Dynamic analysis of slab track on multi-layered transversely isotropic saturated soils subjected to train loads

The dynamic responses of a slab track on transversely isotropic saturated soils subjected to moving train loads are investigated by a semi-analytical approach. The track model is described as an upper Euler beam to simulate the rails and a lower Euler beam to model the slab. Rail pads between the rails and slab are represented by a continuous layer of springs and dashpots. A series of point loads are formulated to describe the moving train loads. The governing equations of track-ground systems are solved using the double Fourier transform, and the dynamic responses in the time domain are obtained by the inverse Fourier transform. The results show that a train load with high velocity will generate a larger response in transversely isotropic saturated soil than the lower velocity load, and special attention should be paid on the pore pressure in the vicinity of the ground surface. The anisotropic parameters of a surface soil layer will have greater influence on the displacement and excess pore water pressure than those of the subsoil layer. The traditional design method taking ground soil as homogeneous isotropic soil is unsafe for the case of RE 1 and RG 1, so a transversely isotropic foundation model is of great significance to the design for high train velocities.     

清代长江三角洲地区重大台风的对比分析

文章从清代的地方志、档案等文献史料中提取台风灾害信息并整理分类,根据台风及其次数的判断依据识别出清前期长江三角洲地区存在7次重大台风灾害,对这7次台风事件从台风过程、灾害分布与路径等方面进行了重建和对比分析。研究结果表明：清前期长三角地区的7次重大台风都发生于农历的六月、七月和八月,正值潮汛期,危害极大;台风过程持续时间短,一般在2~3 d左右。7次重大台风集中分布在浙江的杭州湾附近和长江下游流域两岸,主要在上海市的崇明、奉贤,浙江的余姚、嘉善等沿海地区登陆,然后沿岸向西北方向路径移动,与现代台风路径相比,接近于西北路径型或向北路径。在不同时空背景下台风对区域社会影响存在一定的差异性。     

合肥盆地构造热演化的裂变径迹证据

运用裂变径迹分析方法,探讨分析了合肥盆地中新生代的构造热演化特征. 上白垩统和古近系下段样品的磷灰石裂变径迹（AFT）数据主体表现为靠近部分退火带顶部温度(±65℃)有轻度退火,由此估算晚白垩世至古近纪早期合肥盆地断陷阶段的古地温梯度接近38℃/km,高于盆地现今地温梯度(275℃/km).下白垩统、侏罗系及二叠系样品的AFT年龄(975～25Ma)和锆石裂变径迹(ZFT)年龄(118～104Ma)均明显小于其相应的地层年龄,AFT年龄－深度分布呈现冷却型曲线形态,且由古部分退火带、冷却带或前完全退火带及其深部的今部分退火带组成,指示早白垩世的一次构造热事件和其随后的抬升冷却过程. 基于AFT曲线的温度分带模式和流体包裹体测温数据的综合约束,推算合肥盆地早白垩世走滑压陷阶段的古地温梯度接近67℃/km. 径迹年龄分布、AFT曲线拐点年龄和区域抬升剥蚀时间的对比分析结果表明,合肥盆地在早白垩世构造热事件之后的104Ma以来总体处于抬升冷却过程,后期快速抬升冷却事件主要发生在±55Ma.     

贵州碳酸盐岩红色风化壳次生石英的裂变径迹测年研究

贵州位于青藏高原东南缘,由于缺乏沉积记录其新生代的地质演化历史还不很明晰,而广泛分布于云贵高原的碳酸盐岩红色风化壳可能蕴涵着重要的地质演化信息.本文对贵州多个原位碳酸盐岩红色风化壳中产出的晶体形态较好的石英进行了裂变径迹方法测年.结果显示,石英的裂变径迹年龄数据呈现出较大的变化范围,从 1 Ma到 25 Ma,且远远地小于其三叠纪和寒武纪的母岩年龄;结合贵州 25 Ma到 1 Ma的区域地质演化历史,裂变径迹年龄值可以排除石英来源于母岩碎屑、成岩过程的次生形成以及火山活动产生的热水沉淀或交代形成的可能性,而只能推断为该晶体形态较好的石英于碳酸盐岩风化作用产生的富硅流体中沉淀形成;各剖面石英的年龄值与新生代的青藏高原夷平期、华南红土期、贵州构造稳定期乃至世界范围内的风化气候期有着良好的对应关系,说明次生石英裂变径迹测年具有很好的可行性和可靠性.     

