On December 18, 2023, an Ms6.2 earthquake struck Jishishan County, Gansu Province, in western China. The China Earthquake Early Warning Network (CEEWN) captured extensive near-field ground motion data using high-density microelectromechanical system (MEMS) sensors and force-balanced accelerographs (FBAs). Through noise level and usable frequency range assessments of MEMS/FBA recordings, we compiled a strong- motion dataset encompassing the Ms6.2 mainshock and 13 aftershocks (Ms >= 3.0). Analysis of this dataset revealed distinct source characteristics and site effects through spatial distributions and attenuation patterns of peak ground acceleration (PGA, up to 1.1 g at station N002B), peak ground velocity (PGV), and spectral accelerations (SAs) across various periods. The mainshock's near-fault motions exhibited pronounced short-period energy, with 0.2 s SAs exceeding 1.0 gin intensity zones VII-VIII due to hanging wall effects, soil amplification, and topographic influences. Site-to-reference ratio (SSR) analysis identified site nonlinearity above 1 Hz and amplification between 1 and 10 Hz. Observed PGAs and short-period SAs surpassed ground motion model (GMM) predictions with faster attenuation rates, while long-period SAs (>1.0 s) remained below predictions. Residual analysis of intensity measures (IMs) and horizontal-to-vertical spectral ratios (HVSRs) demonstrated progressive site nonlinearity, showing HVSR frequency reductions and amplitude declines at PGAs >500 cm/s(2). This dataset advances regional ground motion model (GMM) development, while our findings on strong ground motion characteristics offer critical insights for earthquake damage assessment and post-disaster reconstruction.

On 18 December 2023, a Ms 6.2 earthquake struck the Jishishan area in Northwest China, located at the border of the Qinghai-Tibet and Loess Plateau. The earthquake triggered shallow loess landslides, small rock failures, and soil cracks, mainly along hilly gullies and cut slopes at the edges of terraced fields. A rare large-scale flowslide also occurred in irrigated farmland. These seismic landslides and collapses blocked roads, buried farmland, damaged houses, and resulted in many casualties. Field investigations revealed that these geological hazards were concentrated around cultivated land. Consequently, cultivated land was introduced as an engineering geological zoning factor into the seismic geological hazard risk assessment for Jishishan area. The Newmark cumulative displacement model was refined by incorporating lithological uncertainties via the Monte Carlo method. Comparative analysis of coseismic geohazards with and without considering cultivated land suggests that, in loess-covered areas with cultivation activities, the consideration of the disturbed characteristics of soils provides a more accurate probabilistic risk assessment of seismic geohazards. Human cultivation and irrigation activities affect the physical properties of surface soil, the terraced fields around earthquake prone areas have a risk of earthquake-induced geological hazards. This study may offer valuable insights for hazard prevention and mitigation in high fortification intensity loess covered areas.

On December 18, 2023, the M S 6.2 Jishishan earthquake triggered a large-scale liquefaction disaster of loess sites in Jintian and Caotan villages, Zhongchuan town, Minhe County, Haidong City, Qinghai Province. To clarify the micro-mechanism of the liquefaction disaster, the Q3 Malan loess layer of the disaster site and its overlying red silty clay layer samples were selected and quantitatively analyzed for the differences in physical properties, structure, microstructural parameters, and mineral compositions. Based on the discrepancy results, the micro-mechanisms between loess microstructure and macro-mechanical properties of soil and liquefaction disaster were investigated. The research shows that compared with red silty clay, the dynamic index of loess corresponding to the physical indices of Zhongchuan loess obviously exceeds the critical threshold of liquefaction under actual seismic intensity. Additionally, its pore structure is dominated by point contact and weakly cemented overhead macropore structure, and its quantitative pore microstructure parameters and mineral composition show significant liquefaction potential. The comprehensive analysis of the liquefaction mechanism shows that the rapid deformation of the soil skeleton and the destruction of the cementation and contact system of the water-sensitive minerals under seismic loading and hydraulic force lead to the collapse of the overhead macropores, the damage of structural strength, the increase of the complex pore channels, the rapid accumulation of pore water pressure, and the reduction of the effective stress, which leads to the liquefaction of the loess.