Abstract:In this study, a single analytical model was employed to simulate the low-frequency impulsive components in near-fault ground motions, facilitating the investigation of the seismic response characteristics and damage of simply supported beam bridges under near-fault pulse-type ground motions. These components were superimposed with the high-frequency components obtained from the actual near-fault ground motion data after filtering, resulting in a synthesized near-fault pulse-type ground motion as the input. Then, a finite element numerical model was established using a four-span simply supported beam bridge as a prototype. Nonlinear seismic response time-history analysis was conducted to systematically study the effects of factors, including fault distance, number of impulsive pulses, moment magnitude, and the high-frequency components of the synthesized ground motion on the top displacement and damage state of bridge piers, along with the displacement and collision forces on the main beams. The results revealed that the low-frequency components of the ground motion served as the primary influencing factors on the impulsive peak values. Furthermore, the low-frequency impulsive components in the ground motion were used to determine the intensity of the simply supported beam bridge. When the moment magnitude of the ground motion was relatively small, the seismic response of the simply supported beam bridge was greater due to the larger peak value of a single impulsive pulse compared to multiple repeated pulses. Conversely, for ground motions with larger moment magnitudes, the seismic response of the bridge was greater under the action of multiple repeated pulses. The high-frequency components in the ground motion had a relatively minor impact on the structural seismic response; however, they affected the peak and residual displacements of the bridge. The study's findings underscore the fact that the influence of high-frequency components on structural response should not be overlooked during damage analysis.

Abstract:A six-span extradosed cable-stayed bridge with a single cable plane was investigated in this study to assess the influence of wave traveling effect on the earthquake response of multispan extradosed cable-stayed bridges. A finite element model of the full bridge was established using the software MIDAS/Civil, and the multi-point excitation behavior was simulated based on the theory of relative motion. The internal force or displacement response of three key positions, namely pier bottom, tower bottom, and tower top, under multipoint ground motion excitation were analyzed. Furthermore, the variation law of structural internal force and displacement under different apparent wave velocities was also explored. The research results reveal that the traveling wave excitation has a significant effect on the earthquake response of the multispan extradosed cable-stayed bridge. At an apparent wave velocity of 500 m/s, the internal forces or displacements at the most unfavorable key position are approximately 1.2 times those under uniform excitation. Furthermore, traveling wave excitation has adverse effects on the bending moment and shear force at the bottom of the middle pier and side tower, as well as on the displacement at the top of the side tower. As the apparent wave velocity increases, the influence of traveling wave excitation gradually weakens. When the apparent wave velocity exceeds 7000 m/s, the internal forces and displacements at key positions are basically the same as those under uniform excitation. This finding indicates that the influence of traveling wave excitation on the internal force at key positions of the structure can thus be ignored.

Abstract:The use of red clay, a widely-used material for subgrade-filling, easily results in the formation of an aggregate structure with different sizes, which means it has an important influence on the dynamic characteristics of soil. With the goal of investigating the effect of aggregate size on the dynamic characteristics of saturated red clay, a series of consolidation-undrained dynamic triaxial tests under different cyclic stress ratios were conducted in this study on compacted specimens prepared with different aggregate sizes (Dmax =5.0, 2.0 and 0.5 mm) using the dynamic triaxial apparatus GDS. The evolution of dynamic axial strain, dynamic elastic modulus, and damping ratio with aggregate size was analyzed. Several key findings are obtained. (1) The obvious increase in cumulative dynamic axial strain with increasing cyclic number is concentrated within the first 200 cycles, and such axial strain exhibits exponential growth as the cyclic stress ratio increases. (2) The more cumulative dynamic axial strain is observed from specimens prepared with larger aggregate sizes before the allowable cyclic stress ratio. In comparison, more cumulative dynamic axial strain is observed from specimens prepared with smaller aggregate sizes after the allowable cyclic stress ratio. (3) Under the same cyclic stress ratio, the dynamic elastic modulus and damping ratio of specimens with different aggregate sizes, almost align with the same growth tendency as the vibration times increased, thus indicating that the influence of aggregate size on dynamic elastic modulus and damping ratio is only obvious in the initial stage of cyclic loading.

