沉系数预测模型。并与BP神经网络法预测结果进行了对比,结果表明,本模型具有精度高,收敛速度快等特点,将其应用到地表下沉系数预测中是可行的。