Effect of increasing rainfall on the thermal–moisture dynamics of permafrost active layer in the central Qinghai–Tibet Plateau

In the past several decades,the trend of rainfall have been significantly increasing in the Qinghai–Tibet Plateau,which inevitably leads to a change in the surface energy balance processes and thermal-moisture status of the permafrost active layers.However,the influence of mechanisms and associated effects of increasing rainfall on active layers are still poorly understood.Therefore,in this study,a validated coupled numerical water–vapor–heat model was applied for simulating the surface energy components,liquid and vapor water migration,and energy transfer within the permafrost active layer under the action of increasing rainfallin the case of an especially wet year.The obtained results demonstrate that the surface heat flux decreaseswith the increase in rainfall,and the dominant form of energy exchange between the ground and atmospherebecomes the latent heatflux,which is beneficial for the preservation of permafrost.The increasing rainfall will also cause the migration of liquid and vapor water,and the migration of liquid will be more significant.The liquid and vapor water migrationcaused by the increasing rainfallis also accompanied by energy transfer.With the increase in rainfall,the decrease in total soil heat flux directly leads to a cooling effect on the soil,and then the upper limit of the frozen soil rises,which alleviates the degradation of permafrost.These results provide further insights into engineering structures,regional ecological climate change,hydrology,and environmental issues in permafrost regions.

TECTONIC STYLES IN THE SOUTHWEST QINLING AND RELATIONS WITH DYNAMICS OF QINGHAI—TIBET PLATEAU

Based on the studies of geology and geochemistry, A’nymaque—Mianlue limited oceanic basin is comparable to the Paleo\|Tethys on time, sedimentary, biocoenosis, and the type of ophiolite (Coleman, 1984; Deng, 1984; Xu, 1996;Chenliang, 1999). The A’nyemaqen—Mianlue oceanic basin was one of a northeast branches of Paleo\|Tethys (Zhang Guowei, 1995; 1996) .Our researches on deformations reveal that tectonic styles of the Southwest Qinling orogenic belt is obviously influenced by the dynamics of Qinghai—Tibet plateau.Structural deformation analysis suggested that the southwest part of Qinling have undergone 3 major deformation stages in Mesozoic and Cenozoic. Firstly, rock folding at deep\|middle tectonic level and progressively thrusting shearing characterized the deformation of collision. The thrust tectonics are south\|directed, such as A’nymaque, Wenxian—Kangxian and Mianlue thrusting systems, and the deformations took place in T\-2—T\-3. Secondly, the middle\|tectonic level thrusting and sinistral strike\|slip formed at early intracontinental period (J—K), the thrust tectonics was south\|directed and the regional penetrative left\|lateral slips were NW or NWW. Finally, the east\|west extensional deformations which occurred in late Mesozoic and Cenozoic, a series of north\|south directing basins came into being in this stage, Huixian—Chengxian basin and Lixian basin for example, which overlapped the former deformation styles.

Thermal dynamics of the permafrost active layer under increased precipitation at the Qinghai-Tibet Plateau

Precipitation has a significant influence on the hydro-thermal state of the active layer in permafrost regions, which disturbs the surface energy balance, carbon flux, ecosystem, hydrological cycles and landscape processes. To better understand the hydro-thermal dynamics of active layer and the interactions between rainfall and permafrost, we applied the coupled heat and mass transfer model for soil-plant-atmosphere system into high-altitude permafrost regions in this study. Meteorological data, soil temperature, heat flux and moisture content from different depths within the active layer were used to calibrate and validate this model. Thereafter, the precipitation was increased to explore the effect of recent climatic wetting on the thermal state of the active layer. The primary results demonstrate that the variation of active layer thickness under the effect of short-term increased precipitation is not obvious, while soil surface heat flux can show the changing trends of thermal state in active layer, which should not be negligible. An increment in year-round precipitation leads to a cooling effect on active layers in the frozen season, i.e. verifying the insulating effect of "snow cover". However, in the thawed season, the increased precipitation created a heating effect on active layers, i.e. facilitating the degradation of permafrost. The soil thermal dynamic in single precipitation event reveals that the precipitation event seems to cool the active layer, while compared with the results under increased precipitation, climatic wetting trend has a different influence on the permafrost evolution.

