Research Article Kinematic Characteristics of the Jiangsu Segment of the Anqiu– Juxian Fault in the Tanlu Fault Zone, Eastern China

GeoScienceWorld Lithosphere Volume 2021, Article ID 6691692, 20 pages https://doi.org/10.2113/2021/6691692

Hao Zhang,1 Zhongtai He ,2,3,4,5 Hangang Xu,1 Limei Li,1 Jinyan Wang,1 Xin Jiang,1 Qiguang Zhao,1 and Hao Yang1

1Earthquake Administration of Jiangsu Province, Nanjing 210014, China 2National Institute of Natural Hazards, Ministry of Emergency Management of China, Beijing 100085, China 3Southern Yunan Observatory for Cross-Block Dynamic Process, Yuxi 652799, China 4Key Laboratory of Crustal Dynamics, China Earthquake Administration, Beijing 100085, China 5Key Laboratory of Earthquake Dynamics of Hebei Province, Institute of Disaster Prevention, Hebei 065201, China

Correspondence should be addressed to Zhongtai He; [email protected]

Received 26 December 2020; Accepted 2 June 2021; Published 23 September 2021

Academic Editor: zhikun ren

The Tancheng–Lujiang (Tanlu) fault zone is the most active fault zone in eastern China. In this zone, the Anqiu–Juxian fault represents the most recently active fault and has the clearest surface traces and the highest seismic risk. This study comprehensively analyzes the kinematic characteristics of the Jiangsu segment of the Anqiu–Juxian fault using field geological surveys, trenches, shallow seismic reflection surveys, combined borehole section exploration, and middepth seismic reflection surveys. The results show that the Jiangsu segment of the Anqiu–Juxian fault features a single branch in the bedrock outcrop area, with reverse strike-slip motion near North Maling Mountain and Chonggang Mountain and normal strike-slip motion near South Maling Mountain. The sedimentary zone features two normal strike-slip faults (east and western branches), which represent the synsedimentary boundaries of a half-graben rift basin. The kinematic process is represented by rotational movement along the strike-slip fault with a curved path. The resulting tensile and compressive stresses are accommodated by dip-slip movement at both ends of the strike-slip fault. The activity of the Jiangsu segment of the Anqiu-Juxian fault can be divided into two periods. The first period of activity occurred before the later part of the Late Pleistocene, when movement along this curved segment occurred, forming the western branch of the Xinyi segment and the eastern branch of the Suqian segment. The second period of activity started in the later part of the Late Pleistocene and continues today. It is characterized by activity on the western branch of the Xinyi segment and the western branch of the Suqian segment of the Jiangsu segment, while the eastern branch of the Xinyi segment and the eastern branch of the Suqian segment became inactive and can be considered Late Pleistocene faults. The maximum vertical slip rate of the Jiangsu segment of the Anqiu–Juxian fault since the Pleistocene has been 0.28 mm/a. The Jiangsu segment of the Anqiu–Juxian fault formed via dextral strike-slip faulting, mainly due to the southward movement of the region to the east of the fault.

1. Introduction several large earthquakes of magnitude 7 or higher have occurred since records have been kept. The Anqiu–Juxian The kinematic characteristics of a fault zone are important fault was the seismogenic fault of the M 8.5 Tancheng earth- parameters for studying the activity and behavior of the fault quake in 1668 [1–5], and the kinematic characteristics of this zone and evaluating the earthquake risk. The Tancheng– fault have long been a focus of attention in the geosciences. Lujiang (Tanlu) fault zone is an important active fault zone Regarding the kinematic characteristics of the Anqiu–Juxian and boundary tectonic zone in eastern China, also a world- fault since the Late Pleistocene, some scholars believe that famous intraplate strike slip fault within a plate, where they have involved a combination of thrusting and dextral

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strike-slip faulting [6–9], but others believe that they have middepth SRS, the kinematic characteristics of the Jiangsu involved mainly dextral strike-slip faulting with minor segment of the Anqiu–Juxian fault are comprehensively ana- thrusting [3, 10] or only dextral strike-slip faulting [11]. lyzed, and the kinematic pattern of the fault is discussed Due to the destruction of the tectonic landscape by based on the changes in the activity of each secondary fault. human activities, there are few studies on the transcurrent The kinematic model might have implications for the study activity rate of this fault. Jiang et al. [12] used aerial photo- of other intraplate strike-slip faults in the world. The activity graphs from 1960 and measured the characteristic meter- characteristics of the Tanlu fault zone are closely related to scale horizontal displacement of a gully since the start of the westward subduction of the Pacific plate and the Philip- the Holocene and inferred a dextral strike-slip rate since the pine plate, and the kinematic characteristics of the Jiangsu start of the Holocene of 2.2-2.6 mm/a. Li et al. [13] calculated segment of the Anqiu-Juxian fault can reflect the coupling a modern strike-slip rate of 0.9-1.2 mm/a using GPS mea- relationship between the Tanlu fault zone and the subduction surement data. of the Pacific plate since the late Quaternary. Investigations of numerous strike-slip faults have found that large-scale strike-slip faults do not extend along a 2. Geological Background straight line. Generally, they have complex structures, often composed of multiple discontinuous secondary faults The Tanlu fault zone is a large-scale, north–northeast- arranged pinnately or en echelon, with discontinuous step- striking active fault zone in eastern China that extends overs, extensional zones, or uplift zones between them [14– from Heilongjiang in the north to the Yangtze River in 20]. Previous researchers have proposed different models of the south, running through the eastern part of mainland fault slippage by characterizing the kinematics of the various China over a distance of 2400 km [29, 30]. It is also a major secondary strike-slip faults and their connections. For exam- zone of strong seismic activity in eastern China [31–33]. ple, Schwartz and Coppersmith [21] proposed three types of According to its geometric structure and activity, the Tanlu slip models for strike-slip faults, namely, the characteristic fault zone can be divided into four segments from north to seismic model, the uniform slip model, and the variable slip south (Figure 1(a)), namely, the Hegang–Tieling segment model, after studying the San Andreas fault in the United (I), Xialiaohe–Laizhouwan segment (II), Weifang–Jiashan States. Deng [22] proposed a rotational movement model segment (III), and Jiashan–Guangji segment (IV) [26]. Among for strike-slip faults after field observations of the seismic sur- them, the Weifang–Jiashan segment is the most active part of face rupture zone of the Fuyun fault. Gao et al. [23] con- the Tanlu fault zone [4, 5, 34]. The Weifang–Jiashan segment ducted a finite element numerical simulation of rotational is composed of five parallel faults (Figure 1(b)). From east to movement in the Fuyun fault zone. According to their simu- west, they are the Changyi–Dadian fault (hereinafter referred – – lation, the rotational movement causes vertical movement on to as F1), Anqiu Juxian fault (F5), Baifenzi Fulaishan fault – – the two sides of the fault, resulting in a four-quadrant distri- (F2), Yishui Tangtou fault (F3), and Tangwu Gegou fault bution of uplift and subsidence; the tensile stress area sub- (F4). Among them, faults F1,F2,F3, and F4 constitute a struc- sides, forming a basin, and the compressive stress area tural pattern comprising a horst with two grabens, one on uplifts. Wang and Geng [24] further summarized the charac- each side. teristics of rotational motion and characteristic earthquakes Fault F5 is a recently generated fault between faults F1 and and concluded that the rotational motion of strike-slip faults F2 and is the latest fault to have formed in the active era, and is a mechanism that leads to the occurrence of characteristic it has the most obvious surface traces. The maximum hori- earthquakes and that the rotational axis is the location of zontal slip rate of fault F5 reached 2.86 mm/a [35], but no these earthquakes. Chao et al. [25] proposed a model of char- destructive earthquakes have occurred over the past 3000 acteristic earthquakes for the middle section of the Tanlu years on F5, which is very close to the destructive earthquake fault zone by studying the kinematic characteristics and seis- recurrence period. Fault F5 is classified as having the highest – mic activity of the Juxian Tancheng segment. seismic risk [3, 4, 25]. Fault F5 is divided from north to south The kinematic features of the Anqiu–Juxian fault have into the Anqiu segment, Juxian–Tancheng segment, and been revealed by many previous studies on uplifted regions, Jiangsu segment (Figure 1(b), [4, 5, 26]). The total length of such as Maling Mountain and Chonggang Mountain, the Jiangsu segment of fault F5 is 170 km. The overall strike through natural outcrops and trenches [3, 4, 25–28]. How- is 5-15°. This fault is mostly hidden and is only exposed at ever, since the fault is mostly hidden, few studies have been the surface in bedrock outcrops near Maling Mountain, conducted on the kinematic features of the fault in the hid- Zhangshan Mountain, and Chonggang Mountain, where it den region. Previous models of strike-slip faults focus on manifests as the overthrusting of the Wangshi Formation’s the tectonic characteristics of stepovers between the second- purplish-red sandy shale (K2W) onto Late Pleistocene loess. ary faults. In these models, the stepovers were either consid- The crushed zone ranges in width from a few meters to more ered normal faults due to tensile stress or thrust faults due to than 50 m and contains colorful fault gouge [27]. compression, and the changes in the sense of motion (normal The study area is located on the southern edge of the or reverse) of the secondary faults were ignored. In this Yishu hilly and plain region. The topography from northeast paper, by integrating multiple research methods, such as field to southwest shows a high–low–high–low pattern. The geological surveys in the area of outcropping bedrock, tren- sedimentary strata can be divided from top to bottom into ching, shallow seismic reflection surveys (SRSs) in subsi- beds of grayish-yellow silty fine sand and grayish-black dence areas, composite drilling in certain sections, and a clay deposited in the Holocene (Qh); Upper Pleistocene

