Abstract: The Tan-Lu fault zone is the largest active tectonic zone in eastern China, with a complex history of formation and evolution, and it has a very important control effect on the regional structure, magmatic activity, the formation and distribution of mineral resources and modern seismic activity in eastern China. Xinyi City has a very important position as a segmental node in the Shandong and Suwan sections of the Tan-Lu fault zone. Predecessors have conducted research on the spatial distribution, occurrence and activity characteristics of the shallow crustal faults in the Suqian section of the Tan-Lu belt, and have obtained some new scientific understandings and results. However, due to different research objectives or limitations of research methods, previous researches have either focused on the deep crustal structure, or targeted on the Suqian section or other regions. However, the structural style and deep-shallow structural association characteristics of Xinyi section of Tan-Lu belt have not been well illustrated, nor its activity and spatial distribution have been systematically studied. In order to investigate the shallow crustal structure features, the fault activities, the spatial distribution and the relationship between deep and shallow structures of the Xinyi section of the Tan-Lu Fault, we used a method combining mid-deep/shallow seismic reflection exploration and first-break wave imaging. Firstly, a mid-deep seismic reflection profile with a length of 33km and a coverage number greater than 30 was completed in the south of Xinyi City. At the same time, using the first arrival wave on the common shot record, the tomographic study of the shallow crust structure was carried out. Secondly, three shallow seismic reflection profiles and one refraction tomography profile with high resolution across faults were presented. The results show that the Xinyi section of Tan-Lu fault zone is a fault zone composed of five concealed main faults, with a structural pattern of “two grabens sandwiched by a barrier”. The five main faults reveal more clearly the structural style of “one base between two cuts” of the Tan-Lu fault zone. From west to east, the distribution is as follows: on the west side, there are two high-angle faults, F₄ and F₃, with a slot-shaped fault block falling in the middle, forming the western graben. In the middle, F₃ and F₂, two normal faults with opposite dip directions, are bounded and the middle discontinuity disk rises relatively to form a barrier. On the east side, F₂ and F₁, two conjugate high-angle faults, constitute the eastern graben. The mid-deep and shallow seismic reflection profiles indicate that the main faults of the Xinyi section of Tan-Lu fault zone have a consistent upper-lower relationship and obvious Quaternary activities, which play a significant role in controlling the characteristics of graben-barrier structure and thickness of Cenozoic strata. The shape of the reflective interface of the stratum and the characteristics of the shallow part of the fault revealed by shallow seismic reflection profiles are clear. The Mohe-Lingcheng Fault, Xinyi-Xindian Fault, Malingshan-Chonggangshan Fault and Shanzuokou-Sihong Fault not only broke the top surface of the bedrock, but also are hidden active faults since Quaternary, especially the Malingshan-Chonggangshan Fault which shows strong activity characteristics of Holocene. The results of this paper provide a seismological basis for an in-depth understanding of the deep dynamics process of Xinyi City and its surrounding areas, and for studying the deep-shallow tectonic association and its activity in the the Xinyi section of the Tan-Lu Fault.

Key words: Xinyi section of Tan-Lu fault zone, first-break traveltime imaging, seismic reflection profile, crustal structure and tectonics, Quaternary activity

摘要： 新沂市作为郯庐断裂带山东段和苏皖段的分段节点, 具有非常重要的地位。 为研究郯庐断裂带新沂段地壳的浅部结构、 活动性、 空间展布以及深浅构造关系, 文中采用了中深、 浅层地震勘探及初至波层析成像相结合的工作方法, 首先在新沂市南完成了1条长33km、 覆盖次数> 30次的中深层地震反射剖面, 同时利用共炮集记录上的初至波开展地壳浅部结构的层析成像研究, 之后给出了跨断裂的3条高分辨率浅层地震反射剖面和1条折射层析成像剖面。 研究结果表明: 郯庐断裂带新沂段是一条由5条隐伏主干断裂组成的断裂带, 具有 “两堑夹一垒”的构造样式。 中深层和浅层地震反射剖面表明, 郯庐断裂带新沂段各主干断裂具有上下一致的对应关系和明显的第四纪活动, 对新生代地层厚度和堑-垒状构造特征具有明显的控制作用。 浅层地震勘探结果揭示的地层界面形态和断裂浅部特征清楚, 墨河-凌城断裂(F₃)、 新沂-新店断裂(F₂)、 马陵山-重岗山断裂(F₅)及山左口-泗洪断裂(F₁)不仅断错了基岩顶界面, 且第四纪以来存在活动迹象, 尤其是马陵山-重岗山断裂(F₅)具有全新世的强活动特征。 文中的研究结果可为深入理解新沂市及周缘的深部动力学过程、 研究郯庐断裂新沂段的深浅构造组合关系及其活动性提供地震学依据。

关键词: 郯庐断裂带新沂段, 初至波成像, 地震反射剖面, 地壳结构和构造, 第四纪活动性