Abstract:The thicknesses of bound water film of Late Pleistocene loess and paleosol in Weibei, Shaanxi Province, were studied based on nuclear magnetic resonance, specific surface area tests, and theoretical analysis to comprehensively analyze the influencing factors of the engineering properties of loess and paleosol. Experimental results show that the thickness of the bound water film of loess is larger than that of paleosol, and a considerable difference is observed between their thicknesses. This difference can be attributed to the smaller pore volume and size of paleosol than those of loess, while the content of high-valence cations in paleosol is greater than that in loess. In addition, the surface of paleosol particles is distributed with an iron-manganese film; therefore, its hydrophilicity is weak. The relationship between bound water film and engineering characteristics of loess, such as collapsibility and rebound deformation, was analyzed. The collapsibility of loess-paleosol increases with the thickness of bound water film and decreases with the thickness of bound water film. The thickness of the bound water film is positively correlated with the unloading deformation coefficient. Comprehensive analysis shows that the variations in high-valence cation content, particle surface characteristics, and porosity contribute to the difference in bound water film thickness between loess and paleosol. This phenomenon leads to differences in engineering properties, such as collapsibility between loess and paleosol.

Abstract:Chloride ion erosion in bridges in long-term service leads to the degradation of material properties and affects the seismic performance of bridge structures. Accurately evaluating the seismic performance of bridges in service can effectively guarantee and improve the safety of bridge structures. Therefore, seismic fragility analysis considering a time-varying effect is essential. In this study, the time-varying seismic fragility analysis of bridges was carried out. The degradation of material properties caused by chloride ion erosion on the seismic performance of the bridge was considered. Given that seismic fragility analysis involves comprehensive dynamic time-history analysis, the calculation efficiency is low. Thus, the Gaussian process model was used to replace the time-consuming dynamic time-history analysis to improve the efficiency of the analysis. The degradation law of the pier material properties under the action of chloride ion erosion was explored in a three-span continuous beam bridge. Then, the degradation time-varying curves of the longitudinal reinforcement, stirrup, protective layer concrete, and core concrete were established. Based on the Gaussian process and probabilistic seismic demand models, the fragility curves and surfaces of bridge systems with different service years were established. Results show that (1) the strength of the reinforced concrete materials of piers is substantially reduced by chloride ion erosion, and (2) chloride ion erosion obviously increases the seismic fragility of the bridge with high-level damage, and the structure is more prone to high-level damage.

Abstract:To accurately evaluate the self-weight collapsibility characteristics of the Angola red sand site, a field immersion test for monitoring and studying the deformation of ground surface and strata at different depths and water migration regularity was conducted. The standard penetration test (SPT) blow counts before and after immersion were determined, and the difference between the results field and indoor tests was discussed. Results indicate that after immersion, the ground surface of red sand shows continuous uplift deformation. The deformation curve can be divided into four stages: steep rise, slow rise, unstable, and stable. The red sand stratum with a depth of more than 8 m shows collapsible settlement deformation, with a cumulative collapsible settlement of 5.6 mm, which is far lower than the self-weight collapsible settlement calculated by the indoor test (137 mm). The vertical and horizontal permeability rates of red sand are large, and the water content of red sand changes rapidly after water immersion and water cutoff. The water holding capacity of red sand is poor. During water immersion, the saturation of red sand formation is less than 80%, which is unsaturated permeability. The SPT blow counts of red sand formation decrease considerably after water immersion, and softening characteristics are evident. The large permeability coefficient and poor water holding capacity of red sand impede the development of a saturation state, and thus, the measured value of the self-weight collapsible settlement is far lower than the calculated value. In general engineering construction, a design based on the softening characteristics of red sand foundation instead of collapsible characteristics is recommended. The results can not only guide engineering construction in red sand sites but also provide a reference for the collapsibility evaluation of other types of sand.

Abstract:Conventional magnetorheological dampers are usually powered continuously by coils, which not only increase energy consumption but also reduce the service life of a device. Based on the shearing principle of magnetorheological gel (MRG), a novel shearing magnetorheological gel damping device was designed in this paper. The permanent magnets and coils were used to jointly control the magnitude and direction of the device's magnetic field, and the damping force magnitude was controlled by changing the magnetization level of MRG. The device was installed at the bottom floor of a two-story steel frame-structure model, and the shaking table test of the magnetorheological damping structure was carried out using the constant current control method. The control effects of the damping system on different seismic waves under different currents were analyzed. Results show that the MRG damping device can significantly reduce the dynamic response of the structure; the damping effect varies for different seismic waves, and the damping effect decreases with increasing peak acceleration.