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118°E 119°E 118°10′E 118°20′E

(a) 300 km I (b) (c) North Maling Mongolia-Khingan Mountain Orogenic Belt 160 Weifang Hezhuang II Anqiu Bohai Bay X5-1 III Tanlu fault zone Anqiu earthquake 40 120 Xinyi X5-2 North China Block Dabie Orog Fig.1b X5-3 -enic Belt Yellow S ea Shibuzi Tangdian 34°30 ′ N IV 80 South China Block

36°N South Maling

Mountain40 Anqiu segment MLTC

X5-4 Juxian F4 Xinyi river Lake F S5-5 3 F2 Zhang 80 Mountain 120 120 F5 F1 S5-6 40 34°N Linyi Banquan Suqian 80 120 F3 160 200 35°N

Tancheng 280 F1 Juxian-tancheng segment F S5-7 4 F2 Sankeshu 200 Tancheng earthquake 160 200 80

120 40S5-8 Xinyi Fig.1c Tangdian

160 F1 F2 F5

160 120 33°30 ′ N

Geological section map of 120 the seismic reﬂection line 120 160

34°N Suqian 40 40 F2 F 1 200 Chonggang 80 Mountain F Jiangsu segment 4 Sihong F3 160 F 30 km 10 km 5 Sihong 80 160 40

Natural outcrop Earthquake (≥M 7)

Trench Qh 3 Borehole Qp

Seismic reﬂection proﬁles K2w

Fault Ar-Pt1 Figure 1: Tectonic distribution of the Jiangsu segment of fault F5. (a) Tectonic map of the Tanlu fault zone. (b) Fault distribution map of the Weifang–Jiashan segment of the Tanlu fault zone. (c) Tectonic map of the Jiangsu segment of the Anqiu–Juxian fault. I: Hegang–Tieling – – – – segment; II: Xialiaohe Laizhouwan segment; III: Weifang Jiashan segment; IV: Jiashan Guangji segment. F1: Changyi Dadian fault; F2: – – – – 3 Baifenzi Fulaishan fault; F3: Yishui Tangtou fault; F4: Tangwu Gegou fault; F5: Anqiu Juxian fault. Qh: Holocene series; Qp : Upper – Pleistocene; K2w: Upper Cretaceous Wang Formation; Ar-Pt1: Archaean Group Lower Proterozoic. The fault distributions are from the Active Fault Detection and Seismic Risk Assessment Projects of Xinyi City and Suqian City.

brownish-yellow clay with densely distributed calcareous 3. Materials and Methods concretions (Q3); Middle Pleistocene grayish-yellow clay with grayish-green reticulated silty clay (Q2); and Lower Pleisto- According to the geological conditions, such as the topogra- cene grayish-yellow medium-coarse sand and medium-ﬁne phy, geomorphology, and thickness of the Quaternary strata, ﬁ sand (Q1). the methods of eld geological survey and trenching were

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adopted in outcropping areas of the fault, while SRSs, com- groups, fold of 15, sampling interval of 0.5 ms, record length bined borehole section exploration, and a middepth SRS were of 2 s, and minimum offset of 9-36 m. adopted in areas where the fault is buried. Different dating methods were performed on samples from the trenches and 3.2.2. Data Processing. Various digital processing steps of the boreholes according to the stratigraphic characteristics and obtained reflection data were completed by the dedicated approximate age. reflection data processing software GRISYS [36]. The data analysis and processing mainly included basic processes such 3.1. Middepth Seismic Reflection Survey. The middepth SRS as preprocessing, filtering, statics correction, amplitude com- was performed across the Tanlu fault zone. According to pensation, constant-speed scanning, vespagrams, dynamic the site condition requirements for the SRS, a seismic reflec- correction and superposition, distortion removal, modification line approximately 6 km north of South Maling Moun- tion processing, and profile output. The processing sequence tain was selected (Figure 1(b)). The geometric structure of and content were rationally combined and selected based on the middepth part of fault F5 and its contact relationships the task demand. with other branch faults of the Tanlu fault zone were determined according to the results of the middepth SRS. 3.3. Combined Borehole Section. According to the nature of the activity and geometric characteristics of fault F5, the obvi- 3.1.1. Data Acquisition. A French 428XL 24-bit digital seis- ous mutation point of the reflection lineups on the shallow mograph was used. The data recording format was SEG-Y, SRS profile was selected, and combined borehole section pro- the sampling interval was 2 ms, and the record length was filing on both sides of the breakpoint was performed. The 8.0 s. The detector was a DSU1 single-component digital borehole arrangement followed a doubling exploration pat- oscilloscope. The settings of the observation system were as tern [37, 38], with at least three boreholes in the hanging wall follows: number of receiving groups = 1200, excitation mode and three boreholes in the footwall of the fault, and the spac- = midpoint excitation, group interval = 8 m, offset = 120 m, ing between boreholes was no more than 10 m. fold > 30, and common depth point distance = 4 m. The combined borehole sections were located along seismic reflection lines X5-1 and X5-2 (Figure 1(c)), which are 3.1.2. Data Processing. The raw earthquake data were com- the Zhangcang combined borehole section and the Huang- prehensively processed using multiple sets of processing soft- shulu combined borehole section, respectively. The detection ware. The main processing modules, e.g., refraction static results served mainly to verify the SRS results and reveal the correction, frequency division, speed scanning, residual static nature and active periods of fault F5. The nature of the fault correction, and poststack denoising, were used in the pro- activity was mainly analyzed based on the comparison of cessing, and satisfactory processing results were achieved. the marker bed. The marker bed had to meet the following The overall resolution of the time profile was high, the effec- conditions: (1) the rock strata have special lithology and a tive wave band was wide, the interference wave was well sup- special sedimentary structure or special interlayer interfaces; pressed, and the reflected waves were distinct, indicating that (2) no or very few similar strata or interfaces appear longitu- the processing flow of two-dimensional seismic data was dinally; (3) strata or interfaces are distributed stably in the rational, the parameters were appropriately selected, and lateral direction, and the lithology and thickness change little; the quality of the processing results was reliable. and (4) the characteristics are distinct and easy to identify [39]. The active periods of the fault were restricted based 3.2. Seismic Reflection Survey. The SRS was performed mainly on the location of the breakpoint on the fault, the age of the to detect the nature of fault activity in the hidden area of the fault, and the overburdened strata exposed by the combined fault. Based on the results of the above Tanlu fault zone map- borehole section. According to the vertical displacement of ping and the site condition requirements for the SRS, a seis- the marker bed and the dating results of the marker bed, fl mic re ection line was laid across fault F5. From north to the rate of vertical motion of the fault was calculated. south with the Xinyi River as the boundary, the seismic reflection line was divided into lines X5-1 to X5-4 for the 3.4. Dating Methods. To determine the active periods of the Xinyi segment and S5-5 to S5-8 for the Suqian segment fault, dating samples were taken from the trench near Maling (Figure 1(c)) to reveal the geometric structure and fault prop- Mountain and the two combined borehole sections. Accord- erties of the hidden area of fault F5 in the study area. ing to the regional stratigraphic sedimentary characteristics and the dating range of the dating methods, the following 3.2.1. Data Acquisition. Based on our specifications for the dating methods were selected: carbon-14 (14C) dating, opti- acquisition and receiver instrument, excitation methods, cally stimulated luminescence (OSL) dating, and electron expansion arrangements, field data collection and processing, spin resonance (ESR) dating. A total of 13 samples were and interpretation of field tests, the S-Land seismograph (SI, tested, including three samples by 14C dating, 10 samples USA) was selected. The natural frequency of the detector was by OSL dating, and three samples by ESR dating. 40 Hz. The seismic source was a 3-ton KZ-03 controllable The samples for 14C dating were sent to Beta Analytic seismic source for both longitudinal and transverse waves (USA) for processing. The samples were subjected to pickling (Beiao, China), and the frequency of the seismic source was pretreatment before dating, and then, the pretreated samples 20-160 Hz. The parameters of the shallow SRS observation were analyzed using a National Electrostatics Corporation system were as follows: group interval of 3 m, 96 receiving accelerator mass spectrometer and a Thermo isotope ratio

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mass spectrometer to complete the experimental tests. The the levels of trace elements, such as U, Th, and K, in the sam- conventional radiocarbon age was calculated using the Libby ple, along with the water content in the sample and the sam- half-life (5,568 years) and was corrected by isotope fraction- pling depth, the D value of the sample was calculated. Finally, ation. We then used the high probability density method to from the above data, the age of the sample was calculated. calibrate the dating results to the Gregorian calendar [40].

