The seasonal freeze-thaw cycle of frozen soil regulates soil hydrothermal processes and serves as a crucial indicator of climate change in high-latitude cold regions. Monitoring the dynamic evolution of frozen soil structure and composition is essential for infrastructure development, soil conservation and carbon storage regulation. Compared to in-situ borehole measurements and remote sensing, near-surface geophysical methods offer spatially resolved insights into freeze-thaw processes at different depths. In this study, we applied electrical resistivity tomography and ambient noise seismic monitoring to investigate seasonal freeze-thaw cycles at a frozen soil test site in Northeast China. Geophysical data collected over a complete freeze-thaw cycle reveal the coupling between soil structure and hydrothermal properties, with strong consistency observed between physical parameters and hydrological information. Resistivity variations correlate with temperature, water content, and solute concentration across different freeze-thaw stages. Seismic relative velocity changes (dv/v) and surface wave phase velocity changes (dc/c) were negatively correlated with accumulated temperature and groundwater levels, reflecting soil pore freezing and the hydrothermal state of the deep subsurface environment. Meanwhile, the measured data verify that dc/c offers higher spatiotemporal resolution than dv/v. Sensitivity analysis indicate that resistivity is more responsive to shallow thermal exchange, while seismic velocity changes are more sensitive to deep hydrological variations. Integrating pore geometry and water-ice phase mechanisms, we construct a freeze-thaw evolution model for seasonally frozen soil based on combined hydrological and geophysical data. The results validate the effectiveness of geophysical methods for detecting and monitoring frozen soil, and provide technical support for quantifying phase transition mechanisms in freeze-thaw processes.

The city of A & iuml;n T & eacute;mouchent, located in northwest Algeria at the westernmost part of the Lower Cheliff Basin, has experienced several moderate earthquakes, the most significant of which occurred on 22 December 1999 (Mw 5.7, 25 fatalities, severe damage). In this study, ambient noise measurements from 62 sites were analyzed using the horizontal-to-vertical spectral ratio (HVSR) method to estimate fundamental frequency (f0) and amplitude (A0). The inversion of HVSR curves provided sedimentary layer thickness and shear wave velocity (Vs) estimates. Additionally, four spatial autocorrelation (SPAC) array measurements refined the Rayleigh wave dispersion curves, improving Vs profiles (150-1350 m/s) and sediment thickness estimates (up to 390 m in the industrial zone). Vs30 and vulnerability index maps were developed to classify soil types and assess liquefaction potential within the city.

The S-wave velocity (Vs) is a valuable parameter for assessing the mechanical properties of subsurface materials for geotechnical purposes. Seismic surface wave methods have become prominent for estimating near-surface Vs models. Researchers have proposed methods based on passive seismic signals as efficient alternatives to enhance depth of investigation, lateral resolution and reduce field effort. This study presents the Multichannel Analysis of Surface Waves (MASW) utilizing Common Virtual Source Gathers (CVSGs) derived from seismic ambient noise cross-correlations, based on Ambient Noise Seismic Interferometry concepts. The method is applied to passive data acquired with an array of receivers at the Paranoa earth dam in Brasilia, Brazil, to construct a pseudo-2D Vs image of the massif for interpretation. Our findings showcase the adopted processing flow and combination of methods as an effective approach for near-surface Vs estimation, demonstrating its usability also for large earth dam embankments.

Assessing the potential and extent of earthquake-induced liquefaction is paramount for seismic hazard assessment, for the large ground deformations it causes can result in severe damage to infrastructure and pose a threat to human lives, as evidenced by many contemporary and historical case studies in various tectonic settings. In that regard, numerical modeling of case studies, using state-of-the-art soil constitutive models and numerical frameworks, has proven to be a tailored methodology for liquefaction assessment. Indeed, these simulations allow for the dynamic response of liquefiable soils in terms of effective stresses, large strains, and ground displacements to be captured in a consistent manner with experimental and in-situ observations. Additionally, the impact of soil properties spatial variability in liquefaction response can be assessed, because the system response to waves propagating are naturally incorporated within the model. Considering that, we highlight that the effect of shear-wave velocity V s spatial variability has not been thoroughly assessed. In a case study in Metropolitan Concepcion, Chile, our research addresses the influence of V s spatial variability on the dynamic response to liquefaction. At the study site, the 2010 Maule M w 8.8 megathrust Earthquake triggered liquefaction-induced damage in the form of ground cracking, soil ejecta, and building settlements. Using simulated 2D V s profiles generated from real 1D profiles retrieved with ambient noise methods, along with a PressureDependentMultiYield03 sand constitutive model, we studied the effect of V s spatial variability on pore pressure generation, vertical settlements, and shear and volumetric strains by performing effective stress site response analyses. Our findings indicate that increased V s variability reduces the median settlements and strains for soil units that exhibit liquefaction-like responses. On the other hand, no significant changes in the dynamic response are observed in soil units that exhibit non-liquefaction behavior, implying that the triggering of liquefaction is not influenced by spatial variability in V s . We infer that when liquefaction-like behavior is triggered, an increase of the damping at the shallowest part of the soil domain might be the explanation for the decrease in the amplitude of the strains and settlements as the degree of V s variability increases.