Abstract:The three-river basin of the southeast Qinghai—Tibet Plateau has widespread accumulation slopes, which can easily evolve into landslide disasters. In this study, the dynamic response characteristics and failure modes of earthquake-induced accumulation landslides in the Xiaguiwa slope in Batang, Sichuan Province, were investigated with shaking table model tests. Results show that the natural frequency of the slope increases because of the compaction of pores in the early stage of earthquake action. Under the excitation of a Maoxian wave, the slope shoulder responds strongly. Under the excitation of a high-amplitude Maoxian wave, the amplification effect weakens because of the decrease in the overall stiffness of the slope. The Hibert spectrum describes the propagation characteristics of the seismic wave in the slope. When propagating to the slope top, the high-frequency energy of the seismic wave is considerably enhanced. The amplification effect weakens after the seismic wave passes through the accumulation layer. Under the action of strong earthquakes, the response of the slope surface at a certain depth shows a consistent and violent phenomenon. The upper part of the slope will form a “detachment body”, which will show upward and downward jerky motion under earthquake action. The strongest dynamic response appears at the slope surface approaching a slip. The characteristics of the failure mode of the slope are as follows: in the early stage of the earthquake, soil peeling occurs on the slope surface under the coupled action of gravity and earthquake; as the earthquake amplitude increases, relative displacement occurs between the slope shoulder and the accumulation layer, and cracks appear on the surface of the accumulation layer; finally, obvious relative displacement occurs at the slope toe, and the accumulation layer deviates from the bedrock and accelerates to collapse. The sliding process of the slope accumulation layer can be divided into three stages according to the characteristics of seismic signals: (1) stable stage, (2) impending slip stage, and (3) slip stage.

Abstract:The problem that the period reduction cannot be considered in a structural time-history analysis was studied. Structural time-history analyses considering and neglecting the period reduction were compared, and then the amplification coefficient was proposed to amplify the effective peak acceleration of the input ground motion and the seismic response in time-history analysis to consider the amplification effect of period reduction on the structural seismic response in elastic time-history analysis. The influences of involved parameters on the amplification coefficient were studied theoretically. Then, the adjustment effects and differences between the two adjustment methods were compared on the basis of the single-degree-of-freedom system. Moreover, an engineering example was used to verify the effectiveness of the proposed methods considering period reduction in the elastic time-history analysis. The results show that the value of the amplification coefficient is related to the period reduction coefficient, the natural vibration period of the structure, and the characteristic period of the site. For the single-degree-of-freedom system, the two adjustment methods have identical adjustment effects. The seismic shear force and story drift ratio of each floor of the example structure obtained using the elastic time-history analysis are near those calculated by the response spectrum considering the period reduction.

Abstract:Subsidence or even destruction of the foundation of structures in the loess area is often caused by the collapsibility of loess, which poses a serious threat to the infrastructure construction in these areas. Improving loess can help alleviate and reduce the harmful effects of collapsibility. Therefore, this paper investigates the collapsible loess improved by the environmental-friendly degradable industrial waste, that is, lignin. Lignin-modified loess can substantially reduce collapsibility, and the improvement mechanism is explained from the perspective of the deformation mechanism and microstructure. Research results show that 2% lignin content eliminated the collapsibility of the loess sample, and 4% lignin content yielded the best improvement effect. From the perspective of the deformation mechanism, the addition of lignin changes the loess structure. Therefore, the structural instability induced by the collapsibility is released during the pre-pressurization period. From the viewpoint of microstructure, lignin generates new cements between loess particles, which enhances the bonding force between particles. Overall, laboratory experiment results verified the effectiveness of lignin in inhibiting collapsibility. A satisfactory improvement effect is realized by 2% lignin content. The use of lignin conforms to the concept of green construction, improves the utilization rate of industrial byproduct lignin, and provides a new reference for solving the collapsible problem in practical projects.

