Running across the Zhenjiang and Nanjing area, the Mufushan-Jiaoshan Fault is an important near EW-trending fault in Nanjing and Zhenjiang area. It extends from Mufu Mountain through Yanziji, Qixia Mountain, and Longtan to Jiao Mountain of Zhenjiang, with a total length of about 75km. The overall trend of the Mufushan-Jiaoshan Fault is nearly east-west, dipping to the north, the southern side of the fault is Ningzhen Mountain, the north side is the hollow land along the river and the Yangzhou low hilly plain. The fault is divided into the western and eastern sections by the NW-trending fault near Xiashu Town in Jurong, namely the Mufushan-Qixiashan section and the Zhenjiang section.
Due to the long-term activity of the Mufushan-Jiaoshan Fault, the northern part of the Mufu Mountain, Qixia Mountain and other complex anticlines suffered large-scale fault depression, forming the Yizheng Sag in the north and the Ningzhen Uplift in the south of the Yangtze River. There is a significant differential up-and-down movement of the fault block along the fault. In the Yizheng Sag, there are huge deposits of the Upper Cretaceous, as well as the thicker Paleogene and Neogene, indicating that the Mufushan-Jiaoshan Fault is a long-term active normal fault. On the Bouguer gravity anomaly map and aeromagnetic anomaly map, the expressions of the Mufushan-Jiaoshan Fault are very obvious, indicating that the fault has a large cutting depth and is a large-scale fault.
There have been many destructive earthquakes in the Nanjing-Zhenjiang area, most of which occurred at the intersection of NW-trending faults and near-EW-trending Mufushan-Jiaoshan Fault. In particular, the Yangzhou M6 earthquake in 1624 had a great impact, and the Mufushan-Jiaoshan Fault is possibly the seismogenic structure of this earthquake. With the planning and construction of a series of Yangtze River crossing passages across the fault in Nanjing and Zhenjiang, whether the Mufushan-Jiaoshan Fault is an active fault and whether it has a greater earthquake risk also becomes the focus of attention in this area.
It is of great significance to study the nature, characteristics and the latest active times of the Mufushan-Jiaoshan Fault for the prevention and reduction of earthquake disaster in Zhenjiang city and Nanjing city. Previous work mainly focused on the Nanjing section, and judged that its latest activity age is late Middle Pleistocene; there has not been a systematic study on the fault in the Zhenjiang section, and its latest activity age is still unclear. Based on the project of “Urban active fault exploration and seismic risk assessment in Zhenjiang City”, we carried out a series of shallow seismic explorations along the Mufushan-Jiaoshan Fault in the Zhenjiang section, and on this basis, representative points were selected to carry out drilling joint profiling to study the Quaternary activity characteristics of the Mufushan-Jiaoshan Fault. The results are of great significance for urban earthquake disaster reduction, urban planning and land use.
The results of shallow seismic exploration show that the Zhengjiang section of the Mufushan-Jiaoshan Fault is dominated by normal faulting, and the trend is NEE, dipping to the north, with a dip angle of about 50°~60° and a displacement of 3~7m on the bedrock surface. All breakpoints of Mufushan-Jiaoshan Fault show that only the bedrock surface was dislocated rather than the interior stratum of Quaternary.
On the Qiaotou village site, there is no sign of dislocation in the stratum above the Middle Pleistocene, the lower part of Middle Pleistocene Xiashu formation has been dislocated, the displacement of the bottom boundary of the Middle Pleistocene on both sides of the fault is 3.2m. According to the characteristics of dislocated stratum, the latest active age of Mufushan-Jiaoshan Fault is late Middle Pleistocene. There is no evidence of activity since late Pleistocene. The fault activity is dominated by normal faulting on the Jinshan site, and there is no evidence of faulting in the Holocene. Based on the comprehensive analysis, the latest active age of the Zhenjiang section of the Mufushan-Jiaoshan Fault is the late Middle Pleistocene, and there is no evidence of activity since the late Pleistocene. According to the dating results, the latest activity time is after(222±22)ka and before the late Pleistocene.
Affected by the erosion of the Yangtze River, the Quaternary in the study area is dominated by the Holocene, the Lower Pleistocene is absent, and the Middle Pleistocene is absent or thin. Therefore, the stratum displacement identified by drilling is mainly developed in the bedrock and the bottom of the Quaternary, resulting in the uncertainty of identifying the latest displacement of the fault, and it is difficult to identify the precise magnitude of the displacement. This is the shortcoming of this work.
Mufushan-Jiaoshan Fault is a major fault with strong seismic risk in the Nanjing-Zhenjiang area, especially at the intersection between the fault and the NW-trending fault, which has the seismogenic environment of destructive earthquake. It is necessary to attach great importance to the prevention of earthquake damage in the relevant area.

