青藏高原GRACE卫星重力长期变化

本文采用最新的GRACE(Gravity Recovery and Climate Experiment)(RL05)数据,通过水文模型(Global Land Data Assimilation System,GLDAS与Climate Prediction Center,CPC)扣除土壤水及雪水的影响,利用Paulson提供的冰川模型结果扣除GIA(Glacial Isostatic Adjustment)的影响,采用尺度因子的方法减少数据处理过程中误差的影响,最终基于最小二乘计算方法得到2003—2013中国及周边地区长期性重力异常变化情况.结果发现青藏高原有较为明显的重力上升信号,我们认为该信号可能由印度板块俯冲欧亚板块导致青藏高原地壳增厚所引起.接着依据GPS观测结果和艾黎均衡假说构建了地壳形变模型并通过直立长方体模型予以正演模拟分析.以班公湖—怒江断裂带为界将青藏高原划分为南北两大区块,结果显示青藏高原重力异常大致以0.2μGal·a-1的速率在递增,小于GRACE得到的0.3±0.08μGal·a-1的增长速率(对应于地壳增厚速率约3mm·a-1),剩余未解释部分可能与湖水、冰川因素、冻土因素等有关.该结果对于认识青藏高原隆升动力学有一定参考意义.

Secular variation of gravity anomalies within the Tibetan Plateau derived from GRACE data

The Gravity Recovery and Climate Experiment (GRACE) satellites have collected data more than 11 years. With these data as well as the improvement of data processing methods, we can analyze the secular trends of mass variations rather than just the large-scale seasonal variations. Using these data we can study the uplift process and its mechanism of the Tibetan Plateau. In this paper, 11 years of satellite gravity data of GRACE Release 05 models (Center for Space Research (CSR), GeoForschungsZentrum (GFZ), and Jet Propulsion Laboratory (JPL)) from January 2003 to December 2013 were used to reveal the secular trends of gravity anomaly variation within the Tibetan Plateau by means of the least square method. A reduction of hydrological signals from the detected integral secular trends using global hydrological models (Global Land Data Assimilation System, GLDAS and Climate Prediction Center, CPC, averaged) is attempted. The glacier model result provided by Paulson is used to reduce the GIA (Glacial Isostatic Adjustment) effect. Also, we use the scaling factor method to weaken the GRACE post-process errors. At last we obtain the secular trends of gravity anomalies in China and adjacent areas. The results are largely similar to the previous research. Also, we find a remarkable increase signal of gravity in the Tibetan Plateau. Such a change cannot be attributed to the lake expanding and precipitation increase in the Tibetan Plateau. Instead it is possibly caused by the crustal thickening due to the subduction of Indian plate beneath the Eurasian plate. The continuing collision and compression between the India and Eurasia plates result in intense uplift and orogenic extension of the Tibetan Plateau. We built a forward model with 3D rectangular prisms according to the GPS results and Airy isostatic hypothesis. Using the Bangong-Nujiang suture zone as the boundary, the plateau was divided into southern and northern parts. The modeling results show the gravity anomalies are increasing at a rate of 0.2 μGal·a^-1 in the north, which is a little less than the result from GRACE solution 0.3±0.08 μGal·a^-1 (corresponding to a crustal thickening rate of 3 mm·a^-1). The rest unexplained part is possibly related to lakes, glacier, permafrost and others. Meanwhile, our results show the southern part has a rate of -0.62±0.06 μGal·a^-1, which is presumably the combined influence of tectonics and groundwater and so on. It is a challenging to explain the positive signal in the Tibetan Plateau clearly with current knowledge. The new GRACE Follow-On satellites may provide us more means and evidence. With the continuing accumulation of observations, we can combine a variety of modern geodetic techniques (GRACE, GPS, absolute gravity, remote sensing, and so on) to study the geodynamics of the Tibetan Plateau more accurately.