Abstract: Research on a large number of seismic events at home and abroad has indicated that tremendous earthquake hazards in urban areas are mostly attributed to earthquakes caused by active faults buried beneath the cities. The identification of urban buried active faults, therefore, is an important and urgent task. High-resolution seismic exploration is an effective geophysical technique that can be used to identify urban buried active fault at present. High-resolution seismic exploration for urban buried active faults is a sophisticated and systematic project, which involves excitation and receiving techniques, observational system, as well as seismic data processing and interpretation. The seismic source is of the first importance among the other problems that should be solved during the exploration. High-resolution seismic exploration for urban active fault calls for specific performance of the seismic source, because of peculiar environment in urban areas and particular characteristics of urban buried faults. For examples, relatively small offset of the fault requires a wider source spectrum, while strong disturbances in urban areas need a higher anti-jamming capability of the source. A comparative experiment on various types of sources, including vibroseis, vacuum accelerating weight drop, hammer-blow, air gun and explosive is carried out along the traverse across the Bayishuiku Fault. The features of various source spectrums are obtained by using spectrum analysis technique. The comparison of time-stacked sections obtained by using vibroseis, vacuum accelerating weight-drop and hammer blow from the traverse across the Bayishuiku Fault in Fuzhou City is presented in this paper. The effectiveness of various seismic sources in the exploration of urban buried active faults is discussed in detail.

Key words: urban active faults, seismic source, high-resolution seismic exploration, source spectrum, time-stacked section, master frequency, frequency width

摘要： 国内外大量地震震例研究表明,巨大的城市地震灾害主要是由隐伏于城市之下的活动断裂上发生的地震造成的,因此,探测城市活断层是十分必要和紧迫的.高分辨率地震勘探是目前探测城市活断层较为有效的地球物理方法,它包括激发技术、接收技术、观测系统、地震数据处理与解释技术等.而震源是地震勘探的首要问题,城市特定的人文环境和城市活断层的特点对高分辨率地震勘探的震源提出了特殊的要求,较小的断距决定了要有较宽的震源谱,城市较严重的干扰决定了震源要有较强的抗干扰能力.通过在福州市跨八一水库断裂进行的可控震源、真空加速落锤、锤击震源、枪震源以及炸药震源的试验研究,利用频谱分析技术,得到了各种震源谱的特性,并给出了可控震源、真空加速落锤和锤击震源叠加时间剖面对比,探讨了各种震源在城市活断层探测中的有效性.

关键词: 城市活断层, 震源, 高分辨率地震勘探, 震源谱, 叠加时间剖面, 主频, 频宽