Ping Wang

On January 26, 2026, an Ms5.5 shallow-focus earthquake occurred in Diebu County, Gannan Tibetan Autonomous Prefecture, Gansu Province. The affected area lies within the alpine gorge of the Bailong River on the eastern margin of the Tibetan Plateau, a region characterized by rugged topography and complex geological conditions that are typically prone to topographic amplification of ground motion. To address how topographic and site conditions control ground-motion amplification and the resulting spatial distribution of seismic damage, this study selected Dianga Town in Diebu County—the area covered by the earthquake damage survey—as the study area. Field damage surveys, seismic station monitoring data, and FLAC3D three-dimensional numerical simulations were integrated to systematically reveal the relationships among ground-motion amplification, building damage, and slope deformation. Results indicate that the seismic intensity in the study area reached VI–VII on the Chinese seismic intensity scale. Ground-motion amplification was closely associated with the spatially non-uniform distribution of seismic damage: at steep cliffs, slope shoulders, and high-elevation sites, peak ground acceleration (PGA) amplification factors approached 2.0, and buildings at these locations experienced significantly more severe damage than those at other sites. Seismic loading also altered the shear strain distribution pattern of the slope, causing the zone of concentrated shear strain to redistribute and extend toward the residential area. Topographic relief, excavation-induced free faces, and elevation differences were identified as the primary factors contributing to topographic amplification in the studied alpine gorge; in particular, an elevation difference of only about 100 m produced pronounced differences in seismic damage. These findings qualitatively reveal the mechanism of ground-motion amplification and provide a scientific basis for seismic fortification and geological hazard mitigation in villages and towns within alpine gorge areas on the eastern margin of the Tibetan Plateau.

Due to the complex terrain and topographical constraints of the Loess Plateau, flat land suitable for engineering construction is extremely limited. To address this issue, filling gullies and leveling land has become a common solution, resulting in the widespread use of loess fill slopes across numerous infrastructure projects. With the increasing frequency of extreme rainfall events worldwide, the stability of these loess fill slopes under rainfall conditions has become critically linked to the safety of engineering structures, as well as to public and property security. This study investigates the failure mechanisms of loess fill slopes subjected to intermittent rainfall using indoor physical model testing. The experiments monitored changes in soil pressure, pore water pressure, and displacement within the slope, alongside observations of crack development to analyze the progression of slope instability. The key results are summarized as follows: (1) The evolution of soil pressure and pore water pressure is significantly impacted by the form and pattern of rainfall. All three monitored parameters (e.g., soil pressure, pore water pressure, and displacement) exhibited consistent macroscopic deformation behaviors. Around the 10 ^th h of rainfall, bulging at the slope toe and minor deformation were observed. By the 25 ^th h, sharp fluctuations and peak values appeared in both soil and pore pressures, accompanied by a sudden displacement increase of approximately 25 mm, signaling large‐scale slope sliding; (2) Crack development during intermittent rainfall followed a sequence: surface erosion and expansion, crack initiation and soaking‐induced softening at the slope toe, crack propagation and interconnection, and ultimately progressive tensile failure extending from the slope toe to the crest; (3) The failure and instability of loess fill slopes under intermittent rainfall are driven by a combination of rainwater infiltration, erosion, soaking, and wet–dry cycles. The drying period between rainfall events facilitates the expansion and extension of cracks, which subsequently serve as preferential seepage pathways during further rainfall, accelerating water infiltration and triggering slope instability; (4) Owing to the relatively low rainfall intensity used in the model, the observed failure can be classified as a static landslide, which explains the relatively low values of measured soil and pore water pressure throughout the test. These results offer valuable guidance for the design of support systems and drainage infrastructure in loess fill slopes, and provide practical insights for early‐warning systems, hazard prediction, and disaster risk reduction strategies.

On 18 December 2023, a 6.2-magnitude earthquake struck Jishishan, affecting multiple counties and cities in Gansu and Qinghai Provinces. The seismic intensity of the meizoseismal area was VIII, resulting in extensive structural damage and building collapses. A damage assessment was conducted of the epicenter and surrounding high-intensity zones. To understand the typical structures and characteristics of the buildings that were damaged in these high-intensity zones, this study summarizes the characteristics of the damage to typical rural houses, compares the damage of the rural houses across different sites, and analyzes the causes behind these variations. The findings of the study indicate the following: (1) Timber and some brick–timber structures, due to their age, insufficient material strength, and lack of adequate connections between parts of the building, primarily experienced severe damage or total collapse, characterized by through-wall cracks, partial collapses, or complete collapses. (2) Brick–concrete structures predominantly suffered moderate to severe damage due to factors such as improper layout, uneven façades, and inadequate or incomplete seismic measures. The observed damage included significant wall cracks and extensive damage to two-story buildings. (3) Frame structures, mainly used for public facilities like schools, hospitals, and health centers, exhibited strong integrity and excellent seismic performance, resulting in minimal to no damage, with damage largely confined to non-load-bearing components. (4) The amplification effects of seismic waves in thick loess basin areas, slope sites, and the hanging wall effect of faults exacerbated structural damage to rural houses located in certain villages within the high-intensity areas. The results of this study can serve as a reference for post-disaster reconstruction and seismic retrofitting of buildings and contribute positively to enhancing the disaster resilience of rural housing.