3.4.1. OSL Dating Method. We analyzed samples via OSL at 4. Results the Key Laboratory of Quaternary Chronology and Hydro- Environmental Evolution, China Geological Survey. The 4.1. Natural Outcrops and Trenching. The Jiangsu segment of middle section of each sample, which was not disturbed, fault F5 passes northward through North Maling Mountain, was used for measurement. We dried and ground 20 g of each South Maling Mountain, and the Xinyi River and extends sample to measure the U, Th, and K contents. We added southward to Chonggang Mountain (Figure 1(c)). Due to hydrogen peroxide and hydrochloric acid to the remaining the heavy outcrop coverage, most of the segment is located sample to remove carbonates and organic matter. We then in the border zone between the uplifted low hills and alluvial isolated the particle groups from 4 to 11 μm by using the plains. hydrostatic settlement method. We treated the particle Several natural outcrops can be seen on the eastern side groups with fluorosilicate to obtain fine-grained quartz for of the sand pit approximately 200 m northeast of Hezhuang further measurement. The dose equivalent (DE) of the sam- on North Maling Mountain (Figures 2(a)–2(d)). The fault is ple was determined by using a Risoe DA-20-C/D OSL auto- dominated by eastward shortening and thrusting. The sand- measuring system. The natural OSL dose was measured via stone of the Wangshi Formation on the eastern side of the the middle-grain single-aliquot regenerative-dose (SAR) fault is thrust onto the clayey silt stratum on the western side. method. The U, Th, and K contents contributing to the envi- Two sets of fault gouges can be seen in the fault zone, with ronmental dose rate (D) were measured with an ELEMENT thicknesses of approximately 30 cm. The directional distribu- inductively coupled plasma mass spectrometer. Finally, the tion of the sand and gravel of the Wang Formation forming a sample ages were determined according to the equation westward arc east of the fault and the fault gouge show that Age ðAÞ = DE/D [41–44]. Using the saturation index method the fault is dominated by thrust activity (Figures 2(a) and to fit the DE value ensured that the dating results of the sam- 2(b)), and the fault at the surface has a dip of approximately ples with unsaturated growth curves were accurate, while the 45°. Before its destruction by human activities, the western dating results of the samples with saturated growth curves Q3 loess atop the Wangshi Formation sandstone was nearly were omitted. The final sample dating results were compared horizontal (Figure 2(d)), and the strata in the natural sand with the regional stratigraphic sedimentary ages to determine pit on the western side of the fault were deposited horizon- the correct dating results. tally. The dip direction of the fault is approximately 96° (Figure 2(c)). No branch faults were developed on the west- 3.4.2. ESR Dating Method. The sampling principle of ESR ern side of the fault. The trench results near North Maling dating samples was strictly followed during sampling, and Mountain [26] therefore indicate that F5 is mainly domi- all samples were prepared and tested in the Metrology and nated by thrust activity. According to the OSL results, this Testing Department of the China Institute of Atomic Energy. segment of fault F5 was active in the Holocene. For sediment, the ESR dating can be expressed as follows: The South Maling Mountain trench exposes a fault zone age ðTÞ = total dose of natural radiation ðTDÞ/annual (Figure 3(a)) that is approximately 1.5 m wide, with three radiation dose ðDÞ. Approximately 100 g of the sample was developed faults, all of which are normal faults. The western taken from the center of the raw sample, weighed on a bal- side of the fault is purplish-red sandy conglomerate, and the ance, and dried in an oven at low temperature (below 45°C) eastern side is grayish-yellow clay. The dip angle is approxi- until it reached a constant weight. From this weight, the mately 56°. The South Maling Mountain uplift area is domi- moisture content of the sample was calculated. The samples nated by eastward extension and normal faulting. According 14 were physically ground, sieved, and chemically processed to to the results of C dating (Table 1), this segment of fault F5 obtain samples with higher quartz contents. The ESR mea- was active in the Holocene. surement was performed with a Bruker EMX ESR spectrom- The segment on the southern bank of the Xinyi River eter (BRUKER, Germany). According to the sample type and (Figures 2(e) and 2(f)) reveals that the bluish-gray clay stra- estimated age, the corresponding ESR dating signal was used. tum rich in large calcareous concretions on the eastern side The Ge center and E’ center signal were used at room tem- of the fault has been thrust onto the blackish-brown clay on perature, and the E’, Al center, or Ti center signal was used the western side. The top of the calcareous concretion-rich at low temperature. Finally, the TD was calculated by fitting stratum on the eastern side is uneven, while the top of the cal- and extrapolating the intensity of the ESR signals of different careous concretion-rich stratum on the western side is rela- irradiated samples. The annual dose determination was per- tively flat. The offset of the calcareous concretion-rich clay formed with a thick-source alpha counter (Daybreak 583, stratum is nearly 1 m, and the offset of the brownish-gray clay UAS) that was used to analyze the U and Th contents in is approximately 30 cm. Zhang et al. [27] determined the age the sample, and we ensured that the count reached a certain of the top of the brownish-gray clay stratum to be 3:8±0:3ka level. The K content in the samples was analyzed with an BP by OSL. Therefore, this segment of fault F5 was active in FR640 flame photometer (Shanghai, China). According to the Holocene.

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1 m 95°∠45° (a) (b)

4 m W 1 m S

K2w sandstone

96°∠0° Q3 loess

96°∠48°

1 m W

3.8±0.3 kaB.P. (Zhang et al. 2015)

92°∠64° (e) (f)

Silty clay Clay Coarse sandy conglomerate Iron concretion-containing clay Mud belt Calcareous concretion clay Calcareous concretion Sampling point of OSL dating Cultivated layer Fault Figure – 2: Characteristics of activity in the outcropping area of fault F5.(a d) Natural outcrop near North Maling Mountain. (e, f) Outcrop on the southern bank of the Xinyi River.

Cao et al. [28] excavated a trench on the western side of The dip angles of the faults are all relatively gentle (approxi- Chonggang Mountain. The Wangshi Formation sandstone mately 50°) and are close to 0° in some local areas, indicating on the eastern side of the fault is thrust over yellowish- that the fault is dominated by thrust activity. Fault F5, brown clay on the western side (Figure 3(b)). Faulting on exposed in the South Maling Mountain trench, is an east- the eastern side of the fault is densely developed, whereas dipping normal fault with a dip angle of approximately 56°, the western side contains no branch faults. The dip angle of and branch faults are developed on the eastern side of the the fault is approximately 50°, and it steepens downward. main section. Therefore, the faults at North Maling Moun- According to the dating results, this segment of fault F5 was tain and Chonggang Mountain in the bedrock outcrop area active in the Holocene. have different activity patterns than those at South Maling The analysis of the above fault activities in the North Mountain. Maling Mountain, Xinyi River, and Chonggang Mountain areas shows that the old strata on the eastern side of fault 4.2. Shallow Seismic Profiles. Through data processing and fl F5 have been thrust over at-lying Pleistocene or Holocene single shot record comparison, a total of 16 faults were strata on the other side. On the eastern side of the fault, revealed by eight shallow seismic profiles. According to the branch faults are densely developed, and the formation is relative positions of the faults, the faults were divided into fi largely deformed. The formation on the western side of the two branches: F5E and F5W. On the shallow seismic pro les, fl fault is relatively at, and no branch faults have developed. fault F5 is mainly manifested in three activity modes: (1)

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ML-14C-1

1 m

87°∠56° (a)

2.5±0.1 kaB.P. (Cao et al. 2018)

1 m 85°∠50° (b)

Sampling point of 14C dating Sampling point of OSL dating Fault Figure 3: Characteristics of activity in the trench area of fault F5. (a) South Maling Mountain trench. (b) Trench near western Chonggang Mountain, Cao et al. [28].

Table 1: Results of 14C dating.

