地质力学学报

The evolutionary process of Cenozoic Asian monsoon

LIN Xu, WU Zhonghai, DONG Yanyu, XIE Yuanyun, LIU Haijin, LI Zhaoning

Objective The formation of monsoon climates is attributed to the seasonal reversal of wind direction and precipitation caused by the difference in thermal capacity between land and ocean. Asia is recognized as the most prominent region globally, with monsoon climates, that affect the largest population. The heavy rainfall accompanying monsoons can result in various secondary disasters, substatially jeopardizing human safety and productivity in the region. Consequently, comprehending the formation process of the Asian monsoon holds paramount importance. Methods This study aim to employ geological concepts to establish a connection between the past and present, providing an overview of the components of Asian monsoons, identifying the primary factors influencing their formation and evolution, and summarizing research progress on the South Asian and East Asian monsoons based on sediment records from key Asian locations. Results The findings indicate that during the Cenozoic, the collision between the Indian Plate and the southern margin of the Asian continent altered the distribution of land and sea in Asia. Consequently, the Tibetan Plateau experienced initial uplift, contributing to the emergence of monsoon climates in South Asia and East Asia. However, at this stage, the East Asian region was still primarily influenced by the planetary wind system, and the East Asian monsoon was in its early stages, predominantly restricted to the southern margin of the South China Plate in a localized manner. In contrast, the South Asian Monsoon covered a relatively extensive area. This discrepancy may be attributed to the delayed opening of marginal seas in the East Asian region compared to the relatively earlier occurrence of land and sea distribution in South Asia. However, as the Tibetan Plateau continued to uplift and approach its current altitude during the middle to late Cenozoic, the Asian monsoon entered a strengthening phase, notably impacting regional geological evolution processes. Since the middle to late Cenozoic, the development of the North and South Polar ice caps and the upliftment of the Tibetan Plateau have controlled the Asian monsoon, leading it to undergo multiple stable periods of development. Conclusion The development and evolution of the East Asian and South Asian monsoons are mainly driven by the distribution of sea and land in the Asia, the upliftment of the Tibetan Plateau and the global climate change during the Cenozoic. Significance These findings provide valuable insights into the scientific and rational utilization of the Asian monsoon for conducting systematic Earth science research in Asia.

Characteristics of life-cycle stages and reservoir control in the development of extensional faults in the Dongying Sag

