Ensuring the accuracy of free-field inversion is crucial in determining seismic excitation for soil-structure interaction (SSI) systems. Due to the spherical and cylindrical diffusion properties of body waves and surface waves, the near-fault zone presents distinct free-field responses compared to the far-fault zone. Consequently, existing far-fault free-field inversion techniques are insufficient for providing accurate seismic excitation for SSI systems within the near-fault zone. To address this limitation, a tailored near-fault free-field inversion method based on a multi-objective optimization algorithm is proposed in this study. The proposed method establishes an inversion framework for both spherical body waves and cylindrical surface waves and then transforms the overdetermined problem in inversion process into an optimization problem. Within the multi-objective optimization model, objective functions are formulated by minimizing the three-component waveform differences between the observation point and the delayed reference point. Additionally, constraint conditions are determined based on the attenuation property of propagating seismic waves. The accuracy of the proposed method is then verified through near-fault wave motion characteristics and validated against real downhole recordings. Finally, the application of the proposed method is investigated, with emphasis on examining the impulsive property of underground motions and analyzing the seismic responses of SSI systems. The results show that the proposed method refines the theoretical framework of near-fault inversion and accurately restores the free-field characteristics, particularly the impulsive features of near-fault motions, thereby providing reliable excitation for seismic response assessments of SSI systems.

This study introduces a simplified analytical method to extract shear wave velocity profiles from seismic waves evoked by explosives, providing a time-efficient solution to the conventional Multichannel Analysis of Surface Waves (MASW) method. Controlled ammonium nitrate emulsion explosions were used at five research sites throughout Thailand with different geological conditions to capture ground motion data through a 16-geophone array during field investigations. This direct analysis evaluates surface wave arrival times in real-time while implementing elastic theory-derived empirical factors for analysis. The proposed method delivers results that match MASW-derived profiles yet require fewer complex procedures and shows Vs30 variations from 4.43 to 38.33%. The simplified method delivered the most accurate results in areas displaying gradual soil property transitions and showed reduced precision when dealing with abrupt soil type or mechanical property shifts. The new method transforms petroleum exploration seismic data into geotechnical applications by delivering dependable shear wave velocity profiles with lower complexity and using fewer resources. It is specifically valuable for limited-budget engineering projects or difficult-to-access locations.

Geophysics and Geotechnical Engineering commonly use 1-D wave propagation analysis, simplifying complex scenarios by assuming flat and homogeneous soil layers, vertical seismic wave propagation and negligible pore water pressure effects (total stress analysis). These assumptions are commonly used in practice, providing the basis for applications like analysing site responses to earthquakes and characterizing soil properties through inversion processes. These processes involve various in situ tests to estimate the subsurface soil's material profile, providing insights into its behaviour during seismic events. This study seeks to address the limitations inherent to 1-D analyses by using 3-D physics-based simulations to replicate in situ tests performed in the Argostoli basin, Greece. Active and passive source surveys are simulated, and their results are used to determine material properties at specific locations, using standard geophysical methods. Our findings underscore the potential of 3-D simulations to explore different scenarios, considering different survey configurations, source types and array sets.

Subsurface processes significantly influence surface dynamics in permafrost regions, necessitating utilizing diverse geophysical methods to reliably constrain permafrost characteristics. This research uses multiple geophysical techniques to explore the spatial variability of permafrost in undisturbed tundra and its degradation in disturbed tundra in Utqia & gdot;vik, Alaska. Here, we integrate multiple quantitative techniques, including multichannel analysis of surface waves (MASW), electrical resistivity tomography (ERT), and ground temperature sensing, to study heterogeneity in permafrost's geophysical characteristics. MASW results reveal active layer shear wave velocities (Vs) between 240 and 370 m/s, and permafrost Vs between 450 and 1,700 m/s, typically showing a low-high-low velocity pattern. Additionally, we find an inverse relationship between in situ Vs and ground temperature measurements. The Vs profiles along with electrical resistivity profiles reveal cryostructures such as cryopeg and ice-rich zones in the permafrost layer. The integrated results of MASW and ERT provide valuable information for characterizing permafrost heterogeneity and cryostructure. Corroboration of these geophysical observations with permafrost core samples' stratigraphies and salinity measurements further validates these findings. This combination of geophysical and temperature sensing methods along with permafrost core sampling confirms a robust approach for assessing permafrost's spatial variability in coastal environments. Our results also indicate that civil infrastructure systems such as gravel roads and pile foundations affect permafrost by thickening the active layer, lowering the Vs, and reducing heterogeneity. We show how the resulting Vs profiles can be used to estimate key parameters for designing buildings in permafrost regions and maintaining existing infrastructure in polar regions.