Sample number Laboratory number Depth (m) Sample type Test method Calibrated age (ka BP) HS7 515330 2.3 Dark gray clay AMS 2790 ± 30 ZC-1 487307 1.7 Dark gray clay AMS 3920 ± 30 ML-14C-1 504607 1.2 Carbon chips AMS 6770 ± 30 Determined by Beta Analytic, USA.

the reverse fault (Figure 4(a)). With the F5-1 fault as the characteristics. The wave sets on the eastern and western ff boundary, there are obvious di erences in the in-phase axes sides of the F5W-3 fault are abundantly developed. At this fl between the eastern and western sides. Two sets of re ected fracture point, the in-phase axes of the Pg, P2, and P1 wave wave groups P1 and Pg were developed on the western side sets are obviously displaced and segmented and curved. On fl fl of F5-1. The P1 re ection energy is weak, and the phase axis the eastern side of the F5W-3 fault, only the top surface re ec- is relatively flat in the cover layers. The Tg wave group (bed- tion wave group (Pg) of bedrock is developed, and the top rock surface reflected wave) was more stable, with fewer ups surface reflection wave group (Pg) of bedrock has been and downs. Within the scope of Nos. 750 to 810, the Pg wave uplifted considerably. The fall of the Pg wave group on the group indicates rapid uplifts, the phase axes are obviously eastern and western sides of the fault is approximately 230 faulted, and a diffracted wave pattern is developed at the fault ms. The reflection wave sets between the two faults are abun- site. On the eastern side of the fault breakpoint of F5-1, only a dant, showing obvious depression and bending characteris- Pg wave group is developed, and this wave group is obviously tics, and diffraction waves are developed, which reflects the uplifted and shows a trend of continuing uplift to the east. strong bending deformation of the strata under the influence According to the detection results of the combined borehole of tectonic activities. According to the combined borehole fi fi pro le (Figure 5), the depth of each wave group and the fault pro le across the F5W-3 fault (Figure 6), the depth of each location are reasonable. The shallow seismic profile in wave group and the fault location are relatively reasonable. Figure 4(d) shows the characteristics of reverse fault activity. The shallow seismic profiles in Figures 4(c), 4(f), and 4(h) (2) The fault depression characteristics of the superimposed show similar fault depression characteristics. (3) Both nor- fi pro le (Figure 4(b)) show that the F5 fault is bounded by mal faults and reverse faults are developed (Figure 4(e)). the F5W-3 fault and the F5E-2 fault, showing fault depression The bedrock on the western side of fault FW-9 is shallow,

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W E Distance (m) Distance (m) 400 500 600 700 800 900 1000 1100 700 900 1100 1300 1500 1700

a t (s) Pg P Pg 0.2 1 P1 0.1 P P1 2 0.4 P Pg 2 0.2 P g P 0.6 g 0.3

F5-1 0.8 0.4 1.0 F 5W-3 F 0.5 5E-2 1.2 X 5-1 X 5-2 (a) (b)

300 500 700 River 900 1100 1300 1100 1200 1300 1400

P Pg g P P1 0.1 g P1 P g 0.2 0.1 Pg P g 0.3 0.2 0.4

F 0.5 F F 5-6 5-7 F 5E-4 0.3 5W-5 0.6 0.7 X 5-4 X 5-3

500 600 700 800 900 900 1000 1100 1200 1300 1400 1500

P1 P1 P g P P1 Pg 1 Pn P2 P2 0.1 0.1 P2 P P g P g P g P4 0.2 n

0.2 Pg 0.3

0.3 0.4 F F5E-10 F 5W-11 F 5E-8 5W-9 0.5 0.4 0.6 S 5-5 S 5-6

(e) (f) 1470 1830 2190 2550 2910 3548 3668 3788 3908 4028 4148 4268 P P P P P1 1 1 1 1 P1 P 0.1 2 P P P2 P P P 2 2 2 P2 2 3 P P3 P P 0.2 P 3 3 P 3 0.2 g P3 P 3 n P P n Pg P n 0.3 Pg g P n P g 0.4 0.4 Pg Pg 0.5 F 5E-12 0.6 F5W-14 0.6

F F5W-16 F 5-13 S 5-7 0.7 5E-15 S 5-8 (g) (h)

Figure 4: Two-way travel time seismic profiles along the fault (seismic reflection line X is located in Xinyi city, and seismic reflection line S is located in Suqian city). Line S modified according to Xu et al. [45].

and the cover layer is very thin, while the bedrock surface on Formation sandstone and the Quaternary strata on the east- the eastern side of FW-9 suddenly deepens to 50-120 m, and ern side. The F5E-8 fault faulted the P1,P2, Pg, and P4 wave the fault corresponds to the contact between the Wangshi groups from top to bottom, and the section is roughly parallel

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E 10 m ZC1 ZC3 ZC5ZC6 ZC4 ZC2 760 ()(1) 804 810 816 827 850 30 ZC1 ()(2) Q Qh h Q3 2.52.5 (3) 3.2 Q3 20 p 6.4 p oslosl-1-1 9.5 Q2 ososl-2l-2 (4) Q2 p 117.57.5 p 10 (5)() 1 (6)() 19.919.9 Qp ESRESR-2-2 24.224.2 (7) K 0 EESR-3SR-3 28 m 2288 m 2w EESR-4SR-4 30 m (8)(8) –10 oslosl-1-1 1 Qp oslosl-2-2 40 m

–20 number oslosl-3-3

ple oslosl-4-4 (9)(9) oslosl-5-5

Sam Sample number

Elevation (m) Elevation –30

–40 69.6 (10)(10) –50 N2S2S –60 (11)(11)

92.892.8 –70 (12)(12) K2w2w 9966 m 9955 m

Silty clay FFineine sand-stonesand-stone CalcareousCalcareous concretion clayclay MMedium-coarseedium-coarse sandsand Clay FauFaultlt BrecciaBreccia coarsecoarse sandsand SSamplingampling point ofof 14C ddatingating BrecciaBreccia SamplingSampling poipointnt of OSL datindatingg Iron–manganese concretion cclaylay SamplingSampling point ofof ESRESR FineFine sandsand

Figure 5: Combined borehole section of Zhangcangcun.

to the FW-9 fault, showing upward thrusting of the hanging Holocene active fault and F5E being the Late Pleistocene wall (eastern side). The apparent fault displacement is active fault. approximately 3-10 m, the fault plane is inclined to the east, According to the seismic profile (Figure 4), seismic and the apparent dip angle is steep, indicating a reverse fault. reflection line X5-1 on the south side of North Maling The properties of each fault can be seen in Table 2, in which Mountain shows thrusting and extrusion, extending south- the age of activity is determined according to the combined ward to the sedimentary basin, where the normal faulting borehole section. The bedrock top dislocation revealed by and extension have a double-branching-to-triple-branching each fault varies greatly, which generally shows that the bed- transition, shifting back to thrusting and extrusion at seismic rock dislocation distance between the subsidence areas of reflection line X5-4 and the Xinyi River area. To the south in Xinyi city and Suqian city is greatest and gradually decreases the Suqian segment, the activity changes to normal faulting, on both sides. According to the bedrock dislocation of the the double branching shifts to triple branching, and it shifts eastern and western branches of the fault, the bedrock dislo- back to the extrusion and thrusting along a single branch cation distance of F5E in the Xinyi segment is longer, approx- near Chonggang Mountain. The Jiangsu section of fault F5 imately 160-180 m, and the bedrock dislocation distance of is mainly composed of eastern and western faults in the bur- F5W is shorter, approximately 20-30 m. In the Suqian section, ied area, which gradually merge into a single fault in the the bedrock dislocation distance of F5E is large, with a maxi- North Maling Mountain, South Maling Mountain, and mum of approximately 280 m, and the dislocation distance of Chonggang Mountain bedrock outcropping areas, and sec- the western branch is small, approximately 30-50 m. Xu et al. ondary faults are developed in the center of the basin. [45] and Cao et al. [28] conducted a large number of seismic A comparative analysis of the activity characteristics of profiles and combined borehole profiles for the Suqian sec- the eastern and western faults in the Xinyi and Suqian seg- tion, and they concluded that the Suqian section of fault F5 ments shows that the Jiangsu segment of fault F5 can be is mainly composed of two main faults that tilt toward each divided into two branches according to the amount of other and developed nearly vertically, with F5W being the bedrock top displacement. One branch is the west-dipping

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HS1 HS4 HS7 HS6 HS5 HS3 E HS2 820 (1) (3) 873 881 890 903 920 1020 Qh 25 (2)() HS7HS7 2.323 4 (4)() 4.848 1.11 5.9 (5)() 15 111.81.8 ()(6) ① 17 14.714.7 14.9 6.2 19.5 ① 3 (7)(7) 1919.9.9 Q 5 221.11.1 p 23.523.5 (8)(8) ② 28.2 –5 30.6 (9) 24.11 34.8 2 40 (10) ② Qp –15 40.5 ③ 4040.4.4 ((11)11) 4545 46 –25 (12)() (13) 5454.7.7 –35 664.14.1 Elevation (m) (14)(14) 34.5 ③ 66.9 Q1 –45 (15) p 77 (16) (17) –55 779.59.5 (18) 86 m –65 10 m 100 m 100 m –75 100100 m 102 m 100 m

SiltySilty claclayy Cultivated lalayeryer CalcareousCalcareous concretion-rich clayclay Medium-coarseMedium-coarse sandsand Iron-manIron-manganeseganese concretion-rich claclayy FFaultault BrecciaBreccia coarse sandsand Sampling point of 14C dating ClayClay

Figure 6: Combined borehole section of Huangshu Road.

