Abstract:To construct road engineering in red mudstone regions, local materials are often used as subgrade fillers because of the shortage of materials and cost problems. To study the applicability of red mudstone fill material, weathered red mudstone fill material from a site in Yongdeng County, Gansu Province, was selected as the research object. A series of consolidated undrained (CU) triaxial shear laboratory tests was conducted to explore the effects of water content, confining pressure, and compaction degree on stress-strain curve, peak (residual) strength, and shear strength index. Furthermore, different types of stress-strain curves were fitted with the corresponding models. The results show that water content, confining pressure, compaction degree affect the physical and mechanical properties of the red mudstone fill material. For curves conforming to strain softening law, the fitting effect of the generalized hyperbolic model of Shen Zhujiang is not good. For curves conforming to strain hardening law, the fitting effect of the Duncan-Chang model is good. The research results provide a reference for the treatment and maintenance of red mudstone subgrades in Gansu Province.

Abstract:To improve the seismic isolation technology of long-span and super-long-unit continuous girder bridges, we proposed a novel seismic isolation system by introducing a negative stiffness device (NSD) into the bridge and compared it with the combined isolation system of viscous dampers and friction pendulum bearings. The finite-element model of the full bridge was established based on CSiBridge software. The NSD was simulated by an elastic multisegment line. The friction pendulum bearing and viscous damper were simulated using the bilinear restoring force model and Maxwell model, respectively. Nonlinear time-history analysis was conducted by inputting three seismic waves to investigate the seismic response of the bridge under the novel seismic isolation system. Results show that NSD and viscous damper can effectively reduce the bearing displacement of the long-span and super-long unit continuous girder bridge. The NSD performs better than the viscous damper in terms of controlling the internal force response of the pier and the acceleration response of the beam. The NSD presents a good application prospect in the seismic response control of long-span and super-long unit continuous girder bridges.

Abstract:Vibration produced by blast excavation of tunnels has a great influence on the safety of adjacent ancient buildings. To study the propagation law of blasting vibration waves, predict the ground vibration effect, and analyze the safety of adjacent ancient buildings, the dynamic response of Labuleng Temple under a blasting load was predicted using field measurements combined with numerical simulation analysis. The results show that (1) particle vibration velocity increases with explosive quantity, and attenuation ratio increases with vibration velocity, indicating fast and slow attenuation of high-and low-frequency vibrations, respectively. (2) Blasting load is applied to the elastic boundary or contour plane of tunnel excavation, and dynamic simulation results show that their vibration velocity is consistent at intermediate or far distances larger than 40 m; therefore, applying the load on the contour plane of the tunnel excavation is reasonable. (3) Volume waveform at the free interface of blasting seismic wave is reflected to form Rayleigh waves propagating along the surface. Combined with the numerical simulation of the propagation law of seismic waves in the mountain, a complex vibration zone is formed in the mountain by reflection and superposition. (4) When the local seismic wave reaches the Labuleng Temple, radial, vertical, and synthetic vibration velocities have peak values of 0.000 672, 0.000 448, and 0.000 807 cm/s, respectively, which are far less than the safety vibration control standard of ancient buildings.

Abstract:To further evaluate the seismic performance of isolated curved girder bridges under seismic excitation, the influence of seismic excitation direction on their fragility was studied. A finite element model of an isolated curved girder bridge with laminated rubber bearings was established by APDL. Near-fault ground motions in the same seismic event were selected from PEER, and horizontal bidirectional ground motions were input according to the proportion specified in the code for nonlinear dynamic time-history analysis. The seismic fragility curves of the components were calculated by combining the seismic response and damage index. Considering the change in seismic excitation direction, seismic fragility surfaces of the components (pier and bearing) and bridge system were obtained using MATLAB programming and the influence of seismic excitation direction on the fragility of the isolated curved girder bridge was analyzed and discussed. The results show that under different limit states, the tangential damage probability of each pier is obviously greater than that in the radial direction. The tangential fragility of each bearing is slightly greater than the radial fragility, with little difference. The tangential fragility of bridge members (pier and bearing) strongly depends on the seismic excitation direction, whereas the dependence of radial fragility is weaker; with an increasing damage level, the fragility of members becomes more sensitive to the seismic excitation direction. The fragility of the bridge system, which is insensitive to changes in the seismic excitation direction, is closer to that of the most vulnerable component because of the high correlation between the responses of the components. When evaluating the seismic performance of the isolated curved girder bridges, the influence of the seismic excitation direction on their seismic fragility should be considered to make the fragility analysis results more reasonable and reflect their actual damage state more accurately.

