华山山前断裂中段晚第四纪活动的地貌表现及响应

Geomorphic Expression and Response of the Activity along the Middle Section of Huashan Front Fault in the Late Quaternary Period

调查了华山山前断裂中段(石堤峪-杜峪)晚更新世以来,尤其是全新世以来的断层构造地貌,讨论了它们的成因、特点及对断裂活动的响应关系。断层构造地貌主要包括:断层三角面、断层陡坎、洪积阶地、埋藏型洪积扇以及冲沟裂点。对各大沟峪峪口的洪积阶地进行了大比例尺微地貌测量,并在部分沟峪两侧沿断层崖陡坎及冲沟沟床布置了测线。结合T1、T2级洪积阶地位错测量结果及其14C年龄计算得到,华山山前断裂中段6000a-2000aB.P.的垂直滑动速率为1.485mm/a;2000aB.P.以来的垂直滑动速率为3.73mm/a。最后结合野外调查与理论认识,建立了正断层作用下洪积阶地与埋藏型洪积扇的演化模式。本研究结果支持华山山前断裂是1556年华县814级地震发震构造的观点。

Based on the field investigation of 1：50000 geological and geomorphological mapping of Huashan Front Fault, we analyze the fault tectonic landforms of the middle section of Huashan Front Fault （from Shidiyu to Duyu）, since the late Pleistocene and especially Holocene, and discuss their responses to the activity of the fault. The fault landforms mainly include： fault facets, fault scarps, ladder-shaped diluvial terraces and buried pluvial fans, bedrock scarps in gully mouth, drop water, and nickpoints in gully bed. We also conduct a large scale micro-geomorphology survey of diluvial terraces in mouth of main gully by RTK, and design measuring lines along fault scarps and gully profiles in part gully. Moreover, by combining the result of displacement measurement in T1, T2 diluvial terrace and their 14C ages, we calculate out that the vertical slip rate of the middle section of Huashan Front Fault is 1.485mm/a since 6000a--2000a B.E, and 3.73mm/a since 2000a B.E. In the end, based on the field investigation and theoretical understanding, we build the evolution pattern of diluvial terraces and buried pluvial fans which under the action of normal fault. This study supports the view that Huashan Front Fault is the seismogenic structure of Huaxian great earthquake, 1556.