Table 2: Nature of activity at each breakpoint in the Jiangsu segment of fault F5. Name of each seismic reﬂection line Breakpoint number Bedrock apparent displacement Apparent dip Fault nature Activity period X5-1 F5-1 68 E Reverse fault Q1 F5E-2 180 W Normal fault Q2-3 X5-2 F5W-3 30 E Normal fault Q4 F5E-4 160 W Normal fault Q2-3 X5-3 F5W-5 20 E Normal fault Q4 F5-6 3 W Normal fault X5-4 F5-7 50 E Reverse fault Q4 F5E-8 3-10 E Reverse fault Q3 S5-5 F5W-9 35 E Normal fault Q4 F5E-10 50 W Normal fault Q3 S5-6 F5W-11 280 E Normal fault Q4 F5-12 0 W Normal fault S5-7 F5E-13 70 E Normal fault Q3 F5W-14 120 E Normal fault Q4 F5E-15 15-25 E Normal fault Q3 S5-8 F5W-16 18-30 W Normal fault Q4

eastern branch of the Xinyi segment and the east-dipping displacement less than 50 m. In the synsedimentary bound- western branch of the Suqian segment, with bedrock dis- ary of the basins controlled by the eastern and western placement greater than 160 m. The other branch is the east- branches of the fault F5 Jiangsu segment in the subsidence dipping western branch of the Xinyi segment and the west- area, the branch with a larger bedrock displacement controls dipping eastern branch of the Suqian segment, with bedrock the formation of the rift basin. The controlling fault in the rift

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basin has gradually changed from the eastern branch of the 4.3.2. Combined Borehole Section near Huangshu Road. The Xinyi segment to the western branch of the Suqian segment, row of boreholes near Huangshu Road crosses fault F5 and and the transition area is from South Maling Mountain to features a total of seven boreholes and a total length of 638 seismic reflection lines S5-5. The latest activity in the Jiangsu m. The holes were arranged on both sides of the western fl segment of fault F5 (after the Holocene) moved along the breakpoint (stake number 1612) of seismic re ection line western branch, forming a half-graben rift basin. The eastern X5-2, with a minimum borehole spacing of 8 m (Figure 8). branch of the Jiangsu segment of fault F5 was inactive, and According to the regional strata, the Zhangcang com- secondary faults were developed in the rift basin, forming bined borehole section strata comparison, and the sample the three faults in Tangdian and Sankeshuxiang. dating results (Table 1), the strata exposed in this segment are Quaternary strata. The lithologies in the boreholes are 4.3. Results of Combined Borehole Section Exploration shown in Table 6. The depth of the Holocene bottom boundary ranges from 2.3 m to 5.9 m, and the main lithology is 4.3.1. Combined Borehole Section of Zhangcangcun. The row grayish-black and grayish-brown silty clay. The depth of of boreholes in Zhangcangcun crosses fault F5 and is approx- the bottom boundary of the upper Pleistocene is 23.5-40.4 imately 2.5 km from North Maling Mountain, where natural m, and the main lithology is grayish-yellow, bluish-gray, outcrops are observed (Figure 7). The boreholes were and brownish-gray clay. The calcareous concretions are uni- deployed on both sides of the seismic reflection line X5-1 formly distributed in masses, and black iron–manganese breakpoint (stake number 804). concretions are densely distributed. The depth range of the According to regional stratigraphic comparison and sam- bottom boundary of the middle Pleistocene is 28.2-54.7 m, ple dating results (Tables 1, 3, and 4), the combined borehole and the main lithology is grayish-yellow and yellowish-gray section at this site revealed that the strata are mainly Quater- clay. The grayish-green kaolin is distributed in patchy and nary (Q), the Neogene Suqian Formation (N2s), and the lamellar shapes. The bottom of the lower Pleistocene system Upper Cretaceous Wangshi Formation (K2w). The litholo- was not observed, but the main lithology of this stratum is gies in the boreholes are shown in Table 5. The depth of grayish-white and yellow medium-coarse sand, with gravel the Holocene bottom boundary ranges from 2.1 m to 3.2 m, and calcareous concretions. and the main lithology is grayish-black and grayish-brown According to the analysis of the combined borehole sec- silty clay. The depth range of the upper Pleistocene bottom tions (Figure 6), the brownish-red clay layer (6) was selected boundary is 7.6-8.9 m, and the main lithology is grayish-yel- as marker bed ①, the middle Pleistocene clay layer (8) was low, bluish-gray, and brownish-gray clay, in which calcare- selected as marker bed ②, and the lower Pleistocene brown ous concretions are uniformly distributed in masses, and clay bed (10) was selected as marker bed ③. According to black iron–manganese concretions are densely distributed. the comparison of the marker beds, the row of boreholes The depth range of the bottom boundary of the middle Pleis- reveals an east-dipping normal fault. The fault extends tocene is 17.8-19.9 m, and the main lithology is grayish- downward between boreholes HS6 and HS7. The depth of yellow and yellowish-gray clay. Grayish-green kaolin is dis- the upper fault point is approximately 4 m. The thickness dif- tributed in porphyritic and lamellar layers, and black iron– ference between the Holocene gray and black clay beds on manganese concretions are densely distributed. The depth both sides is obvious, and the displacement of the marker range of the bottom boundary of the lower Pleistocene is beds increases downward. The displacement of each marker 24.2-69.6 m, and the main lithology is grayish-white, gray- bed is shown in Table 7. The western branch of fault F5 was ish-black, or yellow medium-coarse sand intercalated with active in the Holocene. gravel. The depth of the bottom boundary of the Neogene Suqian Formation ranges from 91.5 to 92.8 m, with mainly 4.4. Middepth Exploration Results. Through the comparison grayish-white or grayish-green medium-coarse sand interca- of data processing and single shot records, in the stacking lated with brownish-yellow clay and grayish-yellow or time profile (Figure 9), a total of four major groups of fi fl brownish-yellow silty ne sand beds. Data from the four re ected waves were tracked, namely, the TQ wave, TK wave, boreholes in the eastern Suqian Group are missing. TG1 wave, and TG2 wave. Among them, the TQ wave features According to the stratigraphic comparison (Figure 5), the are clear, the reflected wave energy is strong, the continuity is bedrock has an obvious displacement of 69.3 m. The ZC-5 good, the frequency is high, and it is easy to identify and fl borehole crosses the fault, and there are two obvious fault track. The re ected wave group of the TK wave is messy, with planes with dip angles of 80° and 71°. On both sides of the lower frequency and poor continuity. In some areas, there is fault are purplish-red gravelly clay and grayish-yellow grav- weak reflection or no reflection, which is obviously different elly sandy clay. The breccias are mostly purplish-red, appear- from the overlying layer and the underlying layer, so it is only fl ing as east-dipping reverse faults. This row of boreholes marked uniformly. The re ected frequency of the TK wave is exposes two faults, corresponding to the two fault planes relatively low, generally in the range of 35-40 Hz, and the exposed by the boreholes. The two faults form a fault zone, characteristics of the TG1 wave group are similar to the atti- which extends upward between the ZC-5 and ZC-6 bore- tude of the upper strata, but the wave group has strong holes. According to the stratigraphic comparison, the bottom energy and good continuity, and the resolution is obviously ff of the middle Pleistocene and the bottom of the upper Pleis- di erent from that of the overburden strata. The TG2 tocene in boreholes ZC-5 and ZC-6 hardly change in depth. reflected wave group has good continuity, and the attitude ff Fault F5 appears as an early Pleistocene fault at this point. and energy are obviously di erent from those of the upper

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N Borehole number ZC1 ZC3 ZC4ZC5ZC6 ZC2 Borehole stake number 760 804810 816 827 850 Borehole spacing 44 6 6 11 23

Mountain

North Maling Distance (m) 500400 600 700 800 900 1000 1100

Pg 0.2

P1 0.4 F5

Pg 0.6 F5-1

Zhangcangcun X 5-1 0.8 X5-1

Two-way travel time (s) travel Two-way 1.0

1.2 200 m1000

(a) (b)

Fault Natural outcrop Seismic reﬂection line Composite drilling section

Figure 7: Combined borehole section location and borehole distribution map of Zhangcangcun.

Table 3: Results of OSL dating.

