秦岭北缘古地震基岩崩塌和滑坡施密特锤暴露年龄  

SCHMIDT HAMMER EXPOSURE AGE DATING OF ANCIENT EARTHQUAKE-INDUCED BEDROCK LANDSLIDES AND ROCK AVALANCHES IN THE NORTHERN MARGIN OF QINLING MOUNTAINS

作　　者：石文芳 徐伟 尹金辉[1] 郑勇刚[1] SHI Wen-fang;XU Wei;YIN Jin-hui;ZHENG Yong-gang(State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China;China Earthquake Disaster Prevention Center,Beijing 100029,China)

机构地区：[1]中国地震局地质研究所,地震动力学国家重点实验室,北京100029 [2]中国地震灾害防御中心,北京100029

出　　处：《地震地质》2022年第6期1384-1402,共19页Seismology and Geology

基　　金：中国地震局地质研究所基本科研业务专项(IGCEA1903);中国地震局地震科技星火计划项目(XH20074)共同资助;地震联合基金(U1939201)。

摘　　要：地震崩塌、滑坡是较为严重的地震次生灾害,研究地震崩塌、滑坡发生的时代及其活动规律,从而恢复断裂带古地震活动历史、地震复发周期,有助于地震危险性评价及地震灾害防御工作。文中选择秦岭北缘断裂带和华山山前断裂中段被历史文献记录的地震基岩崩塌、滑坡为研究对象,使用施密特锤测量416个岩块的反弹值,并对其进行统计分析,计算了崩塌、滑坡体暴露岩石的风化因子,讨论了施密特锤暴露测年法的分辨率,评估了施密特锤测年的可靠性,同时建立了古地震基岩崩塌、滑坡历史记录年代与反弹值参数之间的关系曲线。结果表明:施密特锤暴露测年方法提供了一种简单、快速、廉价、无破坏的原位相对测年方法,初步建立的岩石风化因子-年龄校正曲线为T=(19723±888)×f_(w)-(2145±166),基于该校正曲线,可以对形成年龄>500a的基岩崩塌和滑坡进行分期,为确定秦岭北缘古地震基岩崩塌、滑坡形成时代提供一种新的相对测年手段。施密特锤岩石反弹值还可用来评估宇宙成因核素暴露测年样品是否存在先期暴露、翻滚、二次埋藏等复杂暴露历史带来的核素继承浓度问题,帮助选择合格的宇宙成因核素测年样品的采集地点,保证测年数据的可靠性,提高测年效率。在秦岭北缘的气候和岩性条件下,岩石经历2ka风化后,表面强度减小约(25%±1%),约1ka后减小(16%±1%),约0.5ka后减小(15%±1%)。It is difficult to use traditional trenching and field geological investigation to yield the age of paleoseismic events along active fault in western mountainous areas of China where the geomorphic trace mark and sediments are often eroded or altered by human activities.The recurrence interval of paleoearthquake possesses greater uncertainty.It is necessary to yield ages of paleoearthquake event from different ways and examine the reliability of paleoearthquake results.In these regions,an earthquake with magnitude greater than 7 can produce rock avalanches around 200~400km away from the epicenter,such as the Wenchuan earthquake in 2008,due to their structure setting of strong neotectonic activity and the higher topographic relief.Therefore,the seismic bedrock landslide and rock avalanche can record the occurrence time,intensity and damage of strong earthquake in the mountainous area.This provides a new way to assess the frequency and intensity of paleoearthquake occurring in the intraplate continental areas(such as the north-south seismic zone)where strong earthquakes recurred for hundreds to thousands of years based on the seismic landslide records.Identifying ancient earthquake bedrock collapse relics in Quaternary deposits and accurately determining their ages will not only help broaden the study on the recurrence history of active fault,but also assess the earthquake risk in mountainous area.As shown by previous studies,the Schmidt-hammer exposure-age dating(SHD)method is a relatively simple,rapid,cheap and non-destructive in-situ exposure age dating method.In this study,ancient earthquake bedrock landslides and rock avalanches with known historical records distributed on the Qinling northern piedmont fault and the Huashan piedmont fault are used to preliminarily establish the rock weathering factor with age calibration curve.The rebound values of rock surface at dozens of sampling sites of each rock avalanche and landslide are measured by Schmidt hammer and analyzed statistically.The weathering factor of the

关 键 词：古地震 基岩崩塌和滑坡 施密特锤 秦岭北缘 相对测年 

分 类 号：P315.2[天文地球—地震学] P597[天文地球—固体地球物理学]