纵横波联合勘探应用于栟茶河断裂活动性的调查与研究

栟茶河断裂自20世纪50年代石油部门勘探发现以来,由于缺乏确凿的证据,地学家们对其活动性一直存在争议。目标断裂所在测区基岩顶面埋深约在800~1 600m,单一的地震勘探方法难以深浅兼顾且单波勘探经常存在局限性。为了调查栟茶河断裂的空间位置、产状及性质,重新厘定其活动性,在同一条测线上同时进行高分辨率的浅层地震P波和SH波勘探,通过采用不同的地震波激发震源和观测系统参数,获得沿测线不同埋藏深度的地下细结构图像,揭示栟茶河断裂的形态和特征,尤其SH波地震剖面更加清晰地反映出超浅层地层和构造空间特征。结果表明,测线控制范围内的栟茶河断裂为近东西走向、视倾角约为60~75°、倾向N的正断层,该断层错断了新近纪和早第四纪地层,有可能断错了晚更新世地层。本文的纵、横波联合勘探实例证实了多波勘探的优越性。

Application of Joint Exploration with P-and SH-waves to theInvestigation and Research of Benchahe Fault Activity

The Benchahe Fault has been received much attention and research interest because of its importance and complexity. However, in the absence of definite evidence, there is little consensus regarding its structure and spatial distribution; the fault activity, in particular, is ambiguous. Bedrock top surface depth is about 800~1 600 m in the area where our target is located; however, a single exploration method is unlikely to identify both deep and shallow targets at the same time and has limitations. To investigate the spatial location, characteristics, and activity of the Benchahe Fault, a high-resolution shallow seismic P-and SH-wave survey profile was carried out across the fault. Fine structures at different depths beneath the profile were obtained and the patterns and characteristics of the fault were determined. In particular, the SH-reflection profile revealed evidence of tectonic deformation. The results show that the Benchahe Fault is a normal fault that runs nearly EW, and dips to the N with a dip angle of 60~75°. Based on the sections, we can speculate that the up-breakpoint of the south branch of the fault dislocated the top surface of the Middle Pleistocene, and may have dislocated the bottom of the late Pleistocene stratum interface. In this paper, we show that this multi-level seismic exploration method is an effective means of locating buried faults and studying their activity in areas with thick overburden. Joint inversion of P-and SH-waves was effective for locating the buried fault in thick Quaternary sediments and determining its activity. While the two methods corroborate each other in the overlapping buried depth range, the SH-wave exploration method can compensate for near-surface layer and rift structure information that is lost in P-wave exploration.