舟山地区主要断裂对新建宁波至舟山铁路工程安全影响研究

Research on the Impact of Major Faults in Zhoushan Area on the Safety of the New Ningbo-Zhoushan Railway Project

摘要:

舟山地区断裂发育情况十分复杂，是否存在可能产生地表断错的活动断裂，对新建宁波至舟山铁路工程的抗震设防以及工程抗断参数的选取，具有十分重要的意义。通过对舟山地区的野外地震地质调查，以及水域的浅层地震勘探工作，对舟山地区主要断裂的第四纪活动性进行了研究，获得了以下初步认识：柴桥—伍佰岙断裂为前第四纪断裂；沙岙—戴家断裂主体为早第四纪断裂，局部段落的最新活动时代为晚更新世早期；花厅里—紫薇断裂和昌化—普陀断裂最新活动时代为中更新世；马岙—定海断裂和大丰—长白断裂的最新活动时代为早更新世。沙岙 —戴家断裂与工程线路相交段为晚更新世活动断裂，出于工程安全考虑需采取抗断措施，其它断裂可不考虑抗断问题。在沙岙—戴家断裂及其影响范围内避免修建不易抗震和不易修复的工程，并且避免修建站房等建筑结构工程，在避让时应考虑上盘效应。建议线路穿越沙岙—戴家断裂范围采用有砟轨道；建议采用易修复的柔性路基工程通过，路堤内加强抗震性稳定性措施和长期变形观测。根据地震地质背景分析，东西向昌化—普陀断裂与北东向沙岙—戴家断裂、镇海—宁海断裂的交汇部位，为破坏性地震可能的发生部位；场址区及邻区存在发生6级左右地震的孕震环境。

Abstract:

The fault distribution and characteristics in the Zhoushan area are highly complex. The presence of active faults that could cause surface faulting is crucial for the seismic design and the selection of anti-fault parameters for the new Ningbo-Zhoushan railway project. This study, based on field seismic geological surveys and shallow seismic exploration in the waters, investigates the Quaternary activity of major faults in the Zhoushan area, leading to the following preliminary findings: The Chaiqiao Wubai'ao fault was identified as a pre-Quaternary fault; the Sha'ao-Daijia fault was primarily an early Quaternary fault, with recent activity in some local sections dating back to the early Late Pleistocene; the Huatingli-Ziwei fault and the Changhua-Putuo fault were most recently active in the Middle Pleistocene; and the Ma'ao-Dinghai fault and the Dafeng-Changbai fault had their latest activity in the Early Pleistocene. The section of the Sha'ao-Daijia fault intersecting the project route was an active fault from the Late Pleistocene. For engineering safety, anti-fault measures should be taken, while other faults did not require such considerations. Construction of earthquake-vulnerable and difficult-to-repair structures should be avoided within the influence range of the Sha'ao-Daijia fault, and station buildings or other structures should not be constructed in this area. When rerouting, the hanging wall effect should be considered. The use of ballast track across the Sha'ao-Daijia fault zone was suggested, along with flexible subgrade engineering design that is easy to repair. Additionally, seismic stability measures and long-term deformation monitoring were recommended for embankments. Based on the seismic geological background analysis, the intersection of east-west Changhua-Putuo fault, northeast Sha'ao-Daijia fault, and Zhenhai-Ninghai fault was a potential site for destructive earthquakes. The site and its surrounding areas were found to have seismogenic potential of earthquakes of around magnitude 6.