Abstract:

On October 20, 849 A.D. (October of the third year of Dazhong, Emperor Xuanzong of Tang), a great earthquake occurred near Baotou City, Inner Mongolia Autonomous Region, causing serious destruction of castles, military camps, and civilian houses and thousands of deaths. At present, the basic parameters of this earthquake (e.g., epicenter location, intensity, and magnitude) are controversial. In this work, the relevant historical records were systematically integrated. Further discussion was performed on the seriously affected towns, such as Yunjia Pass or Yunjia Town, because their locations were inconclusive. In addition, the earthquake intensity and locations of the main damaged places were reevaluated, the isoseismal map of the earthquake was modified, and the basic parameters such as earthquake magnitude and epicenter location were corrected. Results show that the isoseismal line of the earthquake in 849 A.D. is asymmetrically spindle- shaped, with its long axis in a nearly east-west direction and its short axis in a nearly north- south direction. The seismic intensity in the meizoseismal area can reach X-X⁺ degrees. The epicenter is located near Baotou City, Inner Mongolia (40.6°N, 110.3°E), with a magnitude of about 7.8±0.3 or 7 . On the south side of the isoseismal line, the earthquake has affected a large area (including Hetao Basin and its south area), with heavy earthquake damage and slow attenuation of seismic intensity. On the north side, almost no earthquake damage has been reported. Correspondingly, the attenuation of seismic intensity is fast, and the affected area is quite small. The isoseismal line shows that this earthquake belongs to a typical normal faulting earthquake, and the seismogenic structure is the middle- western segment of the Daqingshan piedmont fault. Our results on the epicenter location and earthquake magnitude, which are based on historical earthquake data, are consistent with previous findings based on active faults. This study indicates that the earthquake in 849 A.D., which occurred in the northern margin of Ordos, has a magnitude of about 7 . Further study must be conducted on the upper magnitude limit of future earthquakes and the risk of large earthquakes in this area.

Abstract:As an active fault developed in the Longzhong Basin, understanding the activity of the Xigongyi-Lidian fault is essential for assessing the seismic hazards in the Longzhong Basin and the remote response of the collision between Indian and Eurasian plates. The results of remote sensing interpretation and seismic geological survey show that: (1) the Xigongyi-Lidian fault is located in the central part of Longzhong Basin, with a length of about 120 km, an NWW strike, an NW dip, and a dip angle of 75°-80°. (2) The segmental feature of the fault activity is prominent. The central part of the fault is located in the Caledonian granite uplift area, and the surface is not exposed. On this basis, the fault is divided into east and west. (3) New activity in the western section is evident and mainly manifested as linear cliffs, steep slopes with a height of several meters, and left- lateral offsets in mountain ridges and gully water systems. The eastern section has a serious artificial transformation of surface structure and geomorphology and developed landslides in the loess area. (4) Combined with 14C dating results, preliminary investigation reveals a possible Holocene activity in the western section, and the nature of the activity is thrust and left- lateral strike- slip. The vertical slip rate since the Holocene is 0.342 mm/a±, and the maximum left- lateral slip rate since the Late Pleistocene is 1.60-1.67 mm/a. (5) Since the Late Pleistocene, at least two seismic events occurred in the western segment: one before (11 808-11 401) a B.P. and another between (6 291-6 120) a B.P. and (5 309-5 050) a B.P. (6) Combined with previous research data, this study concludes that the western section of the Xigongyi-Lidian fault may be the seismogenic fault of the Huining M7 earthquake in 1352, which was caused by the left- lateral thrust of the NWW- trending fault under the effect of NEE- trending tectonic stress in this area.