Abstract:As a dynamic-sensitive structure, the changes in the offshore wind turbine structure are easy to affect the fundamental frequency of the system. The fundamental frequency of the system is key to the structure and foundation design of offshore wind turbines; hence, it is of great engineering significance to accurately calculate the fundamental frequency of the system. Based on the Euler-Bernoulli beam theory, considering the pile-soil interaction, added water mass, and the variable section characteristics of the tower, a calculation method of the transverse fundamental frequency of the single-pile offshore wind turbine system was established using the reverberation-ray matrix method. The accuracy and effectiveness of the proposed method were verified by a practical project, and the fundamental frequency excursion factors of the system were comprehensively analyzed. The analysis results showed that the pile-soil interaction, the added water mass, and the variable section characteristics of the tower all have a significant effect on the fundamental frequency of the system. The sensitivity of the system's fundamental frequency to different parameters is as follows: buried depth of pile foundation ＞ pile diameter ＞ modulus of foundation soil ＞ upper mass ＞ seawater depth ＞ wall thickness of pile foundation. When the buried depth of the pile foundation, the pile diameter, the foundation soil modulus, and the wall thickness of the pile foundation exceed the critical value, the change of parameters has little effect on the fundamental frequency of the system. To a certain extent, this paper revealed the influence law of fundamental frequency excursion factors of the system, thus providing a reference for the structure design of offshore wind turbines.

Abstract:This study presents an integrated seismic isolation design methodology tailored for special fortification buildings in compliance with the Standard for Seismic Isolation Design of Buildings.The approach was applied to a design project for a special fortification building situated in Kunming City. The structural design process was executed using the YJK software. Subsequently, seven seismic-motion time histories that meet the specified criteria were selected, and a dynamic elastic-plastic time-history analysis of the structure was conducted under seismic fortification, rare, and extremely rare earthquake scenarios using the ETABS analysis platform. The inter-story displacement angle and the floor horizontal acceleration under seismic fortification align with regulatory standards. During rare seismic events, the structure's inter-story displacement angle, floor horizontal acceleration, tensile and compressive stresses, and horizontal displacement of the isolated rubber bearings also conform to specifications. In the event of extremely rare earthquakes, the inter-story displacement angle and horizontal displacement of the isolated rubber bearings meet the prescribed requirements.The tensile and compressive stress limits of the isolated rubber bearings are maintained at 1 MPa and 20 MPa, respectively, indicative of a safety-focused approach. Results from the dynamic elastic-plastic time-history analysis confirmed that the isolation structure has effectively met the seismic fortification objectives by remaining intact during earthquakes, being repairable in rare seismic events, and averting collapse in extremely rare seismic circumstances.

Abstract:To reduce the damage and loss of bridge substructure during earthquakes, avoid casualties, and achieve rapid repairs after earthquakes, this study proposes an external replaceable energy dissipating links (EREDL)-precast segmental concrete-filled steel tubular pier based on the structural design concept of resilience. EREDLs with different levels of strengths were set at the joints of two groups of piers, and quasi-static tests were conducted on the piers under horizontal low cyclic loadings. Upon comparing the deformation of the two groups of piers, the results show that EREDL with Q355 strength is more resistant to deformation. Furthermore, a comparative analysis of the hysteretic curves, energy dissipation capacity, residual displacement, and degradation stiffness of two groups of piers reveals that the increase of EREDL strength within the range of 5% offset rate reduces the bearing capacity and increases the residual displacement of the pier. Overall, the research results can provide an important reference for the design and seismic performance optimization of precast segmental bridge piers.

Abstract:The dynamic response of oil well casings during earthquakes is crucial for the safety of oil well production and operation. In this work, a mechanical model for the transverse vibration of oil well casings was established based on the theory of elastic foundation beam and soil-structure interaction. Moreover, the numerical models for site soils without oil well casing and oil well casing-soil were established using the finite element and time-history analysis methods. The dynamic response characteristics of oil well casings subjected to El-Centro waves with varying peak accelerations were also investigated. The results indicate that, with increased burial depth, the displacement and acceleration responses of the casing and soil decrease, while the reduction amplitude increases. The seismic dynamic response of site soil is decreased due to the casing, while the reduction amplitude is small. The casing's seismic dynamic response is most pronounced at the surface (0 m), highlighting the nonlinear characteristics of soil. The casing produces stress concentration near the surface (0 m), representing the most critical position. The sudden change of stress occurs at the position where the soil stiffness changes considerably, with peak stress values fluctuating continuously in 2-6 and 9-12 s, resulting in severe deformation and damage to the casing. Furthermore, the acceleration time-history curve of the casing lags behind the input seismic wave time-history curve by 0.08 s. Soil deformation near the surface (0 m) is more severe than that in deep soil, and the acceleration time-history curve exhibits distinct multipeak characteristics. The research findings serve as a theoretical foundation and provide technical support for seismic design, safe production, operation, and maintenance of oil wells.