利用GPS高精度监测数据开展青藏高原现今地壳运动与形变特征研究进展

青藏高原由于所处大陆构造位置的特殊性,造就其成为全球现今地壳构造运动最为强烈的区域之一。青藏高原及其周边地区发育有多条深大活动断裂带,是强震易发区,同时也是研究大陆内板块构造运动机制的天然试验场。GPS以其时空分辨率高、覆盖范围广、观测精度高等特点,被广泛应用于地壳形变监测研究中。目前,通过已建立的中国地壳运动观测网络(CMONOC-Ⅰ)与中国大陆构造环境监测网络(CMONOC-Ⅱ)获得的GPS高精度地壳运动速度场,能够清晰地揭示青藏高原近20年来地壳构造运动与形变现状。通过系统总结利用GPS监测数据开展青藏高原现今地壳运动与形变特征的研究进展,回顾了用于监测青藏高原地壳运动的GPS数据来源与高精度数据处理方法及策略,探讨了不同参考基准对GPS速度场处理结果的影响,并分别从动力学和运动学两方面全面阐述了当前用于青藏高原地壳运动与形变分析模型。综合模型计算结果从浅部与深部两方面深入剖析了青藏高原现今地壳运动与形变特征,并从板块运动构造动力学机制角度详细解译了青藏高原现今区域动力学背景及其影响下的珠穆朗玛峰隆升机制。最后对利用GPS技术开展青藏高原地壳运动与形变监测成果作了概述总结,并进一步展望了未来青藏高原地壳形变监测研究的重要发展趋势。

青藏高原及其东南前陆地壳运动的GPS监测

作为世界上最高最大最活动的青藏高原,以其独特的自然地理条件吸引了广大学者和科研人员的关注,在此地区开展的各项研究工作.本文主要介绍了利用GPS监测青藏高原及邻区所得到的速度矢量场.观测结果表明:高原南北向收缩、高原物质东流、高原东部地区地壳物质相对喜马拉雅汇聚区作大规模的顺时针旋转等高原动力学特征.并就其产生原因进行了初步分析.

汶川大地震前GPS时间序列的振荡分析

采用复小波分析技术,分析了中国大陆GPS基准站水平向时间序列的多时间尺度和周期性变化特征。结果表明,青藏高原GPS站的南北分量在2007年初至汶川大地震发生前,出现一个周期的准同步周年振荡异常,且向北方向的半周期波峰振幅明显高于各点在印尼苏门答腊巨震后大尺度北东向长趋势运动的加速度,这可能是导致龙门山闭锁段破裂的重要触发因子。这种振荡的周期集中在汶川大地震前355～375天,与地球绕太阳公转周期非常一致。

基于Monte Carlo方法的由GPS观测计算地应变率的误差分析

在利用GPS观测计算地应变率中,应变率的误差分布在地球动力学研究中非常重要.为解决这一问题,文中提出基于MonteCarlo技术,利用GPS观测的速度计算地应变率进行误差分析的方法;以青藏高原地区为例,利用带有误差的GPS观测数据进行了大量、独立的应变率重复计算,然后运用统计方法给出了应变率分量及其误差的分布.结果显示青藏高原的喜马拉雅及中东部地区地应变率的东西向、南北向及剪应变率分量的误差相对较大,但整个青藏高原及附近地区应变率结果稳定可靠;研究结果进一步表明,由GPS观测计算应变率的误差主要决定于GPS观测速度的误差,在变形小的区域(如中国东部地区),目前GPS的观测精度还不能完全满足地应变率计算的要求.

基于GPS观测的昆仑山8．1级地震微动态变形研究

借助板内块体的刚性运动、应变综合模型,利用青藏块体东北缘地区的GPS基准站连续观测数据,通过计算各测站累计差分位移得出该区域变形参数动态变化。结果表明,2001年昆仑山8.1级地震前后变形参数时间序列存在一致的变化趋势,同震变化明显的参量有东西向应变、最小主应变、面膨胀率与第二剪应变。该综合模型可以解释昆仑8.1级地震引起区域应变释放、调整的机制。研究还认为利用区域变形参数组合有可能识别出大震临震异常。