Abstract:The Changma Basin is an intramontane basin located at the western end of the Qilian Mountains. Previous studies focused on the structural deformation of its surrounding faults (such as the Changma fault), but its internal deformation is rarely studied. This paper presents studies on a newly discovered normal fault in the northwestern part of the Changma Basin on the basis of remote image interpretation, field investigation, trench excavation, differential GPS survey, and radioactive carbon (¹⁴C) dating. The fault is approximately 4 km in length, with a general strike of NE and dips NW. Its geomorphology is characterized by scarps, staircase scarps, and fault troughs. The height of the fault scarp is 0-5.6 m, which increases gradually from southwest to northeast. The fault activity is dominated by normal faulting, and its latest activity is determined in Holocene. The results suggest that due to the NW- trending growth of the northeastern margin of the Qinghai-Tibet Plateau, an NW-SE extension occurred in the Qilian Mountains, and the normal fault in the Changma Basin was formed by the SE extension.

Abstract:Qc is one of the important physical parameters to describe the attenuation of seismic waves underground. It can reflect the intensity of seismic activities and the degree of inhomogeneity of the underground media in a local area. In this work, the seismic records of 1 252 M ＞ 2.0 earthquakes with epicenter distance less than 100 km received by five fixed digital seismic stations in the focal area of the 1932 Changma earthquake and its adjacent areas from 2008 to 2020 were selected to calculate and analyze the attenuation characteristics of code wave in this area using Aki's single scattering model. Results show that: (1) the attenuation relationship between frequency f and Qc values with window lengths of 20, 30, and 40 s are Qc=^(71.76±8)f^(1.10±0.04), Qc=^{(103.83±17)f(1.04±0.06)}, and Qc=^(120.77±22)f^(1.00±0.06), respectively. (2) The spatial distribution diagram of Qc values plotted by Kriging interpolation indicates a correlation between the distribution of Qc values and the geologic structure and seismic activity in the focal area of the Changma earthquake and its adjacent areas. (3) The low Q₀ and high η in the study area are consistent with the strong tectonic activity in the region.

Abstract:On August 26, 2021, an M5.5 earthquake occurred in Aksai County, Jiuquan City, Gansu Province. It is a significant earthquake in the western Qilian segment of the northeastern Tibetan Plateau. To investigate the seismogenic structure of this earthquake, this study used the broadband seismic waveform data recorded by the regional seismic network to inverse the focal mechanism solutions of Aksai M5.5 mainshock and the M3.7 aftershock by applying the cut and paste method. Furthermore, the double- difference location method (HypoDD) was employed to relocate the earthquakes in the study area from January 1, 2021 to November 29, 2021. Results show that the Aksai M5.5 earthquake is an event dominated by thrusting. After relocation, the earthquake events are distributed intensively: the focal depth of Aksai M5.5 mainshock is 14.1 km, and those of aftershocks mainly range within 15-25 km. On the basis of the integrated analysis of focal mechanism solutions, the relocation results of seismic sequence, and the regional tectonic background, the southern margin fault of Danghenanshan is the seismogenic fault of the M5.5 earthquake. In light of these findings, attention should be paid to the risk of moderate- to- strong earthquakes in the western Qilian Mountains in the future.

Abstract:This work applies the double- difference tomography method for the tomography and relocation of earthquakes in the source area of Luding MS6.8 earthquake and its surrounding areas using the seismic phase data of 103 990 earthquakes (27.5°-31.5°N, 100°-104°E) recorded by Sichuan digital seismic network. Results show that: (1) the aftershock sequence is mainly distributed on the southwest side of the Xianshuihe fault in the NW direction, with a length of about 60 km. The focal depths are mostly concentrated at 5-15 km and exhibit symptoms of increasingly deepening from north to south. On the basis of the spatial distribution of the aftershock sequence and the location of the mainshock, the southeast section of the Xianshuihe fault is proposed as the seismogenic fault. In addition, branch faults may have occurred at the northern and southern ends of the aftershock sequence. (2) On the basis of the spatial distribution of background earthquakes, foreshocks of the Luding mainshock are speculated to have occurred. The high- velocity anomaly body on the northwest side of the mainshock may block the NW- trending rupture of the Luding earthquake. Given the weak mechanical property of the southeast section of the Xianshuihe fault, the Luding earthquake is inferred to have ruptured unidirectionally in the SE direction. (3) A weak S- wave low- velocity layer and a high- wave velocity ratio are found at a depth of 30 km below the focal area of the Luding earthquake. Previous studies found a high- conductivity layer and a low- resistivity layer in the mid- lower crust of the study area. The mainshock is located near the earth heat flow isoline with a heat flow value of 65 mW·m², so fluid may be found in the crust at 30 km below the focal area. Furthermore, the Luding earthquake occurred at the junction of high and low velocities where stress is easy to accumulate and release, resulting in rupture. A large amount of stress might have accumulated in the focal area, and the fluids in the crust flow into the seismogenic fault, weakening the fault. Finally, the combined effect of the two factors led to the occurrence of the Luding MS6.8 earthquake.