Annual Water Sample Borehole Sample Embedment Sample Sample U Th K Equivalent dose, Dy content Age (ka) number number number depth (m) layer type (ppm) (ppm) (%) dose (Gy) (Gy/ka) (%) 18G–165 ZC-1 OSL-1 6.5-6.67 (4) Clay 1.64 7.91 1.67 474:69 ± 20:52 2:88 ± 0:12 18.3 164:8±10:8 18G–166 ZC-1 OSL-2 9.38-9.55 (4) Clay 1.75 8.09 1.58 631:56 ± 16:91 2:79 ± 0:11 21.3 >226.0 18G–167 ZC-6 OSL-1 4.65-4.90 (3) Clay 2.73 9.55 1.43 329:80 ± 10:33 3:14 ± 0:13 19.9 105:0±6:7 18G–168 ZC-6 OSL-2 7.75-7.96 (3) Clay 2.21 8.61 1.58 384:99 ± 15:83 3:03 ± 0:12 18.3 127:1±7:9 18G–169 ZC-6 OSL-3 8.6-8.82 (4) Clay 1.52 6.98 1.69 365:30 ± 19:51 2:71 ± 0:11 21.0 134:8±10:3 18G–170 ZC-6 OSL-4 9.6-9.8 (4) Clay 1.47 7.81 1.52 436:86 ± 15:75 2:62 ± 0:10 20.2 166:6±8:0 18G–171 ZC-6 OSL-5 11.2-11.4 (4) Clay 1.759 9.74 1.75 561:66 ± 32:21 3:11 ± 0:12 26.8 180:9±12:6 Determined by the Key Laboratory of Quaternary Chronology and Hydro-Environmental Evolution, China Geological Survey.

strata. Most areas are easily compared and traced, and the average velocities of different wave groups, as well as the characteristics are obvious at the two ends of the seismic pro- depth of the seismic wave travel time and drilling data, shows fi les. By comparative analysis of regional geological data and that the TQ wave group represents the Cenozoic bottom fl borehole data, the stratigraphic units from shallow to deep interface re ection wave, the TK wave group represents the fl include Quaternary, Neogene, Cretaceous, Sinian, and Lower Cretaceous internal re ection wave, the TG1 wave group rep- Proterozoic. The Cretaceous unit is thick and mainly con- resents the Sinian system interface reflection wave, and the fl tains the sandstone and conglomerate of the Wang Group, TG2 wave group represents the upper interface re ection which has an angular unconformable contact with the upper wave of the Proterozoic East China Sea group of metamor- Neogene and the lower Sinian or Proterozoic Donghai Group phic gneiss. gneiss basement, and the Quaternary unit on the eastern side In the seismic reflection line range, in addition to the of F1 has an angular unconformable contact with the Prote- Cenozoic stratigraphy, which is relatively thin with small rozoic Donghai Group gneiss. Comparative analysis of the changes, the shallow stratigraphy in general has large

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Table 4: Results of electron spin resonance dating.

Borehole number Sample number Sampling depth (m) Lithology Annual dose (Gy·ka-1) Paleo-dose (Gy) ESR age (ka) ZC-1 ESR-2 28.4-28.62 Medium-coarse sand 4.52 3097 ± 650 685:3 ± 143:8 ZC-1 ESR-3 30.43-30.58 Clay 2.47 2034 ± 948 824:5 ± 384:3 ZC-1 ESR-4 32.44-32.59 Clay 2.87 2862 ± 554 995:7 ± 192:7 Determined by China Institute of Atomic Energy Science.

Table 5: Lithologies in borehole ZC-1.

Depth of stratum Stratum Thickness (m) Lithologic description bottom (m) Brownish-yellow and brown clayey silt, horizontal bedding, clay content accounting for (1) 1.6 1.6 approximately 30%, and plant rhizomes on the top. Grayish-black clay, smooth-cut surface, color gradient, soft plastic, with black iron– (2) 2.5 0.9 manganese concretions at the bottom, scattered sporadically. Yellowish-gray, yellowish-brown, and yellowish-green clay, with a rough-cut surface, densely (3) 6.4 3.9 distributed yellow-white calcareous concretions, and primary accumulation. Black iron– manganese concretions are scattered in patches with a diameter of approximately 5 mm. Brownish-yellow, yellowish-brown, and yellowish-green clay, with brownish-red silty clay (4) 17.5 11.1 on the top. Green kaolin is evenly distributed in variegated and lamellar patterns. Brownish-yellow or grayish-white medium-ﬁne sand, with clay silt on the top, following a (5) 20 2.5 normally graded distribution, and rusty yellow iron concretions are scattered sporadically. Dark-gray gravel-bearing medium-coarse sand, which is mainly composed of feldspar quartz. (6) 24 4 Gravel content approximately 5%, maximum size approximately 3×1cm, and poor sorting. Grayish-yellow and yellow coarse sand, coarse sand gravel, with coarse sand mainly at the (7) 30.2 6.2 top and bottom, with high gravel content in the middle, with a maximum gravel size of approximately 6×5cm, poor sorting, and angular shape. Gray, brownish-gray, and yellowish-gray clay, rough cut surface, thin layer of grayish-yellow coarse sand, yellow-white calcium concretions evenly distributed, secondary leaching (8) 41 10.8 deposits, black iron–manganese concretions scattered sporadically, and a diameter of concretions approximately 1 cm. Grayish-yellow and gray coarse sandy conglomerate, in which the top gravel content is low, (9) 69.6 28.6 the bottom gravel content is higher, the distribution is normally graded, the maximum size of the gravel is approximately 5×4cm, the sorting is general, and the shape is angular. Grayish-white and gray medium-coarse sand, with horizontal bedding, intercalated with (10) 80.1 10.5 thin layers of sandy clay, occasionally with gravel, and rusty yellow iron concretions distributed in porphyritic and laminar patterns. (11) 92.8 12.7 Grayish-yellow and grayish-white clay, sandy clay, and developed cross-bedding. Purplish-red sandstone; the top is weathered into a block, and the bottom is completely (12) 96 3.2 columnar.

changes in the lateral direction. Mesozoic strata are influ- According to the morphology and characteristics of the enced by changes in basement undulations, and thickness reflection lineups, such as the breaks, bifurcation mergers, changes are evident, with the greatest thickness deposited in distortions, and lineup occurrence changes, a total of six the graben-like region of the Tanlu fault zone. The coexis- faults are interpreted, five of which are relatively stable in tence of folds and faults in the stratum, with obvious changes scale (F1-F5), while the sixth is a newly discovered fault fl in occurrence, shows a strong in uence of tectonic activity. located between F3 and F4, provisionally named F3w. The tec- Below the Mesozoic boundary is the Sinian system, whose tonic pattern is characterized by one horst with a graben on overall thickness in the Tanlu fault zone is thick in the west each side, with the western graben being wide and gentle and thin in the east, with obvious changes in stratigraphic and the eastern graben being narrow and steep. Fault F5 is occurrence and undeveloped folds, controlled by the deep located inside the eastern graben and features a single- basement and more developed fault structures. The top of branch normal fault with an apparent westward dip and an the Proterozoic boundary, as the basement of the Tanlu fault apparent dip angle of 86°. It extends upward below the bot- zone, controls the sedimentary and tectonic morphology of tom interface of the Cenozoic boundary and cuts downward the entire Tanlu fault zone. through the bottom interface of the Cenozoic boundary (TQ),

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HS1HS4 HS7 HS5HS6 HS2HS3 Borehole number 820 873 881 890 903 920 1020 Borehole stake number 53 17 9 13 17 100 Borehole spacing

Distance (m) 700 900 1100 1300 1500 1700

Pg P1 P1 0.1 P2 P Pg 2 0.2

Pg 0.3

0.4

Two-way travel time (s) F 5W-3 F 0.5 5E-2

X 5-2

Figure 8: Borehole distribution along Huangshu Road.

