Although the late Quaternary slip rate of the Northern Margin Fault of the Huaizhuo Basin(NFHB)was studied approximately 30 years ago using thermoluminescence and geomorphic methods,the underlying uncertainty cannot be neglected,considering the limitations resulting from age and displacement measurements.Accordingly,we attempted to re-estimate the late Quaternary slip rate of the NFHB using high-precision remote sensing image interpretation,large-scale geological and geomorphic mapping,paleoseismic analysis,and Quaternary geochronology testing.The results,based on stratigraphic dislocation and age constraint in the trenches,show that the present deformation of the NFHB has been dominated by the extension,with a vertical slip rate~0.04-0.11 mm/a.We estimate a vertical slip rate of~0.06 mm/a,with an R^(2) value of~0.91,which is much lower than the~0.5 mm/a result estimated previously.There are three possible reasons for this discrepancy.The first is the limitation resulting from dating and displacement measurements in earlier studies;the second is the slip decomposition caused by multiple branches of the NFHB,which leads to the low slip rate observed at a single fault;and third possible explanation is that the fault may be locked at present with a low slip rate,which means that the earthquake hazard of the NFHB cannot be ignored,and more in-depth research,such as geodetic and intensive observations of earthquake precursors,is urgently needed.This discovery poses a new challenge for the active study of the NFHB and the northeast corner of the Ordos Plateau in the North China Block.
Li Lu-weiYu Zhong-yuanQiu Chun-miaoWang Wen-xuanZhao QianZheng Rong-yingYang Yan-Lin
祁连山东段发育了多条大型活动断裂,如近东西向展布的天桥沟-黄羊川断裂及北西西向展布的金强河断裂、毛毛山断裂、老虎山断裂等,在马雅雪山北麓、宝泉山隆起北缘还发育了一条整体呈北西-北西西向展布的马雅雪山断裂。其中,前人已对天桥沟-黄羊川断裂、金强河断裂、毛毛山断裂、老虎山断裂的晚第四纪活动开展了大量的研究,相比而言,马雅雪山断裂的研究程度还较低,其最新构造活动特征及其与区域主干活动断裂之间的关系等尚不清楚。马雅雪山断裂构成了天祝盆地与南部山体、丘陵的分界线,迹线清晰,断层三角面、断层槽谷多见,局部冲洪积阶地可见线性展布的断层陡坎,显示出断裂在晚第四纪有一定的活动。本研究对马雅雪山断裂西部的金强河段开展了实地调查,重点对马营沟及小黑刺沟2处的阶地断层陡坎开展了高精度地形地貌测量及阶地地貌面定年,对滑动速率进行了厘定。研究结果表明,马雅雪山断裂金强河段晚第四纪活动显著,断裂最近强震活动发生在8.21~3.43 ka BP,晚更新世晚期以来的垂直滑动速率为0.45~0.63 mm/a。