Abstract:In this study, the reverse annual variation of “low values in winter and high values in summer” in two measuring channels of geoelectrical resistivity at Dingxi station was analyzed using numerical simulation and convolution filtering, and the medium- and short- term anomalies of the resistivity data were extracted using the adaptive variation amplitude method. Results show that the annual variation of geoelectrical resistivity at Dingxi station is mainly influenced by seasonal variation and rainfall. The convolution filtering method can fit the effect of short- term rainfall and remove the annual variation of geoelectrical resistivity. However, the low values breaking the annual variation in 2021 have minimal relation with the rainfall and seasonal interference. Before the Jiuzhaigou M7.0 earthquake in 2017 and the Menyuan M6.9 earthquake in 2022, a significant short- to- medium term decline anomaly with a maximum decline of 0.983% appeared. After the Menyuan M6.9 earthquake in 2022, the abnormal pattern in the variation amplitude still exists even with the annual variation removed in the two channels. From the perspective of spatial characteristics, the geoelectrical resistivity at Dingxi station is indicative of the southeast Gansu and the middle- east section of the Qilian Mountains, so attention should be paid to the strong earthquake risk in these areas.

Abstract:Earthquake preparation and occurrence is accompanied by geoelectric field anomalies at different frequencies. However, the statistical characteristics of the correlation of the different frequency components of the geoelectric field with earthquake magnitude (energy) remain unclear. In this study, the geoelectric field data of Dulan station was decomposed into different frequency components using the wavelet transform, and the shifting correlation method was used to analyze the correlation of the different frequency components of the geoelectric field with seismic events within 400 km of the station. We calculated the dominant azimuth of the telluric field before and after the Maduo M_S7.4 earthquake in Qinghai Province to retrospectively verify the results. The following conclusions were drawn: (1) the different frequency components of the Dulan geoelectric field show anomalies during the earthquake preparation and occurrence and a certain correlation with the magnitude (energy) of seismic events. High- frequency components (3.4 and 8 h) are correlated with seismic events in the sequence of 5.0 and ≥ 5.0 earthquakes. For 5.0 earthquakes, the correlation is evident about 25 (±5), 10, and 5 days before the earthquake. For 5.0 earthquakes, the correlation is evident about 55, 35, 15, and 5 days before the earthquake. By contrast, the low- frequency component (24 h) demonstrates a significant correlation only with seismic events in 5.0 earthquakes 55, 35, 20, and 5 days before the earthquake. (2) Anomalies are observed in the dominant azimuth of the telluric field of the low- frequency component (24 h) about 55 (±5) and 20 (±5) days before the Maduo M_S7.4 earthquake. A high consistency is detected between the occurrence time and the statistical characteristics of correlation, possibly due to the interaction between seismogenic faults and solar and lunar tides. Data on the correlation of the low- frequency components of the geoelectric field with mid- strong earthquakes have some value for the analysis and investigation of destructive earthquakes. Additional observation data and typical earthquake cases are warranted to explain the statistical characteristics of seismic anomalies in the geoelectric field.

