宁波育王山山前断层探测结果的工程应用问题

DISCUSSION ON ENGINEERING APPLICATION BASED ON THE EXPLORATION OF YUWANGSHAN FAULT ZONE

基于宁波市活断层探测与地震危险性评价工作的结果,结合相关规范,对评价结果的工程应用问题进行了初步分析和探讨。结果表明,在进行工程建设时,对于育王山山前西支断层,不需要考虑避让;对于育王山山前东支断层,虽然在6级设定地震条件下,无直接的地表错动发生,但会产生一定幅度的地表变形带,因此,丙类和丁类建筑可以不考虑避让,但建议甲类和乙类建筑尽可能避让一定的距离。由于在设定地震条件下近断层强地震动加速度峰值分区中存在一个面积约6km2的略高于现行地震区划图标准的范围,建议对该范围内已建建筑物的抗震能力进行鉴定,确定是否需要进行抗震加固,对新建、扩建、改建工程按地震区划图进行抗震设防时可适当参考本文的结果。根据大碶盆地的软土分布特征,结合近断层强地震动评价结果,认为在育王山山前西支断层以东,存在一个面积约30km2的可能震陷区。震陷量≥5cm,建议在进行工程建设时考虑这一因素。鉴于探测结果的工程应用直接关系到防震减灾对策的制定,应综合考虑城市安全与经济投入2个方面的因素。

Combined with the consideration of relative codes, this paper mainly presents a preliminary analysis on the engineering application of Yuwangshan Fault zone based on the results achieved in the project of active fault exploration and seismic hazard assessment in the city of Ningbo. The conclusions we get from it are as follows. We don＇t have to take safety distance into account as to the west section of Yuwangshan Fault in engineering and construction because it has not been active since mid-Pleistocene, whereas, as to the east section of this fault, there＇s no need to consider the safety distance about Ⅲ-type and Ⅳ-type buildings, nevertheless, the case is different for Ⅰ-type and Ⅱ-type buildings because the potential surface deformation to some extent will occur with the scenario earthquake of 6. 0, even if no direct surface offset. Due to the existence of about 6km^2 area where near-fault peak ground accelerations lightly exceeds the present-day standard,the authors put forward a package of aseismatic solutions which consist of the identification of aseismatic capability to buildings in the area and consideration of this factor in new building s＇ construction. There＇s a potential area of seismic settlement of 30km^2 which may sink 5 cm or above according to the characteristics of distribution of soft soil as well as the assessment of near-fault strong ground motion in the east of the west section of Yuwangshan Fault. We should not ignore this important resuit. Given the importance of the results to the policy-decision for the mitigation of seismic disasters, we should seek for the trade-off between the safety and economic rationality in engineering application analysis.