黄陵隆起中-新生代隆升作用的裂变径迹证据

通过对8个样品磷灰石裂变径迹年龄和3个样品锆石裂变径迹年龄的测定以及时间-温度热演化历史的反演,研究黄陵隆起中新生代的隆升作用过程,结果表明：黄陵隆起自晚三叠世200Ma开始隆升,表现为持续的隆升过程,经历了4个阶段：200Ma～160Ma±的缓慢隆升冷却作用阶段;160Ma～98．4Ma的快速隆升冷却阶段,岩体进入磷灰石部分退火带中;之后进入了一个构造相对稳定的阶段,样品滞留在部分退火带中;随后36．7Ma～28．4Ma以来,再次快速隆升剥蚀冷却。两次快速的隆升作用指示了中扬子地区两次强烈的构造活动和构造变革。作为印支期以来持续的古隆起,黄陵隆起周缘地区是中扬子地区海相油气运聚有利的指向区。     

利用磷灰石裂变径迹对断层摩擦生热探测或测量的初步探讨

以青藏高原东北缘断裂带为研究对像,对利用磷灰石裂变径迹热年代学对地震断层滑动摩擦生热的探测或测量进行了初步探讨。其基本思路是利用磷灰石裂变径迹热年代计的热敏感,通过对横跨断层垂直方向断层岩和围岩的磷灰石裂变径迹年龄及围限径迹长度分布的对比分析,对断层滑动摩擦生热进行探测。本次研究对来自3个断层剖面的13个样品进行了磷灰石裂变径迹分析,样品包括断层主滑动面上的断层泥、碎裂岩和断层围岩,分析结果并没有获得断层摩擦生热的证据,表明这些断层在地震滑动过程中的摩擦增温非常有限,没有达到磷灰石裂变径迹热年代计体系可加载热信息的温度－时间要求。结合前人已有的相关研究,对利用磷灰石裂变径迹热年代学对地震断层滑动摩擦生热进行探测或测量存在的主要问题及可行性进行了初步总结和探讨,认为只适应于对震级大、断层滑动距离和速率大,摩擦强度强,位于一定深度有大量摩擦热生成,并使断层附近增温达到或超过磷灰石裂变径迹部分或完全退火温度的断层进行滑动摩擦生热的探测或测量,将是一种潜在的能对地震断层滑动摩擦生热或增温进行测量的“热量计或温度计”。     

Denudation History of South China Block and Sediment Supply to Northern Margin of the South China Sea

On the basis of apatite fission track (AFT) analyses,this article aims to provide a quantitative overview of Cenozoic morphotectonic evolution and sediment supply to the northern margin of the South China Sea (SCS).Seventeen granite samples were collected from the coast to the inland of the South China block.Plots of AFT age against sample location with respect to the coastline show a general trend of youngling age away from the coast,which implies more prolonged erosion and sediment contribution at the inland of the South China Sea during post break-up evolution.Two-stage fast erosion process,Early Tertiary and Middle Miocene,is deduced from simulated cooling histories.The first fast cooling and denudation during Early Tertiary are recorded by the samples along the coast (between 70 and 60 Ma) and the inland (between 50 and 30 Mu),respectively.This suggests initial local erosion and deposition in the northern margin of the SCS during Early Tertiary.Fast erosion along the coast ceased since ca.50 Ma,while it had lasted until ca.30 Ma inland,indicating that the erosion was transferred from the local coastal zone initially toward the continental interior with unified subsidence of the northern margin,which resulted in the formation of a south-dipping topography of the continental margin.The thermal stosis in the South China block since ca.30 Mu must det'me the time at which the northern margin became dynamically disconnected from the active rifting and stretching that was taking place to the south.The lower erosion rate is inconsistent with higher sedimentary rate in the Pearl River Mouth basin during Late Oligocene (ca.25 Ma).This indicates that the increased sedimentation in the basin is not due to the erosion of the granite belt of the South China block,but perhaps points to the westward propagation of the paleo-Pearl River drainage related to the uplift of the eastern margin of Tibet plateau and southward jumping of spreading axis of the South China Sea.The socond erosion acceleration rate of the Middle Miocene (ca.14 Ma) cooling could have been linked to the long-distance effect of uplift of the Tibet plateau or due to the enhanced East Asian monsoon.     

