四川华蓥山断裂带晚第四纪逆走滑特征及地震意义
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摘要
华蓥山断裂带是四川盆地东界断裂带。前人认为该断裂带的最新活动时代为中更新世中期至晚更新世早期。作者近期野外调查发现了华蓥山断裂带晚第四纪走滑活动证据,位于华蓥山断裂带中段高县罗场镇兴场垇口村,称为兴场垇口断裂,该断裂长15km,走向NE30°,横切该区山体、造成多条水系扭曲,形成地表壮观的逆坡向右旋断错地貌。该断裂断错距今(14.86±1.26)ka地层,断裂的晚更新世晚期垂直活动速率为0.15mm/a,右旋走滑活动速率0.31mm/a,为晚更新世晚期右旋逆走滑活动断裂。
Huayingshan Fault Zone is the biggest fault along the eastern margin of the Sichuan basin. Previous studies considered that the most recent active period of this fault is from middle Pleistocene to late Pleistocene. However,some new evidence has been found recently with the measuring technology of photogrammetry and chronological analysis method of geomorphology and tectonics. Our field investigation indicates that the newest activity of the relatively small Xingchangaokou Fault in the Huayingshan Fault Zone is late Quaternary. The Xingchangaokou Fault is more than 15 km long,NE30°-trending,dipping to southeast. This fault shears the ridge and the water system,results in obvious and grand-scale geomorphologic features by the thrust and right-lateral displacement of the fault. The latest time of rupture was at about(14.86±1.26)ka BP.,during the late Pleistocene. Estimates of moment magnitudes based on empirical relationships with rupture length indicate the possibility of Mw 7 earthquake in this area. According to the empirical relationship of Deng(1993),the lateral displacement caused by a 7~7.9 earthquake is 5~6m in southwest China. So the right-lateral displacement rate is 0.31mm/a. At the same time,the vertical displacement is 2.7m occurred about (17.62±1.49)ka BP. So the vertical displacement rate is 0.15mm/a. According to these observations,the newest active period of this fault is after late Pleistocene. All these results may provide better constraints on the assessment of the crustal stability for this area.
Huayingshan Fault Zone is the biggest fault along the eastern margin of the Sichuan basin. Previous studies considered that the most recent active period of this fault is from middle Pleistocene to late Pleistocene. However,some new evidence has been found recently with the measuring technology of photogrammetry and chronological analysis method of geomorphology and tectonics. Our field investigation indicates that the newest activity of the relatively small Xingchangaokou Fault in the Huayingshan Fault Zone is late Quaternary. The Xingchangaokou Fault is more than 15 km long,NE30°-trending,dipping to southeast. This fault shears the ridge and the water system,results in obvious and grand-scale geomorphologic features by the thrust and right-lateral displacement of the fault. The latest time of rupture was at about(14.86±1.26)ka BP.,during the late Pleistocene. Estimates of moment magnitudes based on empirical relationships with rupture length indicate the possibility of Mw 7 earthquake in this area. According to the empirical relationship of Deng(1993),the lateral displacement caused by a 7~7.9 earthquake is 5~6m in southwest China. So the right-lateral displacement rate is 0.31mm/a. At the same time,the vertical displacement is 2.7m occurred about (17.62±1.49)ka BP. So the vertical displacement rate is 0.15mm/a. According to these observations,the newest active period of this fault is after late Pleistocene. All these results may provide better constraints on the assessment of the crustal stability for this area.
引文
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中国地震局地质研究所编.1979.中华人民共和国地震构造图.北京:地图出版社.
邓起东,于贵华,叶文华.1993.地震地表破裂参数与震级关系的研究.见:活动断裂研究编委会编,活动断裂研究理论与应用.北京:地震出版社.
邓起东,陈社发,赵小麟.1994.龙门山及其邻区的构造和地震活动及动力学.地震地质,16(4):389～403.
贾秋鹏,贾东,朱艾斓等.2007.青藏高原东缘龙门山冲断带与四川盆地的现今构造表现:数字地形和地震活动证据.地质科学,42(1):31～44.
丁道桂,汤良杰,钱一雄等.1996.塔里木盆地形成与演化,166～167.南京:河海大学出版社.
郭正吾.1996.四川盆地形成与演化.北京:地质出版社.
嵇少丞,王茜,许志琴等.2008.亚洲大陆逃逸构造与现今中国地震活动.地质学报,82(12):1644～1667.
罗志立,刘树根,宋鸿彪等.1994.龙门山造山带的崛起和四川盆地的形成和演化.成都:成都科技大学出版社.
唐荣昌,韩谓宾主编.1993.四川活动断裂与地震.北京:地震出版社.
许志琴,杨经绥,姜枚等.1999.大陆俯冲作用及青藏高原周缘造山带的崛起.地学前缘,6(3):139～151.
尹功明,陈献程,宋方敏等.2008.安徽南陵NW向第四纪断层的发现及其意义.中国地震局地质研究所学位论文.
中国地震局地质研究所编.1979.中华人民共和国地震构造图.北京:地图出版社.
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