中国大陆及邻近地区上地幔顶部Sn波速度层析成像

Sn WAVE TOMOGRAPHY IN THE UPPERMOST MANTLE BENEATH THE CHINA CONTINENT AND ADJACENT REGIONS

利用《中国地震年报》中 4 36 4 6条Sn射线的走时资料 ,采用层析成像方法反演了中国大陆地区上地幔顶部的Sn波速度结构 .主要结果是 :①全国平均Sn速度为 4 .5 5km s,速度变化量从 - 0 .14km s到 +0 .15km s.②整体上中国Sn速度分布是东低西高 ,塔里木盆地、准噶尔盆地、吐鲁番—哈密盆地以及柴达木盆地东端、四川盆地及其南部地区等是明显的高Sn速度区 ,鄂尔多斯地台和台湾海峡也是Sn速度较高地区 ,整个华北盆地、渤海湾东部、山西北部和郯庐断裂带 ,Sn速度都比较低 .另外 ,长江中下游地区、青藏高原北部和南北地震带地区 ,Sn速度也较低 .③Sn速度变化分布和构造活动、地壳厚度以及大地热流变化有关 ,分别求得了速度与地壳厚度和大地热流的线性回归方程 .④Sn速度变化和Pn速度变化的区域分布总体上是吻合的 .

The Sn velocity image in the uppermost mantle beneath the China continent is constructed by the tomography method using 43646 travel times from Annual Bulletin of Chinese Earthquakes. Main results are: ① The average Sn velocity is 4.55km/s in whole China, and velocity perturbations vary from -0.14km/s to 0.15km/s. ② In general, Sn velocity is low in eastern China and high in western China. The remarkable high Sn velocity mainly exists in the Tarim, Juggar, Turpan-Hami, eastern Qaidam, Sichuan basins and the region south to the Sichuan basin. In the Ordos platform and Taiwan straits, the Sn velocity is high. The low Sn velocity mainly appears in the whole North China basin, east to the Bohai bay, northern Shanxi, and the Tancheng-Lujiang fault zone. In addition, in the middle and lower reaches of the Yangzi river, the northern Qingzang plateau and the South-North seismic zone, the Sn velocity is slightly low. ③ The Sn velocity variations are related to tectonic activity, crustal thickness and the Earth's heat flow. We obtain a linear regression relation between the Sn velocity and the crustal thickness and a linear regression relation between the Sn velo- city and heat flow. ④ The Sn velocity variations are generally consistent with the pattern of Pn velocity variations.