In this study, the loess hill site of an elevated bridge section in Tongwei‐Qin’an of the Baolan high‐speed railroad was selected as the research object, and the vibration acceleration of the loess hill site under the elevated bridge was tested in the field under the train operating load. The results show that under the same intensity of train load, the time range of vibration acceleration observed by field test and numerical simulation decays linearly with increasing distance from the source, while the amplification effect appears in the loess hill site at a greater distance, and the vibration duration also appears to increase. The vibration acceleration waveforms at each observation point observed by field tests and numerical simulations are similar, and the peak vertical acceleration at each observation point obtained from numerical simulations is overall greater than the peak acceleration at each point obtained from field tests, with a_{Simulated− max} / a_{Observated− max} values ranging from 1.04 to 1.63. The Fourier spectrum frequencies recorded by numerical simulation and field test are mainly concentrated in the range of 1∼40 Hz, but the difference between the main frequencies recorded by the two is large. The main frequency of the energy spectrum recorded by the numerical simulation is around 15 Hz, which is the same as the main frequency of the energy spectrum vibration of the input vibration wave, and the main frequency of the energy spectrum vibration recorded by the field test is around 25 Hz.

Loess is characterized by high dynamic vulnerability due to its macro-porous and weakly cemented structure. Under the action of medium strong earthquake, it can induce earthquake subsidence, landslide, liquefaction, and other seismic geological disasters. （Zhang Z L，2016）The existing evaluation methods for earthquake subsidence are limited in scale simulation and seismic source simulation, leading to the deviation between the evaluation results and the actual situation. At the same time, the existing calculation method of seismic subsidence does not fully consider the structural environment factors, resulting in the deviation between the evaluation result and the actual situation, which is not conducive to reducing the construction cost. Therefore, it is urgent to improve the existing evaluation methods for earthquake subsidence. Developed a device to simulate the overburden pressure of the soil layer, and the model test of loess subsidence under strong earthquake was carried out in this study. The result of research shows that（1）The overburden pressure device can simulate the consolidation of soil at different depths and effectively reduce the boundary effect.（2）Axial deformation is the result of horizontal shear stress and vertical compression stress. Under the simultaneous amplification effect of upper earthquake, the soil subjected to shear damage is cracked. （3）Compared with the triaxial evaluation results, the evaluation results of shaking table test can provide a theoretical basis for correcting the phenomenon that the evaluation result of dynamic triaxial test is 1/3 larger than that of model test.

A large-scale shaking table test was conducted with simulated earthquakes and groundwater to study the dynamic response and instability mechanism of a loess slope with a saturated bottom. By examining the acceleration, dynamic pore water pressure, corresponding soil pressure and observed macroscopic failure behaviour of the slope under different shaking intensities, the dynamic responses of acceleration and pore water pressure of the loess slope were analysed. By comparing the time history curve of acceleration with the time history curves of pore water pressure and surrounding soil pressure, we found that the instability failure of the slope was first due to the continuous vibration that caused the local structure of the slope soil to be damaged, forming locally saturated soil and the rise in the groundwater table during shaking. Then, the saturated soil liquefied under the action of strong vibration, and the liquefied soil mass slid under the action of a high-intensity earthquake force. Finally, the acceleration and spectral characteristics of the pore water pressure changed sharply with a shift in the predominant frequency at the liquefied locations under a high shaking intensity. The significant changes in dynamic pore water pressure mainly occurred when the shaking components in the low-frequency bands below 1 Hz. This implied that the shift in the frequency mainly resulted from the damage in the structure of the loess slope after high-intensity shaking. These results help us better understand the triggering mechanism and failure mechanism of saturated loess slopes during the Minxian-Zhangxian earthquake.

