小江断裂带中段古地震与多断层破裂行为研究

Since the Wenchuan earthquake in 2008, a few large earthquakes resulted in highly complex multifault rupture systems in the world. The multifault rupture behavior and its deformation mechanism has become a new trend in the study of active structures and seismic dynamics. Along the Xiaojiang fault zone, an important part of the southeastern border zone of the Tibetan Plateau, tectonics and seismic activity are very strong. The danger of an earthquake M7 or higher in the future seems to be imminent. There are more than 20 secondary faults developed in the middle segment of this fault zone, and they merge into one major fault in the deep, forming a complex block-boundary strike-slip fault system with the possibility of multifault rupturing. The paleoseismic trenching techniques and dating techniques, which have come a long way in recent years, can provide strong technical support for the study of paleoearthquakes and rupture behavior in the Xiaojiang fault zone. Pre-research on the segment revealed that the 1733 Dongchuan M7(3/4) earthquake and 1500 Yiliang M≥7 earthquake were likely to produce multifault rupture. Based on these and previous works, combining the latest research results of deep detection and GPS observations, this study intends to carry out a detailed investigation of historic earthquake ruptures and paleoearthquakes on the middle segment of the Xiaojiang fault zone, and then analyze and discuss its multifault rupture behavior on the paleoseimic time scale, to accumulate basic data and understanding for research as fault avoidance, seismic hazard assessment, and the present structural deformation and seismic dynamics on the southeast edge of the Tibetan Plateau.

2008年汶川地震以来，国内外多次大震发生了多断层破裂。多断层破裂行为与变形机制已成为活动构造与地震动力学研究新动向。小江断裂带是青藏高原东南边界带的重要组成部分，构造和地震活动十分强烈，未来发生7级以上地震的危险性似乎已迫在眉睫。断裂带中段发育20余条次级断裂，并在深部汇为一体，组成一复杂的块体边界走滑断裂系统，存在多断层破裂可能。近年来已有长足发展的古地震探槽技术和测年技术，为研究断裂带的古地震与破裂行为提供了强有力的技术支撑。预研究调查发现，1733年东川7(3/4)和1500年宜良≥7级地震很有可能就是多断层破裂。基于此，在前人工作基础上，结合深部探测与GPS观测最新研究成果，本项研究拟在小江断裂带中段开展历史地震破裂和古地震翔实调查，在古地震时间尺度上探讨和分析其多断层破裂行为，为断层避让与地震危险性评估以及青藏高原东南缘现今构造变形与地震动力学研究积累基础资料和认识。

2008年汶川地震以来，国内外多次大震发生了多断层破裂。多断层破裂行为与变形机制已成为活动构造与地震动力学研究新动向。小江断裂带是青藏高原东南边界带的重要组成部分，构造和地震活动十分强烈。断裂带中段发育20余条次级断裂，并在深部汇为一体，组成一复杂的块体边界走滑断裂系统，存在多断层破裂可能。在前人工作基础上，结合GNSS观测最新研究成果，本项研究在小江断裂带中段开展了历史地震破裂和古地震翔实调查，以及有限元模拟，在古地震时间尺度上探讨和分析了小江断裂带的多断层破裂行为。并对与小江断裂带相似的鲜水河-安宁河断裂系和理塘断裂带的多断层破裂行为开展了研究。获得的主要认识和进展如下：（1）1833年嵩明地震仅破裂了小江断裂带西支，而东支未同时破裂。西支断裂不同破裂段之间既有独立的破裂事件，也有多断层同时破裂事件；（2）小江断裂带东、西支等之间的一些次级断裂未发现全新世破裂迹象。现今左旋走滑环境下，小江断裂带东、西支主断裂之间局部地段存在挤压隆起蠕滑变形，对穿经断裂带的铁路等工程具有挤压隆起破坏效应；（3）1786年康定南73/4级地震也是一次多断层破裂事件，鲜水河断裂带的磨西断裂和大凉山断裂带北端的石棉断裂都发生了破裂，而安宁河断裂带北段则未破裂。安宁河断裂带北段和鲜水河断裂带的雅拉河断裂是未来最有可能发生地表破裂事件的断裂段；（4）理塘断裂带既有分段独立破裂，亦有两段同时破裂，全段破裂则可划分为3个破裂旋回，而破裂旋回的时长从8000年、2000年，缩短到最新旋回的500年，反映理塘断裂带的大震活动正在加剧。部分成果已应用于铁路工程建设。