JI Qingjia, ZHOU Weiwei, HAN Runsheng, HU Yang

Objective Faults are among the most prevalent geological structures in oil and gas basins. Because of their significant connection to oil and gas resources, they have consistently attracted the attention of experts and scholars in the field, making them a hot research topic. Although previous researchers delved tirelessly into the correlation between faults, oil, and gas, new theoretical breakthroughs have been steadily emerging and have been used to promote advancements in oil and gas exploration. Nonetheless, there continues to be a dearth of thorough investigations into the underlying links between faults and the formation and distribution of oil and gas reservoirs, as well as methods for comprehensively and quantitatively defining the connections between faults and oil and gas. Methods The formation of a fault from inception encompasses multiple stages of development, including implicit and explicit stages, and differentiating the diverse growth stages of a fault, ranging from the initial embryonic stage to the terminal stage, poses a significant challenge. To address this issue, the Dongying Sag in the Bohai Bay Basin was selected as the focal point of this study. By employing physical and numerical simulation techniques, the researchers sought to replicate the entire life cycle evolution of the Chennan Fault, a basin-controlling boundary fault, from its embryonic stage to its terminal stage while elucidating the distinct characteristics of each stage. Building upon this foundation, the relative ages of the primary faults in the Dongying Depression and the various modes of fault activity at different stages were qualitatively and quantitatively determined, leading to the establishment of a reservoir-control model. Results The research findings indicate that normal faults tend to grow in six distinct stages: the embryonic stage (0 < RA (relative age) ≤ 1), characterized by microfractures or induced fracture zones; juvenile stage (1 < RA ≤ 2), with an intermittent connection of fault geometry; mature stage (2 < RA ≤ 3), marked by the connection of plate-like fault geometry and clear fault throw; declining stage (3 < RA ≤ 4), in which induced fracture zones form on both sides of the fault core, resulting in a shovel-like fault geometry; terminal stage (4 < RA ≤ 5), ramp-flat fault geometry, which has complex derived structures; and death stage (5 < RA ≤ 6), in which fault movement stops or undergoes inversion. The activity pattern of a fault is intricately linked to the duration and intensity of its age. Stable continuous, and high-intensity fault activity promotes the evolution of faults into their terminal stage. Research on reservoir control traps indicates that faults can create reservoirs at all stages of their development. However, as faults age, their ability to control reservoir formation strengthens. The types of traps influenced by faults transition from individual, isolated structures to a variety of arrangements. Moreover, the diversity of oil and gas reservoirs evolves from singular to multifaceted, and the size of these reservoirs expands from small to large. The embryonic and juvenile stage faults primarily influence closure; the mature stage faults predominantly impact sand and reservoir; and the declining stage and terminal stage faults primarily govern the overall distribution range of source rocks, as well as the migration, accumulation, and dissipation of oil and gas. Conclusion The reservoir control potential of the Chennan Fault was assessed by considering factors such as reservoir control advantages, the degree of oil and gas enrichment, and the scale of oil and gas accumulation. The reservoir control capacity of the Chennan Fault was classified as “strong.” Reevaluation of the fault’s reservoir control potential from the perspective of its developmental and evolutionary stages significantly enhances and elevates theoretical research on fault reservoir control and also advances exploration efforts in established mature areas. [Significance] Identifying the formation age and evolutionary patterns of extensional faults has immense theoretical and practical importance for comprehending alterations in the fault’s reservoir control capabilities. Moreover, it offers crucial guidance for oil and gas exploration, particularly for enhancing the reserves in existing exploration areas.

Differences in crustal stress direction in the southern section of the Huayingshan fault zone in Sichuan Basin: Insights from in situ borehole image logging

TANG Rong, LI Jinxi, LUO Chao, CAI Hongyan, XIE Rongjie, LIU Aodong, GONG Zilong

Objective The Huayingshan fault zone, the largest fault zone within Sichuan Basin, exhibits notable differences in geological structures on both sides. Historically, earthquakes with a magnitude of ≤5 have occurred frequently along this fault zone, which remains relatively active to this day, disturbing the crustal stress field of the basin. Clarifying the crustal stress state of the Huayingshan fault zone can enhance our understanding of its active deformation and its tectonic and seismic activities and serve as a reference for subsequent research regarding this fault zone. Currently, geostress studies in this area rely mainly on analyzing seismic data, whereas the investigation of borehole data remains relatively scarce. Methods We collected and collated imaging data regarding borehole collapse and borehole-induced tensile fractures from eight borehole logging sites in the southern segment of the Huayingshan fault zone; the geostress directions of these eight boreholes were determined by analyzing these data. Subsequently, a comprehensive analysis of the geostress characteristics was performed by combining the data regarding China’s modern stress field and the earthquake focal mechanism solutions in the southeastern margin of Sichuan Basin. Results The maximum horizontal principal stress in four boreholes located in the southern region of the southern segment of the Huayingshan fault zone was oriented in the NWW-SEE direction, which aligns with the regional stress field direction in Sichuan Basin; only one borehole in the southern region exhibited a maximum horizontal principal stress in the NEE—SWW direction, representing a counterclockwise deviation relative to the regional stress field of Sichuan Basin. Meanwhile, the maximum horizontal principal stress in all three boreholes in the central region of the southern segment of the Huayingshan fault zone was also oriented in the NEE—SWW direction, representing a counterclockwise deviation relative to the regional stress field of Sichuan Basin. Conclusion Through the comprehensive analysis of the above results and the tectonic features and basement properties of the study area, the following conclusions are drawn: (1) The deviations in stress direction in the southern segment of the fault zone are primarily caused by the combined effects of changes in the basement properties of the region, tectonic stress near the boreholes, and the regional stress field. (2) The geostress characteristics obtained in the present study, along with the focal mechanism solutions of earthquakes in the southern segment of the Huayingshan fault zone, indicate that the stress direction in the southeastern margin of Sichuan Basin is relatively divergent, resulting from the combined effects of complex local structures and the regional stress field in this region. Significance The present study aims to supplement the geostress data regarding the southern segment of the Huayingshan fault zone based on borehole data, analyze the current stress field state of the rock mass, and determine the direction of the maximum horizontal principal stress. These findings will provide supporting geostress data for subsequent research on the frequent seismic activities in this region.