Abstract:As a type of liquefiable sand, the sand in Taian, Liaoning Province, has liquefaction resistance, which is of great engineering importance. To explore the improvement effect of nano colloidal silica (CS) on the liquefaction resistance of Taian sand, a series of undrained dynamic triaxial tests was conducted to compare the liquefaction characteristics of pure and treated sand samples. The effects of CS concentration and curing time on the dynamic characteristics of the sand samples were analyzed. The research results indicate that (1) CS improves the liquefaction resistance of Taian sand. Under the action of a dynamic load, no liquefaction damage occurs in the treated sand samples. (2) The dynamic pore pressure and dynamic strain of the samples rapidly decrease at first and then stabilize with increasing the CS concentration and curing time. When the CS concentration increases to 4% and the curing time reaches three weeks, the improvement effect of the sample's liquefaction resistance is not obvious. (3) The hysteresis curve of CS-treated sand samples becomes more stable than that of the pure sand samples. With increasing CS concentration, the damping decreases first and then tends to be stable, and the dynamic elastic modulus gradually increases and then tends to be gentle, with a certain fluctuation. With increasing curing time, the damping decreases and the dynamic elastic modulus increases. The research results provide a reference for sand liquefaction treatment in the Taian region of Liaoning Province.

Abstract:The problem of insufficient pullout capacity in a friction pendulum bearing and the need to optimize its vibration isolation performance led to the proposal of an adaptive magnetic levitation uplift-restraint friction pendulum bearing (AMFPB). This novel solution was developed by integrating the traditional FPB with semi-active control concepts. A theoretical analysis of the AMFPB was performed based on magnetic circuit theory. The analysis resulted in deriving the electromagnetic force formula for the U-shaped electromagnet. Additionally, formulas for calculating the stiffness, period, and equivalent damping ratio of the AMFPB were established. To further validate these theories, a displacement-electromagnetic force test was conducted on the U-shaped electromagnet. Concurrently, a finite element model of the AMFPB was established to analyze the hysteretic characteristics and pullout performance of the AMFPB under different displacement amplitudes, electromagnet turns, and input currents. The displacement-electromagnetic force test results of the U-shaped electromagnet matched the theoretical findings. Moreover, the calculated hysteretic curve of the AMFPB closely mirrored the numerical simulation result. A standout feature of the AMFPB is its ability to adjust its own stiffness and energy consumption in response to an increase in sliding displacement. This unique characteristic makes the AMFPB advantageous in controlling bearing displacement.

Abstract:The scattering issue of shear horizontal (SH) waves from solid elastic piles in a single row was analyzed using the wave function expansion technique and Graf's addition theorem. By changing a single variable, we analyzed the effects of the pile-soil shear modulus ratio and the number of piles on the vibration isolation capabilities of row piles. Our results show that when dimensionless frequency is low to medium, the dimensionless displacement curve beyond the row piles tends to zero at infinity. As the number of piles increases, the vibration isolation effect also gradually improves. However, the ratio of dimensionless displacement changes greatly in the range of 0-70a following the piles, leading to unstable and poor vibration isolation performance. When the pile-soil shear modulus ratio is less than 500, the vibration isolation effect within the range of 250a-380a proves to be satisfactory. Conversely, when the pile-soil shear modulus ratio is equal to or exceeds 500, there is no substantial increase in the vibration isolation effect. This suggests that the pile can be regarded as a rigid pile at this time. In instances of medium dimensionless frequency, the vibration isolation effect performs well within the 100a-120a range. The ratio of dimensionless displacement in this range experiences a sudden increase before gradually decreasing. However, as the dimensionless frequency escalates to high frequencies, the vibration isolation effect shows minor variation with different numbers and exhibits good performance close to the row piles.

