2024 Vol. 30, No. 2

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Active tectonics and strong earthquakes: A preface for the special issue
WU Zhonghai, ZHENG Wenjun, REN Junjie, REN Zhikun
2024, 30(2): 181-188. doi: 10.12090/j.issn.1006-6616.20243002
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Active tectonics is not only the manifestation of the latest crustal activity but also the leading cause of strong earthquakes. With its complex active tectonic system, China has become an area with particularly severe seismic activity and related hazards worldwide. Therefore, a deep understanding of active tectonic characteristics and the occurrence patterns of strong earthquakes in China can help scientifically prevent or mitigate the risk of seismic disasters in urban planning and major engineering construction projects. In order to timely exchange the latest achievements in the field of active tectonics and strong earthquakes, this special issue on Active Tectonics and Strong Earthquakes selected 12 representative papers, mainly covering six different fields, including the earthquake-controlling process of active tectonics, paleoearthquakes, surveying and detection of active faults, seismic geological hazards, application of remote sensing technology and reservoir-induced earthquakes. Based on the new achievements of this issue and the research trends in related fields at home and abroad, it is suggested that future research on active tectonics and strong earthquakes should focus on four aspects: (1) comprehensive understanding of regional seismic hazards from the perspective of active tectonic evolution and active fault systems; (2) quantitative and refined field investigations of active tectonics; (3) application of high-precision remote sensing and various dating techniques continuously expanding the scope and timing of paleoearthquake research; (4) human-induced earthquakes.
The earthquake-controlling process of continental collision-extrusion active tectonic system around the Qinghai-Tibet Plateau: A case study of strong earthquakes since 1990
WU Zhonghai
2024, 30(2): 189-205. doi: 10.12090/j.issn.1006-6616.2023186
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  Objective  The Qinghai-Tibet Plateau is one of the most seismically active regions along the Mediterranean-Himalayan seismic belt. Understanding the earthquake-controlling effect of the active tectonic system in this region is crucial for analyzing regional strong earthquake hazards.  Methods  We analyzed earthquake activity with MW≥6.0 since 1990 and their tectonic mechanism around the Tibetan Plateau, focusing on the continental collision-extrusion tectonic system.  Results  The results show that the system plays a significant role in governing regional strong earthquake activity. Specifically, MW≥6.5 earthquakes primarily occur along the main boundary fault zone of this tectonic system, exhibiting a relatively regular spatio-temporal migration process. Moreover, the multi-layered extrusion-rotation active tectonic system in the eastern Tibetan Plateau constitutes the primary earthquake-controlling structure of the strong earthquake process since 1990, followed by the thrust faults of the Himalayan foreland. Therefore, the extrusion tectonic system of the Qinghai-Tibet Plateau should be the focus for the trend analysis of the strong earthquake activity in the future, especially the most active secondary extrusion tectonic units such as the Bayan Har block. Comparative analysis of strong earthquake activities in and around the Anatolian plate reveals similar continental collision-extrusion tectonic systems and earthquake-controlling effects in this area, indicating that this tectonic system is a typical earthquake-controlling structure in the intracontinental orogenic belt.  Conclusion  Further comprehensive analysis suggests that the active tectonic system can significantly control regional strong earthquake activity. Firstly, most of the strong earthquake events occur in the main boundary fault zone of the fault block in the tectonic system. Secondly, the strong earthquake events along different structural zones in the tectonic system often have linkage effects or mutual triggering relationships, and the complex or particular structural sites are often where double earthquakes or earthquake swarm activities easily occur. Thirdly, when a certain structural unit or tectonic zone in the tectonic system is in an active stage, strong earthquake clustering phenomena occur.  Significance  A thorough understanding of the coordinated deformation relationships between major active faults in the tectonic system, the segmented rupture behavior of strong earthquake activity in active fault zones, and the characteristics of "long period, quasi-periodicity and clustering" of strong earthquake recurrence in situ on active faults will assist in more accurately assessing the future seismic hazard of active fault zones when analyzing the future trend of strong earthquake activity based on the active tectonic system.