Abstract:The northeastern margin of the Tibetan Plateau has been struck by a series of large earthquakes since the Haiyuan M8.5 earthquake in 1920, including the Gulang M8.0 earthquake in 1927 and the Changma M7.6 earthquake in 1932. The region has entered a cluster period of intense seismic activity. A 3D Maxwell viscoelastic finite element model was established to simulate the coseismic and postearthquake Coulomb stress evolution of 17 earthquakes above M6.7 in the study region since 1920 to investigate the correlation between these earthquakes and the regional seismic hazards in the northeastern margin of the Tibetan Plateau. Results indicate that after the 1920 Haiyuan M8.5 earthquake, 13 of the 16 subsequent earthquakes occurred in regions with positive Coulomb stress change. This finding implies that the interaction between earthquakes may be one of the primary reasons for regional earthquake clustering. After the sequence of 17 earthquakes, the following faults are observed to be located in areas with positive Coulomb stress: Altyn Tagh fault, western Qaidam Basin fault, middle section of east Kunlun fault, northern Elashan fault, southern Gonghe Basin fault, southern Riyueshan fault, Zhuanglanghe fault, Lixian-Luojiapu fault, western Chengxian Basin fault, western Wenxian fault, southern Longhoushan fault, eastern Liupanshan fault, eastern segment of the north margin of western Qinling fault, western Haiyuan fault, and eastern Qilian fault. The cumulative Coulomb stress changes in these faults are greater than 0.01 MPa, indicating a significant risk of future earthquakes.

Abstract:On December 25, 1932, an M_S7.6 earthquake occurred near Changma Town, Yumen City, Gansu Province (epicenter: 39.70°N, 96.70°E). This movement is another strong earthquake along the Qilian Mountains-Hexi Corridor seismic zone in the northeast margin of the Tibetan Plateau following the Haiyuan M_S8.5 earthquake in 1920 and the Gulang MS8.0 earthquake in 1927. This group of large earthquakes, which is extremely rare in terms of time and space, has attracted extensive attention from many scholars. It is generally believed to be a typical example of an inland seismic activity migrating from east to west along the related fault zone. Using the program PSGRN/PSCMP and relevant results of previous geological surveys, this study established the fault rupture model of the Changma earthquake on the basis of elastic dislocation theory. The 3D coseismic deformation field of the surface generated by the Changma earthquake was simulated and calculated using the viscoelastic half- space layered model. The triggering effects of the Coulomb stress changes of the Haiyuan earthquake, the Gulang earthquake, and their superposition on the Changma earthquake were also studied. Results show that the Haiyuan earthquake, Gulang earthquake, and their superposition do not exceed the empirical threshold of possible triggering earthquakes. Therefore, the Changma earthquake may not have been affected by the Coulomb stress changes caused by Haiyuan and Gulang earthquakes. The simulation results in this work can provide a theoretical basis for explaining the seismogenic process of the Changma earthquake.

Abstract:Comparative observation of radon detectors serves as a basis for exploring the operating performance of instruments and provides reliable data for seismic research. A calibration experiment of dissolved radon in water was carried out using a DDL- 2 radon detector with an AlphaGUARD P2000 radon detector as the passive calibration instrument. The radon concentration response of the DDL- 2 radon detector was analyzed, and the comparative observation experiment of DDL- 2 and FD- 105K radon detectors was conducted. Results show that: (1) the deviations of calibration K values are within 4.827 6%, which meets the current technical requirements of seismic monitoring observation and instrument calibration. (2) The dynamic change of radon concentration can be described by the DDL- 2 radon detector. Using the Origin 2018 data analysis software to draw a fitting curve for radon concentration, we provide a mathematical model for the change of radon value. During bubbling, the radon concentration experiences a rapid rise period, a gentle period, and a stable period. In the stable period, the change range of radon concentration is about 5.0 Bq/L, and the curves change in different forms. (3) Using Origin 2018 as the comparative analysis data, we found that compared with the FD- 105K radon detector, the DPL- 2 and AlphaGUARD P2000 radon detectors are more sensitive to the diurnal variation of radon concentration and the coincidence degree of their radon measurement curves is higher.

