中国上地幔剪切波速度结构的初步研究

PRELIMINARY STUDY OF UPPER MANTLE SHEAR VELOCITY STRUCTURE OF CHINA

本文通过合成SH波理论地震图的方法,利用SS-S走时和SS波波形资料,研究了我国上地幔剪切波速度结构。初步结果表明,我国大陆上地幔可以分成两个独立不同的速度结构模型:一是青藏高原;另一是中国大陆东部。两部分均存在剪切波低速层,但埋藏深度不同,高原部分是100km,东部地区是60km,两部分的差异大约在350km以下趋于消失。在405km和660km深处存在剪切波的速度间断面。400km以下青藏高原和中国大陆东部地区剪切波的速度结构与北美洲、北大西洋西部、欧洲、阿尔卑斯带地区的结构一致,说明在这几个地区上地幔剪切波速度结构的横向变化在400km以下很小。

In this paper SS-S travel times and SS waveforms have been used to study the upper mantle shear velocity structure of China by modeling SH synthetic seismograms. We primarily divide China continent into two different regions. The one is Qinghai-Tibet plateau, and the another is eastern part of China continent. There are low velocity zones (LVZ) in these two regions, but the depths of LVZ are different. The depth is 100 km for plateau, 60 km for eastern region, and the difference of two regions gradually disappear below the 350 km. The two regions have first order discontinuities of shear velocity at 405 km and 660 km. Below 400 km, the shear velocity structure of China is the same as in North America, Northwest of Atlantic Ocean, Europe and Alpine belt. This result shows that there are little heterogeneity of upper, mantle shear velocity below 400 km between these regions.