Late Quaternary tectonic activity and strong earthquake generation mechanism around the boundary zone of the Ordos active-tectonic block, central China
ZHENG Wenjun, SUN Xin, LEI Qiyun, GONG Zhikang, WANG Yin, LIU Xingwang, LI Chuanyou, FENG Zijian
2024, 30(2): 206-224. doi: 10.12090/j.issn.1006-6616.2023154
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  Objective  The Ordos block, with typical boundary zone activity, is located in the center of mainland China. Influenced by the remote action of the Tibetan Plateau in the southwest and the Pacific Plate in the east, each boundary zone of the Ordos Block exhibits distinct tectonic activity and deformation characteristics. This study aims to provide insights into the characteristics of strong earthquake generation and the future seismic risk along the boundaries of the Ordos active block.  Methods  This study systematically summarizes research achievements made in the study of active faults and the seismogenic mechanism of strong earthquakes around the Ordos Block over the past few decades, providing a systematic overview of the characteristics of fault activity and seismic generation mechanisms along the block' s periphery.  Conslusion  The differences in fault activity in each boundary zone determined the differences in the earthquake-breeding strong tectonic environments. In the southern section of the western boundary, the faults are mainly characterized by strike-slip, reverse strike-slip, and thrust owing to the influence of the northward compression and expansion of the Qinghai-Tibet Plateau, resulting in complex structural deformation styles within the boundary zone. In the northern section of the western boundary, the latest expansion boundary of the Qinghai-Tibet Plateau is characterized by dextral movement along the Sanguankou-Niushoushan fault. The Yinchuan Basin in the northern section of the western boundary zone is a typical fault basin with basin-controlling faults exhibiting dextral strike-slip characteristics, and earthquakes are primarily of the standard strike-slip type. The Hetao Basin on the northern boundary is controlled by normal faults on its northern side, with historical and ancient earthquakes concentrated on the northern boundary faults. The Weihe Basin on the southern boundary exhibits relatively complex structural features, comprising two sets of normal faults. Historical major earthquakes mostly occur at the southern edge of the basin, with moderate seismic activity in the central-northern part of the basin. The Shanxi Graben system on the eastern boundary comprises multiple rift-type basins. Historical major earthquakes exhibit a pattern of stronger activity in the south and weaker activity in the north. The northern basins are influenced by the Zhang-Bo tectonic belt, resulting in significant changes in basin trend and fault movement characteristics, often possessing the structural conditions necessary for earthquakes of around M 7.0. Overall, in the typical fault activity zones surrounding the Ordos active block, future strong earthquakes are more likely to occur in seismic gaps or transition zones of fault systems, where significant time has passed since the occurrence of major earthquakes or at the intersections of tectonic zones.
Structural deformation characteristics of active anticline and their implications for seismogeological disaster effect under compression setting in the Late Cenozoic
YANG Xiaoping, CHEN Jie, LI An, HUANG Weiliang, ZHANG Ling, YANG Haibo, HU Zongkai, ZUO Yuqi
2024, 30(2): 225-241. doi: 10.12090/j.issn.1006-6616.2023136
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  Objective  Thrust faults and their associated folds are important structures of continental tectonic deformation, widely distributed at plate boundaries and within plates. The activity of these thrust faults can trigger severe seismic disasters, such as the 1999 Chi-Chi earthquake in Taiwan and the 2008 Wenchuan earthquake. However, research on surface ruptures and associated disasters caused by thrust faulting is relatively limited, mainly due to the complexity of their fault propagation processes. Studying thrust faults and their associated folds could enhance the capability of seismic hazard risk assessment and better predict earthquakes and potential secondary disasters.  Methods  This paper first introduces the meanings of fold-related faults and fold scarps and explains the impacts of surface uplift and lateral extension deformations on topography. Taking the Tian Shan active fold zone as an example, the paper focuses on analyzing the structural characteristics and landform deformation patterns of the Hejing thrust-and-fold belt in the northern margin of the Yanchi Basin and the Mingyaole anticline in the southern piedmont of the Tian Shan. It also discusses various types of structures, such as thrust faults, fold-related faults (flexural faults, flexural slip faults, and conjugate shear faults), and their effects on landforms. Based on this, the paper explores the relationship between the growth process of active folds and the formation of seismic geological disasters.  Results and Conclusion  It is believed that in a compressive tectonic environment, the growth of active folds and the formation of fault-related folds cause building displacement, tilting, and damage, thereby generating geological disasters. In particular, it emphasizes that the tilting of the ground on both sides and the footwall of active anticlines during the process of crustal shortening, vertical uplift, and lateral expansion poses a threat to the safe operation of major engineering structures. Simultaneously, the bending deformation caused by regional crustal shortening presents potential seismic risks and triggers geological hazards for significant linear engineering projects spanning active anticlines, warranting attention.
