The Tanlu fault zone is the most active fault zone in eastern China. It has been active mainly along the Anqiu-Juxian Fault(AJF)since the Quaternary. Predecessors have done a lot of research on the age, paleoearthquake and geometry structure of the AJF, but most of them focus on the exposed area of the fault, and relatively few studies on the buried section. Using field geological survey, shallow seismic exploration, drilling, and paleoearthquake trench, this paper focuses on the geometry structure of the Xinyi section(the buried section)of the AJF, and analyzes its geometry distribution characteristics in the plane and the structural relationship between the deep and the shallow parts, thus filling the gap of the activity characteristics of the Xinyi section of the AJF. The results show that the Xinyi section of the AJF can be divided into three sections from north to south: the Beimalingshan-Guanzhuang section, the Guanzhuang-Tangdian section and the Tangdian-Xindian section.
The Xinyi section of the AJF, mainly manifested as strike-slip and normal faulting, has a right-handed and right-step distribution. The step-over zone with~900m in width and~16km in length is dominated by extension, leaving a length-width ratio of 18:1, much larger than the traditional pull-apart basin ratio of 3:1. According to the shallow seismic profile, the shallow seismic line in the Guanzhuang-Tangdian section revealed the extensional fault depression basin on the north side of the terrace, and the bedrock top of the basin gradually became shallower toward the north. The top of the bedrock in the shallow seismic survey line on the north side of the Nanmalingshan suddenly became deeper, and the NNE-trending compressional near-EW basins of the Nanmalingshan and Tashan developed. The two basins were formed from different origin. With the activity of the Anqiu-Juxian Fault and the erosion and deposition of the Shu River, the two basins gradually developed and merged into a composite basin, and the basin structure was consistent with the Quaternary stratigraphic isopach.
The Xinyi section of the Anqiu-Juxian Fault presents the deformation characteristics of the same genesis and coordinated geometric structure in the deep and superficial layers, showing a single branch in the deep, cutting through the Cretaceous strata, extending and rupturing upward along the contact interface between the bedrock mountains and the Quaternary soft soil layer in the superficial layer. The fault is shown as a single branch in the north and south Maling Mountains, and ruptured to the surface in many places. In the pull-apart basin in the middle of the fault, the thickness of the Quaternary system is more than 300m. When the Anqiu-Juxian Fault ruptures to the upper part, it divides into two branches, the east and the west, which are concealed and stand opposite to each other in the shape of “Y”, forming the Anqiu-Juxian Fault. On the east-west boundary of the fault, the latest activity is along the west branch of the fault, which is a Holocene active fault. When it extends to the basement rock mass of the Maling Mountains in the north and south, the depth of the upper fault point gradually becomes shallower until it is exposed.
The vertical movement of the Xinyi section of the AJF shows the four quadrants characteristics of uplift and subsidence. The extensional area forms a pull-apart basin, while the compressive area constitutes an uplift. The vertical bedrock offset of the Guanzhuang-Tangdian section, with the maximum vertical offset of~230m, gradually decreases to both sides. It can be concluded that the Xinyi section of the AJF presents a spiral-like pivot movement.

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.

Running across the urban areas of Changzhou, Wuxi and Suzhou, the NW-trending Su-Xi-Chang Fault is an important buried fault in Yangtze River Delta. In the respect of structural geomorphology, hilly landform is developed along the southwest side of the Su-Xi-Chang Fault, and a series of lakes and relatively low-lying depressions are developed on its northeast side, which is an important landform and neotectonic boundary line. The fault controlled the Jurassic and Cretaceous stratigraphic sedimentary and Cenozoic volcanic activities, and also has obvious control effects on the modern geomorphology and Quaternary stratigraphic distribution.
Su-Xi-Chang Fault is one of the target faults of the project "Urban active fault exploration and seismic risk assessment in Changzhou City" and "Urban active fault exploration and seismic risk assessment in Suzhou City". Hidden in the ground with thick cover layer, few researches have been done on this fault in the past. The study on the activity characteristics and the latest activity era of the Su-Xi-Chang Fault is of great significance for the prevention and reduction of earthquake disaster losses caused by the destructive earthquakes to the cities of Changzhou, Wuxi and Suzhou.
Based on shallow seismic exploration and drilling joint profiling method, Quaternary activities and distribution characteristics of the Su-Xi-Chang Fault are analyzed systematically. Shallow seismic exploration results show that the south branch of the Su-Xi-Chang Fault in Suzhou area is dominated by normal faulting, dipping to the north-east, with a dip angle of about 60° and a displacement of 3~5m on the bedrock surface. The north branch of the Su-Xi-Chang Fault in Changzhou area is dominated by normal faulting, dipping to the south, with a dip angle of about 55°~70° and a displacement of 4~12m on the bedrock surface. All breakpoints of Su-Xi-Chang Fault on the seismic exploration profiles show that only the bedrock surface was dislocated, not the interior strata of the Quaternary.
On the drilling joint profile in the Dongqiao site of Suzhou, the latest activity of the south branch of Su-Xi-Chang Fault is manifested as reverse faulting, with maximum displacement of 2.9m in the upper part of Lower Pleistocene, and the Middle Pleistocene has not been dislocated by the fault. The fault acts as normal fault in the Pre-Quaternary strata, with a displacement of 3.7m in the Neogene stratum. On the drilling joint profile in the Chaoyang Road site of Changzhou, the latest activity of the north branch of Su-Xi-Chang Fault is manifested as reverse faulting too, with maximum displacement of 2.8m in the bottom layer of the Middle Pleistocene. The fault acts as normal fault in the Pre-Quaternary strata, with a displacement of 10.2m in the bedrock surface.
Combining the above results, we conclude that the latest activity era of Su-Xi-Chang Fault is early Middle Pleistocene. The Su-Xi-Chang Fault was dominated by the sinistral normal faulting in the pre-Quaternary period, and turned into sinistral reverse faulting after the early Pleistocene, with displacement of about 3m in the Quaternary strata. The maximum magnitude of potential earthquake on the Su-Xi-Chang Fault is estimated to be 6.0.

