冲沟裂点在华山山前断裂古地震研究中的应用  

Application of Paleoearthquakes Based on Knickpoint Distribution of Huashan Front Fault

作　　者：马冀[1] 徐良鑫[1] 张艺[1] 李高阳[1] 杨晨艺 MA Ji;XU Liangxin;ZHANG Yi;LI Gaoyang;YANG Chenyi(Shaanxi Earthquake Agency,Xi’an 710068,China)

机构地区：[1]陕西省地震局,陕西西安710068

出　　处：《灾害学》2020年第4期61-65,共5页Journal of Catastrophology

基　　金：国家自然科学基金青年科学基金项目(41502205);陕西省自然科技基础研究计划(2018JM4019);陕西省地震局“十二五”关中地区大震危险性评价项目。

摘　　要：河流水系对外部环境变化的反应非常敏感,尤其在活动构造区域,冲沟裂点能够迅速反映河流基准面的下降,作为记录断层活动的重要标志。由此,为提供通过冲沟裂点的发育特征来揭露对应断裂的活动历史的机会。该文以位于渭河盆地东南缘的华山山前断裂为例,利用宇宙成因核素10Be暴露测年技术,和断裂1 km范围内由Lidar数据获得的高精度DEM提取的冲沟裂点信息,对山前被断裂切割的冲沟中发育的一系列裂点的期次和地形参数进行了厘定。同时,依据冲沟裂点的10Be暴露年龄建立了冲沟裂点序列与华山山前断裂古地震事件之间联系。研究结果表明,以仙峪为典型代表的华山山前冲沟中普遍发育4期裂点,垂直位移分别为6.4 m,4.3 m,3.5 m和5.1 m,均小于在冲积扇上得到的华山山前断裂的断错位移量。冲沟裂点的10Be暴露年龄显示华山山前断裂是一条复发间隔约4~5 ka的活动断裂,在该断裂上曾发生过至少3期地震事件,分别为公元1556年、距今4 439~6 691 a和距今9 189~12 407 a。由此可以看出,冲沟裂点能够作为判定断裂活动的地貌证据,其暴露年龄与古地震事件发生时间大致相当。但受冲沟差异侵蚀作用的影响,由冲沟裂点记录的垂直断错位移量并不能代表断层实际的垂直位移量。Stream system is very sensitive to the change of external environment, especially in active tectonics.Knickpoints, as one of geomorphological markers, respond commonly to base-level fall by regional uplift. The Huashan front fault, located at the southeastern margin of Weihe basin, is one of the faults slipped in 1556 Huaxian ■ earthquake with ~8 m surface vertical offset.There’re series of knickpoints along the gullies perpendicular to the fault. A light detection and ranging(LiDAR) is conducted to generate a high resolution DEM to get a longitudinal profile of the stream and knickpoints. The resolution is high enough to reveal true topographic description and extract the knickpoints within 1 km from the fault accurately. Terrestrial in situ cosmogenic nuclides(TCNs)dating techniques is used to restrict the exposure age of these knickpoints and help establish paleoearthquake sequence. The study shows that Huashan front fault is an active fault with a recurrence of 4~ 5 ka. There are 3 paleoseismic events occurred in A.D 1556, 4439~6691 a and 9189~12407 a respectively. It also reveals that the knickpoints are the evidence of tectonic activities, which retains part of the seismic offsets, yet not complete.

关 键 词：断错地貌标志 裂点 古地震序列 机载激光雷达扫描(LiDAR)测量 10Be暴露定年 

分 类 号：P315[天文地球—地震学] X43[天文地球—固体地球物理学]