南海北部陆缘珠江口盆地岩石圈热结构   总被引：1，自引：0，他引：1       下载免费PDF全文

唐晓音  黄少鹏  张功成  杨树春  胡圣标 《地球物理学报》2018,61(9):3749-3759

沉积盆地岩石圈热结构特征是岩石圈构造-热演化过程的综合反映和盆地热史恢复的约束条件，对盆地动力学研究和油气资源评价具有重要意义.由于海洋勘探难度大、勘探程度低，相对于大陆地区，边缘海盆地比较缺乏岩石圈热结构方面的研究.本文在收集整理珠江口盆地及邻区大地热流数据的基础上，补充收录了自2003年以来发表的新数据，绘制了研究区最新版的大地热流等值线图；基于中美合作双船地震剖面揭示的深部地壳结构计算了研究区的壳-幔热流、深部温度以及"热"岩石圈厚度.研究表明，珠江口盆地地壳热流介于18.7~28.6 mW·m^-2，地幔热流介于36.9~91.4 mW·m^-2，壳幔热流比值0.23~0.75；由陆架、陆坡至中央海盆，在地壳热流逐渐减小的情况下地表热流逐渐递增，说明地表热流分布主要受深部热作用控制；盆地"热"岩石圈厚度介于34.0~87.2 km，平均65.5 km，反映出显著拉张减薄的特征.  相似文献   

滇西南地区南汀河断裂带三维深部电性结构及其孕震环境   总被引：3，自引：0，他引：3       下载免费PDF全文

叶涛  黄清华  陈小斌 《地球物理学报》2018,61(11):4504-4517

南汀河断裂带为滇西南地区活动断裂体系中规模最大的一条北东向断裂，其构造活动及地震危险性一直备受关注.本文基于覆盖云南境内南汀河断裂带的大地电磁测深宽频带阵列数据，利用大地电磁三维反演解释技术，首次获得了南汀河断裂带的精细三维深部电性结构.在上地壳深度，南汀河断裂带西南段与中段的电性结构表现出沿构造走向的高导条带特征，北东段表现为高阻结构.该高阻结构可能为临沧—勐海花岗岩体的电性反映，指示南汀河断裂可能未切穿该花岗岩带.在中下地壳深度，南汀河断裂带西南段存在大范围高导层，北东段则表现为整体性的高阻地壳，因此南汀河断裂北东段可能具有发生强震的介质结构背景.南汀河断裂带西南段的耿马地震区深部呈现北东向与北北西向的"X"型高导构造样式，该高导结构以南存在一个显著高阻异常体，1988年耿马M_S7.2地震以及2015年沧源M_S5.5级地震均发生于该高阻体与"X"型高导条带的电性边界.青藏高原东南缘绕东构造结流入滇西地区的中下地壳流可能受到南汀河断裂北东段中下地壳高阻体的阻挡而呈分流式分布于保山地块以及澜沧江断裂以东.  相似文献   

华南陆缘高热流区的壳幔温度结构与动力学背景          下载免费PDF全文

张健  王蓓羽  唐显春  董淼  艾依飞 《地球物理学报》2018,61(10):3917-3932

华南陆缘是我国重要的矿产、地热资源区.晚中生代以来，在太平洋板块西向俯冲，地幔热对流活动共同作用下，该区出现多期岩浆-热事件和大规模爆发式成矿作用.在前人研究基础上，本文利用地表热流观测资料、地震剪切波资料、重力位球谐系数，计算了壳-幔温度结构，分析了动力学背景.计算结果表明：华南陆缘东南沿海地带，地壳10 km以浅温度达200℃以上，居里点温度475℃，莫霍面平均温度550℃.地壳浅层较热，花岗岩中放射性元素衰变放热是地壳浅层地下水热活动的重要热源，但地壳总体温度不高，为"冷壳热幔"型热结构.地幔中，90 km深度，温度950~1250℃；120 km深度，温度1050~1400℃；150 km深度，温度1200~1450℃；220 km深度，温度1500~1700℃."热"岩石圈底界深度在110~150 km之间，西深东浅.岩石圈内，地幔应力场为挤压-伸展相间格局；岩石圈之下，地幔应力场为一个以南昌为中心、长轴NE-SW向的椭圆.分析认为，晚中生代以来，太平洋板块的西向俯冲，导致华南陆缘在区域性SE向地幔对流背景上叠加局域性不稳定热扰动，在175~85Ma期间，上地幔物质向上流动，形成不同的岩浆活动高峰期.同时，岩石圈地幔受俯冲洋壳流体的影响，含水量高，黏度小，在地幔流切向应力场作用下，岩石圈底界由西向东"波浪"状减薄.现今岩石圈之下仍具备地幔小尺度热对流温度条件，但除地表浅层外，地壳整体温度不高，岩石圈构造稳定.  相似文献   