The Tan-Lu Fault Zone(TLFZ), a well-known lithosphere fault zone in eastern China, is a boundary tectonic belt of the secondary block within the North China plate, and its seismic risk has always been a focus problem. Previous studies were primarily conducted on the eastern graben faults of the Yishu segment where there are historical earthquake records, but the faults in western graben have seldom been involved. So, there has been no agreement about the activity of the western graben fault from the previous studies. This paper focuses on the activity of the two buried faults in the western graben along the southern segment of Yishu through combination of shallow seismic reflection profile and composite drilling section exploration.
Shallow seismic reflection profile reveals that the Tangwu-Gegou Fault(F₄)only affects the top surface of Suqian Formation, therefore, the fault may be an early Quaternary fault. The Yishui-Tangtou Fault(F₃)has displaced the upper Pleistocene series in the shallow seismic reflection profile, suggesting that the fault may be a late Pleistocene active fault. Drilling was implemented in Caiji Town and Lingcheng Town along the Yishui-Tangtou Fault(F₃)respectively, and the result shows that the latest activity time of Yishui-Tangtou Fault(F₃)is between(91.2±4.4)ka and(97.0±4.8)ka, therefore, the fault belongs to late Pleistocene active fault.
Combined with the latest research on the activity of other faults along TLFZ, both faults in eastern and western graben were active during the late Pleistocene in the southern segment of the Yishu fault zone, however, only the fault in eastern graben was active in the Holocene. This phenomenon is the tectonic response to the subduction of the Pacific and Philippine Sea Plate and collision between India and Asian Plate. The two late Quaternary active faults in the Yishu segment of TLFZ are deep faults and present different forms on the surface and in near surface according to studies of deep seismic reflection profile, seismic wave function and seismic relocation. Considering the tectonic structure of the southern segment of Yishu fault zone, the relationship between deep and shallow structures, and the impact of 1668 Tancheng earthquake(M=8(1/2)), the seismogenic ability of moderate-strong earthquake along the Yishui-Tangtou Fault(F₃)can't be ignored.

The fault F₅ is considered as the most active fault in the Tanlu fault zone(Yi-Shu fault zone), which is located from Weifang of Shandong Province to Jiashan of Anhui Province, with a length of 360km. It has always been a focus of concern to many geoscientists because of its complexity and importance. But, for a long period of time, there exists biggish indetermination in the accurate position and active ages of the fault F₅ in Suqian section of Tanlu fault zone. Seismic reflection exploration is the main technique in present urban active faults detecting. In order to investigate the spatial distribution, characteristics and activities of the fault F₅ in covered terrains, we carried out a systematic survey to the fault with shallow seismic prospecting method and obtained the accurate position and development characteristics of the fault. The results show that the fault F₅ continues to develop toward south rather than ending at the Huancheng South Road of Suqian City. F₅ is mainly composed of two main faults, which dip in opposite directions and almost vertically. Near the Sankeshu town, F₅ is composed of three faults with right-stepping, forming a small pull-apart basin with length of 6km, width of 2.5km, controlling the deposition of Neogene and Quaternary strata. By combining the results of composite drilling section and trenching, we make a conclusion that the western branch of fault F₅ is a Holocene active fault, and the eastern branch is a Pleistocene active fault. Our general view is that fault F₅ is a Holocene active fault.