北大西洋风暴轴高低空分布及其能量诊断

利用1979~2013年NCEP再分析数据,通过经验正交分解对比了前冬时期北大西洋风暴轴的高低空分布,并用涡动动能(Eddy Kinetic Energy,EKE)方程对风暴轴高低空分布型差异进行了诊断。研究结果表明:上层和下层第一空间分布型差异巨大,对流层下层风暴轴中心偏北,靠近极地,而上层风暴轴中心偏西南,靠近北美沿岸。EKE方程诊断结果表明:正压转换项在高低空符号相反,导致了EKE在上、下层分布出现显著差异,即上层正压转换项为负,在扰动发展中起能量耗散作用,而下层正压转换项为正,且极大值区域对应下层EKE极大值区域,为风暴轴下层向极区域增强的主要原因。而斜压转换和非地转位势通量散度在上层均为正,且远大于下层,为风暴轴上层涡动能量维持的原因,也从涡动能量收支上解释了风暴轴的主体出现在上层。     

A Dynamical Statistical Model for Prediction of a Tropical Cyclone

A dynamical statistical method is applied for operational forecasting of the Bay of Bengal tropical cyclone “Nargis” of April–May 2008. The method consists of three forecast components, namely (a) analysis of Genesis Potential Parameter (GPP) and maximum potential intensity, (b) track prediction, and (c) 12 hourly intensity prediction for forecasts up to 72 hours. The results of the study showed that GPP could provide necessary predictive signal at early stages of development on the further intensification of the low pressure system into a tropical cyclone. The landfall forecast position errors by different operational numerical models (NWP) showed landfall position errors ranging from 10 km to 150 km and landfall time error ranges from 6 hours early to 6 hours delay. The dynamical statistical model is capable to provide 12 hourly nearly realistic intensity forecasts up to 60 hours of forecast.     

Apatite Fission Track Thermochronology of Granite from the Xiazhuang Uranium Ore Field, South China: Implications for Exhumation History and Ore Preservation

Xiazhuang uranium ore field, located in the southern part of the Nanling Metallogenic Belt, is considered one of the largest granite-related U regions in South China. In this paper, we contribute new apatite fission track data and thermal history modeling to constrain the exhumation history and evaluate preservation potential of the Xiazhuang Uranium ore field. Nine Triassic outcrop granite samples collected from different locations of Xiazhuang Uranium ore field yield AFT ages ranging from 43 to 24 Ma with similar mean confined fission track lengths ranging from 11.8 ± 2.0 to 12.9 ± 1.9 μm and Dpar values between 1.01 and 1.51 μm. The robustness time-temperature reconstructions of samples from the hanging wall of Huangpi fault show that the Xiazhuang Uranium ore field experienced a time of monotonous and slow cooling starting from middle Paleocene to middle Miocene (~60–10 Ma), followed by relatively rapid exhumation in the late Miocene (~10–5 Ma) and nearly thermal stability in the Pliocene–Quaternary (~5–0 Ma). The amount of exhumation after U mineralization since the Middle Paleogene was estimated as ~4.3 ± 1.8 km according to the integrated thermal history model. Previous studies indicate that the ore-forming ages of U deposits in the Xiazhuang ore field are mainly before Middle Paleocene and the mineralization depths are more than 4.4 ± 1.2 km. Therefore, the exhumation history since middle Paleocene plays important roles in the preservation of the Xiazhuang Uranium ore field.