Abstract:To accurately and efficiently identify structural damage in bridges, we propose a method based on a double-layer deep belief network (DBN). This approach combines deep learning with structural dynamic characteristics of structural engineering. First, the initial three vertical vibration frequencies of the structure, along with the first three vertical vibration modal displacements of midspan nodes, are taken as parameters. These parameters serve as the input data for the first-layer DBN to identify the damage location of the structure. Following this, the differences in the modal displacement of the first-order vertical vibration are taken as parameters. These are then used in the second-layer DBN to predict the extent of the structure damage. As a case study, we applied this method to the Zhengzhou-Xuchang suburban railway bridge. The calculation results show that when the error is not considered, the results of the structural damage identification method based on the double-layer DBN are precise. When the noise level does not exceed 10%, the accuracy of the location identification results is 100%. Even when the noise level does not exceed 15%, the maximum absolute error of quantitative identification results is not larger than -1.15%. Compared with the traditional BP neural network method, the proposed method demonstrates higher recognition accuracy and a stronger capability to resist noise.

Abstract:To reasonably reflect the influence of bond-slip performance degradation of corroded steel bars on the seismic performance of reinforced concrete (RC) structures, stress-slip relationship of steel bars was deduced based on an existing bond stress distribution model. Then, a bond-slip constitutive model considering the corrosion damage of steel bars was established by analyzing the influence of corrosion on bond-slip mechanism between concrete and steel bars. Based on existing pull-out test results, the rationality and accuracy of the proposed model were verified by comparing it with the Cheng model by only considering the influence of the longitudinal reinforcement corrosion rate. Based on the finite element platform OpenSEES, fiber beam-column and zero-length section elements were connected in series. The bond-slip model proposed in this paper was nested in the steel bar constitutive model of the zero-length section element; thus, a corrosion damage fiber beam-column model considering bond-slip was established. The accuracy of the proposed model was verified using quasistatic test results of six corroded RC columns. These results show that the hysteresis curve calculated by the proposed corroded RC fiber beam-column model considering bond-slip agrees well with the experimental hysteresis curve, and the maximum error of cumulative energy consumption is not more than 15%. In addition, factors affecting the slip of the corroded steel bar were studied using parameter analysis. The results show that yield and ultimate slips obviously decrease with increasing volume stirrup ratio and slightly change with an increasing ratio of concrete cover to steel bar diameter.

Abstract:For the careful examination of the mechanical behavior of saturated coral sand, a series of undrained cyclic triaxial tests was performed on saturated coral sand (Chibishi). The effects of different relative densities (D_r) and cyclic stress ratios (CSRs) on the excess pore water pressure (Δu), axial strain ε_a, and dynamic strength of coral sand were explored. Three main types of “Δu”, including uniform rising in the early stage, sudden rising in the early stage, and sudden rising in the late stage, can be developed in the presence of various CSRs. In addition, a new pore pressure model was used to characterize the pore pressure ratio r_u with uniform growth and sudden increase in the early stage. Under the same D_r, the number of cycles gradually decreased with the CSR when the axial strain with double amplitude ε_DA = 5% was considered. Under equivalent dynamic load, differences in the development of cyclic liquefaction resistance for various coral sands were detected. This study enriches the understanding of the liquefaction characteristics of coral sand and provides a reference for the seismic design of nearshore and coastal projects.

Abstract:In the aftermath of an earthquake, prompt damage assessment of bridge structures is a crucial step toward restoring traffic flow. This study focuses on representative railway rectangular bridge piers, validating the reliability of the finite element modeling method through four sets of quasistatic tests. We conducted endurance time analyses on 1 000 sets of data derived from the finite element model of bridge piers in both longitudinal and transverse directions. To fit the seismic dynamic response requirements, we constructed a BP neural network and established a rapid evaluation model for assessing seismic damage to railway rectangular bridge piers. The efficacy of this model was then confirmed through its application to a three-span concrete beam bridge. Our findings suggest that the reinforcement ratio, stirrup ratio, shear span ratio, and axial compression ratio are the four main factors affecting the seismic damage of piers. Meanwhile, the aspect ratio and the strength of both concrete and steel bars emerge as secondary factors. Under a design earthquake with a PGA of 0.32g, the probabilities of minor damage to the bridge, as calculated by numerical analysis and rapid evaluation of the neural network model, are 96.7%, 44.6%, 49.1%, and 96.7%, and 95.6%, 40.4%, 60.9%, and 95.8%, respectively. The probabilities of moderate damage are 40.1%, 1.2%, 1.6%, and 40.1%, and 37.4%, 2.3%, 6.0%, and 37.7%, respectively. The BP neural network algorithm can effectively establish the relationship between structural parameters and seismic responses, producing output errors within an acceptable range and exhibiting a high degree of regression. The BP neural network-based bridge seismic damage assessment model demonstrates excellent universality and can effectively replace some numerical simulation calculations.

