关键词: 安宁河断裂, 晚第四纪, 地层地貌序列, 位移速率

Abstract: The Anninghe Fault is an important active fault along the eastern boundary of Sichuan-Yunnan active tectonic block,and the study of its distribution feature of displacement rates in the late Quaternary is of fundamental importance for understanding the dynamic theory on Chinese continent,boundary dynamic process of the active block and the recurrence interval of large earthquakes. The active Anninghe Fault in late Quaternary has the length of 160km and consists of two segments. Zimakua is an area where the latest neotectonic rupture trajectories are relatively simple and the offset geomorphologic sequences are well developed. Using the methods of detailed geomorphic and geological survey,digital image analysis,total station instrument survey,excavation of trench and dating,the paper makes an analysis on the geomorphologic sequences of the strata and obtains some new results as follows: The terrace(step)T₃ consisting of moraine deposits was formed at about 20ka BP and offset by the Anninghe Fault with a left-lateral displacement of (84±3)m and a vertical displacement of 18m. On the base of the moraine deposits overlies terrace(step)T₂ of mainly alluvial deposits formed at 10～7ka BP with the maximum left-lateral displacement of about 40m,an average of (36±4)m,and a vertical displacement of about 11m. Terrace T1 is composed mainly of the alluvium and partial dammed-pond deposits which were formed during 3～2.2ka BP. The earliest event that offset the T1 happened at 1.7kaBP.Three events have been discovered since 1.7kaBP and the cumulative left-lateral displacement is 10.5m and the vertical displacement 2.3m. So,the left-lateral displacement rates are 6.2mm/a,3.6～4mm/a,3.8～4.2mm/a and the vertical rates are 1.4mm/a,1.1mm/a,0.9mm/a(at least)on average in about 2.6ka,10ka and 20ka,respectively. The proportion of horizontal to vertical displacements is about 4:1. That means the vertical rate on Anninghe Fault is about 25% of horizontal slip rate. The left-lateral slip rate in late Holocene is well consistent with GPS measurement. The change of the left-lateral rates in different stage is also consistent with recurrence interval of paleoearthquakes. It means that there is alternation between strong and weak activities of the Anninghe Fault.

Key words: Anninghe Fault, late Quaternary, stratigraphic and geomorphic sequences, displacement rates