Running across the east of Zhenjiang city, the Wufengshan-Xilaiqiao Fault and Dantu-Jianshan Fault are two important NW-trending faults in Zhenjiang area. They controlled the Cretaceous stratigraphic deposition and Mesozoic volcanic activities, and also have obvious control effects on modern geomorphology and Quaternary stratigraphic distribution.
There have been many destructive earthquakes in Zhenjiang area, most of which occurred at the intersection of NW-trending faults and near EW faults. It is of great significance to study the nature, characteristics and the latest active age of the NW-trending faults in Zhenjiang area for the prevention and reduction of earthquake disaster in Zhenjiang City, but the past targeted research work and the knowledge of activity of the faults are very limited. Based on the project of “Urban active fault exploration and seismic risk assessment in Zhenjiang City”, a series of shallow seismic exploration work has been carried out on the two major NW-trending faults in Zhenjiang area, and representative points were selected to carry out drilling joint profiling to study the Quaternary activity characteristics of these two faults. The results are of great significance for urban earthquake disaster reduction, urban planning and land use.
The results of shallow seismic exploration show that the Wufengshan-Xilaiqiao Fault is dominated by normal faulting, dipping to the northeast, with a dip angle of about 60° and a displacement of 5~9m on the bedrock surface. The Dantu-Jianshan Fault is dominated by normal faulting, dipping to the southwest, with a dip angle of about 50°~55° and a displacement of 2~7m on the bedrock surface. All breakpoints of Wufengshan-Xilaiqiao Fault and Dantu-Jianshan Fault reveal that only the bedrock surface was dislocated, not the interior stratum of Quaternary.
On the Dalu site, there is no sign of dislocation in the stratum above the Middle Pleistocene, and the bottom boundary of the Middle Pleistocene has been dislocated, with a displacement of 2m. The dislocation of the bottom boundary of the lower Pleistocene is 3.2m on both sides of the fault, and the maximum displacement of the bedrock surface is 9.1m. The characteristics of the fault surface developed in the drill cores indicate that the latest activity of the fault is of sinistral normal faulting. According to the characteristics of dislocated stratum, the latest active age of Wufengshan-Xilaiqiao Fault is early Middle Pleistocene. On the Fangxian site, there is no sign of fault in the stratum above the Middle Pleistocene, and the bottom of the Middle Pleistocene may be affected by the fault. The displacement of the bottom boundary of Baishan Formation on both sides of the fault is 2m, and the maximum displacement of the bedrock surface is 6.7m. Due to the insufficient evidence of dislocation of Baishan Formation, the latest active age of Dantu-Jianshan Fault is estimated to be between early Pleistocene and early Middle Pleistocene.
The NW-trending Su-Xi-Chang Fault is an important regional fault in the Yangtze River Delta region. Its latest active age is the early Middle Pleistocene, and the displacement in the Quaternary is about 3m. The Wufengshan-Xilaiqiao Fault and the Dantu-Jianshan Fault can be regarded as spatial extension of the Su-Xi-Chang Fault to the northwest, and their activities are also consistent. This study shows that the two NW-trending faults in the Zhenjiang area have significant activity since the Quaternary, and are the main faults with relatively high earthquake risk in this area. Therefore, the intersection of these two faults with EW-trending faults and NE-trending faults should be the focus of attention for earthquake damage prevention in the Zhenjiang area.
The bedrock depth in the Zhenjiang area is relatively shallow, and the stratification difference within the cover layer is small, resulting in an unsatisfactory effect by the geophysical exploration methods. The Lower Pleistocene of the Quaternary system is basically missing, and the boundaries of the Middle and Upper Pleistocene are difficult to distinguish. Developed mainly in the bedrock and the bottom of the Quaternary, the stratum displacement is difficult to judge whether it was caused by sedimentary difference or fault activity. Therefore, the quantitative study of fault activity in this paper is still insufficient.

