川西理塘高原冰蚀湖记录的晚更新世古地震事件

Late Pleistocene Paleoseismic Events Recorded by Glacial Erosive Lake in the Litang Plateau,Western Sichuan

湖相沉积具有高分辨率的沉积记录,而更新世以来的冰水湖泊可以记录冰期与间冰期的地质事件,具有重要的地质意义.川西高原地处青藏高原东南缘,是中国地势变化最为显著的过渡地带,发育较为完整的冰川地貌.川西理塘高原毛垭盆地发育由冰川堰塞湖形成的连续稳定的16 m湖相剖面,为纹层状泥与粉砂互层,在下部层位(深度约12.68 m和13.26 m)发现了由地震触发的软沉积物变形构造,其形态特征主要表现为液化卷曲、球‒枕构造、液化底劈和层间滑动褶皱变形,通过放射性同位素AMS 14C测年得到两期软沉积物变形事件的年龄为33850~33110、37254~36042 cal.BP.指示该地区在±37~33 ka期间至少发生过两期古地震事件:早期发生在37~36 ka之前,震级大于7级,晚期则发生于33 ka之后,震级6~7级左右.

Glacial lacustrine deposit has high-resolution sedimentary records,which has great geological significance.The Quaternary glacial and interglacial events can be recorded by the lacustrine deposit.The Litang Plateau,located in the southeastern margin of the Qinghai-Tibetan Plateau,is the transition zone with the most significant terrain changes in China,and it has well developed glacial landform.A continuous 16 m-thick lacustrine section is measured in the Maoya Basin,western side of the Litang Plateau,which is formed in a glacial-dammed lake.It is composed of laminated mud and silty sand layers,and the soft-sediment deformation structures at the depth ranging from 12.68 to13.26 m were triggered by earthquake events.The main structures of the pliable sediment deformation include liquefied curling deformed layer,ball-pillow structure,liquefied diapir and interlayer slipping fold deformation,morphologically.Based on the AMS 14C radionuclide dating,the age interval is obtained at 33850-33110 cal.BP and 37254-36042 cal.BP.It indicates that at least two paleoseismic events occurred in this area during±37-33 ka.The earlier event occurred before 37-36 ka with magnitude above 7,and the later event occurred after 33 ka,with magnitude of around 6-7.