Rayleigh‐Wave Phase Velocity Distribution in China Continent and its Adjacent Regions
Rayleigh‐Wave Phase Velocity Distribution in China Continent and its Adjacent Regions
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DOI：
10.1002/cjg2.1218
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发表时间：
2008-03
期刊：
影响因子：
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通讯作者：
G. Yi;H. Yao;Jie-shou Zhu;R. Hilst
中科院分区：
文献类型：
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作者：
G. Yi;H. Yao;Jie-shou Zhu;R. Hilst
利用中国及邻区102个地震台站的瑞利波垂直分量记录和两站分析资料，测量了538条独立路径20~120 s周期段的台站间基模瑞利波相速度频散。利用频散资料反演了中国大陆及其邻近地区（70° ~ 140°E，18° ~ 55°N）21幅20 ~ 120 s、间隔5s的相速度图。 检测板测试结果显示中国大陆中东部地区横向分辨率可达3°，而西部及边邻地区大约5°.研究区相速度的空间分布在104°E左右的中国西部和东部有明显的差异。短周期（20~35 s）的相速度图受地形和地壳厚度的影响。在这些图上，西部的特征是低相速度，东部显示相对高的相速度。塔里木盆地、青藏高原及其东缘（松潘-甘孜地块）是研究区最突出的低速构造。蒙古西部也出现了大范围的低速异常。四川盆地、扬子地块、华南地块、松辽盆地、日本海、蒙古东部等地的相速度相对较高。在较大的周期内，青藏高原中部低速异常的横向尺度变小，而喜马拉雅逆冲断层和塔里木盆地下部的相速度则增大。这意味着青藏低速区的南部、西北部和东部都被地震快构造所包围，这可能控制了机械强度较弱的地震慢物质向东南方向迁移，远离中央高原。同时，东部大面积区域的相速度相对较低，表现为周期较短的快速相速度，表明岩石圈相对较薄，存在明显的软流圈。随着青藏高原低相速度异常的减弱，印支地块北方及其邻近海域、东海、吉林东北深震区、日本海、中朝地块至蒙古东部等地在120 s周期出现了显著的低相速度异常。而在上扬子地块（包括四川盆地）出现了高相速度，说明古地块相对稳定。中国南北地震带在20 s ~ 120 s周期内具有相对较低的相速度，成为中国大陆东西部岩石圈相速度特征不同的天然分界线。
Using a two-station analysis and vertical component records of Rayleigh waves from 102 seismograph stations in China and adjacent areas, we measured inter-station fundamental mode Rayleigh-wave phase velocity dispersion in the period band 20~120 s for 538 independent paths. The dispersion data were then used to invert for 21 phase velocity maps from 20 s to 120 s with 5 s interval in the continental China and its adjacent regions (70° ~ 140°E, 18° ~ 55°N). Checkerboard tests show that the lateral resolution is about 3° in central-eastern China and about 5° in western China and adjacent regions. The spatial distribution of phase velocities in the study area is significantly different for the parts of China to the west and east of approximately 104°E. The phase velocity maps at shorter periods (20~35 s) are influenced by topography and crustal thickness. On these maps, the western part is characterized by low phase velocities and the eastern part shows relatively high phase velocities. The Tarim basin, the Qinghai-Tibet plateau, and its eastern margin (the Songpan-Garze block) form the most prominent low velocity structures in the study region. A large-scale low velocity anomaly also appears in western Mongolia. The Sichuan basin, the Yangtze block, the south-China block, the Songliao basin, the Sea of Japan, and eastern Mongolia are marked by relatively high phase velocities. At larger periods, the lateral size of the low velocity anomaly beneath central Qinghai-Tibet becomes smaller whereas the phase velocities increase beneath the Himalayan thrust and Tarim Basin. This implies that the Qinghai-Tibet low velocity area is surrounded by seismically fast structures to the south, northwest, and east, which may control a southeastern migration of mechanically weak, seismically slow material away from the central plateau. Meanwhile, a large area in the eastern part which appears fast at shorter periods shows relatively low phase velocity, suggesting a relatively thin lithosphere and a pronounced asthenosphere. As the low velocity anomaly beneath Qinghai-Tibet plateau becomes weaker, the northern Indo-China block and its adjacent off-shore areas, East China Sea, Northeast China's deep-earthquake region in Jilin Province, Sea of Japan, and the Sino-Korean block to eastern Mongolia are marked by prominent low phase velocity anomalies at the period 120 s. However, high phase velocities appear in the upper Yangtze block (including the Sichuan Basin), which means that the ancient block is relatively stable. The North-South Seismic Belt in China has relatively low phase velocity from periods 20 s to 120 s, and becomes a natural boundary separating the continental China into the eastern and western parts with different lithospheric phase velocity features.