Abstract:An unreinforced masonry structure is prone to severe damage and collapse during earthquakes because of its poor seismic resilience. In this study, seismic resilience was used as a parameter index for analyzing the seismic capacity of the reinforcement of an unreinforced masonry structure. A finite element model for the unreinforced masonry structure in buildings was established using the software ANSYS. The input waves were the Wenchuan earthquake wave, the Hanshin earthquake wave in Japan, the Kern earthquake wave in the United States, the Chi-Chi earthquake wave in Taiwan, China, and an artificial earthquake wave. Resilience index and resilience grade were used in evaluating the seismic resilience of an unreinforced masonry reinforcement system in terms of repair cost, repair time, and personnel casualties after an earthquake. Results indicate that (1) the inter-story displacement, inter-story shear stress, and extent of damage in the unreinforced masonry structure are greater than those of the unreinforced masonry with reinforcement system during rare, fortification, and frequent earthquakes; (2) the maximum seismic resilience index of the reinforced masonry structure is 0.877, and the minimum seismic resilience index of the unreinforced masonry with reinforcement system is 0.908 at different earthquake intensities; (3) the unreinforced masonry structure suffer from severe damage levels and heavy casualties and needs long time and high costs for post-disaster reconstruction when different seismic waves are inputted. By contrast, the unreinforced masonry structure with a reinforcement system has a high proportion of minor damage and few casualties and can be reconstructed in a short time with low costs.

Abstract:Based on the damage characteristics obtained from the post-earthquake investigation of shallow foundation abutments, a shallow foundation abutment with anchor plates was designed for an anchor plate retaining wall. The seismic performance of the proposed abutment was evaluated with the quasi-static test and finite element software ABAQUS. The effects of various factors, namely, steel strand diameter, anchor plate layout, ratio of anchor plate area to abutment back area, elastic modulus of abutment backfill, and steel strand length, on the seismic performance of the proposed abutment were explored. Results indicate that the bearing and energy dissipation capacities of the abutment improve after the anchor plate is used. The primary causes of structural failure are soil failure and steel strand fracture, and the abutment and anchor plate remain undamaged. Increasing the diameter of the steel strand in a certain range can considerably improve the bearing capacity of the structure and impede stiffness degradation. The bearing capacity of the abutment is basically unaffected by the different arrangements of the anchor plate. The initial bearing capacity of the structure is high when the ratio of the anchor plate area to the abutment back area is large, but the stiffness degradation is fast in the later stage. The length of the steel strand should not be excessively large beyond the design requirements.

Abstract:Strong aftershocks often occur after earthquakes, increasing the extent of structural damage. Thus, the influence of aftershocks on structures in seismic design and structural damage assessment is an important topic. In this study, the NGA-West2 database was used in establishing the date set of mainshock-aftershock sequence-type ground motions. Based on damage equivalence theory, the peak ground acceleration (PGA) amplification factor under mainshock-aftershock ground motions was defined. Then, the average PGA amplification factor spectra of the structure with a single degree of freedom system under different relative intensities and different site conditions were obtained through dynamic time-history analysis. The prediction equation of the PGA amplification factor spectrum was constructed through regression analysis, and the discreteness of the statistical results was analyzed. Results show that the PGA amplification factor spectrum is less affected by site conditions but affected by the relative intensity of mainshock-aftershock ground motions, and the value of the amplification factor spectrum decreases with increasing period. The spectral prediction equation can provide the PGA amplification requirement of the mainshock under target damage, and it can be used as the adjustment coefficient of a design spectrum. In addition, this equation considers the influence of aftershocks in a seismic design and structural damage assessment of a structure.

Abstract:Ensuring the safe operation of road traffic routes primarily depends on the fast and reliable testing of the load-bearing stiffness of service bridges. This paper presents a load stiffness assessment method for simply supported girder bridges based on a modal test of local measurement points. An actual, simply supported girder bridge is used as the test object to verify the feasibility and accuracy of the proposed method. The schemes of symmetric and eccentric loads used in conventional bridge load tests were designed, and the measured static deflection of the mid-span section of the simply supported girder bridge under each condition was obtained. Modal tests of joint and local points were conducted based on the ambient excitation to predict the modal deflection of the mid-span section of the simply supported girder bridge, and the calibration coefficient of structural deflection was calculated with the theoretical deflection. Results show that under symmetric and eccentric loads, the maximum relative error between the modal deflection of the mid-span section predicted by the modal test of joint points and that measured in the static load test is less than 5.7%. The load-bearing stiffness of the bridge can be accurately assessed using the modal test of joint points on the mid-span section and the bridge deck. The modal deflection predicted by the modal test of local measuring points with sensors only in the mid-span section is equivalent to that predicted by the modal test of joint measuring points, and the relative error between them is less than 2%. The deflection calibration coefficient of the mid-span section predicted by the modal test of local measuring points is in good agreement with the measured value from the static load test.

