Remote Sensing Detection and Geological Verification of the Qiaobei Town-Suqian Fault: A Case Study of the Sihong Section

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Remote Sensing Detection and Geological Verification of the Qiaobei Town-Suqian Fault: A Case Study of the Sihong Section

https://doi.org/10.21203/rs.3.rs-4384216/v1

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The Tan-Lu Fault Zone, a significant geological structural boundary in Eastern China, has historically been the source of numerous major earthquakes. This study zeroes in on a pivotal branch of this fault zone—the Qiaobei Town-Suqian Fault, situated in Sihong County. Present knowledge regarding the seismic activity patterns and potential hazards of this fault segment is somewhat restricted. Through the synthesis of remote sensing technology and field investigations, this paper endeavors to precisely delineate the geographical distribution of the Qiaobei Town-Suqian Fault in the vicinity of Sihong, aiming to provide scientific backing for regional earthquake risk evaluation and disaster prevention initiatives.

Earth and environmental sciences/Solid earth sciences/Geophysics

Earth and environmental sciences/Solid earth sciences/Seismology

Qiaobei Town-Suqian Fault

Sihong Section

Remote Sensing Detection

Active Fault

Geological Verification

China, situated on the southeastern edge of the Eurasian Plate and adjacent to both the Pacific Ring of Fire and the Eurasian Seismic Belt, emerges as a focal area for frequent tectonic activities globally. In recent years, the country has witnessed the profound impacts of earthquakes on its national well-being and socio-economic development. This underlines the imperative for conducting thorough investigations into active faults. Particularly, the in-depth interpretation of active faults, spatial distribution, geometry, and kinematic characteristics through high spatial resolution remote sensing imagery is critical. Such analysis is essential for elucidating their distribution, traits, and correlation with seismic activities, which, in turn, is crucial for enhancing the precision of earthquake risk assessments and devising effective disaster prevention and mitigation strategies.

The Tan-Lu Fault Zone represents a prominent northeast-trending major fault system in East Asia, stretching approximately 2400 kilometers across eastern China and is known for its recurrent seismic activities. The magnitude 8½ earthquake in Tancheng, Shandong, in 16681-4, alongside subsequent studies, has unveiled evident signs of Late Quaternary activity in the fault zone stretching from south of the Huai River to the Nushan Lake area, indicating its potential for destruction5-11. The Qiaobei Town-Suqian Fault, a significant branch of this system, exhibits a relatively discernible activity line from Xinyi to Suqian. However, its specific activity characteristics and potential seismic risks near Sihong County remain inadequately explored.In this context, remote sensing technology emerges as a critical tool. With its wide-ranging observational capacity and the ability to provide clear, visual insights into fault structures, remote sensing not only deepens our understanding of these geological features but also sets the stage for further studies and precise development planning12.

The focus of this research is Sihong County, situated in the northwestern part of Jiangsu Province, bordering the lower reaches of the Huai River and the eastern perimeter of Hongze Lake. The geographic coordinates of this area range from 33°12'43" N to 33°35'10" N latitude and from 118°02'19" E to 118°19'38" E longitude. This location lies at the juncture of the Yangtze River Delta economic zone and the Huai River ecological economic belt, featuring a complex geographical environment and prominent geological structural characteristics. These are mainly manifested through the geological activities of two significant branches of the Tan-Lu Fault Zone—the Qiaobei Town-Suqian Fault (Fig. 1, F1) and the Wangzhuang-Suxi Fault (Fig. 1, F2), with the former being the primary subject of this study due to its pronounced geological activity, which is evident in significant fault geomorphological phenomena13.

As an essential extension of the Tan-Lu Fault Zone, the Qiaobei Town-Suqian Fault has been a site of considerable geological activity throughout history14. Through meticulous topographical and geomorphological examinations, coupled with the analysis of satellite imagery, a geomorphological escarpment approximately 10 meters in height was identified on the eastern side of the Daxie Reservoir. This feature signifies the area's historical geological activity, aligning with the behaviors of the Qiaobei Town-Suqian Fault. Moreover, shallow artificial seismic explorations conducted by the Jiangsu Province Earthquake Engineering Research Institute along this fault have unearthed its deep structural and activity traits, such as variations in fault zone width, fault composition characteristics, and displacement within reflector groups. These findings further underscore the Qiaobei Town-Suqian Fault's complexity and dynamism.

