云南曲靖-昭通断裂带北段晚第四纪以来的古地震

Research on Paleo-earthquakes in Late Quaternary along the Northern Part of Qujing-Zhaotong Fault, Yunnan Province

一、前言云南曲靖-昭通断裂带北段南起昭通盆地,北止玛瑙以北,全长180km。该断裂带自南向北主要由大关口断裂、中坝断裂、高桥断裂、大毛滩断裂、玛瑙断裂和利店断裂组成。

Based on field investigation and trench excavation,many paleoseismic relics have been identified and studied along the northern part of Qujing-Zhaotong Fault,Yunnan Province.The geological and morphologic features of the relics include seismic faults,colluvial wedges,fault scarplets,seismic landslide masses,as well as paleoseismic liquefaction.These features reveal the fault segmentation and their levels of activities.Three Holocene paleoearthquakes have been recognized from fault scarplets and drainage offsets near Zhongbacun village.Along Damaotan fault segment,which is the most active segment of the northern part,paleoseismic relics typically appear from which 7 paleo-events are identified.Three of the 7 events occurred in Holocene,probably greater than magnitude 7.The recurrence interval of paleo-earthquakes in the early-to-mid Holocene is estimated as about 3 ka.However,the interval between the 1974 Yongshan earthquake and the 1844 Yuanheng earthquake was just 130 years.Does the recurrence interval tend to be shorter?Anyhow,from available data,we conclude that Damaotan and Zhongba segments have been more active than Daguankou and Gaoqiao segments in Holocene.