基于GPS的青藏块体东北缘运动特征分析

利用2010年、2012年、2014年3期GPS大地测量数据和通过加权平均生成的2010～2014年平均速度场数据,探讨了青藏块体东北缘地区的地壳运动以及形变变化特征。结果表明:①青海省内部呈NE向运动的地壳变化特征,西南最快,约为25.0 mm/a,由西南至西北逐渐减低;②在阿拉善与鄂尔多斯块体的阻挡下,河西走廊与甘东南地区地壳运动接近正E方向,且运动速率随"2010—2012—2014"的时间线依次降低,表明其地壳内部发生了应力积累现象;③青海内部西南至西宁东北方向,主要呈NE向挤压、NW向拉张的变化特征。

Lithospheric Evolution and Geodynamic Process of the Qinghai-Tibet Plateau: An Inspiration from the Yadong-Golmud-Ejin Geoscience Transect

Abstract The Tibet Geoscience Transect (Yadong-Golmud-Ejin) has revealed the basic structures, tectonic evolution and geodynamic process of the lithosphere of the Qinghai-Tibet plateau. The evidence of northward thrusting of the Indian plate beneath the Himalayans on the southern margin and to southward compression of the Alxa block on the northern margin has been found. They were the driving forces causing the plateau uplift. The plateau is a continent resulting from amalgamation of eight terranes. These terranes are separated by sutures or large-scale faults, and different terranes have different lateral inhomogeneities and multi-layered lithospheric structures. At depths of about 20–30 km of the crust in the interior of the plateau there commonly exists a low-velocity layer. It is an uncoupled layer of the tectonic stress; above the layer, the upper crustal slices were thrust and overlapped each other and the rocks underwent brittle deformation, thus leading to shortening and thickening of the upper crust. Below the layer, the lateral change of the structure of the lower crust varies most greatly and ductile deformation occurs. The lower crust velocity of southern Tibet shows the reversed feature; whereas the lower crust velocity of northern Tibet increases and displays strong gradient variation and the character of the double Moho. On the whole, the Moho of the plateau is greatly undulatory. Although the crust of the Qinghai-Tibet Plateau has a great thickness, the lithosphere does not thicken markedly. The plateau is in a state of bi-directional compression. The unstable change of the Moho, the interaction between the crust and mantle and between the lithosphere and asthenosphere caused by the sinking of the lithospheric mantle and the strike slip and extension of the crust are the major dynamic factors for maintaining the present height and scope of the Qinghai-Tibet Plateau.

Hydrochemical Dynamic Characteristics and Evolution of Underground Brine in the Mahai Salt Lake of the Qaidam Basin Qinghai-Tibet Plateau

The mineral rock salts present in the Mahai Salt Lake of the Qaidam basin exhibit high solubilities in water. In addition, the multicomponent underground brine exhibits a high salinity and is easily precipitated. In the natural state, brine transport in the brine layer is extremely slow, and the brine is in a relatively stable chemical equilibrium state with the rock salt media. However, during mining, both the seepage and the chemical fields fluctuate significantly, thereby disrupting the equilibrium and leading to variations in the chemical composition and dynamic characteristics of the brine. Therefore, we selected underground brine from the Mahai Salt Lake, collecting a total of 183 brine samples over three stages of mining（i.e., the early stage of underground brine extraction, the initial stage of mining, and the later stage of mining）. Using a range of analytical techniques, the chemical dynamics of the underground brine water and its evolution were systematically studied. We found that evaporation and enrichment were the main mechanisms of underground brine evolution in the Mahai Salt Lake, with cation exchange and mineral dissolution/precipitation being key factors in determining the dynamic characteristics and evolution of the brine.

Motive force of Qinghai-Tibet Plateau moving to east

A calculation formula on spherical pattern of Qinghai-Tibet plateau moving model is established. Tibet massif moves norward by east in speed of 28 mm/a, Ganshu-Qinghai massif moves to northeast in speed of 15 mm/a, Qomolangma Feng moves northward by a few east in speed of 35 ～42 mm/a. The low latitude perimeter is longer than the nigh latitude perimeter. When the Tibet massif moves northward, its latitude perimeter must be contracted and the Tibet massif must move eastward by Coriolis. Coriolis force is inertial in earth rotation. It makes the fall body turning to east and the rising block turning westward. In the Northern Hemisphere, it makes the northward body turning to east and the southward block turning to west.This is the reason why the tectonic zones of western Pacific are different from those of eastern Pacific.

