中国大陆中轴构造带及其两侧的现今地壳垂直运动

Recent Crustal Vertical Movement in the So-called Central Axis Structure Zone in the Continent of China

利用中心年代分别为1964、1979及1993的3期精密水准复测资料研究中轴(构造)带及其两侧(东经90.5°至113.5°,北纬21.5°至42.0°)的现代地壳垂直运动。结果表明中轴带及其两侧近30多年的运动趋势与最近十几年运动趋势十分一致。而且与该地区的地势地貌有良好的相关性,几个垂直形变的高梯度带均分布在本区两个大盆地(四川盆地与柴达木盆地)周边。整个形变态势表现出明显的继承性运动特征。但在70年代,该区的垂直运动经历了一次明显的变化或反向。联系到同一时期中轴带南部的一系列7级以上强震的发生,提示大区域的垂直形变的趋势变化可能是强震活跃的一种指示。文中还利用得到的地壳垂直形变图研究了区内南—北、东—西向穿切几个主要构造单元的9条剖面的地壳垂直运动特征和它们的时空演化,结果进一步证明1969～1979年间,我国中西部比较强烈的地壳垂直运动与我国地震活动高潮期一致。纬向剖面的运动特征清楚地显示出东经100～105度的经向带内,整个研究区可分为地壳垂直运动速率西高东低的东、西两区;而经向剖面又可将这东、西两区分出以某些纬向高变化窄带为界的纬向区块。文中还详细讨论了这些区块所对应的构造单元的现今运动特征。

In the paper, the precise re-leveling data of three periods with the central epochs of 1964, 1979 and 1993 are used to study the recent vertical crustal movement in the so-called Central Axis (Structure) Zone and its adjacent areas (90. 5°E^113. 5°E, 21. 5°N^42. 0°N). The results show that the motion trends in the zone in the last more than 30 yeas coincide very well with the trends in the latest more than 10 yeas. In addition, there is a better correlative relationship between the motion trends and the terrain and landform in the area. Some belts with high-gradient vertical movement are distributed in the surrounding areas of two major basins (Sichuan basin and Qaidam basin) in the study region. The general deformation situation shows some inherited motion feature. But in the 1970s, the vertical motion in the region underwent an obvious change or reversion. Taking a series of strong earthquakes occurring in the same period in the southern part of the zone into account, the trend variation of vertical deformation in a large area may be an indication of strong seismic activity. The vertical motion features and their temporal and spatial evolutions along 9 profiles that cut across several major structure units in the region are also studied in the paper using the obtained vertical crustal deformation contour map-s. The results further show that the strong vertical crustal motions in the middle and western parts of China during the period of 1969 -1979 were consistent with the period of high seismic activity. The motion features on the profiles along the latitude lines clearly show that according to the velocities of vertical crustal motions the entire studied region can be divided into the eastern and western parts in the zone from 100°E to 105°E. The vertical motion velocity in the western part is higher, while in the eastern part is lower. Moreover, according to the motion features shown on the profiles along the longitude lines, each of the two parts (eastern and western parts) can be further divided into some local blocks distributed in the N-S direction by some narrow belts with rapid changes in the E-W direction. The recent motion characteristics of structure units corresponding to the local blocks are also discussed in detail in the paper.