Abstract:In Changjiang County, located in the southwest mountainous area of Hainan Province, geological hazards have occurred frequently in recent years owing to the complex geological conditions and frequent engineering activities in the area. Therefore, studying the susceptibility of geological hazards in this region for the prevention, monitoring, and early warning of geological hazards has great practical significance. To evaluate the susceptibility of geological hazards in Changjiang County, the rock-soil mass, elevation variation coefficient, slope, fracture, undulation, river, road, and rainfall were selected as assessment indicators. The evaluation was conducted using four models: information value, certainty factor, logistic regression of information value (LRIV), and logistic regression of certainty factor. The results indicate that the high-susceptibility areas of geological hazards in Changjiang County are mainly distributed along roads and rivers in the mountainous areas, while the extremely low-susceptibility areas are located in the plains. The AUC values of the four models, 0.755, 0.749, 0.766, and 0.764, respectively, indicate that the prediction accuracy meets the requirement of susceptibility assessment and that the LRIV model is more reliable and accurate than the three other models. The findings of this research can provide a scientific basis for the prevention, monitoring, and early warning of geological hazards in the southwest mountainous areas of Hainan Island.

Abstract:The seismic behaviors of embedded perforated steel plate-reinforced concrete composite shear walls (EPSP-RCCSWs) are investigated in this study. In particular, two perforated steel plate shear walls and one EPSP-RCCSW were designed and fabricated based on the boundary condition and out-of-plane buckling constraint, after which the quasi-static test was carried out on these specimens. Then, the hysteretic behavior, lateral stiffness degradation, and energy dissipation capacity of shear walls were compared and analyzed through the experimental phenomena and data. The analysis results reveal that the EPSP-RCCSW realizes the two-stage design concept, which states that the embedded steel plate and the encased concrete provide lateral stiffness together under small earthquakes, and the encased concrete collapses to consume energy while providing out-of-plane restraint for the steel plate under large earthquakes. Furthermore, the reinforced concrete composite shear wall has high lateral stiffness, strong energy dissipation capacity, and good seismic performance. The force transmission mechanism of the tension band can be adjusted artificially, and the local bending and tearing caused by the buckling of nonperforated steel plates can be avoided by weakening the perforation of the steel plate. The results also indicate that the perforated steel plate specimen connected on four sides has better integrity and more sufficient tension band development. Moreover, the ultimate bearing capacity and lateral stiffness of the EPSP-RCCSW are significantly higher than those of perforated steel plate shear walls. The corresponding story drift also exceeds the limit of the elastic-plastic drift ratio of frame shear-wall structure (1.0%) with ultimate bearing capacity. Meanwhile, the bearing capacity and lateral stiffness tend to be the same as those of the perforated steel plate shear wall when the drift displacement reaches 4.0%. The viscous damping coefficient and energy dissipation capacity of the EPSP-RCCSW are significantly higher than those of the perforated steel plate shear wall. Moreover, the bearing capacity of the composite shear wall is approximately the sum of the bearing capacities of the perforated steel plate and the reinforced concrete walls. While the ductility of the composite wall is not as good as that of the perforated steel plate shear wall, the internal steel plate continues to bear the load and dissipate energy due to the constraint of the encased concrete plate.