Detection of the Late Quaternary activity of the Liaocheng-Lankao Fault in the south-central part of the North China Plain: Discussion on the seismogenic mechanism of the 1937 Heze M 7.0 earthquake
LIU Guangying, LIANG Kuan, LI Zhipeng, MA Baoqi, LONG Tao, LI Lei, TAN Xin, LI Haoyang
2024, 30(2): 242-259. doi: 10.12090/j.issn.1006-6616.2023088
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  Objective  The North China Plain (NCP) is one of the most populated and economically developed areas in China and is a region with a high level of seismic hazards. Studying the Quaternary activity of the faults and the seismogenic mechanism of the large earthquakes in NCP is conducive to exploring the seismogenic pattern of intraplate earthquakes and reducing the damage caused by seismic hazards. The Liaocheng-Lankao fault (LLF) is an important buried deep major fault in the south-central part of the NCP. The activity of the LLF and its relationship with the 1937 Heze M 7.0 earthquake is still highly controversial.  Methods  In this study, the activity of the Liaocheng-Liaokao fault is finely studied by combining shallow seismic exploration, drilling, and Quaternary dating methods.  Results  Shallow seismic reflection profile ZF-2 reveals that the strata below 145 m are obviously displaced, and the strata above 145 m are disturbed. The Bachengsi drilling profile reveals 16 sets of marker layers and three west-dipping normal faults Fa, Fb, and Fc; they form a "compound Y" structure in the profile, of which Fa displaces the bottom boundary of the Holocene (burial depth of approximately 38.9 m) and is an early Holocene active fault. It also reveals four paleoseismic events since the Late Pleistocene, with vertical displacement of 1.2±0.2 to 3.7±0.2 m for a single event. Based on the stratigraphic offsets in the boreholes, the average vertical slip rate of this fault is calculated to be about 0.1±0.05 mm/a for the early Late Pleistocene and 0.35±0.04 mm/a for the late Late Pleistocene-middle Holocene. The fitted age-depth curves by the test results of seven 14C samples and four OSL samples can be divided into two segments. Within the depth range of 0 to 86.0 m (approximately 21 to 0 ka), the age and depth of the strata conform to the formula y=(253.69±16.56)x+(924.72±681.36), from which the average deposition rate of this section is calculated to be 3.94±0.26 mm/a. Within the depth range of 102.9 to 145.4 m (approximately 128 to 59 ka), the age and depth of the strata conform to the formula y=(1470.67±259.91)x+(-95061.92±30190.73), from which the average deposition rate of this section is calculated to be 0.68±0.12 mm/a. The vertical slip rate of the LLF and the sedimentation rate of the Dongpu Sag have increased significantly since the late Late Pleistocene. The intensity lines of the Heze M 7.0 earthquake show an asymmetric butterfly shape.  Conclusion  The 1937 Heze M 7.0 and M 6${\raise0.7ex\hbox{$3$} \!\mathord{\left/{\vphantom {3 4}}\right.}\!\lower0.7ex\hbox{$4$}} $ earthquakes formed "Z" -shaped ground fissure zones, which can be divided into three sections: the southeastern section (section A), the middle section (section B), and the northwestern section (section C). The long axis of the intensity lines and the distribution of the surface rupture of the 1937 Heze M 7.0 coincide with the NNE-striking Xiaoliu-Xieyuanjie and NWW-striking Dongming-Chengwu faults in location and striking. The analysis of the intensity lines, surface rupture distribution, focal mechanism solution of the 1937 Heze M 7.0 earthquake and M 6${\raise0.7ex\hbox{$3$} \!\mathord{\left/{\vphantom {3 4}}\right.}\!\lower0.7ex\hbox{$4$}} $ earthquakes, and regional stress implies that the Xiaoliu-Xieyuanji fault and the Dongming-Chengwu fault are the seismogenic faults of the 1937 Heze M 7.0 earthquake. The LLF, as the deep major fault in the region, controlled the accumulation of stress, stimulated the earthquake with its deep movement, and reduced the effect of the seismic energy westward, acting as the regional seismic controlling fault of the 1937 Heze M 7.0 earthquake.  Significance  This article proposes a method for fine detection of the localization, structure, latest activity age, sliding rate, and paleoseismic sequences of the buried fault and also proposes a pattern of seismicity in which seismogenic faults do not coincide with the regional seismic controlling fault. It provides new insights into the characterization of seismicity within the NCP and can provide the geological basis for urban and rural planning, high-speed railway design, and earthquake prevention and disaster reduction project construction in this region.