Anqiu-Juxian Fault is an important fault in the Tanlu fault zone, with the highest seismic risk, the most recent activity date, and the most obvious surface traces. Due to lack of credible geological evidences, there is big controversy on the Holocene activity in the Jiangsu segment of this fault. Research on the characteristics of late Quaternary activity in the Jiangsu segment of Anqiu-Juxian Fault, particularly its latest activity time, is of great significance to assessment of its earthquake ability and seismic risk. Based on field investigations on the Jiangsu segment of Anqiu-Juxian Fault, and combining with the results of fault activities identification on this fault in Suqian City, we discussed the characteristics of its activities in late Quaternary. Multiple geological sections we found in this study and the results of fault activities identification in Suqian City all indicate that there was an ancient seismic event occurring in middle period of Holocene in the segment from southern Maling Mountain to Suqian City; but the trench at Houchen village did not show any evidence of Holocene activity on the Chonggangshan segment of this fault. Based on method of shallow seismic exploration, we carried out a systematic exploration of this fault to get its accurate position and activity characteristics. The results show that Anqiu-Juxian Fault in Suqian City is mainly characterized by dextral strike-slip, associated with both thrusting and extensional movement in different positions. A series of low hills were formed along the fault in the north of Suqian City, and a small graben basin was formed in the south of Suqian City, both are controlled by the dextral strike-slip movement of this fault. The Jiangsu segment of Anqiu-Juxian Fault in general is characterized by dextral strike-slip with thrusting movement. But some parts of it are characterized by dextral strike-slip with extensional movement. The Jiangsu segment of Anqiu-Juxian Fault experienced a number of activities since the late Quaternary, with an obvious activity in Holocene. The seismic activities of Jiangsu segment of Anqiu-Juxian Fault have the characteristic of high intensity and low frequency. Its activities decrease gradually from north to south as a whole.

Active fault is one of potential geohazards in cities. Locating and dating buried active faults in urban areas have been a difficult issue in active fault exploration. In this paper, we take the detection of the buried active fault performed at Hehuan Road in the north of Suqian city as an example. We preliminarily mapped the fault through field investigation and shallow seismic reflection survey technique. Furthermore, based on the principle of doubling section method, we conducted multiple drilling to constrain the upper faulted point which is located in a range of 5m in horizon and 4.4~6.1m in depth. Finally, we determined the exact location and latest activity of the fault by trenching. Obviously, good results have been acquired on the accurate location and activity of the Suqian segment of Anqiu-Juxian Fault using multi-level and multi-means detection method. Besides, we observed from the detection at the Hehuan Road site that at least four paleoseismic events occurred during the past 80000 yrs, and the result indicates that the latest faulting event on the fault is younger than(5.9±0.3)ka BP and the buried active fault at the Hehuan Road is a Holocene active fault. The result of buried active fault detection at the Hehuan Road site provides quantitative parameters for evaluation of seismic hazards and planning the width of safety distance in Suqian City.

Running diagonally across the urban area of Xuzhou, the Feihuanghe(the abandoned Yellow River)Fault starts from Jiahezhai in the northwest, extending southeastwards through Sushantou, Xuzhou City and Liangtang along the abandoned Yellow River till the north of Wangji Town of Suining County, striking NWW, dipping SW, with a total length of about 70 kilometers. It is a buried fault, crosscutting Xuzhou-arc structure. There are significant topographic features indicating the existence of the fault on the earth's surface, which are clearly displayed in remote sensing images. There have been no devastating earthquakes occurring along the fault since the recorded history.
Feihuanghe Fault is one of the target faults of the project "Urban active fault exploration and seismic risk assessment in Xuzhou City". Few researches have been done on this fault in the past. The previous analysis assumes that the fault is a sinistral transtensional fault with extensional faulting in the Xuzhou-Suzhou arcuate structure at first and transtensional faulting of the Neocathaysian system later.
Based on field geological survey, shallow seismic exploration and composite drilling section method, Quaternary activities of Feihuanghe Fault are analyzed. Shallow seismic exploration results show that the Feihuanghe Fault is composed of a NE-trending south branch and a SW-trending north branch, forming a graben structure with the width of 1～2km. All breakpoints of the Feihuanghe Fault on the seismic exploration profiles show that only the bedrock surface was dislocated, not the interior strata of the Quaternary. The composite drilling profiling results show that Feihuanghe Fault has dislocated the strata of Mid Pleistocene, but not the top surface of Mid Pleistocene. Furthermore, we discovered a secondary fault of Feihuanghe Fault exposed at Fengshan Hill, and its latest activity date is the mid period of Mid-Pleistocene inferred from the cementation degree of gouge, dating results and geomorphic features. Combining the above results, we conclude that Feihuanghe Fault is of sinistral strike-slip in the early stage, and extensional faulting since the Quaternary, and the latest activity date is the middle period of Mid Pleistocene. Controlled by the tectonic setting, the activities of the NW-trending faults in Xuzhou area are significantly weaker than that of the NW-trending fault in adjacent southwest Shandong.