THE HIGH RESOLUTION SEISMIC TOMOGRAPHIC IMAGE IN QINGHAI—TIBET PLATEAU AND ITS DYNAMIC IMPLICATIONS

The Qinghai—Tibet plateau and its surrounding areas including Indian subcontinent, Xinjiang, Mongolia, is a largest lithosphere convergence place in the world, which characterized by continent\|continent collision with a thick crust and lithosphere. The high resolution seismic surface wave tomographic inversion has been conducted for studying the 3D velocity structure of crust and upper mantle in those areas. The seismic surface waveform data are from the archives of the CDSN, GSN and GEOSCOPE. About 2400 long period surface waveform recordings are available for both dispersion and waveform tomographic inversion. The block inversion by grid 1°×1°in Qinghai—Tibet plateau and 2°×2°in the surrounding areas were adapted. The resulting maps show the high resolution 3D shear wave velocity variation from earth’s surface to 400km depth.

联合GPS和GRACE研究青藏高原南部地区垂直形变的季节性波动

利用青藏高原南部地区GPS站点近10a（2004年至2014年）的观测资料,结合重力场恢复与气候实验卫星（Gravity Recovery and Climate Experiment,GRACE）同时期观测数据反演得到的该区域水文负荷变化引起的垂向位移,发现该地区利用GPS和GRACE获取的垂向位移时间序列存在一定相关性,多数站点的相关系数在0.7左右,特别是沿喜马拉雅造山带区域内的站点相关性更高;此外,大部分站点（例如CHLM、KKN4）拟合的周期项振幅和相位也较为一致。计算GRACE估算垂直信号改正GPS结果前后的加权均方根误差（weighted root mean square,WRMS）,并定义R（WRMS）来表征GRACE改正GPS垂向季节性波动的有效性,其数值越接近1表明GPS和GRACE数据具有越大的一致性。研究发现GPS站点的R（WRMS）有明显差异：最大和最小值分别是0.96（TPLJ）和0.24（XZGE）,平均值为0.64,这与青藏高原南部地区垂直运动的复杂性有关,存在多种因素（构造运动、冰川均衡调整、大气和非潮汐海洋负荷,水文负荷、GPS交点年误差等）的共同作用。

青藏高原块体相对运动模型的GPS方法确定与分析

利用武汉测绘科技大学在１９９３年、１９９５年观测的两期ＧＰＳ资料，具体分析了青藏高原各块体相对运动情况。目前青藏高原大约以３３．４ｍｍ／ａ，Ｎ３０°Ｅ方向向西伯利亚运动，其中巴颜喀拉块体、羌塘块体、拉萨—冈底斯块体和喜马拉雅块体大约分别以１７．３ｍｍ／ａ±３．１ｍｍ／ａ，Ｎ３５°Ｅ；２５．７ｍｍ／ａ±５．１ｍｍ／ａ，Ｎ３３°Ｅ；３８．９ｍｍ／ａ±６．１ｍｍ／ａ，Ｎ２９°Ｅ；４６．０ｍｍ／ａ±６．２ｍｍ／ａ，Ｎ２７°Ｅ方向朝西伯利亚运动，而西藏块体大约以２８．５ｍｍ／ａ±５．０ｍｍ／ａ速率，Ｎ３１°Ｅ方向朝西伯利亚运动，这些结果与地质结果符合。文中还给出了各块体相对运动的欧拉向量。

基于定位观测站图像实现草原植被覆盖度自动化提取的方法比较

植被覆盖度是草原生态监测和研究中极其重要的指标。本研究采用无人值守定位观测站获取样方图像数据集,比较选取多种提取算法,旨在解决定位连续观测中不同样方的大量图像数据集如何自动化提取植被覆盖度指标的难题。本文使用绿度指数法、随机森林(RF)、支持向量机(SVM)和反向传播(BP)神经网络不同图像分割方法提取不同草地类型的覆盖度,并讨论绿度指数之类的阈值分割方法与机器学习方法的优劣、3种机器学习算法产生不同分类效果的原因以及覆盖度数值产生误差的主要原因。结果表明,机器学习算法可灵活解决定位观测站样方图像集的快速自动化提取植被覆盖度问题。绿度指数阈值分割方法应用于植被覆盖度的分割效果较差;RF算法在高寒草原的分割精度较高,SVM在温性草原和温性荒漠草原中分割效果较高,BP神经网络在高寒草甸的覆盖度提取中更有优势。本研究可为新时代草原生态监测的信息化和智能化监测设备研发提供重要的参考依据。