Abstract:The impact and destructive capacity of debris flow on bridge piers are influenced by factors such as debris flow velocity, solid matter content, and solid particle composition. On this basis, a novel protective grille designed to shield bridge piers from debris flow erosion is proposed. The protective grille works by continuously regulating the solid particles in the debris flow, reducing the bulk density, the solid particle size, and impact force, thereby effectively protecting the bridge piers. A series of laboratory model tests were carried out to investigate the impact of structural parameters on the protection effect. Results indicate that: (1) As the drainage angle increases, the reduction rates of bulk density and coarse particle content in the debris flow within the grille initially increase and then decrease, following a quadratic function relationship; (2) As the grille span increases, the reduction rates of bulk density and coarse particle content consistently increase, displaying a linear relationship; (3) The scour height of the debris flow at the grille decreases as the relative opening spacing of the grille increases, showing an exponential function relationship. By contrast, the scour height gradually increases with the drainage angle, exhibiting a linear relationship. Meanwhile, through theoretical analysis, a method was developed to determine the structural parameters of the novel grille, including the drainage angle, span, height, and spacing. This approach provides a foundation for engineering design.

Abstract:Two methods based on finite state machine (FSM), namely state model-driven and table-driven, were investigated in this study to solve the problems of poor maintainability and difficult secondary development in the implementation of nonlinear constitutive models using traditional programming methods. Through comparison, the results reveal that the table-driven method can efficiently describe nonlinear constitutive models. Then, the stress-strain hysteretic curve of the Davidenkov constitutive model was modified, from which two construction forms of the hysteretic curve were proposed: failure point and correction point type. The results reveal that the modified Davidenkov model can correct the shortcoming of the “n-fold method” model, in which the shear strain reversely reaches the upper limit shear strain and is unable to enter the failure state, so it is more reasonable to be used in simulating the dynamic stress-strain relationship of soil, especially using the failure point model to simulate the shear stiffness of soil under cyclic loading and unloading. Based on the programming method of FSMs and the table-driven method, the constitutive programs of the Davidenkov model and its modified models were compiled, thereby verifying the effectiveness and correctness of the proposed method.

Abstract:In this study, the failure characteristics of loess-mudstone interface landslides under heavy rainfall were investigated, and their stability was evaluated. In particular, physical model tests, finite element numerical simulation, and theoretical analysis were conducted to reveal the deformation and failure characteristics of loess-mudstone interface landslides and improve the theoretical analysis and calculation methods, taking a landslide incident that occurred in Hui County, Longnan City, Gansu Province, as a case study. Several results were obtained. (1) Under the action of continuous heavy rainfall, the soil near the loess-mudstone interface is always in a saturated state. The main deformation process of loess-mudstone interface landslide is sliding-crack, with a composite failure mode of traction-push. (2) Landslide stability gradually decreases with the increase in rainfall intensity. After conducting multiple sets of landslide model tests to determine the landslide initiation times under different rainfall intensities, the results reveal that rainfall intensity and the landslide initiation time are logarithmically related. (3) Upon simulating the displacement changes of loess-mudstone interface landslide, it is revealed that the pore water pressure at the interface between loess and mudstone is the highest and gradually diffuses and decreases. This result is consistent with the actual infiltration characteristics of loess-mudstone interface landslides, thus verifying the accuracy of the conclusions obtained from the landslide model test. (4) Based on the traditional unbalanced thrust force method, the stability calculation method is improved, and the landslide stability is evaluated considering the influence of the seepage force generated by rainfall infiltration. The results indicate that the landslide stability coefficient is significantly lower than that required by the code, indicating that the time from the beginning of rainfall to slope instability is shorter than the conventional prediction value. The research conclusions provide an important basis for the research and prevention of landslide disasters.

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Abstract:Due to the subway's operations, high-frequency interference occurs on the tiltmeters in the Qingdao area. Furthermore, the daily interference occurs simultaneously with the subway's operation time. After conducting a qualitative analysis of data obtained from five sets of borehole tiltmeters in the Qingdao area, the results reveal that the tiltmeters within 2 km of the subway are disturbed by the subway's operations. However, when the distance exceeds 15 km, the tiltmeters are no longer affected by subway interference. At the same time, to quantitatively analyze the interference characteristics of the subway, the variational mode decomposition (VMD) method was used in this study to decompose the data of tiltmeters affected by the Qingdao subway interference. The accuracy of the K value of the VMD decomposition layer and the effectiveness of denoising were also verified using the generalized S transform. The findings indicate that the borehole tiltmeters undergoing interference from different subway lines in Qingdao have five interference mode components. Upon removing these components and reconstructing the data, the signal-to-noise ratio of the data is improved, effectively improving data availability.