Late Quateranry paleoseismicity of the Xitieshan-Amunikeshan section of the northern margin fault of the Qaidam Basin
YAO Shenghai, GAI Hailong, YIN Xiang, LIU Wei, ZHANG Jiaqing, ZHANG Zhanxian
2024, 30(2): 260-274. doi: 10.12090/j.issn.1006-6616.2023114
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  Objective  The northern margin fault zone of the Qaidam Basin is a regional active fault zone in the northern part of the Qinghai-Tibet Plateau, forming the boundary fault of the northern Qaidam Basin and the Qilian Mountains. Studying its late Quaternary paleoseismic activity is of great significance for understanding the seismic recurrence cycle and seismic hazard of the northern margin fault zone of the Qaidam Basin.  Methods  Through geological survey, remote sensing interpretation, trench excavation, OSL geological dating, and analysis of paleoseismic events, the paleoseismic events of the northern margin fault of the Qaidam Basin (Xitieshan-Amunikeshan section) were studied.  Conclusion   The study reveals that the trench profiles exposed five relatively reliable paleoseismic events, with occurrence times of approximately 60 years ago for Event E1, 3.1±0.3 to 3.4±0.3 ka for Event E2, 7.5±0.3 to 8.1±0.3 ka for Event E3, 10.1±0.4 to 11.4±0.4 ka for Event E4, and 12.1±0.4 to 12.8±0.4 ka for Event E5. Using the paleoseismic incremental limiting method, the seismic recurrence cycle of the northern margin fault of the Qaidam Basin (Xitieshan-Amunikeshan section) is estimated to be 2.6 to 3.4 ka. The most recent event departure time for the Amunikeshan section is 60 years ago, and for the Xitieshan section, it is 3.1±0.3 ka, suggesting a higher likelihood of destructive earthquakes in the future for the Xitieshan section compared to the Amunikeshan section of the northern margin fault of the Qaidam Basin.  Significance  This result can provide a better understanding of the paleoseismic events, recurrence intervals, and other aspects of the northern margin fault of the Qaidam Basin, which has guiding significance for seismic forecasting, prediction, and evaluation of future seismic hazards of this fault.
Late quaternary slip rate and paleoseismic sequence of the Cuopuhu section of the Litang-Yidun fault, western Sichuan, China
WANG Shiyuan, WANG Jing, LI Fupeng, TAO Zhigang, LIANG Mingjian, LIU Shao, QU Miao, ZHANG Liwen, ZENG Weizu, JIN Yunxia
2024, 30(2): 275-288. doi: 10.12090/j.issn.1006-6616.2023060
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  Objective  The Litang-Yidun fault is a left-lateral strike-slip active fault zone extending approximately 130 km in the Sichuan-Yunnan rhombic block in the Holocene. As a significant seismogenic structure controlling seismic activity in the Litang area of western Sichuan, research on both paleoseismicity and surface ruptures primarily focuses on the Litang and Damaoyaba sections, with relatively limited study on the Cuopuhu section in the northern part. Detailed investigation of the Cuopuhu section can provide fundamental information on its activity characteristics, paleoseismic events, and slip rates.  Methods  The Cuopuhu section of the Litang-Yidun fault was investigated using field surveys, high-precision mapping, trenching, and 14C dating methods to explore its slip rate and paleoseismic events. Two trench sites were excavated at the foothills of Dongou Mountain to identify the relationships between faulting and strata, sedimentary characteristics, and fault motion.  Conclusion  Four paleoseismic events were identified: Event Ⅰ occurred before BC 3382±60 a; Event Ⅱ occurred between BC 3382±60 a and BC 1094±51 a; Events Ⅲ and Ⅳ occurred after AD 1330±44 a. The recurrence intervals of the four earthquakes are approximately 0.4±0.3 ka, 2.42±0.1 ka, and 2.40±0.1 ka, respectively. Based on the calculated intervals, Events Ⅰ and Ⅱ, and Events Ⅱ and Ⅲ, Ⅳ, have recurrence intervals of about 2.4 ka. Events Ⅲ and Ⅳ occurred after AD 1330±44 a, making it difficult to determine their sequence and exact timing. It can be inferred that the Cuopuhu section of the Litang-Yidun fault likely has a recurrence interval of about 2.4 ka for paleoseismic events, with a possibility of seismic events with recurrence intervals of 0.4±0.3 ka. By comparing the research data between the Cuopuhu section and the Litang and Damaoyaba segments, differences in paleoseismic events between the Cuopuhu section and the other sections are evident. However, the seismic activity of different fault sections has shown a sustained strengthening trend since the Holocene. Based on mapped fault scarps and moraine ridges from the last glacial period, the average slip rate of the Cuopuhu section since the Late Pleistocene is estimated to be 4.15±0.5 mm/a, similar to the slip rates of different branches of the Litang-Yidun fault in the late Quaternary period.  Significance  This study provides information on the tectonic features, paleoseismicity, and slip rates of the Litang-Yidun fault, aiding in a better understanding of the seismic history and structural deformation patterns in the area and giving more data for medium- and long-term earthquake prediction in the future. It also contributes to the seismic risk assessment of relevant projects along the Sichuan-Tibet Railway.
