地震折射和反射方法研究郯庐断裂带宿迁段的浅部构造特征

郯庐断裂带是中国东部最大的一个活动构造带,其内部结构非常复杂,不同区段表现出不同特征的构造样式.本文采用浅层地震反射波成像技术对郯庐断裂带宿迁段的近地表结构进行了高分辨率成像,利用该区已有的深地震反射剖面数据,采用初至波层析成像方法获得了郯庐断裂带的浅层P波速度结构.结果表明,郯庐断裂带宿迁段是一个由多条断裂以及凹陷和隆起构成的复杂构造带,且新生代地层厚度和地震波速分布明显受到断裂的影响与控制.郯庐断裂带的东、西两侧为基底隆起区,近地表速度结构呈现为明显的高速特征,新生代地层厚度小于200m.郯庐断裂带总体显示为低速凹陷结构,新生代地层厚度在300～600m之间变化,最厚处位于宿迁市的陵城镇附近.郯庐断裂带宿迁段主要由5条断裂构成,从这些断裂的上断点埋深和第四纪活动特征来看,郯庐断裂带的东边界断裂F_1和西边界断裂F_4的活动性相对较弱,为第四纪早期活动断裂.断裂F_2和F_3控制了郯庐断裂带内部的新生代凹陷,两者的活动时代分别为中更新世和晚更新世.安丘—莒县断裂F_5位于断裂F_1和F_2之间,由2条相向而倾的分支断层F_5和F_(5-1)构成,其活动时代分别为全新世和晚更新世.研究结果为进一步认识郯庐断裂带宿迁段的近地表特征及其活动性提供了新证据.

Exploration of shallow structural characteristics in the Suqian segment of the TanLu fault zone based on seismic refraction and reflection method

The TanLu fault zone is the largest active tectonic belt in eastern China. Its internal structure is extremely complex and different sections show different tectonic styles. In this paper, the shallow seismic reflection imaging technology is applied to obtain the high-resolution near surface structure in the Suqian section of the TanLu fault zone. Meanwhile, basing on the deep seismic reflection profile data, a first-break wave imaging method is used to acquire the P-wave velocity structure of the TanLu fault zone. The results show that Suqian section of the TanLu fault zone, a complex tectonic zone, is composed of multiple faults and depressions and uplifts, and the thickness of Cenozoic strata and the distribution of P-wave velocity are obviously affected and controlled by this fault zone. Also, the eastern and western sides of the TanLu fault zone are the basement uplift areas, and the near surface velocity structure presents an obvious high-speed feature, with the Cenozoic strata thickness less than 200 meters. In short, The TanLu fault zone is generally a low-speed depression structure, the thickness of the Cenozoic strata varies from 300 meters to 600 meters, and the thickest part is located near the Lingcheng town in Suqian City. Besides, the Suqian section of the TanLu fault zone consists of five fractures, according to the buried depth of the upper breakpoints of these fractures and the characteristics of the Quaternary activity, the eastern boundary fault F₁ and the western boundary fault F₄ of the TanLu fault zone are weak active relatively, which are the early quaternary active faults. The Cenozoic depression inside the TanLu fault zone are controlled by the fault F₂ and F₃, the active times of which were separately the middle Pleistocene and late Pleistocene. The Anqiu-Juxian fault, located between the faults F₁ and F₂, is composed of two contrary tendency branched faults F₅ and F_5-1, whose active times were Holocene and late Pleistocene. In conclusion, the results of this study provide a new evidence for further understanding of the near-surface characteristics and activity of the TanLu fault zone in Suqian segment.