Abstract:The deformation and failure mechanism of medium-steep bedding rock slopes under earthquake action is relatively complex. A medium-steep bedding rock slope with a rock dip angle greater than the slope angle was designed and fabricated using shaking table tests. The dynamic response characteristics and failure modes of the slope were examined under unidirectional and coupled seismic wave actions. The experimental results reveal a distinct nonlinear elevation amplification effect on the horizontal dynamic acceleration of the model slope. Remarkable nonlinear amplification and surface effect were observed within a depth range of 20 cm from the slope surface. Moreover, the dynamic response of the slope is more pronounced under coupled seismic waves. Under low amplitude and low frequency conditions, the slope exhibits a stronger dynamic response to natural waves than to sine waves. The peak horizontal acceleration (PHA) amplification factor of the slope increases with the amplitude. As the frequency increases and approaches the natural frequency of the slope, the PHA amplification factor experiences a significant increase. Coupled seismic waves further enhance the PHA amplification factor across various waveform, amplitude, and frequency conditions. Compared with other seismic waves, coupled seismic waves exert a more destructive impact on the slope. The failure process of medium-steep bedding rock slopes under earthquake action can be categorized into three stages: crack generation at the upper part of the slope, crack expansion and penetration, and sliding in the upper slope region, leading to slope instability.

Abstract:After the “9·5” Luding earthquake in 2022, a series of coseismic landslides and collapses occurred in the earthquake area, leading to the extensive accumulation and formation of loose solid debris. Under the action of heavy rainfall, the possibility of debris flow outbreak in the mountainous areas after the earthquake was greatly improved. On September 20, 2022, a once-in-a-decade heavy rainfall occurred in Nichang Gully, Caoke Township, Shimian County, resulting in a debris flow outbreak. During this event, massive amounts of debris flow rushed out of the gully and accumulated in the river, causing the river to be blocked. On August 14, 2023, another debris flow broke out in Nichang Gully again, leading to the silting-up of a new check dam downstream. In this study, FLO-2D was used to analyze the dynamic evolution processes of the Nichang Gully debris flow with and without a dam when the rainfall frequency reached 10%. Furthermore, the model accuracy was verified using the method of evaluation coefficient Ω . The results indicate that the modulus evaluation coefficient Ω of the dynamic evolution of Nichang Gully debris flow using this simulation method is 1.59, indicating the model's reliability. Meanwhile, the prediction of debris flow under three rainfall frequencies of 5%, 2%, and 1% was carried out. The simulation results of debris flow with prevention and control engineering under a rainfall frequency of 10% were coupled with the actual movement results of the “8·14” debris flow in Nichang Gully. The results indicate a preliminary judgment wherein the outbreak frequency of the “8·14” debris flow is once every 10 years. At the same time, the simulation results of debris flows under rainfall frequencies of 2% and 1% indicate that both lead to the failure of the control effect of the check dam. As the debris flow materials rush out of the gully, this incident causes the blockage of the river. With the change in rainfall frequency from 5% to 1%, the scope of debris flow threat also increases gradually. Overall, the threat of debris flow in Nichang Gully can be effectively reduced by adding retaining measures for the debris flow, building and maintaining the drainage channel project, and inspecting and dredging the check dam before the start of the rainy season each year.

Abstract:The amplification effect of ground motion on infrastructure found in loess sites was investigated in this study. Taking a simply supported beam bridge as the research object, a pile-soil-bridge model considering the horizontal coupling effect of the El-Centro wave was established based on finite element theory. The analysis focused on acceleration response, spectral characteristics, and displacement response, clarifying the pile-soil interaction characteristics in loess areas. The results reveal that the relative pile-soil displacement and the peak acceleration of pile foundation show an apparent increasing trend with the increase in peak ground accelerations (PGA). Furthermore, as the elevation rises, the PGA amplification factor and Fourier amplitude increase gradually, while the predominant frequency of structure gradually shifts to the low-frequency direction. Compared with the far-field soil, the peak acceleration of loess soil around the pile in the range of 0-20 m increases by 30.87%. With the increase in pile length, the relative pile-soil displacement and the acceleration response of the pile foundation also show an obvious increase. Furthermore, the increase in pile diameter can effectively reduce the relative displacement of pile and soil and a structure's acceleration response.