Abstract:The year 2022 marks the 90th anniversary of the Changma earthquake. Earthquake early warning plays an increasingly important role in protecting people’s life and property safety. In recent years, China has invested in the construction of earthquake early warning projects; however, the experience of early warning operation and maintenance is poorly summarized. In this work, the waveform data of typical abnormal spikes from earthquake early warning stations in Gansu Province were taken as the research object, and the spectrum analysis of abnormal waveforms was carried out through Fourier transform to explore the frequency band range of interference sources causing abnormal waveforms. Results show that the dominant frequency of abnormal spike waveform is 0.2-46 Hz. In particular, the dominant frequency of the direct current’s interference on the waveform is 0.2-15 Hz, and that of the mains supply is 30-46 Hz. When the transmission lines of the mains supply and intelligent power supply are connected to the cycloid, the main supply and direct current cause interference with the waveform, thus forming a spike waveform. This study used the spectrum analysis method to quickly and accurately screen interference sources, providing a new idea for the operation and maintenance of earthquake early warning.

Abstract:Bound water in the soil is an important factor that controls the physical, chemical, and mechanical properties of clay soil. In this study, tests on the specific surface area and isothermal adsorption are conducted on a series of artificial mixed clay soil and two types of natural red clay to determine the specific surface areas, types, and contents of different bound water in clay soil. On this basis, the quantitative relationship between bound water in clay and certain influencing factors (e.g., mineral composition and specific surface area, including others) are discussed. Results reveal that (1) The specific surface area of clay has a positive correlation with the mineral content; (2) In the isothermal adsorption method, RH=0.90 and RH=0.98 are the dividing points of strongly bound water, weakly bound water, and free water in clay soil; (3) The adsorbed water content of mixed clay soil with the same mineral composition increases linearly with the montmorillonite content and specific surface area; (4) The adsorbed water content of natural red clay has a positive correlation with the total mineral composition and specific surface area, in which the clay mineral content is the most fundamental influencing factor.

Abstract:In this paper, a low- damage self- centering precast concrete (LDSCPC) frame joint with a replaceable mild- steel damper was proposed. A series of pseudostatic tests on full- scale specimens were conducted to study the seismic performance of the joint under earthquakes and its performance recovery after replacing them with mild- steel dampers. Based on the test results, parametric analysis and design optimization of the bolt preload, as well as the horizontal and vertical energy dissipation strips of the joint, were performed using the ABAQUS refined finite element model. Results show that the hysteretic performance and bearing capacity of the mild- steel damper LT12, as well as the energy capacity of LT14, is superior. Increasing the size and thickness of the damper energy dissipation strips can improve the energy dissipation capacity of LDSCPC frame joints during the early stage of loading. A large bolt preload can significantly improve the energy dissipation capacity of LDSCPC frame joints. When the preload is 155 kN, the mild- steel damper can almost achieve the ideal energy dissipation performance.

Abstract:Studying the mechanism of landslides and preventing disasters using small baseline subset InSAR (SBAS- InSAR) technology are important to monitor the time- series deformation of landslide- prone areas. In this paper, the time- series deformation characteristics of the Moli landslide in Goye Town, Zhouqu County, Gannan City, Gansu Province, were analyzed using the SBAS- InSAR technique. The deformation distribution map and temporal deformation characteristics of the Moli landslide area were obtained from the optical remote sensing image data from 2018 to 2021. Combined with other exploration results, the accuracy of the deformation monitoring results was verified, thereby confirming the reliability of the SBAS- InSAR technology for monitoring the deformation of superlarge landslides. Results show that the plane of the Moli landslide exhibits the shape of a “long tongue,” with a maximum length of 1 500 m in the sliding direction, and the landslide body is narrow at the top and wide at the bottom, with an average width of 240-530 m and an area of 53 × 10⁴ m. In addition, the deformation rate at the front part of the Moli landslide is greater than that at the middle and rear parts, and the maximum deformation rate of the front edge is up to 140 mm/a. Deformation of the Moli landslide continues to occur even today; hence, the deformation monitoring should be further enforced, and emergency evacuation and relocation measures should be taken. This study provides a reference for the resurgence damage mechanism and emergency response of superlarge landslides in the study region.