Study on coseismic surface deformation of the 2023 Turkey MW7.8 and MW7.5 double strong earthquakes using optical image correlation method
KANG Wenjun, XU Xiwei
2024, 30(2): 289-297. doi: 10.12090/j.issn.1006-6616.2023144
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  Objective  On February 6, 2023, double strong earthquakes of MW7.8 and MW7.5 occurred consecutively within 10 hours in the Kahramanmaraş province in central-southern Turkey. After these double-strong earthquakes, domestic and foreign seismologists studied coseismic surface deformation using field measurements, GNSS, and differential InSAR methods. However, owing to the limitations in the techniques employed, the current coseismic surface deformation results suffer from low spatial resolution and missing data near fault surface ruptures. This study aims to address these limitations and comprehensively present the coseismic surface deformation of the double earthquakes in Turkey.  Methods  Using Sentinel-2 optical image data, the east-west and north-south surface coseismic deformation fields of Turkey' s double-strong earthquakes were obtained using the image correlation method, and these surface deformations were converted into sinistral strike-slip displacement along the fault direction.  Results  The deformation field results showed that the surface rupture lengths of the double earthquakes are approximately 280 and 130 km, respectively. The average strike-slip displacement of the first MW7.8 earthquake is 4.2±1.66 m; the maximum strike-slip displacement is 6.9±0.81 m. The average strike-slip displacement of the subsequent MW7.5 earthquake is 4.9±2.45 m, and the maximum strike-slip displacement is 9.6±1.16 m.  Conclusion  Comparison of the horizontal displacement results obtained using the COSI-Corr method and field measurements revealed that the maximum horizontal displacements obtained using the two methods are consistent. In contrast, the average displacement results obtained using the COSI-Corr method are slightly larger than the horizontal displacement results obtained using field measurements, attributed to the inclusion of "off-fault" deformations.  Significance  This study not only provides deformation data and constraints for the fault-slip inversion model but also deepens the understanding of factors controlling the rupture behavior of strike-slip faults.
Late Quaternary surface deformation and tectonic implications of the Bue Co strike-slip fault system in central-western Qiangtang block
HAN Shuai, WU Zhonghai, WANG Shifeng, GAO Yang, ZHANG Shengting, LU Shiming, ZHANG Minggao
2024, 30(2): 298-313. doi: 10.12090/j.issn.1006-6616.2023086
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  Objective  The Bangong-Nujiang Suture Zone (BNSZ) serves as a boundary between the Qiangtang and Lhasa terranes of the Tibetan Plateau. The geometric structure and deformation characteristics of the "V" -shaped conjugate strike-slip faults along this late Quaternary boundary are important for understanding the spatially variable responses and tectonic models formed within the plateau as a result of the India-Eurasia plate collision. However, previous studies have primarily focused on the kinematic properties and activity rates of strike-slip faults in the eastern segment of the suture zone. The scarcity of information on the activity characteristics of strike-slip faults and paleoseismic events in the western segment of the suture zone has hindered our understanding of regional tectonic deformation and seismic activity. The Bue Co fault system, located in the western section of the BNSZ, is a (conjugate) strike-slip fault system consisting of the NE-trending Bue Co and NW-trending Lamu Co faults.  Methods  This study employs a combination of remote sensing interpretation and field surveys, utilizing high-resolution Digital Surface Models (DSM) collected by unmanned aerial vehicles (UAV) to conduct a detailed analysis of surface ruptures and systematically decipher the geometric morphologies and late Quaternary deformation evidence of the NE-trending Bue Co Fault and the NW-trending Lamu Co Fault in the western section of the BNSZ.  Results  This study revealed significant fault activity since the late Quaternary period, with evidence of recent large earthquakes that caused surface ruptures extending >60 km along both faults. The Bue Co fault exhibits left-lateral strike-slip, with recent seismic displacements ranging from 3.7 to 4.2 m, whereas the Lamu Co fault shows right-lateral strike-slip with minimum displacements of 2.7 m. Both faults display normal faulting components in their surface rupture zones, and the vertical displacements are cumulative across landforms of various ages, indicating long-term fault activity. The latest activity intensities of the NW and NE faults in the western BNSZ were similar, suggesting that the deformation of the southern boundary of the Qiangtang block may be controlled by both fault sets, which extend into the interior of the block.  Conclusion  These findings reveal that (1) both the Bue Co and Lamu Co faults can generate strong earthquakes of magnitude ≥7, indicating active tectonic deformation and a high seismic hazard potential in the western section of the BNSZ; (2) the deformation in the western BNSZ is concentrated along the NW-trending strike-slip faults and active along the NE-trending strike-slip faults, which may jointly control the southern boundary of the eastward extrusion of the Qiangtang terrane and have extended into the interior of the terrane; and (3) the continuous deformation pattern is supported, revealing that material within the Tibetan Plateau is driven by mid-lower crustal flow extruding eastward, with the southern boundary of the extrusion potentially continuing northward through a series of strike-slip and normal faults.  Significance  These conclusions deepen our understanding of the activity and seismic potential of strike-slip faults in the western BNSZ and provide novel insights into the internal tectonic deformation patterns and dynamic background of the Tibetan Plateau. Furthermore, this study provides an essential theoretical foundation for regional stability assessments and disaster mitigation planning.