利用GRACE改正GPS测站垂直方向的周期变化

处理青藏高原南部GPS站点多年的观测资料,结合地球重力场恢复和气候实验(gravity recovery and climate experiment,GRACE)数据反演得到的该区域地表质量变化引起的垂直方向变化值,发现该地区GPS观测的垂直方向时间序列与GRACE反演的地表垂向位移存在较大的相关性,多数站点的相关性在80%以上,部分站点的相关性甚至达到了95%以上。进一步研究发现,GPS和GRACE两种空间大地测量技术获得的时间序列存在较为明显的周期性周期变化,并且振幅和相位较为一致,利用GRACE改正GPS垂向观测值并定量计算其有效性。

青藏高原草地物候动态及其对驱动因子的响应

植被物候动态是多重因子影响的结果,尤其在对外界扰动响应敏感的青藏高原草地生态系统。本研究利用2000-2020年MODIS 16 d合成的归一化植被指数(normalization difference vegetation index, NDVI)数据,选用动态阈值法提取了青藏高原逐年的植被物候期,探究了青藏高原草地物候动态变化及其对驱动因子的响应。结果表明:1) 2000-2020年青藏高原草地生长季始期(start of the growing season, SOS)从西北向东南呈提前趋势,每年提前约0.19 d;草地生长季末期(end of the growing season, EOS)整体呈推迟趋势,每年推迟约0.19 d;草地生长季长度(length of the growing season, LOS)由西北向东南逐渐增长。2)风速和连续5 d最大降雨(yearly maximum five-day precipitation, RX5day)是影响草地LOS的主要因素,且因子间两两交互作用要强于单个因子对植被物候的影响,尤其表现在RX5day与温度和风速与温度之间的交互。3)草地LOS与风速和RX5day的回归系数有明显的空间异质性。藏北高原草地LOS随风速增大而变长,随RX5day增大而变短。青海高原和藏南谷地的草地LOS随风速增大而变短。川藏高山峡谷区草地LOS随RX5day增大而变长。综上,本研究可为研究区内生态系统保护和畜牧业的发展提供一定科学依据。

青藏块体东北缘水平应变场与构造变形分析

利用青藏块体东北缘地区 1993与 1999年GPS观测获得的地壳水平运动速度场结果 ,初步研究了该区的应变场与构造变形。该区应变场以近NE向的主压应变为主体 ,伴随着近NW向的张性应变。河西走廊中、东段 ,尤其是武威断块是压应变最强的区域。应变场形成的剪应变以近EW向的左旋剪切为主体 ,表明该区NWW向的块体边缘主干断裂的活动方式是左旋走滑兼挤压。剪应变高值区主要分布于青藏块体东北边界带的武威、祁连一带。甘青块体与阿拉善块体之间整体左旋扭动速率约为 6mm/a。配合非连续变形分析法 (DDA)数值模拟 ,初步分析了该区的构造应力场背景 ,认为该区相对水平运动和构造变形分布特征不仅是印度板块推挤应力场作用的结果 ,还可能与来自西侧南强北弱的向东的动力作用有关。

青藏高原东缘鲜水河断裂与龙门山断裂交会区现今的构造活动

鲜水河断裂与龙门山断裂交会区具有特殊的构造性质。通过对交会区GPS观测,得到欧亚框架下运动速度场。利用所得的运动速度结果,采用刚性地块假设下的最小二乘法拟合方法,得到川滇、川青、扬子地块运动速度分别为(19.2±2.8)mm/a、(10.7±3.2)mm/a、(9.7±1.6)mm/a,地块运动方向由SE逐渐变成SEE,呈现出顺时针旋卷特征;鲜水河断裂运动速度为(9.3±2.8)mm/a,断裂性质为左旋走滑;龙门山断裂运动速度为(1.2±2.2)mm/a,断裂性质为右旋挤压。