Development characteristics and risk assessment of geological hazards in the mountainous and hilly areas of western Zhengzhou City

ZHANG Jianyu, LYU Dunyu, LIU Songbo, WANG Cuiling, MENG Shuran

Objective The mountainous and hilly areas of western Zhengzhou City have a complex geological environment, affected by rainfall and human engineering activities. Geological hazards such as collapses, landslides, and debris flows occur frequently. In particular, the “7·20” extreme rainstorm that occurred on July 20, 2021 caused many geological hazards, resulting in heavy casualties and huge economic losses. Therefore, analyzing and summarizing the development characteristics of geological hazards and conducting a risk assessment is necessary for this region. At present, the risk assessment of geological hazards is mainly conducted using a single method that has limitations including slightly low evaluation accuracy. In addition, an overall geological hazard risk assessment has not yet been conducted in the mountainous and hilly areas of western Zhengzhou City. Methods Based on the research and analysis of the geological environment background and the distribution characteristics of geological hazards in the study area, eight evaluation factors were selected: slope, landform, engineering geological rock group, elevation, distance from fault, distance from river, rainfall, and human engineering activities. The weighted information method which incorporates elements of the information quantity model and analytic hierarchy process, was used to evaluate the risk of geological hazards in the study area. Results The low-, medium-, and high-risk areas are 1387.14 km², 1803.18 km², and 1066.47 km², respectively, accounting for 32.59%, 42.36%, and 25.05% of the total area, respectively. The medium- and high-risk areas are mainly distributed in the tectonic erosion medium-low mountains and loess hills in the central part of the four cities, the tectonic erosion medium-low mountains south of Dengfeng, and the loess hilly areas in northern Gongyi and Xingyang. The terrain has steep slopes and deep gullies, and the main stratigraphic lithology is clastic rocks intercalated with carbonate rocks, soft and hard rock layers, and loess. Fault structures are developed, and geological hazards are prone to occur under the action of inducing factors and are highly dangerous. The majority (93.11%) of geological hazards are distributed in medium- and high-risk areas, with hazard point densities of 0.1752 km⁻² and 0.2869 km⁻², respectively. The spatial distribution of geological hazard points is consistent with the geological hazard risk assessment results. The rationality of the evaluation results was assessed by a Receiver Operating Characteristic curve, yielding an AUC value of 0.868. The evaluation accuracy met the requirements for hazard assessment. Conclusion Geological hazards have the largest information value in the range of >40° slopes loess hilly landforms, loess engineering geological rock groups, and 24-h maximum rainfall of 500–550 mm. The risk of geological hazards is positively correlated with distance from faults and water systems — the closer the distance, the higher the risk. The risk of geological disasters in the study area is controlled by the terrain slope and landform and is closely related to the lithology of the formation, which is an important factor in inducing geological disasters. The weighted information method, which has high accuracy and rationality, was used to evaluate the geological hazard risk. Significance The results of this study can provide a basis and technical support for geological hazard prevention and management in the mountainous and hilly areas of western Zhengzhou City and serve as a valuable point of reference for urban planning and infrastructure geological hazard risk assessment in the study area.