Development characteristics and susceptibility assessment of coseismic geological hazards of Jishishan MS 6.2 earthquake, Gansu Province, China
LIU Shuai, HE Bin, WANG Tao, LIU Jiamei, CAO Jiawen, WANG Haojie, ZHANG Shuai, LI Kun, LI Ran, ZHANG Yongjun, DOU Xiaodong, WU Zhonghai, CHEN Peng, FENG Chengjun
2024, 30(2): 314-331. doi: 10.12090/j.issn.1006-6616.2024009
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  Objective  On December 18, 2023, an MS 6.2 earthquake occurred in Jishishan County, Gansu Province, China. Coseismic geological hazards induced by the earthquake crucially threatened the safety of personnel and property. Existing research is mainly concentrated in the vicinity of active faults and the concentrated distribution area of hidden danger points. Moreover, no special susceptibility assessment studies have been carried out on coseismic geological hazards in the administrative area of Jishishan County, making it challenging to meet the needs of the county's post-disaster recovery and reconstruction planning. Hence, the development laws of coseismic geological hazards must be summarized and analyzed crucially, and county susceptibility must be analyzed in time to support post-earthquake recovery and reconstruction.  Methods  The development characteristics of coseismic geological hazards are analyzed and summarized through emergency investigations, field surveys, and result analysis. Using the newly added and exacerbated coseismic hazard points identified during post-earthquake investigations as analysis samples, influencing factors were selected using the Pearson correlation coefficient and random forest Gini coefficient analysis methods. Then, a machine learning-random forest model was applied to assess the susceptibility of coseismic geological hazards in Jishishan County.  Results  In analyzing the development characteristics of coseismic geological hazards, we identified 134 instances of increased and exacerbated hazards in Jishishan County. Overall, the degree of development of these hazards was relatively low, with primarily small-scale occurrences. These hazards were categorized into three main types and eight sub-categories: ① Collapse (including cut slope loess collapse, high loess collapse, and high rock collapse); ② Landslide (encompassing loess landslide, secondary sand/mudstone landslide, and potential landslide); and ③ Debris flow (comprising gully debris flow and slope debris flow). In terms of factor selection, 15 influencing factors were screened. Regarding the susceptibility assessment results, the AUC value of the susceptibility assessment results of coseismic geological hazards in most Jishishan counties was 0.961, and the results showed that the areas of extremely high susceptibility accounted for approximately 8.67 %, mainly distributed in Hulinjia, Xuhujia, Liugoujia, and other townships. The statistical results of the proportion of susceptibility zones in 17 townships in Jishishan County showed that the top three townships with the largest proportions of extremely high-susceptibility areas are Hulinjia (24.67%), Xuhujia (21.24%), and Biezang (20.94%).  Conclusion  (1) Most coseismic geological hazards in Jishishan are distributed in the loess hilly area, with few occurrences in the Jishishan area and the right bank terrace of the Yellow River. (2) The influence of elevation and peak ground acceleration (PGA) on hazard occurrence is notably greater than that of other factors, playing a predominant role in developing coseismic geological hazards. (3) Utilizing the random forest model, the susceptibility assessment of coseismic geological hazards in Jishishan County demonstrates high accuracy, with hidden danger points clustered in highly susceptible areas. This alignment between susceptibility assessment results and the spatial distribution of hidden dangers underscores the reliability of the assessment outcomes.  Significance  In addition to identifying existing hidden danger points, this study offers predictive insights into slope deformation and potential landslides significantly affected by seismic cracking. The assessment results exhibit high accuracy and reliability, offering valuable geological safety support for post-disaster recovery and reconstruction planning in the county.