Abstract:The Jiashan—Lujiang fault is a major fault of the eastern branch of the Anhui section of the Tan—Lu fault zone, yet the Quaternary activity characteristics of the Hefei Basin section remain understudied. This paper presents an initial investigation into the geometric distribution characteristics and Quaternary activity of the Hefei Basin section. The study used shallow seismic exploration (high-density electrical exploration and ground-penetrating radar detection) in key concealed areas along the fault, as well as remote sensing interpretation and outcrop profiling in the bedrock outcrop areas. The results indicate that: (1) The Jiashan—Lujiang fault mainly extends northward from the interior of Guhe Basin, located east of Fucha Mountain, through the Zhangbaling Uplift. It should not be confused with the Outang—Qingshuijian fault, which is situated at the eastern foot of Fucha Mountain and the western foot of Zhangbaling Uplift; (2) The Hefei Basin section of the Jiashan—Lujiang fault exhibits distinct linear features, influencing the distribution of linear valleys, ridges, and some rivers, indicating recent activity; (3) The latest activity of the Hefei Basin section of the Jiashan—Lujiang fault is characterized by thrusting, with the most recent movement occurring during the middle-late period of Mid-Pleistocene.

Abstract:Using the strong motion records from 22 near-field stations in the focal area, the directionality of Newmark displacement during the 2013 Lushan M_W6.8 earthquake was investigated. The ground motions were projected using the modified Boore method to analyze the characteristics of Newmark displacement, including changes in directionality, the predominant direction (θ_max), and the ratio of maximum to minimum displacement values (Dn_max/Dn_min). Results show the following: (1) Newmark displacement exhibits distinct peaks and valleys as it changes with direction, and in most cases, the angle between the maximum and minimum directions is generally vertical. (2)Dn_max/Dn_min increases with critical acceleration (a_c); when a_c is large, Dn_max/Dn_min gradually increases with fault distance. In addition, the site type has a certain influence on Dn_max/Dn_min (3) A strong correlation exists between θ_max and the direction of coseismic displacement on both sides of the fault, but a weak correlation is observed on both ends of the fault. The correlation between θ_max and the vertical direction of the fault strike is weak, and θ_max does not notably change with a_c (4) The empirical model of Newmark displacement, which considers Arias intensity and earthquake magnitude, yields the best prediction effect of Newmark displacement when considering directionality.

Abstract:Gansu Province, one of China's provinces with high seismic intensity, has made notable progress in the informatization of earthquake disaster defense in recent years. However, technical systems for earthquake disaster defense at the municipal and county levels remain underdeveloped, resulting in issues such as ineffective resource integration across the province and limited data information services. Based on the earthquake disaster risk survey in Gansu Province, this study aims to develop a comprehensive earthquake disaster defense service platform at the provincial, city, and county levels. The platform integrates the display, query, and service of data related to earthquake hazards, disaster-bearing bodies, and earthquake disaster risk assessments. It also facilitates the unified aggregation and delivery of risk survey results across the three levels. Through various formats such as web pages, maps, and statistical charts, the platform provides informatization services for earthquake disaster risk prevention and control across Gansu Province. It aims to fully satisfy the operational requirements of earthquake departments at all levels and comprehensively enhance the seismic damage prevention and control capabilities across the entire province.

Abstract:The northwestern region of Yunnan Province (25°—27°N, 99°—101°E) lies along the western boundary of the Sichuan—Yunnan rhomboid block, a zone marked by active tectonic movements. This region is among the most seismically hazardous in China, requiring a comprehensive understanding of its seismogenic structures. In 2020, we analyzed continuous waveforms from 69 short-period stations in the area. We extracted Rayleigh surface-wave phase-velocity dispersion curves using cross-correlation of ambient noise and time-frequency analysis. We derived the Dl S-wave velocity structure beneath the study area using the direct inversion method of surface-wave dispersion based on ray tracing. The results reveal significant variations in the crustal velocity structure, particularly in segmented features along major fault zones. For example, at a depth of 5 km beneath the Weixi—Qiaohou fault zone, high velocities are observed in the northwestern section, whereas low velocities dominate the southeastern section. Similarly, the Chenghai fault zone exhibits high velocities in its northern segment and low velocities in the southern segment. In the Binchuan Basin, a low-velocity anomaly of approximately 5 km suggests the presence of a substantial sedimentary layer. Shallow crustal wave velocity correlates closely with terrain relief, with low velocities observed in basin areas and high velocities in mountainous regions. The 2021 Yangbi M6.4 earthquake occurred in a transition zone between high and low S-wave velocities. In addition, low-velocity zones of varying extents are identified in the middle and lower crust, potentially providing a seismogenic environment for the earthquake.

