基于GPS应变、地震应变率与震源应力场对帕米尔高原现今构造变形特征的分析          下载免费PDF全文

潘正洋  邵志刚  周云  王洵  解孟雨  艾萨·伊斯马伊力 《地球物理学报》2020,63(3):1143-1154

研究帕米尔高原的构造变形特征对于理解印度板块向北推挤过程中的应变分配方式以及应力转换模式具有重要的意义.本文利用区域GPS应变场、地震应变场与震源应力场分析帕米尔高原的构造形变特征.主要结论为:(1)该区域变形主要以NNW-SSE或近N-S向的挤压为主,在高原内部伴有明显的近ENE-WSW或E-W向拉张,应力方向在帕米尔高原与塔吉克盆地区域呈现逆时针旋转的趋势,而在塔里木盆地则显示几乎与帕米尔高原的一致的应力状态,这可能与两侧盆地块体的强度差异有关.(2)安德森断层参数A∅显示帕米尔高原北缘与西侧区域为逆断层应力状态,在高原内部为正断层应力状态,这与GPS应变的结果显示的应变主要集中在主帕米尔断裂与阿莱谷地附近而在高原内部应变较低是一致的,另外应力在喀喇昆仑断裂北段的方向基本平行于断层走向,以及断层北端较低的滑动速率,这说明了地壳挤压缩短可能是帕米尔高原主要的的构造变形特征,并不支持由于边界走滑断裂导致的应变分异或者块体挤出的模式.(3)综合考虑地震应变方向与SHmax从帕米尔北部NNW-SSE方向到天山北部的近N-S方向的转换,GPS应变方向在帕米尔高原两侧盆地都存在不同程度的旋转,应力场安德森参数A∅显示的应力状态以及SKS的结果显示的近ENE-WSW方向,我们认为印度板块向北推挤与天山造山带碰撞导致帕米尔高原不对称的径向逆冲是帕米尔高原现今构造变形的主要成因与构造模式.  相似文献   

Late Holocene changes in vegetation and atmospheric circulation at Lake Uddelermeer (The Netherlands) reconstructed using lipid biomarkers and compound‐specific δD analysis          下载免费PDF全文

《第四纪科学杂志》2018,33(1):100-111

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Prediction of vegetation anomalies over an inland river basin in north‐western China          下载免费PDF全文

Jing Fu  Jun Niu  Bellie Sivakumar 《水文研究》2018,32(12):1814-1827

Vegetation cover plays an important role in linking the atmosphere, water, and land and is deemed as a key indicator in the terrestrial ecological system. Therefore, it is of great importance to monitor vegetation dynamics and understand the mechanisms of vegetation change, including that driven by climate change. This study examines (a) the evolution of vegetation dynamics over the Heihe River Basin in the typical arid zone in north‐western China using nonparametric Mann–Kendall test and Thiel Sen's slope; (b) the relationships between remotely sensed vegetation indices (normalized difference vegetation index [NDVI] and enhanced vegetation index [EVI]) and hydroclimatic variables based on correlation analysis; and (c) the prediction of vegetation anomalies using a multiple linear regression model. For the analysis, the Moderate Resolution Imaging Spectroradiometer NDVI/EVI product and the gridded daily meteorological data at a spatial resolution of 0.125° over the period 2001–2010 are considered. The results indicate that vegetation cover improved over a large proportion during 2001–2010, with a significant trend towards warm and wet, characterized by an increase in average annual temperature and precipitation by 0.042 °C/year and 5.8 mm/year, respectively. We test the feasibility of NDVI and EVI in quantifying the responses of vegetation anomaly to climate change and develop a statistical model to predict vegetation dynamics in the basin. The NDVI‐based model is found to be more reliable than the EVI‐based model, partly due to the vegetation characteristics and geomorphologic properties of the study region. The proposed model performs well when there is no lag time between meteorological factors and vegetation indices for grassland and cropland, whereas 1‐month lead time prediction is found to be best for forest. The soil water content is introduced as an extra explanatory variable, which effectively improves the prediction accuracy for different land use types. In general, the predictive ability of the proposed model is stable and satisfactory, and the model can provide useful early warning information for regional water resources management under changing climate.  相似文献   