Comparing threshold definition techniques for rainfall‐induced landslides: A national assessment using radar rainfall          下载免费PDF全文

Benjamin Postance  John Hillier  Tom Dijkstra  Neil Dixon 《地球表面变化过程与地形》2018,43(2):553-560

Translational landslides and debris flows are often initiated during intense or prolonged rainfall. Empirical thresholds aim to classify the rain conditions that are commonly associated with landslide occurrence and therefore improve understating of these hazards and predictive ability. Objective techniques that are used to determine these thresholds are likely to be affected by the length of the rain record used, yet this is not routinely considered. Moreover, remotely sensed spatially continuous rainfall observations are under‐exploited. This study compares and evaluates the effect of rain record length on two objective threshold selection techniques in a national assessment of Scotland using weather radar data. Thresholds selected by ‘threat score’ are sensitive to rain record length whereas, in a first application to landslides, ‘optimal point’ (OP) thresholds prove relatively consistent. OP thresholds increase landslide detection and may therefore be applicable in early‐warning systems. Thresholds combining 1‐ and 12‐day antecedence variables best distinguish landslide initiation conditions and indicate that Scottish landslides may be initiated by lower rain accumulation and intensities than previously thought. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Hierarchically nested river landform sequences. Part 2: Bankfull channel morphodynamics governed by valley nesting structure          下载免费PDF全文

Gregory B. Pasternack  Dastagir Baig  Matthew D. Weber  Rocko A. Brown 《地球表面变化过程与地形》2018,43(12):2519-2532

River corridors exhibit landforms nested within landforms repeatedly down spatial scales. In Pasternack et al. ( 2018 ), a new, scale‐independent, hierarchical river classification was developed that uses five landform types to map the domains of a single fluvial process – flow convergence routing – at each of three–five spatial scales. Given those methods, this study investigated the details of how flow convergence routing organizes nested landform sequences. The method involved analyzing landform abundance, sequencing, and hierarchical nesting along the 35 km gravel/cobble lower Yuba River in California. Independent testing of flow convergence routing found that hydraulic patterns at every flow matched the essential predictions from classification, substantiating the process–morphology link. River width and bed elevation sequences exhibit large, nonrandom, and linked oscillations structured to preferentially yield wide bars and constricted pools at base flow and bankfull flow. At a flow of 8.44 times bankfull, there is still an abundance of wide bar and constricted pool landforms, but larger topographic drivers also yield an abundance of nozzle and oversized landforms. The nested structure of flow convergence routing landforms reveals that base flow and bankfull landforms are nested together within specific floodprone valley landform types, and these landform types control channel morphodynamics during moderate to large floods. As a result, this study calls into question the prevailing theory that the bankfull channel of a gravel/cobble river is controlled by in‐channel, bankfull, and/or small flood flows. Such flows may initiate sediment transport, but they are too small to control landform organization in a gravel/cobble river with topographic complexity. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Analysis of nonstationarity in low flow in the Loess Plateau of China          下载免费PDF全文

Kun‐xia Yu  Lars Gottschalk  Xiang Zhang  Peng Li  Zhanbin Li  Lihua Xiong  Qian Sun 《水文研究》2018,32(12):1844-1857