Application of integrated model based on EEMD-CNN-LSTM for landslide-displacement prediction

LIU Hangyuan, CHEN Weitao, LI Yuanyao, XU Zhanya, LI Xianju

Objective Landslide-displacement prediction is critical when evaluating landslide stability. Despite the achievements of time-series methods based on deep-learning paradigms in predicting landslide displacement, the nonstationary, periodic, and trending characteristics of landslide displacement data cause multivariate predictions of current time-series models to easily overfit. Existing studies primarily focus on improving single models, whereas systematic studies pertaining to multimodel integration methods are scarce. This study aims to develop an integrated model that addresses these challenges and improves prediction accuracy. Methods Considering the volatility of landslide-displacement data and the combined characteristics of their periodic and trending displacement components, a landslide-displacement prediction model combining isolation forest (IF) anomaly detection, ensemble empirical mode decomposition (EEMD), convolutional neural networks (CNNs), and long short-term memory (LSTM) neural networks is proposed. The stepped Baijiabao landslide in the Three Gorges Reservoir area, which is affected by rainfall, is investigated in this study. First, the IF algorithm is introduced to detect anomalies in the original landslide-displacement data. This enables outliers, which can distort the prediction results, to be identified and excluded. Subsequently, EEMD is adopted to decompose the displacement data into intrinsic mode functions (IMFs), which represent the underlying periodic and trend components. This decomposition allows one to analyze the inherent characteristics of the data more comprehensively. Next, a CNN is employed to capture local periodic and trend patterns within the IMFs. CNNs are particularly effective in recognizing spatial patterns and features, thus rendering them suitable for identifying complex patterns in the displacement data. Finally, the overall displacement is predicted using the LSTM model, which is suitable for accommodating sequential data and capturing long-term dependencies. These techniques are integrated to leverage their respective strengths, thereby improving the prediction accuracy. Result The results indicate that the root-mean-square error（RMSE）, mean absolute error（MAE）, absolute percentage error in evaluation (MAPE), and determination coefficient（R²）indices of the EEMD-CNN-LSTM model for predicting the overall landslide displacement under rainfall conditions are 0.4190, 0.3139, 0.2379, and 0.9997, respectively, which signify improvements in the accuracy of the first three evaluation indices by 32.3%, 25.1%, and 7.3%, respectively, compared with those of existing models. This significant improvement demonstrates the model’s robustness in accommodating the complexities of landslide-displacement data under varying conditions. For predictions without rainfall, the RMSE, MAE, MAPE, and R² indices are 0.4302, 0.2908, 0.2431, and 0.9996, respectively, which signify improvements in the accuracy of the first three indices by 31.2%, 31.7%, and 8.7%, respectively, compared with those of existing models. These results highlight the model’s high generalizability across different scenarios, as it can maintain high prediction accuracies regardless of external influencing factors such as rainfall. Compared with conventional LSTM, random forest, and EEMD-LSTM models, the EEMD-CNN-LSTM model offers significant advantages under the influence of rainfall and without rainfall, thus significantly reducing overfitting and improving the prediction accuracy. The hybrid approach effectively captures the intricate patterns in the data, which cannot be achieved by single models. Conclusion In summary, the multimodel integration method based on IF anomaly detection, EEMD decomposition, local-feature capturing by the CNN, and overall prediction by LSTM significantly improves the accuracy of landslide-displacement prediction, particularly under the influence of rainfall. The integrated model not only addresses the overfitting issues typically encountered in time-series prediction models but also enhances the model’s robustness and reliability. The combination of IF for anomaly detection ensures that outliers do not skew the prediction results, whereas EEMD facilitates the decomposition of data into meaningful components. The CNN’s ability to capture local patterns, coupled with the LSTM’s strength in modeling long-term dependencies, enables the establishment of a comprehensive framework that can effectively accommodate the complexities of landslide displacement data.[ Significance ]This study provides an effective multimodel integration method for landslide-displacement prediction, which addresses the overfitting issues in existing models as well as offers substantial scientific significance and practical value. The proposed model’s ability to accurately predict landslide displacement under varying conditions is extremely beneficial to the stability evaluation of landslide-prone areas, thereby contributing to disaster prevention and mitigation efforts. The innovation is based on the systematic integration of anomaly detection, data decomposition, and advanced neural-network techniques, which results in a robust framework that outperforms conventional methods. The findings of this study are applicable to real-world scenarios, thereby enhancing the accuracy and reliability of landslide monitoring systems and supporting informed decision-making in hazard management and infrastructure development.