青岛台体应变短周期气压系数变化原因探讨     

岳龙  徐清风  臧艺博  李志强  刘云  李炜  孙忠礼 《大地测量与地球动力学》2020,40(7):765-770

青岛台体应变短周期(小于128 min)气压系数2018-01出现阶变，通过对观测系统、台站周边施工情况、监测环境等逐项现场核实，排除观测系统、周边施工的影响。利用离散小波变换和回归分析发现，钻孔水位的气压系数与体应变气压系数同步阶变，结合台站钻孔施工当天体应变钻孔水位变化、体应变趋势变化、其他相邻台站水位气压系数变化等数据认为，台站钻孔施工是导致体应变气压系数变化的原因，并定性分析其变化机理。  相似文献   

A novel coupled FDM-DEM modelling method for flexible membrane boundary in laboratory tests     

Hua-Xiang Zhu  Zhen-Yu Yin  Qiang Zhang 《国际地质力学数值与分析法杂志》2020,44(3):389-404

Difficulties are involved in discrete element method (DEM) modelling of the flexible boundary, that is, the membranes covering the soil sample, which can be commonly found in contemporary laboratory soil tests. In this paper, a novel method is proposed wherein the finite difference method (FDM) and DEM are coupled to simulate the rubber membrane and soil body, respectively. Numerical plane strain and triaxial tests, served by the flexible membrane, are implemented and analysed later. The effect of the membrane modulus on the measurement accuracy is considered, with analytical formulae derived to judge the significance of this effect. Based on an analysis of stress-strain responses and the grain rotation field, the mechanical performances produced by the flexible and rigid lateral boundaries are compared for the plane strain test. The results show that (1) the effect of the membrane on the test result becomes more significant at larger strain level because the membrane applies additional lateral confining pressure to the soil body; (2) the tested models reproduce typical stress and volumetric paths for specimens with shear bands; (3) for the plane strain test, the rigid lateral boundary derives a much higher peak strength and larger bulk dilatation, but a similar residual strength, compared with the flexible boundary. The latter produces a more uniform (or ‘diffuse') rotation field and more mobilised local kinematics than does the former. All simulations show that the proposed FDM-DEM coupling method is able to simulate laboratory tests with a flexible boundary membrane.  相似文献   

不同类型洞体应变仪的观测差异性分析          下载免费PDF全文

孙伶俐  蒋玲霞  吕琳  张辉  邓建刚 《地震工程学报》2020,42(1):129-135

运用SPSS中聚类及PCA方法对湖北省7个台站三类基线(石英管、铟钢棒、铟钢管)洞体应变观测记录进行相关统计分析,归纳总结其潮汐参数变化特征差异,并针对观测中自然环境因素影响进行定量分析。结果显示:(1)三类基线中,铟钢棒类M2波潮汐因子、中误差及M1波相对噪声水平较低,铟钢棒管年均漂移量最小;(2)自然环境因素(气压、降水、雷雨、温度)对湖北地区洞体应变观测影响较为显著,等量气压影响下应变量最小的为铟钢管型,等量温度影响下应变量最小的为铟钢棒型。  相似文献   

北部湾地区海砂填料的动力特性分析     

王家全  陈胜前  唐毅  黄世斌  黄钦政 《海洋工程》2020,38(5):149-155

为研究北部湾地区海砂填料的动力特性，采用高级动态三轴测试系统开展循环荷载下的动三轴试验，研究不同围压及不同动应力幅值对海砂动力特性的影响规律。试验结果表明：轴向累计应变随围压增加而减小，围压150 kPa时振次10 000后应变仅为3%；随着动应力幅值的增大轴向累积应变随之增大，且达到破坏标准的时间越短。动弹性模量随着动应力幅值和围压的增加而增大，不同围压下动弹性模量随动应变的增加出现先骤减再略减后稳定的发展趋势，ε_d>0.3%后开始趋于稳定；不同动应力幅值下动弹性模量出现先增后减直至稳定的趋势，其中动应力幅值对动弹性模量有明显的影响，围压影响相对较小。孔压比随动应力幅值增加而减小，随围压增加而增加。  相似文献   