Since the 1970s, remote sensing technology has evolved into an indispensable tool for delineating the characteristics of active surface faults, significantly enhancing geologists' insight into surface transformations. This research employs multisource remote sensing data, ranging from Landsat to Gaofen series satellites, complemented by advanced imaging processing techniques and extensive field geological investigations15. Such a holistic approach enables a detailed examination of the Qiaobei Town-Suqian Fault in Sihong County and its environs, with high-resolution imagery uncovering the fault’s intricate structural nuances.

In order to conduct a comprehensive analysis of active faults in Sihong County and its adjacent areas in the northwest of Jiangsu Province—specifically, to pinpoint the geographical presence and traits of the Qiaobei Town-Suqian Fault—this study amalgamated 0.5-meter resolution Google Earth optical remote sensing imagery, Gaofen-2 (GF-2), and Gaofen-7 (GF-7) images, as well as historical KH satellite images from December 5, 1970, which captured the topography and geomorphology of the region. Furthermore, this research incorporated Level 16 Digital Elevation Model (DEM) data from NASA, offering a spatial resolution of 15 meters, to facilitate geomorphological assessments and accurate fault detail extraction.

Regarding data processing, the gathered remote sensing imagery underwent a suite of preprocessing steps such as image cropping, stitching, and georegistration to guarantee the analysis's accuracy and reliability. Notably, the vintage KH satellite images—through leveraging the technical specs of film cameras (e.g., 70mm film and panchromatic imaging) and rigorous ground resolution enhancement—played a crucial role in fault line identification and geological structure analysis. By employing manual visual interpretation, coupled with supervised/unsupervised classification and knowledge-driven techniques, this study effectively pinpointed key characteristics of the Qiaobei Town-Suqian Fault in proximity to Chonggang Mountain, Shuanggou Town, and Weiying Town within Sihong County.

3.1 Macrogeomorphological Features

By integrating high-resolution remote sensing images with geographic information data from the surrounding areas of Sihong County, this study deeply analyzed the geological fault characteristics of Sihong County and its surrounding regions. KH satellite data from 1970, which recorded the original topography and geomorphology of Sihong County before the economic boom, provided key clues for revealing fault geomorphologies that are difficult to observe under the current context of high urbanization. In the remote sensing interpretation of faults within the urban target areas of Sihong County, we found that the image features of the Qiaobei Town-Suqian Fault (F1) and the Wangzhuang-Suxi Fault (F2) in the KH images are very clear. These early images revealed the apparent NNE trending linear image features of the Qiaobei Town-Suqian Fault, displaying the unique tonal anomaly zones of the fault zone, providing intuitive evidence for understanding the geological activity of the fault. Especially, through the comprehensive interpretation of KH satellite, Google Earth, and Gaofen-2 images, this study identified several key geological fault features:

1) A significant fault scarp formed near Chonggang Mountain in the north of the Qiaobei Town-Suqian Fault, and the disordered twisting of the mountain front plains in the west and the ridge lines in the east, clearly indicating the presence and intensity of fault activity.

2) As the fault extends to the Weiying Town area, the twisted misalignment of nearby ridge lines further confirms its activity.

3) When the fault extends to the vicinity of Shuanggou Town, the obvious twisting of ridge lines, the formation of fault depression lakes, and the topography of the mountain front plains all indirectly confirm the activity of the fault zone.

Although modern urbanization construction makes some fault features not as obvious as those in early images, through precise remote sensing interpretation, we can still identify the basic form and signs of activity of the fault zone. For example, the fault scarp formed near Chonggang Mountain in the north, the mountain front plains on the west side, the disordered movement of ridge lines on the east side, and the scattered string of bead lakes indirectly prove the existence of the fault.

