鲜水河断裂带南东段康定—色拉哈断裂的浅层地球物理勘探

活动断层不仅是产生地震的根源,而且地震时其断层线两侧的建筑物破坏最为严重。因此准确探测出活动断层的位置和分布范围,并采取有效的工程避让措施,可大大降低地震灾害和经济损失。康定—色拉哈断裂作为鲜水河断裂南东段的主干断裂,具备发生强震的地震地质构造条件,因此该断裂所穿越的几个城镇的地震危险性不容忽视。针对康定新城探测场区存在交通条件不便、场地工作面狭窄等问题,在浅层地震反射波法探测工作中采取小道间距、小偏移距、多道短排列接收和共反射点多次覆盖观测的工作方式获取地震反射时间剖面,浅层地震探测结果辅以高密度电阻率成像断面,并结合地表地震地质调查结果,共同揭示康定—色拉哈断裂在康定新城北侧的展布位置、产状规模和近地表构造形态。研究结果发现康定—色拉哈断裂在康定新城北东侧呈左旋右界羽列状展布,经过两岔口村折多河Ⅰ级阶地处该断裂隐伏段近地表倾角约40°～50°,其破碎带及其影响带宽度约110m,随着地形的升高,破碎带的视宽度进一步增加至200m左右,并沿断层垭口向木格措方向延伸展布。浅层地球物理探测成果为判定康定—色拉哈断裂近地表构造活动提供了可靠的地震学证据,也为康定新城的地震危险性评价和制定抗震防灾规划提供了可靠的基础资料。

Detection of the Kangding-Selaha Fault in the Southeast Section of the Xianshuihe Fault Zone Using Shallow Geophysical Method

Active faults are the root causes of earthquakes, so buildings along fault lines experience the most severe damage during earthquakes. Therefore, by adopting a shallow geophysical method to accurately determine the location and distribution range of active faults and implementing effective engineering measures to evade earthquakes, we can greatly reduce earthquake disaster and consequent economic losses. The Kangding-Selaha fault is the main fault in the southeast segment of the Xianshuihe fault zone, with the tectonic condition of strong earthquakes; thus, the seismic risk in the towns passed by the fault cannot be ignored. Because the areas of the new city of Kangding that pass by the Kangding-Selaha fault are in alpine valley regions, such detection areas are subject to inconvenient traffic conditions and narrow working spaces; therefore, to obtain seismic profiles, the detection through shallow seismic reflection must be applied with small trail spacing, small displacement distance, and reception of multiple short arrangements and multiple coverage observations of common reflection points. In this study, shallow seismic detection results are combined with high-density resistivity tomography and seismic and geological survey results of the surface to reveal the spatial distribution, size, and near-surface structure of the Kangding-Selaha fault in the southeast segment of the Xianshuihe fault zone. The Kangding-Selaha fault in the southeastern section of the Xianshuihe fault zone exhibits a left-circle and right-border feather-shaped distribution in the northeast side of the new city of Kangding, and it does not only have a main cross-section. The detection results do not only provide reliable seismological evidence for determining the near-surface tectonic activity of the Kangding-Selaha fault, but also provides reliable fundamental data for seismic risk assessment, earthquake resistance planning and hazard prevention in the new city of Kangding.