Abstract:In the isolation design of bridges in cold regions, the current code only considers the influence of ambient temperature on the mechanical properties of rubber bearings. The code, however, overlooks how temperature affects the properties of concrete materials used in piers. This paper focuses on a two-segment, 3×30 m continuous concrete girder bridge in the alpine region. The aim was to determine the influence of temperature on the bridge's mechanical parameters by conducting a series of tests on the compressive performance of pier concrete materials at different ambient temperatures. Based on the test results, modifications were made to the mechanical parameters of the concrete used in the piers at different ambient temperatures. This allowed for the creation of refined nonlinear finite element models of the entire bridge at different ambient temperatures. Utilizing the incremental dynamic analysis, we discussed the seismic vulnerability of the bridge at different ambient temperatures. The results show that extreme temperature changes the material parameters of pier concrete and the stiffness of bearings, thus causing the natural frequency of the bridge to decrease as temperature increases. In the event of an earthquake, the displacement at the top of the pier top increases by 26.8% at extremely low temperatures. Meanwhile, bearing displacement increases by 19.4% at extremely high temperatures compared with that at normal temperatures. According to the current code, the failure probability of bearings and the entire bridge system is relatively low at extremely low temperatures. However, the failure probability of the structure and components is significantly higher at extremely high temperatures, a factor that should be closely considered during design. Compared to normal temperatures, the failure probability of the pier, bearing, and bridge system at extremely low temperatures increases by 45.0%, 35.2%, and 27.5%, respectively. Therefore, the influence of low temperatures on seismic performance should be considered when designing bridges like this in cold regions.

Abstract:To assess the damage state of reinforced concrete (RC) frame structures after earthquakes and improve the efficiency and accuracy of damage assessment, this study proposes an earthquake damage assessment method based on time-frequency analysis and one-dimensional convolutional neural network (1D-CNN). First, the earthquake damage to a six-story RC frame structure was simulated using incremental dynamic analysis. Based on the maximum story drift ratio, the degree of damage was calibrated to obtain data samples. Second, four different time-frequency analysis methods were applied to process the original signals. Third, an earthquake damage assessment model based on a 1D-CNN was established, and the optimal parameter combination in the model was determined using the Bayesian optimization algorithm. Finally, the generalization ability of the proposed model under noise was evaluated. The results show that among five time-frequency analysis methods, the wavelet-scattering transform method has the highest accuracy, reaching 92.5%, and the fastest calculation speed, taking only 144 s. In addition, the proposed method can maintain a high level of damage assessment accuracy under noise conditions, indicating good robustness and generalization ability.

Abstract:In engineering practices, the deterministic values of the response spectrum in accordance with seismic design codes are generally applied as evolutionary power spectral density (EPSD) parameters of ground motions. Although this treatment is convenient for engineering applications, it comes with two evident disadvantages. On the one hand, parameters are not obtained from measured strong motion records, which makes them highly empirical. On the other hand, the ground motion samples generated by deterministic parameters are extremely regular and exhibit unitary engineering characteristics, which cannot fully reflect the randomness of ground motions. To overcome the abovementioned challenges, we selected 1 766 strong motion records in the main axis direction from PEER and divided them into 15 groups based on the site categories suggested by the Seismic Ground Motion Parameters Zonation Map of China. Subsequently, the EPSD parameters of strong motion records were identified. Combined with the K-S test and BIC information criterion, the optimal probability models for each parameter were determined. Finally, based on statistical modeling results of EPSD parameters, representative time histories of site categories II and III were generated through the dimension reduction method. In contrast to the recommended values from the Code for Seismic Design of Buildings, the parameters suggested in this study were derived from measured records and possessed significant randomness, thus avoiding the simplification and regularization of engineering characteristics of ground motion samples.