An approach for nonstationary low‐flow frequency analysis is developed and demonstrated on a dataset from the rivers on the Loess Plateau of China. Nonstationary low‐flow frequency analysis has drawn significant attention in recent years by establishing relationships between low‐flow series and explanatory variables series, but few studies have tested whether the time‐varying moments of low flow can be fully described by the time‐varying moments of the explanatory variables. In this research, the low‐flow distributions are analytically derived from the 2 basic explanatory variables—the recession duration and the recession coefficient—with the assumption that the recession duration and recession coefficient variables follow exponential and gamma distributions, respectively; the derived low‐flow distributions are applied to test whether the time‐varying moments of explanatory variables can explain the nonstationarities found in the low‐flow variable. The effects of ecosystem construction measures, that is, check dam, terrace, forest, and grassland, on the recession duration and recession coefficient are further discussed. Daily flow series from 11 hydrological stations from the Loess Plateau are used and processed with a moving average technique. Low‐flow data are extracted following the pit under threshold approach. Six of the 11 low‐flow series show significant nonstationarities at the 5% significance level, and the trend curves of the moments of low flow are in close agreement with the curves estimated from the derived distribution with time‐dependent moments of the recession duration and time‐constant moments of the recession coefficient. It is indicated that the nonstationarity in the low‐flow distribution results from the nonstationarity in the recession duration in all 6 cases, and the increase in the recession duration is resulted from large‐scale ecosystem constructions rather than climate change. The large‐scale ecosystem constructions are found to have more influence on the decrease in streamflow than on the increase in watershed storage, thus resulting in the reduction of low flow. A high return period for the initial fixed design value decreases dramatically with an increasing recession duration.  相似文献   

An experimental investigation of the effects of thawed soil depth on rill flow velocity     

Xiaofeng Gao  Xiaonan Shi  Tingwu Lei  Huaqing Liu  Jiahui Yang 《水文研究》2021,35(2):e14043

Water flow velocity is an important hydraulic variable in hydrological and soil erosion models, and is greatly affected by freezing and thawing of the surface soil layer in cold high-altitude regions. The accurate measurement of rill flow velocity when impacted by the thawing process is critical to simulate runoff and sediment transport processes. In this study, an electrolyte tracer modelling method was used to measure rill flow velocity along a meadow soil slope at different thaw depths under simulated rainfall. Rill flow velocity was measured using four thawed soil depths (0, 1, 2 and 10 cm), four slope gradients (5°, 10°, 15° and 20°) and four rainfall intensities (30, 60, 90 and 120 mm·h⁻¹). The results showed that the increase in thawed soil depth caused a decrease in rill flow velocity, whereby the rate of this decrease was also diminishing. Whilst the rill flow velocity was positively correlated with slope gradient and rainfall intensity, the response of rill flow velocity to these influencing factors varied with thawed soil depth. The mechanism by which thawed soil depth influenced rill flow velocity was attributed to the consumption of runoff energy, slope surface roughness, and the headcut effect. Rill flow velocity was modelled by thawed soil depth, slope gradient and rainfall intensity using an empirical function. This function predicted values that were in good agreement with the measured data. These results provide the foundation for a better understanding of the effect of thawed soil depth on slope hydrology, erosion and the parameterization scheme for hydrological and soil erosion models.  相似文献   

Adjustment of self-formed bankfull channel geometry of meandering rivers: modelling study     

