青藏高原及邻区重力时间变化及动力学意义

Based on the Crustal Movement Observation Network of China and the Continental Tectonic Environment Monitoring Network of China, the regional particularities of tidal and nontidal gravity changes will be investigated systematically. As a reference, the gravity observations, recorded with a superconducting gravimeter in Lhasa, are used to configure the regional correction models for high-precision gravity tides and loading effects of environmental variations such as barometric pressure, nontidal changes in ocean level and surface water, which are validated and then refined by the continuous gravity observations from the other stations located on the Tibetan Plateau and its surrounding regions. Combining the repeated parallel measurements of absolute gravity with FG5 and continuous GPS observations, the rate of vertical movement in Lhasa will be evaluated accurately. After removal of the signatures related to gravity tides and loading effects of environmental variations from the repeated absolute and moving relative gravity measurements, the spatial profiles of the temporal gravity changes will be obtained in the Tibetan Plateau and its surrounding regions by means of dynamic adjustment of gravity measurements. Considering the results of regional leveling survey and continuous GPS measurements, the whole tendency of the present-day vertical crust movements and the gravity changes due to the related material movements in the Tibetan Plateau and its surrounding regions will be obtained. Restricted by the achievement of modern geodetic techniques including leveling and GPS, the pattern of the present-day vertical crust movements and the gravity changes in the Tibetan Plateau and its surrounding regions, which are associated with the dynamical processes such as extrusion and dislocation from the Indian Plate, is simulated theoretically by means of numerical techniques of finite elements. Based on the results of regional gravity measurements, the uplifting mechanics of the Tibetan Plateau are investigated. Uplifting of the Tibetan Plateau is one of the hotspot subjects interested extensively in the present studies of the regional continent dynamics. Execution of the project will provide valuable data accumulation and significant constraint for the studies of the regional continent dynamics.

依托"中国地壳运动观测网络"和"中国大陆构造环境监测网络"，系统研究青藏高原及邻区重力潮汐与非潮汐变化特征。以拉萨超导重力仪观测为基准，建立区域高精度重力潮汐和环境负荷改正模型，结合FG5重复对比观测和GPS连续观测结果，精密确定拉萨垂直运动速率。以其他连续重力观测站的观测对改正模型进行检核和精化，并对绝对重力和流动重力观测作精密的重力潮汐和环境负荷改正，精密确定青藏高原及邻区的重力时间变化空间分布特征。结合已有的区域水准和GPS连续观测成果，获得青藏高原及邻区现今地壳垂直运动态势及其伴随的物质运动特征； 以现代大地测量为约束，借助有限元等数值技术，理论模拟挤压和位错等动力学过程导致的青藏高原及邻区现今地壳运动及重力场变化特征，结合区域重力观测结果，探讨青藏高原隆升机制。青藏高原的隆升是现今大陆动力学研究非常关注的热点课题，本项目的实施将为区域大陆动力学研究积累极有价值的数据并提供重要约束

依托“中国地壳运动观测网络”和“中国大陆构造环境监测网络”，系统分析处理了青藏高原及邻区绝对重力测量、相对重力联测、超导重力连续观测和GRACE卫星重力观测资料，研究了该区域重力场变化的时空、频率特征。以拉萨和武汉SG观测为基准，建立和完善了中国大陆重力潮汐基准，建立区域高精度环境负荷改正模型，研究重力潮汐和非潮汐变化特征。结合局部气象、水井和GPS观测结果，通过局部水文过程及其导致的重力变化和垂直为的数值模拟，精密确定拉萨垂直运动速率及其伴随重力长期变化，结果表明，拉萨地处地表抬升并不明显，但存在显著的地壳下沉。对绝对重力和相对重力联测作精密的重力潮汐和环境负荷改正，发展了分段线性动态平差方法，精密确定青藏高原及邻区的重力时间变化空间分布特征。结合已有GPS观测成果，获得青藏高原及邻区现今地壳垂直运动态势及其伴随的物质运动特征，理论模拟挤压导致的青藏高原及邻区现今地壳运动及重力场变化特征，结合GRACE卫星重力观测结果，探讨青藏高原隆升机制。此外，采用震区GPS和重力观测资料，借助有限断层位错及其激发的自由振荡的理论模拟，对汶川和芦山地震的震源参数进行了有效约束，证实了龙门山断裂带南段存在大规模的近水平的滑脱层参与了汶川地震的同震滑动；采用武汉和斯特拉斯堡台SG以及VLBI长期观测资料，根据最小二乘和贝叶斯方法解算FCN参数，发现不同资料获得的FCN周期均存在十年尺度的时间变化，同时在同时期日长变化资料中也发现了类似的十年变化特征，这为进一步研究地球自转十年尺度变化与电磁耦合的相关性提供了非常好的依据；利用球对称、非自转、弹性和各向同性地球模型，通过自由振荡运动方程的数值积分，理论上系统研究了地球内部介质（包括密度、地震波速等）分布异常对内核平动振荡（Slichter模）本征周期的影响，结果表明，目前Slichter模周期理论计算的差异主要来自于所采用的地球模型中内核边界的密度差的差异，为Slichter模的探测及其对地球深内部结构的约束提供理论依据。