Abstract:A simplified analysis model of a soil- inter- story isolation structure was established in this paper based on the lateral- rocking damping system model. The foundation soil was equivalent to the superstructure, and then the expression for dynamic characteristic parameters of the simplified model was derived. The influence of the mass ratio and shear wave velocity of soil on the natural vibration characteristics of the inter- story isolation structure was discussed by analyzing the period ratio and modal participation displacement. Then, the influence of the soil- structure interaction (SSI) effect on the vibration response of inter- story isolation structures under different site conditions was analyzed in the time and frequency domains using virtual excitation and nonuniformly modulated nonstationary random response analysis, respectively. Results show that the structural mass ratio has little effect on the period ratio and modal participation displacement of the structure on a rigid foundation. The SSI effect enlarges the response of each substructure, particularly the response of the lower substructure. The response of each substructure changes significantly with different soil sites, and it increases in soft soil sites.

Abstract:The seismic performance of a novel steel- reinforced concrete (SRC) column with various thicknesses, diameter- thickness ratios of steel pipe, axial compression ratios, and concrete strengths was investigated using numerical simulation. Given the reasonable simplification of the section of the new- type SRC column, the calculation formula for the bearing capacity of the normal section was proposed based on the plane section assumption. Notably, the calculation results are consistent with those obtained from test and numerical simulations. Furthermore, a method for calculating characteristic parameters such as yield point, peak point, failure point, loading stiffness, and unloading stiffness was proposed, and the hysteretic rule of the restoring force model was suggested. Finally, the restoration model of the novel SRC column was established on the basis of three degenerated linear models. The hysteretic curves calculated using the formula are consistent with those obtained from the test.

Abstract:In view of plane strain problems in engineering, according to the plane strain condition and the generalized Hooke's law, formulas for calculating the active and passive earth pressures of noncohesive soil considering the influences of intermediate principal stress and Poisson's ratio were derived on the basis of the SMP, Lade- Duncan, AC- SMP, and generalized Mises strength criteria. Then, the formulas were extended to cohesive soil, and the application range of each formula was discussed on the basis of different strength criteria. Results show that after considering the contribution of intermediate principal stress to soil strength, the active earth pressure calculated based on each strength criterion is less than the Rankine active earth pressure, and the passive earth pressure is greater than the Rankine passive earth pressure. The active earth pressure P_a decreases, and passive earth pressure P_p increases with increasing Poisson's ratio; a larger Poisson's ratio indicates that the earth pressure is closer to the measured value. The range of internal friction angles, which are applicable to the active and passive earth pressures based on the same strength criterion, increases with increasing Poisson's ratio. The calculation formulas based on each strength criterion can well describe the soil pressures on retaining structure, among which the calculation results of the generalized Mises strength criterion are consistent with the actual project. The research results can provide a theoretical reference for calculating soil pressures on retaining structures.

Abstract:Soil nails of steel tubes have been widely used in foundation pit engineering, but their mechanism of uplift bearing capacity remains unclear. According to its supporting principle, three failure modes and four loading stages of soil nails of steel tubes were analyzed. Based on the Coulomb earth pressure theory, a calculation formula for the uplift bearing capacity of the soil nail of a steel tube was derived by taking the gravity of the soil above the sliding soil as uniformly distributed loads. By taking a foundation pit in Lanzhou as an example, the calculation method for the ultimate uplift bearing capacity of soil nail of steel tube introduced in the Technical Specification for Retaining and Protection of Building Excavations was proposed in this paper, and the results of the uplift test were compared and analyzed. Results show that in the failure mode of the soil nail of the steel tube, the bolt body is pulled off, and the anchor body is cut off. In addition, the deformation of soil in front of the anchor is large. The four stress stages include stationary, plastic zone generation, plastic zone expansion, and failure stages. The proportion of uplift provided by the slurry anchor body increases significantly with an increase in the embedded depth of the steel pipe, which is an important component of the ultimate uplift bearing capacity of the soil nail of a steel tube.