Abstract:This study used Dalian Metro as background to study the amplification effect of each soil layer in the heterogeneous site and the seismic response of a layered soil-tunnel system under seismic action. Based on the theory of dynamic response of tunnel structure under seismic action, a three-dimensional finite element model of the layered soil-tunnel was constructed with ABAQUS and a convergence constraint method. The simulation accuracy was verified by a shaking table test. Then, the free field was contrasted with the tunnel site, and the simulation data were analyzed in combination with the acceleration and Fourier curves. Results show that (1) the soil properties and excitation magnitude affect the transmission of seismic waves. As the site gradually increases from shallow to deep, the peak acceleration gradually increases, and the main frequencies and spectrum shapes of different layered media change obviously. (2) The tunnel amplifies the acceleration response in the far field and slightly reduces the dynamic response in the near field. (3) The weak interlayer has an evident influence on the amplification effect of earthquakes. The characteristics of different layered media lead to different soil stiffness, further influencing the dynamic interactions of the layered soil-tunnel during earthquakes.

Abstract:Based on the strong motion records, the amplification effects of 48 stations in Sendai Basin, Japan, were analyzed by using the generalized inversion and HVSR methods. Then, the impacts of site v_S30 and basin depth on the amplification effect were analyzed. Results show that compared with the generalized inversion method, the HVSR method can provide the main frequency of a site, but it underestimates the amplitude of the amplification effect. The amplification effects of the basin induced by shallow earthquakes in different locations outside the basin considerably vary. The amplification effect caused by ocean earthquakes in the southern part of Sendai Basin is the largest, whereas that caused by land earthquakes in the northern part of Sendai Basin is the smallest. The amplification effect of S-wave caused by earthquakes in the southern and eastern parts of the basin shows a strong correlation with v_S30, whereas that in the northern part shows little correlation with v_S30. The amplification effect of the S-wave in the basin is strongly correlated with the depth of the basin in the frequency band of 0.5-5 Hz but is basically irrelevant in the frequency band of 0.25-0.5 and 5-10 Hz.

Abstract:The effects of adjacent cavities on the seismic response characteristics of shield tunnels under horizontal seismic excitation were explored with the incremental dynamic analysis method. Given the segment damage and stress distribution encircling the tunnel, the bending moment ratio was selected as the performance evaluation index, and the peak ground acceleration (PGA) and peak ground velocity (PGV) were used as seismic intensity measures (IMs). Then, the influence of the elliptical cavity on the seismic performance of the segment was expounded, and the seismic vulnerability curves of the tunnel structure were obtained. Results show that the seismic damage probability of the shallowly buried shield tunnel increases because of the effect of the adjacent elliptical cavity. The PGA and PGV can be used as IMs for the development of the corresponding vulnerability curves of tunnels. When the bending moment ratio as damage index and PGV as intensity measure are used, the vulnerability curves are more sensitive to variation in strata than those of PGA. The research conclusion can provide a reference for the formulation of earthquake prevention schemes in regions with potential cavities.