The middle-southern segment of the Tan-Lu fault zone and its adjacent area is located in the joint zone of the North China craton and Yangtze craton. It is a natural test ground for studying the problems of intracontinental collision, continental convergence and growth, geodynamics and lithospheric deformation. Although early research involved the central-south section of the Tan-Lu fault zone and its neighboring areas, it is difficult to carry out a detailed discussion on the S-wave velocity and azimuthal anisotropy in the middle and south section of the Tan-Lu fault zone and its adjacent areas, due to different research purposes and objects, the limitation in selecting research scope or the lack of resolution.
To obtain more detailed crust-mantle velocity structure and azimuthal anisotropy distribution characteristics in the study area, this paper uses waveform data recorded by 261 fixed wideband seismic stations in the middle-southern segment of the Tan-Lu fault zone and its adjacent zone for two consecutive years. The phase velocity dispersion curve of Rayleigh surface wave with 5~50s period was extracted by time-frequency analysis. Then, the study area was divided into 0.25°×0.25°grids, and the two-dimensional Rayleigh phase velocity and azimuthal anisotropy distribution image in the area was retrieved using the Tarantola method.
The phase velocity and azimuthal anisotropy distribution images of 6 representative periods were analyzed. These images reveal the lateral heterogeneity of the crust-mantle velocity structure and spatial differences in azimuthal anisotropy in the middle-southern segment of the Tan-Lu Fault and its adjacent areas. The results show that the distribution characteristics of phase velocity have a good correspondence with geological tectonic units. In the shallow part of the earth's crust, the basins covered by thick unconsolidated sedimentary layers and the bedrock exposed orogenic belts show low and high velocity anomalies, respectively. With the increase of the period(15~20s), the influence of the shallow sedimentary layer is weakened, and the high-speed anomaly appears in some plain areas such as the Hehuai Basin and Subei Basin. The distribution of phase velocity in the lower crust and upper mantle(25~30s)is affected by the thickness of the crust, which is inversely related to the burial depth of Moho surface. For example, the Dabie orogenic belt with a thickness of 40km changes from a short period high-speed to a low-speed distribution.
Due to the differences in the tectonic environment of each geological structural unit in the study area, the azimuthal anisotropy of Rayleigh waves has obvious spatial differences. In general, the strength of anisotropy increases with increasing period(depth), and the direction of fast wave is more regular and followable. Based on the consistent distribution of low velocity and azimuthal anisotropy from the shallow crust to the lithospheric mantle in the Subei Basin, we believe that there may be a strong crust-mantle coupling phenomenon. The results obtained by different seismic anisotropy observation methods are different manifestations of anisotropy. However, due to the one-sided and low-resolution problems of single observation method, it is necessary to carry out joint inversion or comprehensive multiple observation methods.

Site effect, which is related to the amplification of seismic waves, is mostly affected by the thickness and softness of sediment layers. The study of site effect in cities is becoming more and more important to the assessment of ground motions, seismic hazard and engineering seismology. However, in highly populated urban cities, traditional seismic surveys cannot be applied extensively due to their destructive consequences and high cost. The ambient noise, including microseisms and microtremor, could be acquired anywhere and anytime, and thus can serve as an effective source for engineering seismology. In order to get the site effect and distribution of sedimentary layers of Guangzhou area, one hundred QS-05A seismographs with frequency bandwidth of 5s-250Hz were deployed in early 2018 for 35 days. The inter-station spacing of these seismometers is approximately 2~5km. Using continuous ambient noise signals, we obtained the resonance frequency and amplification value beneath each station by horizontal-to-vertical spectral ratio(HVSR)method. Then sedimentary layer thicknesses as well as K-values, which are related to the site vulnerability to ground shaking, were calculated. Our results suggest that the resonance frequencies in Guangzhou area are between 1~6.5Hz. The resonance frequencies increase gradually from 1Hz on the north-east side to 6.5Hz on the south-west side of the study area. The sediment thicknesses change from several meters to about 40m, with the maximum thickness at around the estuary of the Pearl River. This distribution is consistent with the topography. The amplifications are mainly between 2~6. The largest amplification is around the Pearl River and the west part of Baiyun District. In general, the K-values are small(<20), less than the dangerous value, suggesting that Guangzhou area is relatively safe in ground shaking. However, there are three small areas beneath Huadu District, Sanshui District and Nanhai District. They all have K-values greater than 20, suggesting those areas are more vulnerable to earthquake destruction, and higher construction standard is needed. The reliability of our results is further supported by its consistency with topography and borehole data in Guangzhou area. Our results provide important information for shallow underground structure in Guangzhou area, and can be referred as guidelines in urban architecture planning and disaster prevention and mitigation.