3.2 Microgeomorphological Features

This study thoroughly analyzed the fault characteristics of the Qiaobei Town-Suqian Fault (F1) on the north side of Chonggang Mountain, the southwest side of Shuanggou Town, and the southeast side of Weiying Town. We have magnified and displayed the remote sensing interpretation markers of these areas, and conducted a detailed comparison of KH images, Google Earth images, and Gaofen-2 images to observe the fault activity characteristics more clearly. Early KH satellite data recorded the original topography of Sihong County and its surrounding areas before urbanization, providing us with clear evidence of fault activity. These data reveal complex structural topographic features that could only be disclosed through high-resolution remote sensing technology:

1) According to Fig 2, the Chonggang Mountain area shows clear fault clues of the Qiaobei Town-Suqian Fault in KH images (Fig 3(a)(b)). These fault zones extend prominently in the NNE direction, displaying tonal anomalies with vivid contrasts in the colors of the side scarps. Notably, the topographic features of these areas—including the mountain front plains, twisted ridge lines, and scattered small lakes—fully demonstrate the strike-slip activity of the fault. In the Google Earth (Fig 3(c)) and Gaofen-2 (Fig 3(d)) remote sensing images, although the twisting features of the ridges are no longer significant, the distribution of bead-like lakes gradually formed by fault activity can still be observed, indirectly marking the position of the fault line.

2) Fig 4 shows the fault activity characteristics of Shuanggou Town, where the apparent linear fault scarps in the early KH images (Fig 4(b)) transition to the orderly agricultural field layout shown in Google Earth and Gaofen-2 images, reflecting the evolution of surface morphology over time.

3) The terrain near Weiying Town is clearly revealed in the KH images shown in Fig 5, displaying the terrain horizontal slip features reflected by the arrangement of fields. This slip pattern, marked by red arrows in Fig 5(b), points to the right-lateral strike-slip direction of the fault. Fig 6 further presents the geological markers of the Weiying Town area, showing fault depression features formed by front fault activity, which have created a dendritic water system layout, representing typical fault depression lakes. The observed ridge displacement features are closely linked to the orientation of the Qiaobei Town-Suqian Fault.

3.3 DEM Remote Sensing Analysis

Utilizing three-dimensional visualization technology to process the DEM data of the target area (Fig 7), an exhaustive analysis of the Qiaobei Town-Suqian Fault and its activity characteristics and spatial distribution was conducted. Upon observation, the Qiaobei Town-Suqian Fault (F1) is clearly manifested as the most actively faulted, displaying significant fault geomorphology. The 3D DEM shows that its northeastern side is bordered by Chonggang Mountain, with the western edge being a plain characterized by bead-like lakes and intermittent ridge dislocations, marking horizontal misalignment. These features indicate the profound impact of the Qiaobei Town-Suqian Fault on the terrain, especially its geomorphological shaping role as it extends to the southwest.

The research not only deeply analyzed the spatial positioning, fault geomorphology, and dynamic characteristics of the fault but also integrated the results of field surveys. Based on the anomalies identified through remote sensing technology in this study, we conducted detailed field investigations of these special areas. Particularly in the Chonggang Mountain area, where remote sensing interpretation showed anomalies, near the east side adjacent to the Daxie Reservoir, a geomorphic scarp about more than 10 meters high was observed, primarily composed of brick-red Cretaceous Wangshi Group (K2w) fine sandstone. In the process of further exploring this stratigraphic structure, we discovered a thin layer of gravel on top of the steep slope formed by the Wangshi Group fine sandstone, with the roundness and sorting of these gravels being average, most of their grain sizes being about 5 centimeters. Based on these features, we speculate that these strata may belong to the Upper Pleistocene. At the bottom of the scarp, we also observed a layer of about 1 meter thick black-brown silty clay, speculated to belong to the Holocene, below which is the gravel layer of the aforementioned Upper Pleistocene. Since we could not observe deeper stratigraphic structures, we speculate that the bedrock of this area might be the Wangshi Group fine sandstone (Fig. 8). By comparing the regional topography and related geological data, we infer that this landscape might have been formed by the reverse thrust movement of the eastern plate of the Qiaobei Town-Suqian Fault.