Abstract:Based on the different contents of calcium lignosulfonate and curing ages, the water repellency, permeability, and water stability of calcium lignosulfonate were analyzed using the water drop infiltration, penetration, and disintegration tests, respectively, to reveal the influence of calcium lignosulfonate on the hydrological properties of Lanzhou loess. The improvement mechanism of enhanced loess by calcium lignosulfonate is also discussed using X-ray diffraction and scanning electron microscope tests. Results show that the water repellency and stability of loess improved with the addition of calcium lignosulfonate. Moreover, the improvement of calcium lignosulfonate with low content is limited, while the overall performance of loess improved by high-content calcium lignosulfonate is good. However, the effect of reducing permeability is limited. The hydraulic properties of loess improved by calcium lignosulfonate demonstrate age effects: under the curing age of 28 d, a generalized peak value is observed in the hydraulic property parameters of loess improved by calcium lignosulfonate with its content. However, the relationship between peak value and content is different. A certain positive correlation is also observed between the hydraulic and mechanical properties of loess improved by calcium lignosulfonate. No new mineral composition is found in the loess improved by calcium lignosulfonate. However, the thickness of the electric double layer of soil particles becomes thin, and the cementing products wrap the connecting particles and fill the pores, thus improving the hydraulic properties of the loess.

Abstract:The Liuhuanggou Bridge in the Lanzhou—Urumqi high-speed railway, which is near a fault zone, has been threatened by near-fault earthquakes for a long time. In this study, the seismic vulnerability of the bridge was analyzed with a nonlinear finite element model of the bridge containing a three-dimensional soil layer. The model was established by using OpenSees software. Incremental dynamic analysis and probabilistic seismic demand models were adopted, and the four typical continuous piers of the bridge were examined. Given the uncertainty of bridge materials, numerous model-ground motion samples were obtained with the Latin hypercube sampling method for nonlinear dynamic response analysis, and the upper and lower limits of the bridge system’s vulnerability curve were obtained with the first-order boundary method. Results show that the seismic performance of the bridge system is good, and the probability of complete damage is less than 30% under extremely rare earthquakes in the area; the seismic performance of single pier is excellent, and the probability of complete damage is only 6.92% under extremely rare earthquakes; when the earthquake load reaches 0.35g, the pier is at the critical point of elastic stage and plastic stage; the piers with a relatively high height (3^# and 4^#) have greater stiffness and stronger capacity of deformation and dissipation than relatively low piers (1^# and 2^#). This study evaluates the seismic performance of the Liuhuanggou Bridge in Lanzhou—Urumqi high-speed railway during simulated near-fault earthquakes, which can provide an important basis for risk prevention before the earthquake and post-earthquake decision-making on disaster relief and mitigation.

Abstract:Current research on the dynamic response of building structures under the mainshock-aftershock sequence indicates that aftershocks after the mainshock often cause the accumulation of structural damage, resulting in structural crack extension or even collapse. However, the mainshock-aftershock sequence is seldom used in the analysis of earthen sites. In the study, the central pagoda of Ta'er Temple in Suoyang City was investigated. Six natural ground motion records were selected with the target spectrum matching method, and the dynamic responses of the structure under the action of single mainshock and mainshock-aftershock sequence were studied. Results indicate that the change trends of acceleration and displacement responses along the height of the pagoda are basically the same under the action of mainshock and aftershock. The maximum values of acceleration and vertical displacement are located at the apex of the pagoda, whereas the maximum horizontal displacement is located at the combination of the mantle body and pagoda body. The aftershock will expand the scope and degree of the plastic damage caused by the mainshock, especially in the severely damaged parts. Through the above analysis, the weak positions of the central pagoda of the Ta' er Temple are exposed, and improvement measures, such as support reinforcement in suitable parts, are proposed.

Abstract:We developed low-cost magnetic field monitoring equipment to accomplish the rapid establishment of a regional high-density geomagnetic field observation network, which is capable of recording geomagnetic field data and precisely identifying magnetic field anomalies preceding major earthquakes in the meizoseismal region. The devised equipment—based on Internet of Things communication and RM3100 triaxial magnetic sensors—was deployed in the Baodi and Wuqing Districts of Tianjin. Subsequently, the automatic judgment and visual prediction of earthquake precursor anomalies were investigated by employing artificial intelligence data analysis and temporal data storage techniques. The effectiveness of the proposed monitoring equipment was verified during the M2.0 earthquake that struck Baodi, Tianjin, on June 23, 2022, demonstrating its ability to detect anomalies preceding major earthquakes and its sensitivity to small-and medium-magnitude earthquakes over short distances.