the Mesozoic boundary, and the top interface of the Protero- blackish-brown clay on the western side. The thick sediment zoic boundary (TG2). areas of Xinyi city, Suqian city, and South Maling Mountain The deep and shallow structures of the fault zone are are dominated by extensional normal fault activity, with two closely related in terms of spatial location, geometric struc- east–west-branching faults controlling the boundary of the ture, and activity properties, presenting causal correlation half-graben rift basin and secondary faults developing in and depth coordination. Comparing the results of the shal- the basin. low SRS and the combined borehole section, it can be seen that fault F5 is a near-vertical fault in the middle and deep 5.1. Vertical Slip Rate of the Jiangsu Segment of Fault F5. In parts, is dominated by strike-slip activity, and extends into the uplifted areas, such as North Maling Mountain, South the shallow surface layer, which is the easiest to fracture Maling Mountain, and Chonggang Mountain, one side of and features a gradually shallowing dip angle. The shallow the fault is composed of bedrock (the Wangshi Formation), surface bedrock in the mountains and the Quaternary soft and the cover strata are thin or even missing, which makes soil layer are the most easily fractured units. Therefore, fault it impossible to compare with the marker bed, and the verti- F5 in bedrock outcrops, such as those in the North and South cal uplift rate cannot be calculated. The row of boreholes of Maling Mountains and Chonggang Mountain, shows a single Huangshu Road in the subsidence area crosses the western branch with many fractures toward the surface. In thick sed- branch of fault F5. The displacement of the bottom boundary iment areas such as Xinyi city and Suqian city, fault F5 is of the Holocene black clay layer is 1.1 m (Table 7). The age of divided into two branches in the upper part. The latest activ- the black clay 14C dating sample obtained from the trench ity is along the western branch of the fault. The upper break- near Huangshu Road is 2970 ± 30 BP. The depth of the bot- point gradually becomes shallower as it extends toward the tom boundary of the black clay layer in the row of boreholes bedrock mountains. is 4.8-5.9 m. Comparative analysis shows that the age of the black clay layer in seismic reﬂection line X5-1 is 3920 ± 30 5. Discussion BP. The bottom age of the black clay layer in the row of boreholes at Huangshu Road is closer to 3920 ± 30 BP (Table 1). The natural outcrops, geologic trenches, seismic proﬁles, The vertical slip rate of the subsidence zone since the start and combined borehole sections show that the Jiangsu seg- of the Holocene is 0.28 mm/a. According to the SRS, the ment of fault F5 is mainly compressional in the areas of Jiangsu segment of fault F5 can be divided into eastern and North Maling Mountain, the Xinyi River, and Chonggang western branches. Since the Late Pleistocene, because both Mountain. Along the fault in the uplifted area of North Mal- the eastern and western branches have been active, it is ing Mountain and Chonggang Mountain, the Wangshi For- impossible to determine whether the two branches faulted mation sandstone on the side toward the mountain has been together in the same earthquake or separately. Therefore, this thrust onto the Late Pleistocene loess on the side toward the paper only gives the accurate vertical slip rate since the start plain, while the Xinyi River shows that the Late Pleistocene of the Holocene. According to the displacement of the top calcareous clay layer has been thrust onto the Holocene of the bedrock, the western branch of X5-2 exhibits the

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Table 6: Lithologies in borehole HS1.

Depth of stratum Stratum Thickness (m) Lithologic description bottom (m) (1) 1.8 1.8 Backfill soil. Gray, grayish-black clay, gradually lighter in color, soft plastic, black iron–manganese (2) 2.3 0.5 concretions sporadic distribution, more dense at the bottom, concretion diameter of approximately 3 mm. Grayish-yellow and yellow silty fine sand, top sandwich grayish-yellow silt clay, horizontal (3) 5 2.7 hierarchy, normally graded distribution, central sandwich gray silt thin layer, approximately 1 cm thick. The upper grayish-yellow clay, sandwich gray clay (thin layer) approximately 1-3 cm thick, yellow-white calcareous concretions that are densely distributed with a block shape and (4) 8.4 3.4 primary accumulation; the lower part is grayish-yellow and yellow medium-fine sand with horizontal lamination. Greenish-gray and yellowish-gray clay, yellow-white calcareous concretions sporadically (5) 11.8 3.4 distributed, grayish-green kaolin uniformly distributed in patchy and lamellar form. Brownish-red and brownish-yellow clay, smooth-cut, horizontally lamellar, with a thick (6) 14.7 2.9 layer of medium-coarse sand in the middle approximately 8 cm thick and a thin layer of gray clay approximately 1 cm thick. Grayish-yellow and yellow medium-coarse sand, horizontally lamellar, with a thin layer of (7) 23.5 8.8 medium-fine sand, occasionally containing gravel. Yellowish-gray and yellowish-green clay, with a thin layer of gray clay between the upper (8) 28.2 4.7 part approximately 1 cm thick and the grayish-green kaolin in the lower part evenly distributed in a lamellar pattern. Grayish-yellow and grayish-white coarse gravel, low top gravel content, normally graded (9) 40 11.8 distribution, gravel maximum size approximately 5×4cm, poor sorting, angular. Brownish-red and brownish-gray clay, gray clay thin layer uniformly distributed, grayish- (10) 40.5 0.5 black organic matter with a spot-like enrichment distribution. Grayish-yellow and yellowish-gray medium-coarse sand, development of oblique (11) 49.1 8.6 lamination, a thick middle layer of brown clay, occasionally containing gravel. Grayish-green clay and gray clay interactive layer, gray clay approximately 1 cm thick, rust- (12) 51 10.9 yellow iron concretions with spot-like uniform distribution. (13) 65.4 14.4 Gray and grayish-yellow gravelly coarse sand, the development of horizontal stratification. Brownish-gray and yellowish-gray clay, smooth cut, hard plastic, yellow-white calcareous (14) 69.3 3.9 concretions densely distributed in the lower part, grayish-green kaolin clay uniformly distributed in patchy and lamellar form. Grayish-white, yellowish-gray medium-coarse sand, normally graded distribution, the lower (15) 75.4 6.1 particle size is coarse, upper part is finer, occasionally contains gravel, the largest size is approximately 3×2cm. The upper part is brownish-yellow and grayish-yellow clay with grayish-black organic (16) 81.6 6.2 plaque; the lower part is yellowish-gray medium-fine sand, occasionally containing gravel, normally graded distribution. Gray silt clay, silt content in the middle is low, thin sandwich gray clay layer, the bottom rust- (17) 84.3 2.7 yellow iron concretions with a thick layer-like distribution. The upper part is grayish-green and grayish-white medium-coarse sand, occasionally containing gravel; the lower part is grayish-yellow and gray gravel-bearing coarse sand, with (18) 100 15.7 gravel accounting for approximately 10%, poor sorting, angular shape, and sporadic distribution of rust-yellow iron concretions.

Table 7: Displacement of the marker bed distortion. largest displacement in the Xinyi segment of fault F5 since the start of the Holocene. The bedrock top displacement Sedimentary Displacement Sedimentary Displacement decreases to the north and south, so the vertical slip rate strata (m) strata (m) represents the largest vertical sedimentation slip rate in the ② Qh 1.1 (Qp2) 24.1 Xinyi segment of fault F5 since the start of the Holocene. ① (Qp3) 6.2 ③ (Qp1) 34.5 Jiang et al. [12] calculated the horizontal slip displacement to be 9 m by using aerial ﬁlm from 1960, and Jiao et al. [35] used an unmanned aerial vehicle (UAV) to

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Distance (km) E 4 8 12 16 20 24 28 32

TQ TQ TK F T 3W G1 T 1 T G2 TK K TG2

TG1 TG2 2 TG1 TG2

TG2 3

Two-way travel time (s) travel Two-way 4

5 F F F F4 3 F2 5 1

Figure 9: Geological section map of the seismic reﬂection line.

measure the horizontal slip displacement at 10.1 m. By using placement is small. The east-dipping western branch of fault the timing of the latest paleo-earthquakes, these authors cal- F5 in the Suqian segment is transformed into an east-dipping culated the maximum horizontal slip rates to be 2.6 mm/a reverse fault at Sihong Chonggang Mountain. The branch and 2.86 mm/a, respectively. Using the latest fault event time faults merge into one branch in the deep part. The Jiangsu of 3920 yr in this paper, horizontal slip rates of 2.3 mm/a and segment of fault F5 in the study area has a triple curved struc- 2.6 mm/a can be calculated. Considering the influence of ture, with two pivot surfaces developed, namely, between X5- human activities, the horizontal slip rate of fault F5 is more 1 and X5-2 and between X5-4 and S5-5. According to the reasonable at 2.3 mm/a. Fault F5 is primarily characterized activity analysis of different segments of the Jiangsu segment by strike-slip movement, and the ratio of horizontal to verti- of fault F5, this segment has experienced two active periods cal slip rates is approximately 9-10. By comparative analysis, since the beginning of the Quaternary. The first period was Li et al. [13] used the horizontal slip rate of 0.9-1.2 mm/a cal- before the late portion of the Late Pleistocene. Fault F5 moved culated from GPS data in North China from 2009 to 2014; we along the curved structure of the eastern branch of the Xinyi can see that the current horizontal slip rate of fault F5 in the segment and the western branch of the Suqian segment. The Jiangsu section has decreased by half, possibly indicating the bedrock has a large displacement, with a maximum of accumulation of strain energy. approximately 180 m, forming the dominant fault of a half- graben rift basin (Figure 10(a)). The second period occurred 5.2. Kinematics of Faulting of the Jiangsu Segment of the F5 after the later part of the Late Pleistocene. The Jiangsu seg- Fault. The Jiangsu segment of fault F5 is dominated by ment of fault F5 has continued to move along the western strike-slip motion, with compression and thrusting in North branch of the Xinyi segment and the western branch of the Maling Mountain, the Xinyi River, and Chonggang Moun- Suqian segment until the present. The bedrock displacement tain and extension and normal faulting in the sedimentary is small (less than 50 m). The eastern branch of the Xinyi seg- basin and South Maling Mountain and Roach Mountain. ment and the eastern branch of the Suqian segment were The kinematic process is represented by the rotational move- inactive and represent Late Pleistocene faults (Figure 10(b)). ment of the strike-slip fault, and the tensile stress and compressive stress produced are accommodated by the slip 5.3. Kinematics of Faulting of the Tanlu Fault Zone since the tendencies at the ends of the fault, corresponding to normal Latest Paleoseismic Event. Chao et al. [25] studied the slip and reverse faults. Te vertical displacement (evidenced by and earthquake characteristics of fault F5. Based on their fi the displacement of the top of the bedrock) is shown to be ndings, fault F5 can be divided into three segments small at the pivot location in the middle and gradually (Figure 1(b)), namely, the Anqiu segment (northern seg- – increases toward the sides. The Jiangsu segment of fault F5 ment), the Juxian Tancheng segment (middle segment), appears as a curved structure in the superficial layer. From and the Jiangsu segment (southern segment). The Anqiu seg- North Maling Mountain in the north, the east-dipping ment consists of two parallel secondary faults, with the cen- reverse fault gradually changes to a west-dipping normal tral segment dominated by extension and normal faulting, fault in Xinyi city, with the largest bedrock displacement. controlling the Shibuzi rift basin and shifting to extrusion The middle segment is transformed from the east-dipping and thrusting to the north and south. The Juxian–Tancheng normal fault at South Maling Mountain to the west-dipping segment consists of five secondary faults, with the central eastern branch of fault F5 in Suqian, and the bedrock dis- segment dominated by extension and normal faulting,

