中国大陆及其邻域的瑞利波群速度分布图象与地壳上地幔速度结构

THE GROUP VELOCITY DISTRIBUTION OF RAYLEIGH WAVES AND CRUSTAL AND UPPER MANTLE VELOCITY STRCTURE OF THE CHINESE MAINLAND AND ITS VICINITY

利用中国数字化地震台网 (CDSN) 1 1个台站和周边地区的 1 1个 IRIS数字化地震台站记录的长周期面波资料 ,用多重滤波方法测定了在 6 4 7条不同路径上周期从 1 0～ 92 s的基阶瑞利波群速度频散曲线 .采用 Dimtar- Yanovskaya方法 ,反演得到北纬 1 8°～ 5 4°、东经 70°～1 40°范围内 ,2 5个中心周期的群速度分布图象 .结果表明 :在 1 0～ 1 5 .9s周期范围内 ,群速度分布存在着明显的横向不均匀性 .其分区分块特征与大地构造单元有着密切的对应关系 ,两个明显的低速区域分别位于塔里木盆地和东海及北部邻域 ;从 2 1～ 3 3 s逐渐显示出深部构造块体的格局 ;在 3 6 .6～ 40 s周期附近的群速度分布图象中 ,十分清晰地显示出中国大陆岩石圈结构的分区特征 ,南北地震带、青藏高原、华北、华南块体及东北地块的边界非常明显 .本文给出了沿 3 0°N、 3 8°N纬线和沿 90°E、 1 2 0°E经线剖面的群速度随周期分布图象 .在这些剖面上 ,较明显地展示出中国大陆及其邻域地壳上地幔速度结构的基本特征 .各构造块体的深部速度结构差异较大 ,在青藏高原东部地区的地壳中部存在局部低速区域 ;塔里木盆地、扬子地台的上地幔速度较高 ,显示出稳定地台特征 ;华北平原上地幔低速层的埋深浅、厚度大 ;

Based on the long period digital surface wave data recorded by 11 CDSN stations and 11 IRIS stations, the dispersion curve of the group velocities of fundamental mode Rayleigh waves along 647 paths, with the periods from 10 to 92 s, were measured by multi-filter. Their distribution at 25 periods, within the region of (18°～54°N,70°～140°E), was obtained by Dimtar-Yanovskaya method. Within the period from 10 to 15.9 s, the group velocity distribution is lateral inhomogeneous and is strongly related to geotectonic units, with two low velocity zones respectively located in the Tarim Basin and the East Sea with its north regions. From 21 s to 33 s, the framework of tectonic blocks is revealed. From 36.6 to 40 s, the lithospheric subdivision of the China Mainland is obviously uncovered, with distinct boundaries among the South-North Earthquake Belt, the Tibet Plateau, the North China, the South China and the Northeast China. Four cross-sections of group velocity distribution with period along 30°N, 38°N, 90°E and 120°E, are discussed respectively, which displays the basic features of the crust and upper mantle of the Chinese Mainland and its vicinity. There are distinguished velocity differeces among various tectonic blocks. There are Low-Velocity-Zone(LVZ) in the middle crust of the eastern Tibet Plateau, high velocity featured as stable platform in the Tarim Basin and the Yangtze Platform, shallow and thick low-velocity-zone in upper mantle of the North China. The upper mantle LVZ in the East Sea and the Japan Sea is related to the frictional heat from subduction of the Philippine slab and the strong extension since the Himalayan orogeny period.