中国大陆及邻近海域的Rayleigh波群速度分布

利用Rayleigh波群速度资料反演得到中国大陆及其临近海域的(70°E-145°E,10°N-55°N)15-120s周期的群速度分布图像. 塔里木盆地在15s处清楚地显示为低速,在16-33s左右没有显示,但在36-5s显示为高速,说明塔里木盆地有较深的根. 青藏高原块体是44s至120s图像中最为突出的低速块体,南面与印度板块的分界线以及与北面的塔里木盆地、柴达木盆地的分界清晰,其块体中西部的速度低于东部. 泰国清迈附近存在一尺度为1000km左右的低速带,可能是青藏高原块体的物质向东南方向迁移造成上地幔物质上涌的结果. 南北地震带表现为强烈的速度梯度带,西面为低速,东面为高速. 中国南海的中央、日本海中央、菲律宾海表现为海洋性地壳. 菲律宾海的图像与地形及地震带完全吻合. 环绕菲律宾海及日本海存在400km左右宽的低速带,可能是岩浆活动带.

GROUP VELOCITY OF RAYLEIGH WAVE IN CHINESE CONTINENT AND ITS ADJACENT SEAS

Rayleigh waves are used to carry out tomographic inversion and obtain group velocity distribution in East Asia（70°E\₁45°E,10°N\₅5°N） for a period range from 10s to 120s. The Tarim Basin is obviously recognizable for the period of 15s,appearing as a low velocity region,however it can't be seen for 16\₃3s periods,and then appears as a high velocity zone for 36\₈5s periods. This suggests that there exists a deep root under the Tarim Basin. With clear demarcation lines to the Indian plate on the south and to the Tarim Basin and Qaidam Basin on the north,Qinghai Xizang plateau is the most prominent low velocity block for periods of 40\₁20s,and the velocity in its central and western portion is lower than that in the east. The South North seismic belt appears to be a regions with high group velocity gradient. This belt divides the China continent into east and west parts. The velocities in the east part noticeably highter than that in the west part. The central South China Sea,the Japan Sea,and Philippine Sea appear as oceanic crust. The image of Philippine Sea is completely consistent with the geological topography and the seismic zone. Around the Philippine Sea and the Japan Sea,there is low velocity belt of about 400km wide,and it may be a zone with magmatic activities. In the vicinity of Chiang Mai,Thailand,we can see a low velocity block with a scale of 1000km,which may be created as the mass of Qinghai Xizang plateau migrates southeast.