Abstract:To evaluate the damage degree of reticulated shell structures under 3D seismic action, two typical failure characteristics of these structures were analyzed using the incremental dynamic analysis method. By modifying relevant parameters in the formula of the Park-Ang seismic damage model, a damage assessment criterion was developed, incorporating two dynamic response indexes: structural deformation and energy. Moreover, damage performance levels corresponding to various failure states of reticulated shell structures were proposed. Results indicate that the failures of reticulated shell structures can be classified into dynamic strength failure and dynamic instability failure. The modified Park-Ang seismic damage model effectively evaluates the damage degree for these failure modes, with the damage value converging to 1.00 and exhibiting minimal dispersion. The damage degree of reticulated shell structures can be categorized into five levels: basically intact, slight damage, moderate damage, severe damage, and collapse, with corresponding damage limits of 0, 0.15, 0.65, and 1.00, respectively. Finally, by verifying the model with four different types of seismic waves that satisfy the specification, the modified Park-Ang seismic damage model effectively accounts for the coupling effect of displacement and energy consumption, providing a more accurate assessment of the overall damage to reticulated shell structures.

Abstract:On December 18, 2023, an MS6.2 earthquake occurred in Jishishan County, Gansu Province. The ascending and descending Sentinel-1A SAR satellite images were selected and the differential interferometric synthetic aperture radar (D-InSAR) technology was used to obtain the co-seismic deformation field of the earthquake. The results show that the long axis direction of co-seismic deformation field in the line of sight (LOS) direction is NW-SE, and the deformation is positive, indicating an approach towards the satellite and revealing surface uplift. The maximum deformation in the LOS direction of ascending and descending tracks is 12 and 9 cm, respectively. Subsequently, the co-seismic slip distribution was inverted using the steepest descent method with ascending and descending deformation data as constraints. The inversion results show that both the SW-dipping and NE-dipping fault models fit the observed values of InSAR co-seismic deformation field well, indicating that the MS6.2 earthquake is a combined thrust/strike-slip faulting type. The tectonic background and aftershock distribution in the study area were discussed to solve the controversies on the seismogenic fault and its dipping direction of the event. It is inferred that the seismogenic fault of the Jishishan MS6.2 earthquake is a hidden fault striking NW-SE and dipping SW, with a strike of approximately 148.4°, a dip angle of 52°, and a slip angle of approximately 130°, possibly a branch fault of the Jishishan east margin fault. Additionally, the co-seismic Coulomb stress model shows that the eastern section of Lintan-Tanchang fault, the eastern section of Lenglongling fault, the western section of Haiyuan fault, the western section of Lajishan southern margin fault, and the Guide fault are located at the positive-negative transition zone of co-seismic Coulomb failure stress change (ΔCFS), which should be given attention.

Abstract:An M_S6.0 earthquake occurred on September 16th, 2021, and affected 18 towns in Luxian County, Sichuan Province, with varying degrees. The seismic damage of residential houses in these areas is quantitatively analyzed through an onsite survey, and the relationship among house structures, epicentral distance, and degree of residential damage is assessed. A matrix of residential housing vulnerability in typical earthquake-stricken areas of the Sichuan Basin with different intensities is then established. Considering this matrix, the difference in average earthquake damage indexes between the affected areas and other regions that previously experienced earthquakes of the same magnitude is compared. Furthermore, the characteristics and factors that contribute to the residential housing damage in the study area are discussed, and the following conclusions are drawn: (1) The vulnerability of houses from high to low is brick-concrete structures, brick-wood and other structures (civil, wood, and stone structures), and steel-concrete structures; (2) 90% of the housing damage during the Luxian earthquake occurred in the area within 6 600 m from the epicenter; (3) Under two earthquakes with the same magnitude, the damage to residential houses in the basin is 1-2 times lower than that in the mountains. The results of this study can be used as a scientific reference for the rapid assessment of damages, planning, and reconstruction of residential housing after earthquakes in the Sichuan Basin and other earthquake-prone areas.