维西-乔后断裂全新世活动与古地震  

HOLOCENE ACTIVITY AND PALEOEARTHQUAKES OF THE WEIXI-QIAOHOU FAULT

作　　者：常祖峰[1] 常昊[1] 李鉴林 毛泽斌 臧阳[2] CHANG Zu-feng;CHANG Hao;LI Jian-lin;MAO Ze-bin;ZANG Yang(Yunnan Earthquake Agency,Kunming 650224,China;China Earthquake Networks Center,Beijing 100045,China)

机构地区：[1]云南省地震局,昆明650224 [2]中国地震台网中心,北京100045

出　　处：《地震地质》2021年第4期881-898,共18页Seismology and Geology

基　　金：国家自然科学基金(41472204,U2002211)资助。

摘　　要：维西-乔后断裂位于川滇菱形块体的西边界,晚第四纪活动迹象明显,是红河活动断裂带的北延部分,因此加强其活动性研究对深入认识滇西北地区地震地质背景和川滇块体边界构造变形机制具有重要的理论和实际意义。文中依据1︰5万活动断裂填图和国家自然基金项目研究成果,重点介绍了马头水、石岩、玉狮场等探槽揭示出的断裂最新活动时代和沿线古地震事件,结果表明,玉狮场—平坡段为全新世活动段并存在多次古地震事件。马头水探槽揭示出的3条断层断错晚更新世—全新世洪积扇堆积,断错的最新地层的年代为(638±40)aBP和(1335±23)aBP。石岩探槽西段揭露的3条断层断错的最新地层的^(14)C测年结果分别为(4383±60)aBP、(4337±52)aBP和(4274±70)aBP;探槽东段同样揭示发育了3条断层,主断层下盘断错的最新地层的^(14)C年代为(9049±30)aBP,上盘断错的2套断塞塘堆积的^(14)C测年结果分别为(1473±41)aBP和(133±79)aBP。玉狮场探槽揭示出发育了5条活动断层,其中F_(1)与F_(2)断错灰白色含砾黏土和黑色泥炭质土,前者的^(14)C测年结果为(1490±30)aBP,后者的^(14)C测年结果分别为(1390±30)aBP和(1190±30)aBP;F 3与F 4断错灰白色含砾黏土、黑色泥炭质土及上部褐黄色含砂黏土,褐黄色含砂黏土的OSL年龄为(0.6±0.2)ka;F 5断层断错的黏土层的^(14)C年龄为(1490±30)a。盖场探槽揭示出地震楔、软沉积构造变形和砂脉等古地震现象,垂直错距35cm,估计此次地震事件的时间约为28000aBP,震级达7级。玉狮场探槽揭示了2次地震事件,第1次事件的时间为(1490±30)~(1390±30)aBP;第2次事件的时间约为距今600a,推测震级达7级。马头水探槽揭示出垂直错距约1m的地震事件,发生时间约为600aBP,据地震破裂带的长度、宽度、陡坎高度、位错量并结合宜良M≥7地震和缅甸东吁7.3级地震的经验,认为此次地震的震级≥7级。The Weixi-Qiaohou Fault is located in the west boundary of Sichuan-Yunnan rhombic block,and also the north extension segment of active Red River fault zone.Strengthening the research on the late Quaternary activity of Weixi-Qiaohou Fault is of great theoretical and practical significance for further understanding the seismogeological background in northwest Yunnan and the structural deformation mechanism of the boundary of Sichuan-Yunnan block.Based on the 1︰50000 active fault mapping and the research results of the National Natural Science Fund project,this paper mainly elaborates the latest active times of the fault and paleoseismic events along it revealed by exploration trenches at Matoushui,Shiyan,and Yushichang.Matoushui trench revealed three faults developed in late Pleistocene and Holocene pluvial fan accumulation,and the latest ages of faulted strata are(638±40)aBP and(1335±23)aBP,respectively.The Shiyan trench revealed six faults,three in the western section and three in the eastern section.The three faults in the western section dislocated the late Pleistocene and Holocene accumulation,and the^(14)C ages of the latest faulted strata are(4383±60)aBP,(4337±52)aBP and(4274±70)aBP,respectively;the other three faults revealed in the eastern part of the trench offset the Holocene fluvial facies accumulation,the^(14)C age of the latest faulted strata in the footwall of the main fault is(9049±30)aBP,and the^(14)C ages of two sets of faulted sag pond deposits in the hanging wall are(1473±41)aBP and(133±79)aBP,separately.Five active faults are revealed in Yushichang trench.Among them,the F_(1) and F_(2) dislocated the gray-white gravelly clay layer and the black peat soil layer.The^(14)C age of the gray-white gravelly clay layer is(1490±30)aBP,and^(14)C ages of the upper and lower part of the black peat soil layer are(1390±30)aBP and(1190±30)aBP,respectively.The F 3 and F 4 faults offset the gray-white gravelly clay layer,the black peat soil layer and the brown yellow sand bearing clay,and the OSL a

关 键 词：维西-乔后断裂 全新世活动 古地震 探槽 

分 类 号：P315.2[天文地球—地震学]