河北平原水系密度与隐伏活动构造的关系

Relations of Drainage Density to the Hidden Actve Tectonics in the Hebei Plain

以1926年出版的比例尺为1:5万的顺直地形图作为基础图件,用地理信息系统技术对河北平原作水系密度计量分析,揭示隐伏在第四纪巨厚的沉积物之下活动构造的信息。研究结果证实水系线密度统计图与使用其它地球科学方法获得的成果,例如基底活动断块图、地貌类型图和第四纪厚度图都有很好的对应,特别与布格重力图对应更好。研究结果发现水系密度图与布格重力异常图在总体一致性较好的前提下,多处反向异常区均为近代强震发生的区域。提出这种地表水系密度统计研究的成果不仅可以揭示深部隐伏的活动构造,而且具有较明确的时间含义。

In order to determine the distribution pattern of different drainage densities inHebei plain and its response to the recent activities of the hidden tectonic structures, theconcept of the drainage length density is introduced, which means the total drainage length inthe unit of a measuring square or 'window'. The values of density are plotted and contouredfrom a special map of drainage length density by computer. The older the topographic map isused, the more human impacts on drainage density can be excluded. Hence the old Beijing-Hebei topographic maps (l:50,000) published in l926 are used instead of the later onespublished in l974.From the analysis of the distribution pattern of the contoured high-andlow-drainage density areas on these maps, and comparison of these maps with otherprofessional maps of the drainage system, geomorphic types, basement blocks, the Quaternaryisopach, and the Bouguer gravity anomalies, the presend epiceners and earthquake clusters aswell as the historical earthquaks in association with field investigations, the followingimportant points are summarized. (1) The high-density area corresponds with thedownwarping/downfaulting region due to the increase of total drainage length. As a contrast,the low-density area coincides with the relatively upwarping/upfaulting region owing to thedecrease of total drainage length caused by straightening and shortening of river coure. Thesharp gradient zone of drainage density between the high- and low-density areas is coincidentwith the faulting zone. (2) There is an apparent coincidence of the above-stated high--andlow-drainage density zone and their gradient zones with the main distribution patterns of theobjects on the above-listed other professional maps. There can also be seen the coincidence ofintersection of drainage density zones with intersections of faulting zones. (3) All the abovepointed out indicates the sensitive and apparent response of drainage density in the alluvialplain to the recent, Holocene activities of the hidden basement blocks and fault zone with thehistorical and Present earthquakes involved.