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.

Anqiu-Juxian Fault is an important fault in the Tanlu fault zone, with the largest seismic risk, the most recent activity date and the most obvious surface traces. It is also the seismogenic fault of the Tancheng M8 1/2 earthquake in 1668. There are many different views about the southern termination location of surface rupture of the Tancheng earthquake and the Holocene activity in Jiangsu segment of this fault. Research on the latest activity time of the Jiangsu segment of Anqiu-Juxian Fault, particularly the termination location of surface rupture of the Tancheng earthquake, is of great significance to the assessment of its earthquake potential and seismic risk.
Based on trench excavation on the Jiangsu segment of Anqiu-Juxian Fault, we discuss the time and characteristics of its latest activity. Multiple geological sections from southern Maling Mountain to Chonggang Mountain indicate that there was an ancient seismic event occurring in Holocene on the Jiangsu segment of Anqiu-Juxian Fault. We suggest the time of the latest seismic event is about(4.853±0.012)~(2.92±0.3)ka BP by dating results. The latest activity is characterized by thrust strike-slip faulting, with the maximum displacement of 1m. Combined with the fault rupture characteristics of each section, it is inferred that only one large-scale paleo-earthquake event occurred on the Jiangsu segment of Anqiu-Juxian Fault since the Holocene.
The upper parts of the fault are covered by horizontal sand layers, not only on the trench in the west of Chonggang mountain but also on the trench in Hehuan Road in Suqian city, which indicates that the main part of the Jiangsu segment of Anqiu-Juxian Fault was probably not the surface rupture zone of the 1668 Tancheng M8 1/2 earthquake.
In short, the Jiangsu segment of Anqiu-Juxian Fault has experienced many paleo-earthquake events since the late Pleistocene, with obvious activity during the Holocene. The seismic activities of the Jiangsu segment of Anqiu-Juxian Fault have the characteristics of large magnitude and low frequency. The Jiangsu segment of Anqiu-Juxian Fault has the deep tectonic and seismic-geological backgrounds of big earthquakes generation and should be highly valued by scientists.

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.

Based on the remote sensing images interpretation,the spatial distribution of the Fei Huanghe(the ancient Yellow River)fault zone in Xuzhou area was studied and the intersection relationships between Fei Huanghe Fault and Shaolou Fault,and Tan-lu Fault were discussed in the paper.Besides,we researched the deep-seated geometric structure of Fei Huanghe Fault by studying the gravity-magnetic data,and discussed the intersection relationships with the west boundary of Tan-lu Fault. The cutting depth of Fei Huanghe Fault reflected by second order-wavelet transform detail of the Bouguer gravity anomalies is up to 7～8km.The depth reflected by the third order-wavelet and fourth order-wavelet transform detail of the Bouguer gravity anomalies is up to 9～11km and 15～18km,respectively.The results show that the Fei Huanghe Fault extends to Jiuding in southeast direction.The cutting depth is up to 8～9km.The NW-trending Fei Huanghe Fault cut the NE-trending Shaolou Fault,resulting in the change of the tectonic line of the latter from striking N 60°E to N 45°E.Moreover,the Fei Huanghe Fault didn't cut the Tanlu Fault.It is a pre-Quaternary Fault with weak activity.