Abstract:To explore the change law of cumulative plastic strain of loess subgrade under the coupling action of freeze-thaw cycles and traffic loads, remodeled loess in the Xining region was selected as the research object and a series of dynamic triaxial tests was performed using GDS bidirection dynamic triaxial test system. Effects of different freeze-thaw cycles, confining pressure, dynamic stress amplitude, and frequency on the cumulative plastic strain were investigated, and a prediction model for cumulative plastic strain with multiple factors was established by introducing fitting parameters. The results show that the cumulative plastic strain increases with the number of freeze-thaw cycles, and the growth rate slows down and stabilizes after six freeze-thaw cycles. Reducing the dynamic stress amplitude and increasing the confining pressure inhibits the development of cumulative plastic strain. The change in cumulative plastic strain with frequency is not possible at the initial stage of loading but becomes prominent with increasing vibration time, decreasing with increasing frequency. Based on the evolution law of the cumulative plastic strain of samples, the power exponential and logarithmic models were used for fitting, and the latter had a good fitting effect. Considering the influence of the abovementioned four factors on the cumulative plastic strain, a prediction model for the cumulative plastic strain was established, and the predicted value was compared with the measured values to verify the feasibility of the model. The research results provide a theoretical reference for calculating the permanent deformation of loess subgrade in seasonally frozen regions.

Abstract:To improve the deformation capacity of composite rubber bearings with a friction damper and the displacement coordination of friction components, solid and parametric computational models were established based on existing studies. The structure and internal force analysis of the novel composed isolation bearing were studied, and a solid finite element simulation of the friction damper and composed isolation bearing was performed using ABAQUS software. Based on the modeling and nonlinear time-history seismic response analysis of an isolated structure with conventional isolation bearing and the proposed combined isolation bearing, the relationship between the output and structural parameters of the composite bearing was deduced. The research results show that the parametric modeling method of the friction damper adopted in this study is accurate, and the novel composite bearing obviously reduces the tensile stress of the bearing and displacement of the isolation layer, improving the overturning resistance of the structure. The proposed simplified element for the friction damper can greatly improve the calculation efficiency of the finite element model.

Abstract:Determining an additional effective damping ratio is key to designing energy dissipation structures. To explore the influence of the number of floors with dampers on the safety of structure design, this study used a multistory reinforced concrete frame structure in Xinjiang as the research object. Nonlinear time-history analysis and mode decomposition response spectrum analysis of the equivalent structure model were performed. Based on shear force calculation results for each floor, the story damping ratio modification factor was introduced to promote iterative correction of additional effective damping ratio of equivalent structure model. The results show that the story damping ratio modification factor of the equivalent structure model first increases and then decreases with an increasing number of floors with dampers when using the time-history analysis under small earthquakes. Moreover, the reduction rate is the lowest when the number of floors with dampers is three-fifths of the total number of floors. However, an equivalent structure model where no less than two-fifths of the floors have dampers can meet fortification requirements when using the time-history analysis under intermediate earthquakes. Considering the comprehensive cost, the viscous dampers do not need to cover all floors.

Abstract:Based on the shaking table test results of a reinforced soil-retaining wall with rigid/flexible facings, FLAC^3D numerical models of reinforced soil-retaining walls with rigid/flexible facings, modular facing embedded return package structure, modular facing, and gabion facing were established, and the influence of different facings on the horizontal displacement, acceleration response, and seismic earth pressure distribution of the retaining wall was analyzed. The results show that the deformation modes of the retaining walls with different facings slightly differ under static loading. Under the action of vibration, the magnitude of facing deformation is rigid/flexible facing ＜ modular facing embedded return package structure ＜ gabion facing ＜ modular facing. The acceleration amplification factor in the reinforced zone is rigid/flexible facing ＞ modular facing embedded return package structure ＞ gabion facing ＞ modular facing. The acceleration amplification factor is greater at the facing than in the reinforced zone. The acceleration amplification laws and the nonlinear distribution laws of seismic active earth pressure differ among the facings. The position of the resultant force action point is mostly higher than H/3 of the M-O method, and it is less affected by the acceleration amplitude.