The meso-structure of the soil has an important restriction on its engineering properties. Based on dynamic triaxial tests and SEM meso-structure test experiments, this study investigated the meso-scale structural deformation characteristics of Q₃ loess samples treated by physical, chemical, and compound improvement methods, before and after strong earthquakes of typical seismic subsidence loess. On this basis, the seismic subsidence performance of the improved method is given under the conditions of frequent earthquakes, fortifying earthquakes, and rare earthquakes. The results show that 1) the physical improvement method has the most obvious effect on the elimination of macropores and overhead pore structures; 2) the chemical method can generate unique glass beads or flocculated fine structures, which can greatly enhance the strength of the soil and play the role of filling, cementing, or buffering, respectively, in the event of a strong earthquake; 3) for several improved treatment methods, the amount of seismic subsidence increases non-linearly with the increase in peak acceleration; and 4) in the event of frequent earthquakes, the earthquake subsidence can be eliminated by the method of adding fly ash, and when the fortification earthquake comes, the dynamic composite method can completely eliminate the seismic subsidence of the site. The related results can give reasonable suggestions for the treatment of seismic subsidence of different foundations in the “resilient urban and rural” and key engineering construction and seismic design of China’s loess area.

Water content, dry density, void ratio, depth of soil layer, and seismic loading may all exert influence on the seismic subsidence of loess. Many scholars have carried out seismic subsidence tests of loess to simulate the stress on soil using unidirectional (axial) vibration instead of bidirectional vibration. In this paper, we conduct seismic subsidence tests of loess using two different dynamic stress loading methods, unidirectional and bidirectional dynamic stress. In addition, the effects of different dynamic stress loading modes on the development of seismic subsidence of loess are compared for a case-study in northwestern China. The results show that (1) the increasing ratio of radial stress to axial stress has exerted significant influence on the seismic subsidence coefficient of loess under the loading mode of bidirectional dynamic stress (2) there is a critical ratio of radial stress to axial stress for seismic subsidence of loess, ranging from 0.6 to 0.8; when the ratio of radial load to axial load is greater than the critical value, the effect of bidirectional load on the development of seismic subsidence is more remarkable (3) when the ratio of radial load to axial load is smaller, the seismic subsidence of loess calculated by the existing unidirectional stress loading method is safe for engineering projects. However, if the value exceeds the safety ratio range it is dangerous to conduct safety evaluations using the seismic loess subsidence. The prediction value of seismic subsidence at engineering sites directly affects the later foundation treatment and the safety of the overlying structures. The seismic subsidence calculation and evalation method in this study may provide a scientific basis for safety evaluations of loess sites in northwestern China.

The large‐scale shaking table model test, which can directly reproduce the process of slope instability and failure, is an important technical means for the prediction and evaluation of slope seismic stability. However, up to now, the systematic slope stability evaluation method based on the shaking table slope model test has not been established, which limits the application of the expensive shaking table model test in slope seismic design. Therefore, the slope stability evaluation method based on the model test needs to be developed and innovated. In this research, through three loess slope model tests with different rainfall, according to the change law of the peak value of transfer function spectrum, combined with the macrodestructive characteristics of the slope model, an accurate calculation method of the critical instability acceleration of the slope is proposed. Based on the behavior similarity theory, for the shaking table model test of slope whose soil cohesion cannot meet the similarity ratio, the reduction method of applying the critical instability acceleration obtained from the model test to prototype slope is proposed. Based on first‐order natural frequency and damping ratio extracted from the TF spectrum curve, a calculation method for the stability factor F_s of loess slope based on the shaking table model test is proposed, and the stability factors of loess slope under the action of different seismic ground motion would be quantitatively calculated. The above methods provide another effective way for qualitative prediction and evaluation of seismic stability of loess slope.

Taking the loess slope covered on mud rock as a research site, this study is based on theoretical foundation of the Horizontal-to-Vertical Spectral Ration(HVSR) and Sediment-to-Bedrock Spectral Ration(SBSR), site earthquake response of the loess landslide covered on mud rock calculated by use of the software FLAC3D, dynamic response of earthquakes was revealed, the simulation between HVSR and SBSR has been discussed, applicability of HVSR has been was analyzed. The results show that: The maximum horizontal displacement is found in the cliff part of the slope, the peak acceleration is the largest at the back edge of the slope and the vertical interface, as the elevation increases, the dominant frequency moves toward the lower frequency, and the higher frequency components are absorbed, the dominant frequencies obtained by HVSR spectrum ratio and SBSR spectrum ratio, and they are basically consistent with the fourier spectrum, the amplitude of HVSR and SBSR spectrum ratio are similar to the change rule of peak acceleration. Therefore, HVSR method can be applied to study the site effect of loess slope covered on mud rock