基于SLAF测序分析3个塔形马蹄螺群体的遗传结构和多样性*     

黄景  欧泽奎  刘文广  何毛贤 《热带海洋学报》2020,39(5):1-18

塔形马蹄螺(Tectus pyramis), 海洋软体动物, 广泛分布于中国深圳大鹏湾、海南岛、西沙和南沙群岛的珊瑚礁生态系统中。文章采用特异性位点扩增片段简化基因组测序技术(SLAF-seq)对来自深圳(SZ)、三亚(SY)和西沙(XS)的塔形马蹄螺群体的遗传多样性和结构进行分析。通过测序共获得115.74Mb读长数据, 平均测序深度为337.87倍, 测序质量值(Q₃₀)平均为94.07%。研究获得118679个多态性SLAF标签, 获得846502个高度一致的群体单核苷酸多态性位点(SNPs), 其中有155个显著差异SNPs。3个群体的平均观察杂合度(H_o)和期望杂合度(H_e)值分别为0.1441~0.1611和0.2537~0.2695。平均多态性信息含量(PIC)为0.2048~0.2176。通过系统发育树分析、主成分分析和聚类分析, 将45个个体大致分为3个类群, 每个群体的所有个体都可以聚类成一个类群。SZ和SY群体的遗传结构相似, 遗传距离最低(0.2510), 遗传分化系数F_st值最低(0.0818)。但XS与其他两个群体间的遗传分化明显, 尤其是XS和SZ群体(F_st=0.1868)。3个群体的遗传分化可能与海流和地理位置有关。  相似文献   

New formulae for capacity energy-based assessment of liquefaction triggering     

Yasaman Jafariavval 《Marine Georesources & Geotechnology》2020,38(2):214-222

Abstract

Liquefaction of loose saturated soil deposits is a hazardous type of ground failure occurring under earthquake excitations. Therefore, an accurate estimation of liquefaction potential is extremely important in geotechnical engineering. In the current study, a new model is proposed which estimates the level of strain energy needed for liquefaction initiation. A compiled database containing cyclic tests gathered from previously published works was used to develop new models to predict liquefaction potential. M5′ algorithm was used to find the best correlation between parameters. It was shown that not only the derived formulas are acceptably accurate but also they feature a very simple structure in comparison with available formulas in the literature. The proposed equations are accurate, physically sound and uncomplicated. Furthermore, safety factors were given for different levels of risk, which can be useful for engineering practice. In addition, the influence of different predictors on the liquefaction potential was evaluated and also the significance of input variables was assessed via sensitivity analysis. Finally, a new model was introduced for preliminary estimation of liquefaction potential.  相似文献   

Dynamic characteristics of marine soft clay under variable phase difference and initial static shear stress     

Wenqian Dong  Xiuqing Hu  Hongtao Fu 《Marine Georesources & Geotechnology》2020,38(7):770-785

Abstract

Under seismic loading, the soil layer is subjected to multidirectional cyclic shear stress with different amplitudes and frequencies because of the coupling of multiple shear waves and the soil element within a slope or behind a retaining wall is subjected to initial static shear stress before subjected to cyclic loading. Due to the complexity of seismic loading propagation, a phase difference exists between the initial static shear stress and cyclic shear stress. To investigate the influence of the phase difference and initial static shear stress on cyclic shear strain, cyclic modulus, and cyclic strength, a series of laboratory tests are performed on Wenzhou marine soft clay by multi-directional simple shear system, which can simulate the actual state better by controlling the horizontal cyclic stress in the x and y directions simultaneously. As the phase difference varies from 0° to 90°, the dynamic shear modulus increases and cyclic strain accumulation decreases with an increasing number of cycles. The shear strain increases with the initial shear stress.  相似文献