大连半岛地貌,新构造运动与市区安全性

辽东半岛南端的大连半岛是一个刚性断块。其上无活动性大断裂穿过,老断裂多而规模小,在地貌和新地层上无新活动表现。穿越它们的第四纪河、海阶地均平行分布,无明显的垂直或水平错位。整个半岛第四纪以来作整体断块上升。半岛上的小震稀少零星,属刚性断块地壳应力作用下的微破坏活动。位于其上的大连市是安全的,无发生破坏性大震的危险。

GEOMORPHOLOGY,NEOTECTONIC MOVEMENTS AND THE SAFETY DEGREE OF THE CITY ON THE DALIAN PENINSULA, NORTHEAST CHINA

Geomorphological investigation and survey of faults are conducted to identify whether the important industrial harbour city .Dalian .which is situated on the Dalian Peninsula, is tectonical-ly safe(Fig. 1 ). The authors' research provides a postive answer,based on the following morpho-tectonic features; The Dalian Peninsula is a rigid large fault block .consisting of the Upper Proterozoic Sinian formation (quartz sandstones,siliceous slates and limestones) without any considerable active fault to cut through it. Although there is a complicated network of old faults developed in the block , these faults are found to be of small dimension and to have no any evidences for their recent acti-vation on landforms and in Quaternary strata. No distinct tectonic landforms such as fault-controlled gullies, drainage. scarps and cliffs were found. The longitudinal profiles of river terraces in two valleys and of marine terraces along the coastal zone,when extend over faults,demonstrate no obvious deformation and displacement at least since the mid-Pleistocene (Fig. 2,3 and -1). All the buildings, which are located on the two surveyed faults(F11bb&- F83),display no fractures,cracks and deformation.Trenching of the F83 at the construction site in the Normal University of Liaoning Province (Fig. 5)reveals that it is actually a fault zone,cutting through the Sinian quartzite,and slate on the 2nd river terrace,and generating a visible shatter-catasclastic zone of 8m in width. The results of thermoluminescene dating of the fault gouge from two faults in this zone are(21 +1. 0) x 104a and (48 + 2. 2) X 104a respectively. The overlying Quaternary deposits on the Sinian bedrocks in the fault zone are the horizontally layered alluvial grey black clays,sands and gravels,showing no displacement, of them, the quartz sands have been dated by thermoluminescent method to be of (4. 76+0. 24) X 10'a and the grey black organic clays on the both sides of fault zone have been dated by HC method to be of 8 230+150 aBP and 8 270+ 1 00 aBP. This indicates that the fault zone experienced its last activation in the mid-Pleistocene. This activation is not demonstrated by terrace displacement,and it ceased at least before the late Pleistocene. The faults never activated in Holocene and present time. Besides,the earthquakes which occurred on the Dalian Peninsula are found to be minor,rare and scarce. It is believed to be resulted from micro fracturing in the rigid block under the effect of crustal stress. It is concluded from the above discussion that the city Dalian is situated on an intensely up-lifted rigid large fault block without any tectonic conditions which can cause strong fault activa-tion, resulting the geological hazards and destructive earthquakes. Therefore, this city is tectonical-ly safe and could undergo only the indirect effects from the strong fault activation or earthquakes which occur along the active fault zones surrounding the Liaodong Peninsula or from the neigh-bouring earthquake regions.