3D Velocity Structure and Its Tectonic Implications in the East China Sea and Yellow Sea

3D structure of the crust and upper mantle in the studied area has been analyzed from surface wave tomography. The velocity distribution in the uppermost crust is symmetrical on two sides of the central line of the sea, and coincides with the structure of crystalline basement. The essential difference in tectonics between the East China Sea and the Yellow Sea mainly lies in that the velocity structures of their lower crust and upper mantle are identical to those of South China and North China respectively. In the upper mantle there exists a high-velocity zone with a nearly EW strike from the Hangzhou Bay, China, to the Tokara Channel, Japan, along about the latitude of 30°N. It is found that between the East China Sea and the Yellow Sea there are systematical differences in geomorphology, geology, seismicity, heat flow, quality factor and gravity and aeromagnetic anomalies, which is related to both left-lateral shear dislocation and right-lateral tear of the Benioff zone from the Hangzhou Bay to the Tokara Channel.It is inferred that the East China Sea was formed by Cenozoic back-arc extension. The boundary between the North China and South China crustal blocks stretches along the southern piedmont of Mts. Daba-Dabie-Hangzhou Bay-Tokara Channel, and the subduction zone at the Okinawa trench is the eastern boundary of the South China crustal block. The movements of the Pacific plate, Indian plate and upper mantle rather than the Philippine plate subduction have played a dominant role for the modern tectonic movements in East Asia.

The 3-D structure of shear wave in South China and the southward extension of Tanlu fault

By processing the CSND Rayleigh wave data with the matched filter FTAN technique, Rayleigh wave dispersion for southeast China is obtained. The 4°×4°S wave dispersion of the pure path is calculated using random inversion scheme, and 3-D S wave velocity structure is set up. Incorporating the above-mentioned results with wide angle seismic sounding data, we studied structure framework and the extending of faults in this area, which demonstrates that the depth of Moho in South China varies from 30 to 40 km, shallower from west to east. The depth of Moho varies from 25 to 28 km for the offshore. The depth of the asthenosphere in upper mantle varies from 60 to 100 km. The depth difference of layers at the two sides of Tanlu fault is more than 10 km at the south part of the Yangtze River, and the fault extends downward more than 170 km. The fault exceeds the main land at Hainan Island and slips into the southern China Sea. Both Tanlu fault and the huge bend of gravity gradient anomaly are influenced by

东亚及西太平洋边缘海高分辨率面波层析成像

根据欧亚大陆及西太平洋地区 58个数字地震台站约 1 2 0 0 0个长周期波形记录 ,挑选出 41 0 0条面波大圆传播路径 ,采用面波频散及波形拟合反演方法 ,对东亚及西太平洋边缘海地区 (60°E— 1 60°E ,2 0°S— 60°N)的地壳上地幔进行了高分辨率三维S波速度成像 .结果表明 ,从上地壳到 70km深 ,在东亚东部及西太平洋边缘海地区为高速分布 ,西部以青藏高原为中心呈极低速分布 .自地中海经土耳其、伊朗、喜马拉雅山到缅甸、印尼群岛的特提斯汇聚碰撞带 ,显示为低速异常链 .从 85km至 2 50km深 ,在东亚东部及西太平洋边缘海 ,自北向南显示出一条巨型低速异常带 ,西部地区为高速异常分布 .以东经 1 1 0°E为界 ,东西两部分岩石圈、软流圈的结构与深部动力过程有着巨大的差异 .此界线以西主要是印度板块与欧亚板块碰撞引起的岩石圈汇聚增厚区 ,东部则主要是由于软流圈上涌 (地幔热物质上升 )

应用地震CT技术研究长白山火山的岩浆囊

中国火山学专家报导了长白山火山存在一定的潜在的喷发危险性及其地质背景等研究成果；美国、日本、德国的火山学家到该火山区进行过考察，也认为该火山存在一定的潜在危险性；国家科委根据有关方面的建议，已将“长白山火山危险性的研究”列入专项计划之中；其中有一个子课题是“应用地震ＣＴ技术研究长白山火山的岩浆囊”．本文报导的主要内容有：１）１９９４年张禹慎发展的“上地幔Ｓ波三维速度结构的方法”建立上地幔Ｓ波ＲＧ５．５速度模型，该模型能显示全球任一地区、任一剖面、深至５００公里的三维速度结构；他作出世界上２０个火山区，其中有１７个火山区下面均有明显的Ｓ波低速层，在不同程度上反映了＂低速层岩浆囊＂的存在；已作出通过长白山天地火山的３条速度剖面；该模型显示出：在长白山天池火山下面存在速度的负异常达２．５％的“低速囊”，其深度从３８—６５公里；其展布范围约１００—２００公里的范围；２）改进面波品质因数Ｑ值的成像方法，进一步收集２００次地震面波记录资料，应用“卷积反投影方法反演地壳面波品质因数Ｑ值的成像系统”长白山火山及其邻近地区面波Ｑ值分布，看出天池地区Ｑ＝１６１比中国地区Ｑ值的平均值偏低很多；

利用面波方法研究欧亚大陆及周边海域岩石圈结构

根据欧亚大陆及周边海域114个数字地震台站12 000多个长周期波形记录,采用面波频散反演方法,对欧亚大陆及周边海域(20°W～160°E,20°S～80°N)的地壳上地幔进行了高分辨率三维S波速度成像。结果表明,欧亚大陆及其周边海域岩石圈厚度由40～60km(大陆裂谷带)增厚至190～220km(克拉通地区),岩石圈速度变化范围为4.30～4.80km/s。直到400km深度,各个板块和地块的横向差异才逐渐减小。克拉通板块及地块的岩石圈巨厚且具有高速特征,软流圈很薄或不存在;显生宙造山带、边缘海等区域岩石圈较薄且速度较低,软流圈发育。海洋板块的显著特征是VS在岩石圈内异常高,而软流圈速度又异常低,有十分尖锐的速度突变。