Kensuke Naito  Gary Parker 《地球表面变化过程与地形》2020,45(13):3313-3322

We consider the evolution of the hydraulic geometry of sand-bed meandering rivers. We study the difference between the timescale of longitudinal river profile adjustment and that of channel width and depth adjustment. We also study the effect of hydrological regime alteration on the evolution of bankfull channel geometry. To achieve this, a previously developed model for the spatiotemporal co-evolution of bankfull channel characteristics, including bankfull discharge, bankfull width, bankfull depth and down-channel bed slope, is used. In our modelling framework, flow variability is considered in terms of a specified flow duration curve. Taking advantage of this unique feature, we identify the flow range responsible for long-term bankfull channel change within the specified flow duration curve. That is, the relative importance of extremely high short-duration flows compared to moderately high longer duration flows is examined. The Minnesota River, MN, USA, an actively meandering sand-bed stream, is selected for a case study. The longitudinal profile of the study reach has been in adjustment toward equilibrium since the end of the last glaciation, while its bankfull cross-section is rapidly widening due to hydrological regime change in the last several decades. We use the model to demonstrate that the timescale for longitudinal channel profile adjustment is much greater than the timescale for cross-sectional profile adjustment due to a lateral channel shift. We also show that hydrological regime shift is responsible for the recent rapid widening of the Minnesota River. Our analysis suggests that increases in the 5–25% exceedance flows play a more significant role in recent bankfull channel enlargement of the Minnesota River than increase in either the 0.1% exceedance flow or the 90% exceedance flow. © 2020 John Wiley & Sons, Ltd.  相似文献   

Water transport and tracer mixing in volcanic ash soils at a tropical hillslope: A wet layered sloping sponge     

Giovanny M. Mosquera  Patricio Crespo  Lutz Breuer  Jan Feyen  David Windhorst 《水文研究》2020,34(9):2032-2047

Andosol soils formed in volcanic ash provide key hydrological services in montane environments. To unravel the subsurface water transport and tracer mixing in these soils we conducted a detailed characterization of soil properties and analyzed a 3-year data set of sub-hourly hydrometric and weekly stable isotope data collected at three locations along a steep hillslope. A weakly developed (52–61 cm depth), highly organic andic (Ah) horizon overlaying a mineral (C) horizon was identified, both showing relatively similar properties and subsurface flow dynamics along the hillslope. Soil moisture observations in the Ah horizon showed a fast responding (few hours) “rooted” layer to a depth of 15 cm, overlying a “perched” layer that remained near saturated year-round. The formation of the latter results from the high organic matter (33–42%) and clay (29–31%) content of the Ah horizon and an abrupt hydraulic conductivity reduction in this layer with respect to the rooted layer above. Isotopic signatures revealed that water resides within this soil horizon for short periods, both at the rooted (2 weeks) and perched (4 weeks) layer. A fast soil moisture reaction during rainfall events was also observed in the C horizon, with response times similar to those in the rooted layer. These results indicate that despite the perched layer, which helps sustain the water storage of the soil, a fast vertical mobilization of water through the entire soil profile occurs during rainfall events. The latter being the result of the fast transmissivity of hydraulic potentials through the porous matrix of the Andosols, as evidenced by the exponential shape of the water retention curves of the subsequent horizons. These findings demonstrate that the hydrological behavior of volcanic ash soils resembles that of a “layered sponge,” in which vertical flow paths dominate.  相似文献   

渤海海域浮游病毒和浮游细菌的丰度变化与环境因子之间的耦联关系     

王彩霞  吴霖  王毅波  Paterson James S.  Mitchell James G.  胡晓珂 《海洋学报(英文版)》2020,39(6):72-83

Uncovering the role of environmental factors and finding critical factors which harbor significant fractions in governing microbial communities remain key questions in coastal marine systems. To detect the interactions between environmental factors and distributions of virio-and bacterioplankton in trophic coastal areas, we used flow cytometry to investigate the abundance of virio-and bacterioplankton covering 31 stations in the Bohai Sea of China. Our results suggested that the average abundance of total virus(TV) in winter(～2.29×10~8 particles/mL)was slightly lower than in summer(～3.83×10~8 particles/mL). The mean total bacterial abundance(TB) was much lower in winter(～2.54×107 particles/mL) than in summer(～5.43×10~7 particles/mL). Correlation analysis via redundancy analysis(RDA) and network analysis among virioplankton, bacterioplankton and environmental factors revealed that the abundances of viral and bacterial subpopulations depend on environmental factors. In winter, only temperature significantly influenced the abundances of virio-and bacterioplankton. In summer, in addition to temperature, both salinity and nutrient(SiO_2) had a remarkable impact on the distribution of virioand bacterioplankton. Our results showed a clear seasonal and trophic pattern throughout the whole water system, which revealed that temperature and eutrophication may play crucial roles in microbial distribution pattern.  相似文献