Abstract:Building structures in severe cold regions require a cold- proof, warm- keeping, anti- freezing, and anti- earthquake design because of the particularity of the region and climate. Therefore, the vibration response of building structures in severe cold regions under the action of horizontal earthquakes is analyzed in this paper. ABAQUS was first used to build a three- dimensional frame- shear wall structure system. Then, the Timoshenko Beam element in the software was selected considering the shear deformation, and the steel and concrete material models were redeveloped to establish a spatial frame finite element model of the building structure. Finally, three kinds of seismic waveforms were input to analyze the vibration response of building structures in severe cold regions. Analysis results show that when the temperature is between -30 ℃ and 30 ℃, beams and columns of the building frame under different seismic waves show shear failure, and the variation range of inter- story displacement is excellent. The vibration displacement at the top node of the building structure and risk of collapse increase with decreasing ambient temperature in severe cold regions. Therefore, protective walls that can conserve energy and decrease carbon content must be established in building structures of severe cold regions, thereby achieving the seismic effect of low carbon and environmental protection for building structures.

Abstract:The seismic wave input has an important influence on the nonlinear response of a structure. Selecting and inputting appropriate seismic waves for calculation are the primary conditions that must be considered to ensure accurate results for the time- history analysis of a structure. This paper optimizes and proposes a wave selection method that considers the time- frequency characteristics of seismic waves by comparing different modeling methods for the instantaneous spectrum of the seismic wave. Results show that the proposed wave selection method matching of the instantaneous spectrum can effectively control the difference between various selected seismic waves in time and frequency domains and reduce their response dispersion of the time- history analysis of structure, thereby providing a basis for wave selection in actual projects.

Abstract:Risk analysis of loess seismic landslides is critical to urbanization, engineering construction planning, and earthquake disaster prevention in loess areas. In this study, data on historical earthquake landslide hazards in the Minxian-Zhangxian junction of Dingxi City, Gansu Province, were collected and analyzed. Then, an evaluation index system containing eight impact factors, that is, earthquake, slope angle, slope height, slope direction, stratigraphic lithology, average annual rainfall, river basin, and geomorphological type, was summarized and established. Based on the proposed index system, the information value model, logistic regression model, and information value- logistic regression coupling model were used to assess the risk of loess earthquake landslides in the study region. Results show that earthquakes, rivers, and rainfall are the main impact factors of loess landslide disasters, with earthquakes having the most contribution. In addition, the study area can be divided into five risk levels: very high- , high- , medium- , low- , and very- low- risk areas; the very- high- risk areas are primarily concentrated in Minxian, Zhang- xian, and Longxi Counties. Based on the accuracy test results of the receiver operating characteristic curves, the AUC values of the three models are found to be 0.889, 0.617, and 0.898, respectively, and the results of the information value- logistic regression coupling model are more accurate than those of the other two models.