With respect to geology, most coastal terrains are underlain by problematic soils, some of which are liquefiable in nature and may cause sudden failure of engineering infrastructures. Against this background, this study was carried out to investigate the subsurface geology of some Lagos coastal areas and their engineering implications using geophysical and geotechnical methods. To achieve this purpose, the Multichannel Analysis of Surface Waves, Cone Penetration Test, and Standard Penetration Test were deployed. Surface waves measurements were collected using a 24-channel seismograph to which 4.5 Hz twenty-four vertical geophones were connected via the takeouts of the two cable reels. CPT soundings were carried out with a 10-tons motorized cone penetrometer and boring with SPT were carried out as well. The results of the Multichannel Analysis of Surface Waves measurements showed that the shear waves velocity (Vs) ranges from 160 to 470 m/s. The very loose to loose sand delineated have Vs in the range from 170 to 250 m/s. The tip resistance and sleeve resistance values spanned between 4.0 and 72.0 kg/cm2 and 6.0-94 kg/cm2 respectively. The thickness of the liquefiable sands in the study area varied between 2.5 and 18.0 m. At Ikoyi site, owing to the prevalence of loose silty sand, corroborated by the available borehole data and the Liquefaction Potential Index, it is classified as having a high-risk liquefaction and could be responsible for the periodic damages to structural infrastructures such as roads and buildings. The sediments mapped at Okun-Ajah and Badore sites are mainly saturated loose sands with high likelihood to liquefaction with very-high to high risk severity. The study concludes that the presence of these sediments and other factors that could induce ground motion making the study sites potentially susceptible to liquefaction. Hence, an urgent attention must be given to early monitoring measures to address the trend. Study assesses use of electrical resistivity imaging and seismic refraction (via Multi Analysis Surface Waves) methods for near surface mapping/characterization The study sites belong to the wetland, coastal area of the Dahomey Basin, a part of sedimentary basin with sands deposits, peat, clay and their intercalation The shear waves velocity model integrated with CPT data proved to be useful tool for evaluation of soil liquefaction status with the index suggesting low-high-very high risks

The 2011 off the Pacific Coast of Tohoku earthquake caused extensive liquefaction damage to reclaimed land along the Tokyo Bay coast, even though it was approximately 400 km from the epicenter. The characteristics of the liquefaction damage include the fact that liquefaction occurred in soils with a high percentage of fine particles and that the distribution of liquefied and nonliquefied areas was nonuniform. The factors contributing to such nonuniform liquefaction damage included the heterogeneity of the ground materials and their depositional conditions, and the effects of the long earthquake duration. Although these points are certainly valid as reasons for the occurrence of severe liquefaction damage, they do not fully explain the mechanisms of the liquefaction of the fine-grained soils, or the localized extent of the liquefaction. To elucidate the severe and nonuniform damage, seismic response analyses of a multi-layered ground were conducted focusing on the stratigraphic irregularities in the ground beneath Urayasu city. The results showed that the thicker and softer sedimentary layers amplify the slightly long-period component of the seismic motion and increase the shaking at the ground surface. Moreover, the wave propagation in the ground became very complicated owing to the focal effect caused by the refractions and reflections of body waves at the stratum boundary, surface wave excitation at the base of the slope, and amplified interference between body and surface waves. This complex wave propagation contributed to nonuniform surface ground shaking and severe liquefaction damage. In addition, surface waves, which consist primarily of slightly long-period components, can propagate far and wide; as such, they triggered extensive damage owing to delayed shaking phenomena that continue even after the earthquake. The analysis results suggested that multidimensional elasto-plastic seismic response analyses considering stratigraphic irregularities are important for detailed seismic evaluation.

Combining intrusive geotechnical site investigations with non-intrusive geophysical surveys is a cost-effective approach to producing data with varying levels of accuracy, uncertainty, and different spatial scales to better characterize the site's liquefaction properties. Moreover, the demand for three-dimensional (3D) subsurface models in geotechnical engineering is increasing, but the models contain uncertainties and spatial variability associated with the use of relevant stochastic and geostatistical methods, and it remains a challenging task to obtain reliable liquefaction assessment results and the corresponding damage capacity. This study proposes a data-driven and non-parametric form of 3D multi-source fusion Bayesian compressive sampling (3D MSF-BCS) method for assessing 3D soil liquefaction-induced damage capacity. It consists of three main components: (i) 3D MSF-BCS fusing sparse geotechnical data (e.g., cone penetration test (CPT)) and geophysical data (e.g., multichannel analysis of surface waves (MASW)) for 3D site modeling, (ii) quantifying the accuracy and uncertainty of 3D MSF-BCS, and (iii) Soil liquefaction-induced damage capacity analysis in 3D space. The method was applied to numerical examples and a real case study at the Cresselly Place site, and the results showed that the proposed method performs well.

Seismic metamaterials have received extensive research interest due to their bandgap properties, simplicity in design principles, and stability in response. They have been developed to protect buildings or architectures susceptible to damage from surface elastic waves. In practice, the ground soil is generally a multiphase medium, and the influence of its permeability and viscosity on seismic metamaterials is not yet clear. In this work, we developed a formulation that combines Biot's theory and Bloch-Floquet theorem to investigate the complex band structures and transmission properties of Rayleigh and pseudo surface waves (PSWs) for pillared and inclusion-embedded seismic metamaterials in saturated soil. It is shown that the ratio of fluid viscosity and permeability eta/kappa have an impact on the surface wave attenuation and the performances of seismic metamaterials, where the smaller ratio benefits the surface wave broadband attenuation and metamaterials attenuating effects. The complex band structures reveal that inclusion-embedded metamaterials can support the propagation of PSWs having a phase velocity higher than that of the transverse bulk waves. The PSWs are significantly affected by the rubber viscosity due to the mode displacements concentrated in the rubber coatings. The higher viscosity of metamaterials also allows for broadband attenuation of Rayleigh surface waves. The results of this study will present an appropriate way to design viscoelastic seismic metamaterials in saturated soil for low-frequency surface wave attenuation.