Abstract:As a novel variable section foundation, a root foundation can increase the vertical and horizontal bearing capacities of the caisson and pile foundations; however, its effect on the seismic performance of a digging well foundation remains unclear. To clarify the influence of roots on the bearing capacity characteristics of a pier on a digging well foundation, a pseudostatic test was conducted on a railway pier on a root-digging well foundation to examine the characteristics of its hysteretic and skeleton curves. By establishing a finite element model for use in this test, the influence of different root parameters on the energy dissipation capacity and bearing capacity of the pier was discussed. The results show that roots can improve the bearing capacity of the pier on the digging well foundation by fully promoting the participation of the surrounding soil, and the bearing capacity increases nonlinearly with displacement load on the pier top. Test and numerical simulation show that the damage to the root-digging well foundation is mainly caused by the failure of the soil around the foundation; however, the foundation is not damaged. The increase in the length of roots evidently improves the bearing capacity and energy consumption of the pier on the root-digging well foundation. Only when the spacing between the roots is greater than the root width does widening the roots obviously improve the bearing capacity and energy consumption of the pier. Increasing the number of roots obviously improves the bearing capacity of the pier. The effect of arranging roots at the bottom of the foundation is not weaker than that at the side wall, and the roots should not be near the soil surface when they are arranged at the side wall. The research results provide a scientific basis for the applications of root-digging well foundations in railway bridges in China.

Abstract:The attenuation relationship of seismic ground motion is a crucial empirical tool used to estimate the relationship between seismic ground motion and various factors. These factors include earthquake magnitude, distance, and site conditions. Recently, this tool is also called the ground motion prediction equation in China, which is one of the primary methods for estimating seismic ground motion and its influence field. Therefore, it is widely used in seismic zoning and seismic safety evaluation of major engineering sites. Loess is a special soil type that is widely distributed throughout China. In the Loess Plateau of China, which has a complex geological structure, the neotectonic activity is strong and medium-to-strong earthquakes occur frequently. So, the attenuation relationship of seismic motion in this area is unique and complex. Therefore, summarizing the research findings of the ground motion attenuation relationship in the Loess Plateau region of China is significant for promoting seismic research in this area. This paper provides a comprehensive and systematic summary of the research results of Chinese scholars on the attenuation relation of seismic intensity, peak ground acceleration, peak ground velocity, and peak ground displacement in the bedrock and soil sites of the Loess Plateau region. This study also reviews and discusses existing problems and future research directions in the field of ground motion attenuation research in the areas covered with loess. The research results have a significant reference value for scientific and technological personnel engaged in earthquake engineering research in the Loess Plateau region.

Abstract:The operation of electrohydraulic servo earthquake shaking tables can be affected by the system and type nonlinearities, leading to inaccurately reproduced waveforms. We propose a frequency-domain feedforward compensation method based on the power exponential method to improve the control of a shaking table during an earthquake simulation. The performance of the proposed method is evaluated using numerical simulations and actual earthquake shaking table tests. The results show that the proposed method converges quickly and requires fewer iterations than other methods. As a result, the waveform reproduction accuracy of earthquake shaking tables and their control performance can be significantly improved.

Abstract:Large aftershocks can cause additional losses and trigger the risk of building damage. To study the decay law of aftershock sequences, this paper attempts to use the exponential decay model to fit and analyze five aftershock sequences in various regions. The performances of the exponential and traditional aftershock decay models were analyzed using the corrected Akaike information criterion, Bayesian information criterion, and adjusted R². The results show that the ability of the exponential model to describe the decay law of aftershock sequences is close to that of the modified Omori aftershock model and the stretched exponential model, especially the M_S6.0 aftershock sequence in Changning, Sichuan Province, and the M_S5.7 aftershock sequence in the Yiliang county of the Yunnan Province. In these two sequences, the exponential model performed better than the other two models, and the exponential model parameters showed clear physical meanings. The sum of parameters A and r can accurately represent the number of initial aftershocks after a strong earthquake. The deviations in the initial aftershock number of the five aftershock sequences are all less than 1.70%. The parameter k can be used as a characteristic value that reflects the decay rates of the aftershock sequences. The larger the value of k, the slower the decay of the aftershock sequence; and its values are inversely proportional to the magnitude of the main shock.