Abstract:In this paper, a formula for calculating the seismic force and safety factor of the slope was derived using the limit equilibrium method based on the basic principle of pseudo- dynamic and rigorous slice methods (Sarma method). Thus, a corresponding calculation program was developed based on the Python language. Furthermore, a new pseudo- dynamic method for analyzing the seismic slope stability considering the wave propagation effect was achieved, which is suitable for random slip surfaces and slider slices. The effect of ground motion characteristics and structural plane strength on the seismic stability of slopes was also discussed. Research results show that the safety factor fluctuates periodically with changes in the initial phase of seismic waves, and a minimum safety factor is observed. The safety factor decreases with an increase in the amplitude of ground motion and the ratio of seismic wavelength to slope height, and it decreases with a decrease in the shear strength parameters of the structural plane. In addition, the difference and relationship between the pseudo- static and pseudo- dynamic methods were determined on the basis of the wave theory: if the ratio of the seismic wavelength to the slope height is greater than 10, then the results obtained by the two methods are the same; if the ratio is less than 10, then the results obtained by the pseudo- static method are relatively conservative compared with those obtained by the pseudo- dynamic method. Thus, the pseudo- dynamic method is more reasonable.

Abstract:Machine learning cannot achieve good evaluation results in large areas without historical landslide data; hence, this paper proposes a transfer learning method. First, a pretraining model with high accuracy was obtained by combining ten influencing factors, and the extremely seismic zone of the Lushan M7.0 earthquake in 2013 was pretrained using the random forest algorithm. Then, an initial transfer was performed using the direct transfer learning method, and the label numerical points in the northeastern margin of the Qinghai-Tibetan Plateau were supplemented using the “semisupervized” evaluation method. Finally, the pretraining model was further trained using inductive transfer learning to obtain an accurate seismic landslide susceptibility assessment map in the northeastern margin of the Qinghai-Tibetan Plateau. In addition, similarity in the influencing factors before and after the transfer was calculated using the Kullback- Leibler divergence. The accuracy of the proposed model based on transfer learning in the northeastern margin of the Qinghai-Tibetan Plateau was verified by applying it to the extremely seismic zone of the Luding M6.8 earthquake in 2022. This study provides a reference for preventing earthquake- induced landslides in the study region.

Abstract:Aftershocks are produced from mainshock, indicating a certain correlation between them. Thus, establishing a main- aftershock ground motion model will serve as the basis of seismic analysis for engineering structures. Based on the characteristics of a main- aftershock- type ground motion, such as peak acceleration, strong earthquake duration, and predominant frequency of the site, evolution power spectrum models of aftershocks and mainshocks were established in this paper. Then, based on the spectral representation of a nonstationary random process, the main- aftershock- type ground motion can be accurately simulated with three basic random variables using the dimension reduction simulation of the stochastic function. Numerical examples show that the efficiency and accuracy of the dimension reduction simulation used in this paper can meet engineering requirements. Simulated results are consistent with the fitting between response and amplitude spectra of the measured ground motion records. This verifies the superiority of the model and the method developed in this paper, thereby providing an effective way for seismic analysis of engineering structures subjected to main- aftershock stochastic earthquakes.

Abstract:Using an actual project as an example, a three- dimensional numerical model was established based on the shaking table test results and numerical simulation results to study the dynamic response law of the slope- tunnel system under different excitation directions of Lanzhou artificial wave. The dynamic response law of the lining structure was analyzed from the perspective of energy and frequency domains using the wavelet packet transform. Results show that the seismic wave perpendicular to the tunnel axis (X, Z) in horizontal and vertical planes will cause a large response at the maximum buried depth of the tunnel, and the seismic wave parallel to the tunnel axis (Y) in the horizontal plane is most unfavorable to the structure. The low- frequency wave in the frequency range of 0-12.5 Hz primarily causes the tunnel response. In this frequency band, the energy of the vertical seismic wave (Z) occupies the highest proportion compared with other seismic waves. The existence of a lining structure has a certain restraining effect on the deformation of surrounding rock under earthquakes. Seismic waves in the X and Y directions can easily cause the shear failure of surrounding rock near the foot of the slope, and the seismic wave in the Y direction has a remarkable influence on the slope of the tunnel portal section. The seismic wave in the Z- direction leads to the tensile failure of surrounding rock near the top of the slope, thereby producing the most adverse response near the tunnel vault. The research results can be used as a reference for the anti- seismic design of shallow- buried double- arch tunnels under unsymmetrical loading.