中国大陆及其邻近地区的地震层析成象

SEISMIC TOMOGRAPHY OF THE CHINESE CONTINENT AND ADJACENT REGION

本文利用中国地震台网及ISC提供的区域地震和远震的P波走时数据,重建了中国大陆及其邻近地区的三维速度图象。 主要结果是:1.本文给出的速度图象揭示了中国大陆及其邻近地区的地壳和上地幔速度存在明显的横向不均匀性,这种不均匀性甚至在下地幔的1100km深度还依然存在。上地幔的速度图象同地表已知的地质构造特征的相关性可以追踪到110km,从220km以下很难找到它们之间的明显关系。2.45^(-0)km和45^(+0)km深度处的速度图象明显地表示出中国大陆的地壳厚度可以102.5°E附近为界分为两部分:其东部地壳薄,厚度都小于45km;西部有一条自若尔盖—松潘(34°N,102.5°E附近)向西北沿38°N往西至塔里木盆地南缘的分界线;其南部除滇西南之外,整个青藏高原的地壳厚度都大于45km;其北部除天山山脉之外,地壳厚度一般不大于45km.3.110km深度处的速度图象表明,速度异常呈块状分布。同中国大地构造分区略图比较之后发现,其中,扬子准地台和塔里木地台对应于高速区,中朝准地台则大都表现为低速异常;华南褶皱系为低速区,青藏地块南缘喜马拉雅和冈底斯念青唐古拉褶皱系则表现为高速异常。4.220km深度处的速度图象表明,中国大陆相当多的地区软流层有明显的显示。5.同45^(_0)km和45^(+0)km的速度图象一样,400km和600km的速度图?

In this paper,the three-dimensional velocity images beneath the Chinese continent and adjacent regions are reconstructed using P-wave travel time residuals of regional and distant earthquakes recorded by the Chinese seismic networks and ISC.The main results are as follows:1.The velocity images display clearly the lateral heterogeneity of the crust and upper mantle beneath the Chinese continent and adjacent regions, which persists down to at least 1100 km deep.The correlation between the velocity image of the upper mantle and the known surface geological feature can be traced down to a depth of 110km.Below 220 km this correlation is hardly seen.2.The velocity images at depths of 45-0km and 45+0km show clearly that the crust of the Chinese continent is divided into two parts approximately by the 102.5°E longitude.3.The velocity image at a depth of 110 km shows that velocity anomalies appear in block patterns.Comparing the image to the tectonic map of China,we find that the Yangtze para-platform and the Tarim platform correspond to high velocity zones,the Sino-Korean paraplat-form appears mostly as a low velocity anomaly,the South China fold system is a low velocity zone.Note that a dumbbell-shaped east-west trending high-velocity zone exists along the Himalayas at the southern margin of the Tibetan block.4.The velocity image at a depth of 220 km shows that low-velocity zones of the asthenos-phere exist under many areas in the Chine.se continent.Similar to the velocity images of 45-0km and 45+0km,the images of 400 km and 600 km also indicate that a strip of about 200 km wide near 102.5°E divides the Chinese continent into two tectonically different parts.This means that the tectonic differences between the eastern and western part of the-Chinese contnent may exist in the whole upper mantle.