Abstract:Ocean-bottom seismometers represent crucial marine seismic observation instruments. Considering the loud ocean currents and frequent human activities in China's offshore shallow waters, we proposed a chain seismic observation method and designed the mechanical structure of a cabled ocean-bottom seismometer node. First, the overall structure of the seismometer node was designed based on the dimensions and layouts of its internal components. Subsequently, the hull thickness, end cover thickness, and sealing dimension were determined based on theoretical calculations and finite element simulations. Finally, a pressure test verified the pressure resistance and water tightness of the designed seismometer node structure, while a comparative seismic observation test validated the structure's ability to detect natural earthquakes. Considering these accomplishments, the designed cabled ocean-bottom seismometer is planned to be deployed for actual seismic observations in the offshore area of the Zhejiang Province to gather real-time and continuous seismic observation data.

Abstract:To address the modern requirements of emergency response efforts in the digital age, we developed an approach based on the stochastic finite fault method. Specifically, utilizing an underground three-dimensional velocity structure model and v_S30 data from the Menyuan region of the Qinghai Province, we applied the step-by-step iterative ray-tracing method, phase spectrum of Green's function displacement analytical solution, and finite fault method to record strong ground motion simulation data incorporating ground surface amplification effects. Furthermore, considering the Menyuan M6.9 earthquake that struck the Qinghai Province on January 8, 2022, we created simulation maps depicting the peak ground acceleration (PGA) and intensity distributions within the study area. Subsequently, comparing the simulated results with actual PGA records from monitoring stations and field survey intensity data revealed consistent intensity zonation scopes. Moreover, these results validated the utility of the proposed method for rapid assessments of future earthquake disasters, offering valuable insights for postdisaster emergency rescue efforts.

Abstract:The investigation of gas geochemical information before and after an earthquake has high application value in earthquake monitoring and prediction. Thus, this paper investigates the relationship between the spatio-temporal variation of CO and the M_S7.4 earthquake that occurred in Maduo County, Qinghai Province, on May 22, 2021. The accuracy of CO data obtained from the Atmospheric Infrared Sounder (AIRS) was compared with ground data from the Waliguan atmospheric observation station. The CO data retrieved by AIRS before and after the M_S7.4 earthquake were extracted, from which the CO concentrations before and after the earthquake were processed and analyzed using the sliding mean method and difference method. Results indicate the reliability of extracting CO geochemical information from satellite remote sensing data. The CO concentration began to fluctuate and peak two months before the earthquake and then recovered after the earthquake. Furthermore, the change in CO concentration in the epicenter and its vicinity was particularly obvious near the surface. This gradually increased from March, gathered near the epicenter and the seismogenic fault, and eventually reached the maximum value of 18.60×10^-9 by the end of April. The line connected to the centers of the abnormally high values is consistent with the strike of the seismogenic fault and the surface rupture distribution. Barring the influence of background value and seasonal change, it is inferred that the abnormal change in CO concentration is caused by the M_S7.4 earthquake. The CO anomaly can be mainly attributed to the underground gas release and gas production caused by rock extrusion and collision, while the gas chemical reactions in the atmosphere play a secondary role.

Abstract:Earthquake early warning (EEW) systems—as effective tools for seismic hazard mitigation—offer advance alerts several to tens of seconds before the onset of destructive ground motions, prompting the deployment of emergency measures to minimize casualties and property losses. Specifically, these intricate systems rely on rapid and precise real-time magnitude estimations based on EEW parameters for disaster mitigation. To accelerate magnitude estimation speeds, considering 821 records of 190 earthquakes (3.1≤M≤6.6) that struck the Gansu Province and surrounding regions from 2012 to 2020, we examine the correlation between two EEW parameters (characteristic period τ_c and displacement amplitude P_d) and peak parameters (peak ground velocity and displacement) under varying conditions: vertical component, horizontal component, and mean value of the three components of a P-wave at 1-10 s. Subsequently, it establishes a fast calculation model for early warning magnitude estimations. Finally, the estimated magnitudes (M_E) are compared with those recorded by the China Earthquake Networks Center (M_C). Results reveal that while changes in time window durations influence the estimation outcomes, variations in P-wave components exert negligible effects. Moreover, the P_d-based model outperforms the τ_c-based model in predicting the fitting degree, mean value, and standard deviation of the predicted residuals, as well as the residual distribution. Thus, considering the time scale of real-time parameters, magnitude estimations, and the requirement of timely EEW information release, applying the P_d-based model after 3 s of vertical P-wave arrival is recommended for rapid real-time magnitude estimations by EEW systems in the study area.