Abstract:To enhance earthquake prevention and disaster reduction measures in cities, this paper proposes an evaluation system for the resilience of shelters after earthquakes and disaster prevention from the perspective of resilience. Thirty-one shelters in Shanghai were used as an example to verify the feasibility of the proposed evaluation system. Based on the absorption capacity, recovery capacity, and adaptation capacity of shelter resilience, twenty-four indexes were selected to construct an evaluation index system of shelter resilience for earthquake prevention and disaster reduction. A combination of a fuzzy analytic hierarchy process and a cloud model was then used to evaluate shelter resilience. The results show that most shelters in Shanghai are at a moderate level of resilience. The evaluation system can effectively identify the weaknesses of shelters in response to earthquake disasters and propose corresponding targeted measures, thus providing a reference for better resilience planning of urban shelters in China.

Abstract:Based on the mobile geomagnetic data of Tangshan and its adjacent areas obtained from September 2019 to April 2021, we construct the variation model of the lithospheric magnetic field anomaly in the Tangshan area and analyze the spatiotemporal variation characteristics of the lithospheric magnetic field before and after the Guye M_S5.1 earthquake on July 12, 2020. The results show the following: (1) There is a shift in the direction of the horizontal lithospheric magnetic field variation and an obvious decrease in its amplitude before the earthquake; before and after the earthquake, the lithospheric magnetic field experiences a spatiotemporal evolution process of “dispersing from the epicenter to the peripherygathering from the periphery to the epicenterreversing its direction.” (2) The total intensity of the lithospheric magnetic field at measurement points near the epicenter varies regularly in time and sequence, exhibiting the characteristic of “slowly decreasing before the earthquakesharply increasing during the coseismic periodsharply decreasing after the earthquake.” (3) Based on the piezomagnetic effect analysis and the meta-instability model of the fault, we consider that the spatiotemporal variation of the lithospheric magnetic field anomalies before and after the earthquake is caused by the accumulation and release of the in-situ stress of the main faults near the epicenter.

Abstract:Since 2014, the number of component borehole strainmeters in the middle section of the Tianshan Mountains has enormously increased. The high-sampling rate strain data contain significant tectonic information. The extraction of useful earthquake preliminary information from these data has become a top priority. We employ the S-transform and the overrun rate method to analyze the data obtained from eight sets of component borehole strainmeters in the middle part of Tianshan before two M_S6.0 earthquakes. The strain data obtained from five strainmeters provide information on high-frequency anomalies before two M_S6.0 earthquakes; these anomalies gradually increase before the earthquakes, then reach their peak values, and finally disappear before or after the earthquakes. The short-term abnormal signals are mainly concentrated in the 10-720 min frequency band. The S-transform and overrun rate analysis results are in good agreement. Combined with the GPS analysis results of the Jinghe earthquake source area and its vicinity, we observe that the distribution of high-frequency anomalies is in good agreement with the crustal movement field in this area. This indicates that the high-frequency anomalies extracted from the S-transform and overrun rate analysis are credible and can be used as a reference for earthquake case studies of strain observation data.

Abstract:The shape of seismic fault zones is essential for the study of active tectonics and geodynamics. The Maduo earthquake sequence that occurred in 2021 provides rich focal mechanism data and a suitable opportunity for counting the nodal planes of focal mechanisms and estimating the geometry of the seismogenic fault. Herein, the seismogenic fault geometry was determined using a density-based clustering algorithm to analyze the focal mechanism data. First, the central focal mechanism of the Maduo earthquake sequence was solved to obtain accurate data. Then, the results of a strike of 113.5° and a dip of 88.2° were obtained using the DBSCAN method. Finally, by inversion and projection of the stress field on the fault, the relative shear stress and relative normal stress were obtained as 0.84 and -0.79, respectively, and the sliding angle was estimated as -0.72°. The results show that the Maduo earthquake was caused by the stress of northeast-southwest compression and northwest-southeast extension. Then, a large shear stress was generated on the Jiangcuo fault with a nearly east-west orientation, thus causing a left-lateral strike-slip dislocation on the fault.