With the acceleration of urbanization process, solving the earthquake and its associated disasters caused by buried active fault in urban areas has been a difficult issue in the construction of urban public security system. It is difficult to deal with the anti-seismic issues of cross-fault buildings using the existing techniques, therefore, reasonable setback distance for buried active fault in urban area is the only method for the planning and construction at the beginning. At present, theoretical research about setback for active fault is becoming more and more mature, and the mandatory national standard “Setback distance for active fault” will be enacted soon. As a result, how to work on the basis of these theories and national standards is in urgent. In recent years, the exploration of urban active faults was successively completed. However, there are no typical cases of how to make full use of the achievements of urban active fault projects in the follow-up work, and how to guide urban construction based on the project conclusions, so as to ensure urban safety and rational development of urban economy.

In this paper, taking a site along the Anqiu-Juxian Fault in the Tanlu fault zone in Xinyi city as an example, based on the results of 1︰10 000 active fault distribution map, and referring to the stipulation of national standard “Setback distance for active fault”, 12 shallow seismic survey lines with a spacing of less than 50m were laid out firstly, and the results of shallow seismic exploration show the existence of two high-dip faults in the site. Secondly, considering the shallow seismic survey results and the geologic site conditions, five rows of borehole joint profiles were selected along five of the shallow seismic survey lines. Based on the location of the faults and stratigraphy in the site revealed by the borehole joint profiles, and considering the latest research results of Quaternary stratigraphy and the conclusion of urban active faults detection, the west branch fault is constrained to be a Holocene active fault and the east branch fault is an early Quaternary fault. As a result, we precisely mapped the trace, dip and upper breakpoint of the fault in the site based on the shallow seismic exploration and joint borehole profile. The accurate positioning of the plane position of the active fault differs by about 200m from the 1:1000 strip distribution map.

According to the relevant national standards and scientific research results, active faults in the site shall be avoided. Based on the surface traces of active faults revealed by the accurate detection in the site, the active fault deformation zone was delineated, and the range of setback distance for active fault was defined outside the deformation zone. The detection results accurately determined the plane distribution of the active fault in the site, which meets the accuracy of the development and utilization of the site. Based on the accurately located active fault trace, and complying with the forthcoming national standard “Setback distance from active fault”, this study not only scientifically determines the setback distance for active fault in the site, but also releases the scarce land resources in the city. This result achieves the goal of scientifically avoiding potential dangerous urban hidden active fault and making full use of land.

The case detection process confirms that the results of urban active fault detection are still difficult to meet the fault positioning accuracy required for specific site development, and the range of active fault deformation zone within the site must be determined based on the precise positioning method for hidden active faults as stipulated in the national standard “Setback distance for active fault”. The national standard “Code for seismic design of buildings” only specifies the setback distance for active faults under different seismic intensity, but does not provide any clear definition of the accuracy of active fault positioning, so it is difficult to define the required active fault positioning degree and boundary range of the deformation zone of active fault in practice. The national standard “Setback distance for active fault” clearly defines various types of active fault detection and positioning methods, determines the scope of active fault deformation zone and the accurate setback distance for active fault in different cases. The specific case proves that before developing and utilizing specific sites along urban concealed active faults, relevant work shall be carried out according to the national standard “Setback distance for active fault” to effectively resolve the issue about the relations between urban development and urban safety, so the promulgation and implementation of national standard should speed up.

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.

The NE-trending regional deep fault, i.e. the Jintan-Rugao Fault, is a boundary fault between the Subei depression and Nantong uplift, and its research has always received broad attention because of its importance and complexity. For the absence of definite proof, there is little consensus regarding the structure and spatial distribution of the fault among geoscientists, and its latest active time is ambiguous. The study of Quaternary activity characteristics of the Jintan-Rugao Fault is of great significance for earthquake trend prediction and engineering safety evaluation, and for earthquake prevention and disaster reduction in Jiangsu Province. In order to investigate the spatial location, characteristics and tectonic features and redefine the activity of the NE-segment of the Jintan-Rugao Fault, and on the basis of likely location and marker beds derived from petroleum seismic exploration sections, we collect and arrange 4 shallow seismic exploration profiles crossing the fault to conduct high-resolution seismic reflection imaging, following the working concept of ‘from known to unknown, from deep to shallow’. In this study, an observation system with trace intervals of 4~6m, shot intervals of 12~18m, and channels of 90~256 and 15~36 folds is used. In addition, by introducing different tonnage vibroseis to suppress the background noise, the raw data with high SNR(signal-noise ratio)can be obtained. By using the above working method and spread geometry, we obtained clear imaging results of the subsurface structure and fault structure in the coverage area of the survey lines. This exploration research accurately locates the NE-segment of Jintan-Rugao Fault, and further shows that it is not a single fault but a fault zone consisting of two normal faults with N-dipping and NE-striking within the effective detection depth. The shallow seismic profiles reveal that the up-breakpoint on the south branch with stronger activity is at depth of 235~243m, which offsets the lower strata of lower Pleistocene. Combining drilling data around the survey lines, we infer the activity time of this fault is early Pleistocene. The results of this paper provide reliable seismological data for determining the location and activity evaluation of the NE-segment of Jintan-Rugao Fault. In eastern China, where the sedimentary layer is thicker, the latest active age of faults can not be determined entirely according to the latest faulted strata. For a fault passing through the thicker area of new deposits, its latest active age should be based on the tectonic background, seismic activity, present tectonic stress field, topographic deformation, structural micro-geomorphological characteristics, sedimentary thickness of new strata, controlling effect of faults on new strata and the latest strata of faults, and combined with upper breakpoints, morphology, structure and occurrence of faults, the active state of the target concealed faults should be analyzed. If the activity of the fault is judged only by the upper faulted point, it may lead to overestimating the age of the fault activity.