Application of UAV SfM technology in active tectonic research: A case study of the Longmu Co Fault, Northwestern Qinghai-Tibet Plateau
JIANG Chenyi, PAN Jiawei, ZHANG Lijun, LI Haibing, SUN Zhiming, CHEVALIER Marie-Luce, LIU Fucai, SU Qiang
2024, 30(2): 332-347. doi: 10.12090/j.issn.1006-6616.2023192
Abstract (352) HTML (87) PDF (25854KB)(63)
Abstract:
  Objective  In recent years, UAV (Unmanned Aerial Vehicle) SfM (Structure from Motion) technology has been widely applied as an emerging high-precision 3D topographic data acquisition technique in active tectonics research. However, existing domestic research primarily focuses on UAV platforms without RTK/PPK modules. Over the past two years, RTK and PPK technologies have gradually been introduced to UAV platforms, resulting in changes to field data collection and in-office data processing workflows compared to traditional UAV platforms without RTK/PPK modules. The differences in topographic data quality obtained through SfM processing of aerial photographs from UAV platforms equipped and not equipped with RTK/PPK modules under the same scenes and collection conditions still require investigation.  Methods  To address these questions and establish a streamlined data collection and processing workflow for different UAV platforms, a site where alluvial terraces are offset by the sinistral Longmu Co fault, northwestern Qinghai-Tibet Plateau, was surveyed using the DJI M300 RTK UAV (equipped with the Zenmuse L1 LiDAR and a 20-megapixel visible light camera) and the DJI Phantom 4 Pro UAV (equipped with a 20-megapixel visible light camera). Through processing the raw data with SfM technology, high-resolution and high-precision DEM and DOM data were obtained for the study area. Additionally, 16 ground control points (checkpoints) were uniformly distributed in the research area, and their coordinates were measured using the Trimble R8 GNSS receiver in RTK mode to compare and validate the differences in data quality obtained by the two platforms.  Results  The data comparison showed that the visible light camera and LiDAR module carried by the M300 RTK demonstrated high accuracy, with root mean square errors (RMSEs) in the centimeter to decimeter range compared to the RTK-measured ground checkpoints. Compared to SfM data collected at the same time (RMSEX=0.176, RMSEY=0.099, RMSEZ=0.180, RMSEH=0.201, RMSE3D=0.270, unit: m), the Zenmuse L1 LiDAR data exhibited slightly higher accuracy (RMSEX=0.112, RMSEY=0.076, RMSEZ=0.111, RMSEH=0.135, RMSE3D=0.174, unit: m). The uncorrected SfM data from the Phantom 4 Pro had horizontal errors of approximately 1 meter (RMSEX=1.112, RMSEY=1.295, unit: m) and a vertical error of over 200 meters (RMSEZ=249.286, unit: m). After ground control point correction, the accuracy of the Phantom 4 Pro SfM data significantly improved, with RMSE of 0.046 m, 0.058 m, and 0.527 m in the X, Y, and Z directions, respectively. Further analysis of a topographic profile nearly perpendicular to the steep slopes of various terrace risers within the surveyed area revealed that, despite significant elevation discrepancies in the uncorrected Phantom 4 Pro SfM data, it still accurately reflected the relative topographic relief. Subtracting the profile elevation values from their corresponding RMSE, the profile shape closely matched the rest of the data. Based on the acquired DEM data, the displacement of the terrace at this location was measured using LaDiCaoz software, revealing a left-lateral strike-slip displacement of 122.5±5 m and a vertical displacement of 0.8±0.2 m.  Conclusion  The study results indicate that: (1) UAV SfM method and LiDAR technology have significantly improved the resolution of DOM and DEM, enabling more detailed interpretation and analysis of active faults and related structural landforms; (2) RTK SfM technology overcomes the limitations of using ground control points, providing a higher-precision and more efficient solution for micro-landform measurements in the field of active tectonics research; (3) when absolute three-dimensional coordinates in the study area are not crucial, and only relative terrain variations are required, UAVs without RTK modules can still meet the basic requirements for geomorphic fault displacement measurements in the absence of ground control point constraints; (4) combining UAV SfM technology with traditional fault geomorphology analysis and Quaternary dating techniques in high-precision quantitative active tectonics research can offer robust technical support for analyzing fault activity patterns, seismic hazard, landform evolution, and the occurrence patterns of geological disasters.  Significance  Through the aforementioned work, workflows for data collection, data processing, and geomorphic fault displacement measurement using SfM methods in active tectonics research were established for both UAV platforms equipped and not equipped with RTK/PPK modules. The fieldwork considerations and data accuracy of UAV SfM methods were analyzed, providing a reference for selecting UAV platforms and rapidly collecting and processing data for similar studies in the future.