Moving further south to the side of Liangying Road, we once again saw the brick-red Wangshi Group fine sandstone exposed at the surface in our local area, which formed continuity with our previous investigation points in direction and maintained consistency with the trend of the Qiaobei Town-Suqian Fault. The overall geomorphology between these two investigation points is characterized by a steep scarp with the east side being higher and the west side lower, and the inferred fault location from geomorphological characteristics basically matches the remote sensing interpretation results.

In the investigation near Weiying Town, we only observed the direct outcrop profile of the Qiaobei Town-Suqian Fault in the Dahong Mountain area. This outcrop is located about 500 meters east of Songzhuang Village, Fengshan Township, Sihong County, close to the south side of the G344 national highway. The geomorphic features of this area are significant, with Dahong Mountain being isolated and prominent, its highest point exceeding 50 meters in elevation, while the lowest point is more than 20 meters, with a relative height difference of about 30 meters. On the west slope of Dahong Mountain, we revealed the existence of the Qiaobei Town-Suqian Fault, with the fault trending NE20°, displaying the west side as the upper plate. The stratigraphy from top to bottom consists of Upper Pleistocene brownish-red calcareous nodules-containing silty clay, Pliocene brownish-yellow semi-consolidated sandy silty clay, and Miocene brown to gray-white cyclic mudstone gravel debris cemented or semi-cemented silty sandstone, which tilts slightly westward near horizontally(Fig. 9). The upper plate was observed to be displaced downward compared to the lower plate, with the fault dip angle being nearly vertical at the top and gradually becoming horizontal at the bottom, showing typical characteristics of a normal fault. Considering the negative topography presented on the west side of the fault, we speculate that this phenomenon might be caused by the movement of the main fault on the west side, although we cannot accurately determine the activity nature of the fault at this location.

In this study, we combined remote sensing interpretation with field verification to preliminarily determine the distribution of the Qiaobei Town-Suqian Fault near Sihong County, aiming to fill the research gap in the geological structure of this area. The main findings and scientific contributions of this study can be summarized as follows:

Application of high-resolution remote sensing data: This study has shown that, in the Quaternary cover area, although the linear images of active faults are not as obvious as in the bedrock area, the preliminary location of faults can still be effectively identified through high-resolution remote sensing data.

Combination of remote sensing interpretation and field verification: The results confirm that the method of combining remote sensing interpretation with field verification can accurately determine the preliminary location of faults, significantly improving the efficiency of fault location determination. The successful application of this method lays a solid foundation for further detailed studies on fault activity and provides an effective research paradigm for similar geological structure studies.

Importance of the temporal span of remote sensing data: This study emphasizes the importance of using earlier remote sensing data when interpreting faults in urban peripheries. These early data can reveal geomorphological phenomena that have not been modified by human activities, providing crucial information for more accurate fault interpretation.

Competing interests

The authors declare no competing interest.

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Author Contribution

All authors participated in the conception and design of the study. H.W. was responsible for conceptualization, investigation, data curation, and writing the original draft. Z.X. and C.W. handled conceptualization, methodology, and review and editing of the manuscript. J.S., Y.Z., and J.W. were involved in writing the original draft, review and editing of the manuscript, supervision, project administration, and funding acquisition. All authors have read and agreed to the published version of the manuscript. All authors have read and approved the final manuscript.

Acknowledgement

This work is supported by the National Natural Science Foundation of China (41404071) and China Scholarship Council (201304190035). All models in this paper are calculated on the Brutus Cluster, ETH.

Data Availability

All data generated or analysed during the current study available from the corresponding author on reasonable request

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Remote Sensing Detection and Geological Verification of the Qiaobei Town-Suqian Fault: A Case Study of the Sihong Section

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Abstract

Figures

1 Introduction

2 Geologic background

3 Remote Sensing Data

3.1 Macrogeomorphological Features

3.2 Microgeomorphological Features

3.3 DEM Remote Sensing Analysis

4 Field Investigation Verification

5 Conclusion

Declarations

Competing interests

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Author Contribution

Acknowledgement

Data Availability

References

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