宁波育王山山前断层几何结构及新活动时代

Geometrical structure and neomovement's epoch of piedmont fault of Yuwang Mountain in Ningbo,Zhejiang

根据1：10000条带状地质填图所获资料，分析了育王山山前断层的几何结构和新活动时代。断层北起岙张水库大坝东北，向南经河头蕉-竺家-陈家-钱家-俞家-王家一线以西，止于詹家西南，由2条次级段呈羽列式展布，北段为岙张水库-红岩水库段，南段为红岩水库东南-詹家段。剖面上断层地貌显示清楚，西侧为侏罗系构成的育王山低山，东侧为大楔盆地。各条断层皆由多个断面构成宽几米-几十米的断层带。根据探槽、天然剖面特征和OSL、ESR样品年龄测试结果综合分析，断层至少有两期活动，早期活动性质为逆断层，时间为早更新世，晚期活动性质为右旋走滑兼正断或逆断层，时间为中更新世，最新活动时代为中更新世晚期。通过探槽揭露，确定育王山山前洪积扇陡坎是人类活动造成，而非断层陡坎。

On the basis of informations from 1：10000 banded geological mapping, geometrical structure and neomovement＇s epoch of the piedmont fault of Yuwang Mountain have been studied. The fault begins from northeast of Aozhang Reservoir Dam in the north, through the west of the line Hetoujiao-Zhujia-Chenjia-Qianjia-Yujia-Wangjia to the south, ends in the southwest of Zhanjia. There are two plumose secondary faults, the north one is located along Aozhang Reservoir-Hongyan Reservoir, the south one is located along southeast of Hongyan Reservoir-Zhanjia. The geomorphological features of the faults are clear on the section,the Jurassic low mountain of Yuwang Mountain is at the west,the Daxie Basin is at the east. Each fault is composed of several fault surfaces to form a fault belt several meters to several decameters wide. According to the synthesized analysis of prospecting trenches, characteristics of natural sections and dating result of OSL, ESR sample, there are two periods of movement at least. The result of early period movement is to form a reversed fault in early Pleistocene ;the result of later period movement is to form a normal or reversed dextral strike-slip fanlt in middle Pleistocene ;the latest movement is happened in late middle Pleistocene Through exposing by prospecting trenches,it is ascertained that the piedmont pluvial fan＇s steep slope of Yuwang Mountain is formed by human activity,it is not a fault step.