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North Maling North Maling Mountain Mountain

South Maling South Maling Mountain Mountain

Chonggang Chonggang Mountain Mountain

(a) (b) Figure 10: Curved structure of the Jiangsu segment of fault F5. (a) Before the late part of the Late Pleistocene. (b) After the late part of the Late Pleistocene.

controlling the Banquan Basin and shifting to extrusion and Tanlu fault zone as two major movement periods and five thrusting on both sides. The Jiangsu segment is also charac- stages of development, with the Late Cretaceous transform- terized by alternations in the sense of slip, changing from ing from sinistral strike-slip to dextral strike-slip. Some extrusion and thrusting to extension and normal faulting researchers have suggested that the Tanlu fault zone was back to extrusion and thrusting. Based on the comparison right biased in the Early Cretaceous [51]. As the Tanlu fault of the activity characteristics of the Anqiu segment (northern zone has undergone tectonic transitions over multiple segment), Juxian–Tancheng segment (middle segment), and periods, this process has resulted in great variability in the fi Jiangsu segment (southern segment), fault F5 satis es the activity characteristics of the various segments [52]. The lat- characteristics of a curved fault structure. Chao et al. [25, est paleoseismic studies have shown that the kinematics of 26] concluded that the motion of the Anqiu–Juxian fault the Yilan-Yitong Fault Zone (YYFZ) in the late Quaternary represents the characteristic seismic slip based on the nature were dominated by reverse dextral faulting and normal of the motion and the displacement distribution of each strike-slip faulting. Horizontal displacements are the largest segment. Wang and Geng [24] further summarized the char- along the central part of the YYFZ and smallest at both of acteristics of rotational movement and characteristic earth- its ends. The distribution of vertical displacement varies quakes and concluded that the rotational movement of the along the YYFZ, ranging from ~40 cm to ~200 cm along the strike-slip fault is a mechanism that leads to the occurrence entire segment [53]. The Hegang–Tieling segment showed of characteristic earthquakes. Therefore, the kinematic char- local activity in the early Quaternary and has a normal fault – acteristics of fault F5 show rotational movement along a nature. The fault activity of the Xialiaohe Laizhouwan seg- curved structure. ment is strong, manifesting as a strong extensional fault since The Tanlu fault zone plays an important role in the evo- the start of the Quaternary. The development and exposure lution of the lithospheric mantle beneath East Asia, acting as of the Quaternary faulting in the Weifang–Jiashan segment a deep channel for the ascent of melts and fluids, resulting in are the best, and it is characterized by extrusion, thrusting, higher heat flow, higher seismicity, lower P-wave velocity and dextral strike-slip faulting. Additionally, the Jiashan– anomalies, a thinner lithosphere, a higher degree of litho- Guangji segment locally shows early Quaternary normal fault spheric modification, and a greater amount of newly accreted activity [25]. The nature of the activity of the Tanlu fault zone lithosphere near the fault [46]. The Tanlu fault zone origi- from north to south can be described as an extensional nor- nated early in the collisional orogeny of the North China mal faulting–thrusting–extensional normal faulting pattern. and South China plates, followed by translational movement The comparative analysis of the fault F5 kinematic features again during Early Cretaceous tectonic activity associated suggests that during the early Quaternary, the shallow surface with the Pacific plate [47–49]. Zhang and Dong [50] summa- layer of the entire Tanlu fault zone may have been active, rized the process of the Mesozoic kinematic evolution of the forming a curved structure, and the interiors of different

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F5 and branch faults are mostly developed on the eastern side N W E of the main fault. It can be inferred that the Jiangsu segment of fault F5 features southward dextral strike-slip faulting with the region to the east of the fault acting as the active plate (Figure 11).

F5 1 1 6. Conclusions

(1) The natural outcrops near North Maling Mountain, the Xinyi River, and Chonggang Mountain expose fault F5. The old strata on the eastern side of the fault have been thrust over the gently sloping Pleistocene or Holocene strata on the other side, indicating that the fault was highly active in the Late Pleistocene and even in the Holocene, and the latest active period of the fault is shown to be the Holocene. The dip angle of the fault is relatively gentle (approximately Figure 11: Characteristics of curved fault activity in the Tanlu fault 50°) and nearly 0° in some places, which shows that fi zone and relationship between the regional stress eld and plate the main part of the fault is dominated by thrusting movement. (2) According to the seismic profile of the hidden area across the Jiangsu segment of fault F , the main body segments are composed of small curved secondary faults 5 of the Jiangsu segment of fault F5 consists of two (Figure 11). Alternating landscape changes in uplift and sub- branches (eastern and western branches), dominat- sidence areas are formed, and half-graben-type faulted basins ing the synsedimentary boundary of the basin and in the stepovers are developed. Since the middle to late Qua- forming a half-graben rift basin. Secondary faults ternary period, there has been strong activity in the central are developed in the rift basin, forming the three two sections of the Tanlu fault zone, and this activity faults in Tangdian and Sankeshuxiang. The fault con- decreases to the north and south. The Tanlu fault zone has trolling the rift basin gradually changed from the been dominated by activity in one of the curved structures eastern branch of the Xinyi segment to the western (fault F5) since the mid- to late-Quaternary period, while branch of the Suqian segment. Since the start of the the other branch faults (F1-F4) have become inactive. Fault Holocene, the Jiangsu segment of fault F5 has moved F5 has been dominated by the activity of the western branch along the western branch since the Late Pleistocene, while the eastern branch has become inactive. The structural pattern of one horst with (3) The Jiangsu segment of fault F5 is dominated by a graben on either side in the Weifang–Jiashan segment strike-slip motion, with extrusion and thrusting in of the Tanlu fault zone may be due to the formation of a North Maling Mountain, the Xinyi River, and half-graben basin by this curved structure of the Tanlu Chonggang Mountain and extension and normal fault zone, influenced by northwest-dipping faults and faulting in the sedimentary basin, South Maling long-term evolution. Mountain, and Zhang Mountain. The kinematic pro- Since the beginning of the Quaternary, the convergence of cess of this fault is represented by rotational move- the Pacific plate has accelerated, with the Pacific plate and the ment along the strike-slip fault with a curved path, Philippine plate subducting westward and pushing against and the resulting tensile and compressive stresses eastern mainland China. The south–north continent-to- are accommodated by slip at both ends of the continent collision of the Indian plate and the Eurasian plate strike-slip fault. The activity of the Jiangsu segment fi has led to eastward tectonic extrusion in western China, of fault F5 can be divided into two periods. The rst which in turn pushes eastward against eastern China. Based period occurred before the later part of the Late Pleis- on the deep stress environment of the seismic mechanism tocene, when the curved structure of the Jiangsu seg- solution response, Zhu et al. [54] showed that the deep stress ment of fault F5 was active, forming the western environment in the Tancheng–Xinyi segment is dominated branch of the Xinyi segment and the eastern branch by strike-slip and normal faulting, with the main stress ori- of the Suqian segment. The second activity started ented in the northeast direction, and the main stress in the in the later part of the Late Pleistocene, when the Suqian segment is oriented in the nearly east–west direction. western branch of the Xinyi segment and the western Against this background of regional dynamics, fault F5 is branch of the Suqian segment of the Jiangsu segment dominated by dextral strike-slip faulting, with the eastern of fault F5 became active and have continued to be side of the fault moving southward and the western side mov- active up to the present, and the eastern branch of ing relatively northward. We refer to the faster moving plate the Xinyi segment and the eastern branch of the as the active plate of the fault motion. Based on natural out- Suqian segment became inactive and are considered crops and exploratory trenches, our findings reveal that fault Late Pleistocene faults. According to the combined

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