Abstract:To overcome the low accuracies and high error rates of existing P-wave arrival time picking networks, we developed a P-wave pyramid network (PPNet). This lightweight network was designed for high-precision and low-error picking of seismic P-waves by combining the UNet++ codec with a feature filter. Remarkably, the resulting PPNet could analyze and combine seismic phase characteristics. First, a convolution layer with a large convolution kernel and low channel number was incorporated into the encoder module for deep feature extraction from input seismic signals. Subsequently, a feature fusion mechanism was introduced into the feature restoration process of the decoder module to complement the feature information and prevent sequence feature contamination. Finally, feature filters were selectively applied to the final three downsampling modules of the encoder for deep feature sequence exploration, consequently refining the P-wave arrival features and improving pickup accuracy. Experimental results revealed that the P-wave pickup rates of the proposed network reached 80.73%, 94.01%, and 97.81% under error thresholds of 0.1, 0.2, and 0.3 s, respectively, with an average absolute error of 0.078 s and a mean square error of 0.021. Thus, the proposed network outperformed traditional P-wave pickup methods and deep-learning algorithms.

Abstract:A total of 117 seismic events (54 natural earthquakes and 63 explosions) that occurred in the Capital Circle Region (Shunyi, Beijing, Sanhe, and Hebei) from February 2010 to December 2016 were selected in this paper. The multiscale attention residual network was proposed and used to classify the waveforms of earthquakes and explosions. The original seismic waveform was simply preprocessed and intercepted into seismic time series data with the same length, which was directly used as the input of the network model. Then, the deep neural network with the residual module was selected as the basic network. The step of advanced extraction of time-domain waveform features as the input of classification algorithm in traditional waveform classification can be omitted by using the automatic feature extraction ability of the deep neural network. Next, the efficient channel attention mechanism was integrated and improved, after which information from the spatial dimension was integrated into the channel information, thus optimizing the network's attention to key information and resulting in better concentration on essential features. Finally, the multiscale feature fusion was performed using spatial pyramid pooling instead of maximum pooling to obtain more feature information. Ultimately, a multiscale attention residual network was formed. Experimental results show that the highest classification accuracy of the multiscale attention residual network is 97.11%, and the average classification accuracy is 96.53%. The results demonstrate the effectiveness of this approach in seismic waveform classification and provide a new optional approach for seismic-source type identification.

Abstract:On December 18, 2023, an M_S6.2 reverse-type earthquake struck Jishishan County, Gansu Province, along the northern margin of the Lajishan fault zone, Qilian active block. Given that over 20 M5.0 earthquakes have occurred on both sides of the Lajishan fault, investigating its characteristics is paramount. Thus, based on the strike of the Lajishan fault and its aftershock distribution, we deployed a linear dense array in Liuji Town. Considering aftershock events in different directions, we determined travel time delays and amplification effects of body waves. The results identified six (approximately 0.012 s) and 15 (approximately 0.03 s) sampling points of travel time delays for the P-and S-waves, respectively. This confirmed the presence of a nearly vertical low-velocity zone with a width of approximately 150 m along the west side of the array. The obtained results align with teleseismic P-wave similarity coefficient matrix calculations.

Abstract:Rapid casualty assessments during earthquake disasters are crucial for emergency response. Typically, various factors, such as regional geographic environments, population densities, and building structures, have pivotal impacts on earthquake casualties. We adopted a zonal approach to assess earthquake-related casualties in Mainland China. Specifically, to comprehensively consider the differential impacts of earthquakes on diverse regions, the Chinese Mainland was divided into three zones—northwest, southwest, and east—based on population densities, geographical environments, and building structures. Additionally, the samples were further classified based on the maximum earthquake intensities recorded in these regions. Subsequently, employing the random forest method and bootstrap sampling technique, three parameters—earthquake magnitude, seismic area, and population density—were selected based on the importance of each feature. Thereafter, a particle swarm optimization-extreme learning machine (PSO-ELM) model was established for earthquake casualty assessments. Results indicated that the proposed model demonstrated excellent predictive performance, with good applicability and generalization across diverse regions and intensities, thereby offering valuable technical support for earthquake emergency response efforts and seismic risk assessments.