Control of bedrock geology on active structural deformation revealed by changes in geomorphic parameters: A case study of the Fodongmiao-Hongyazi Frontal Thrust, NE Tibet
YANG Yongzhong, LI Zhanfei, REN Junjie, XU Xiwei, LI Kang, CHENG Jia, KANG Wenjun
2024, 30(2): 348-362. doi: 10.12090/j.issn.1006-6616.2023129
Abstract (338) HTML (63) PDF (26475KB)(64)
Abstract:
  Objective  Widely distributed active faults are natural carriers that produce surface-rupture events; multidisciplinary observations have revealed that geometric changes in active faults significantly influence surface-rupture development. However, previous studies on the interaction between the geometric characteristics of active faults and the underlying rock geology have been relatively limited and only confined to observing high-temperature and high-pressure experiments.  Methods  With the development of high-resolution geographic technology and quantitative research methods for active faults, it is now possible to finely characterize the geometric structure of large-scale faults and recognize multiparameter displaced landform characteristics. In this study, we utilized high-resolution topographic data (0.5 m) from the Fodongmiao-Hongyazi Frontal thrust (FFT) on the northeastern margin of the Tibetan Plateau, spanning approximately 120 km in length to identify and compare the parameters and characteristics of the faulted landform with the underlying bedrock geology.  Result  The research results indicate that the geometric characteristics of the fault are segmented and synchronized with the geological background of the bedrock. The shallow geometric structures of the eastern and western sections of the FFT are relatively simple and continuous, and the changes in parameters such as the strike, roughness, and deformation zone width of the fault are relatively small. The fault's geometric structure was rougher in the middle section of the fault, where Silurian granite is located, and the shallow deformation zone was broader than that in the eastern and western segments. The step-width distribution also varied more drastically along the fault.  Conclusion  This study revealed a significant correspondence between faulted landform parameter changes, the boundary of fault segments, and zones of vertical separation attenuation. Additionally, this study suggests that bedrock geology may exert substantial control over the shallow structural deformation of thrust faults.  Significance  The potential impact of the underlying geology should be considered for thrust faults and when analyzing seismic hazards related to active faults.
The impact of the Dagangshan Reservoir impoundment in Sichuan Province on the 2022 Luding MS 6.8 earthquake and its aftershocks
ZHU Jiazheng, SUN Yujun, XIE Zhiyuan, WU Gang
2024, 30(2): 363-376. doi: 10.12090/j.issn.1006-6616.2023095
Abstract (258) HTML (62) PDF (27751KB)(41)
Abstract:
  Objective  The MS 6.8 earthquake that struck Luding County, Sichuan Province, on September 5, 2022, and its aftershocks have drawn widespread attention, especially concerning the potential risks of induced seismicity associated with the construction of high-dam reservoirs in regions with high seismic intensity. Previous studies have explored the possible link between reservoirs and seismic activity, without reaching a definitive conclusion. This study aims to assess the impact of water storage in the Dagangshan Reservoir on the surrounding strata and its correlation with recent seismic events.  Methods  Numerical simulation methods were employed using high-precision digital elevation model (DEM) data, fault data, and reservoir water level information to develop a three-dimensional poroelastic finite element numerical model extending from the surface to a depth of 25 km. By analyzing the hydrogeological conditions, lithology of rock masses, and groundwater dynamic changes, this study evaluated the seismic hazard risk of major faults, such as the Moxi Fault, and calculated variations in Coulomb stress and strata pore pressure at the hypocenter during the occurrence of the earthquake.  Results  The study indicates that, during the MS 6.8 Luding earthquake on September 5, 2022, the pore pressure at the epicenter reached 5 kPa, and the Coulomb stress increased by 3.6 kPa, suggesting that the impoundment of the Dagangshan Reservoir contributed to an increased risk along the Moxi Fault on the northwestern side of the reservoir. Using the source parameters of the MS 5.6 aftershock that occurred on January 26, 2023, it was observed that the impoundment caused a change in Coulomb stress at the epicenter of -0.69 kPa and a pore pressure of approximately 0.32 kPa. It is evident that the reservoir impoundment had a relatively minor impact on the fault activity where the MS 5.6 aftershock occurred and even exhibited a certain inhibitory effect. Moreover, seismic activity was mainly concentrated in two areas on the western side of the reservoir, with both the seismicity and expected magnitudes in these regions reflecting a higher risk of earthquakes.  Conclusion  This study demonstrates a correlation between the impoundment activities of the Dagangshan Reservoir and the occurrence of the Luding County earthquake and its aftershocks. The spatial distribution characteristics of the earthquakes align with the geological stress adjustment patterns following the reservoir impoundment, which played a promotive role in the occurrence of the MS 6.8 main shock, leading to an increased risk of earthquakes in the Moxi Fault region. This finding is significant for understanding the mechanisms of reservoir-induced earthquakes, subsequent aftershock analyses, and earthquake disaster prevention and mitigation efforts.  Significance  The results of this study provide new insights into the complex relationship between reservoir water storage and seismic events. This study offers a scientific basis for future assessments of seismic risks of reservoir design and operation, contributing to improved accuracy in earthquake early warnings and efficiency in disaster prevention and mitigation efforts.

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