Abstract Detection of near-surfaces features such as voids and faults is challenging due to the complexity of near-surface materials and the limited resolution of geophysical methods. Although multichannel, high-frequency, surface-wave techniques can provide reliable shear (S)-wave velocities in different geological settings, they are not suitable for detecting voids directly based on anomalies of the S-wave velocity because of limitations on the resolution of S-wave velocity profiles inverted from surface-wave phase velocities. Therefore, we studied the feasibility of directly detecting near-surfaces features with surface-wave diffractions. Based on the properties of surface waves, we have derived a Rayleigh-wave diffraction traveltime equation. We also have solved the equation for the depth to the top of a void and an average velocity of Rayleigh waves. Using these equations, the depth to the top of a void/fault can be determined based on traveltime data from a diffraction curve. In practice, only two diffraction times are necessary to define the depth to the top ofa void/fault and the average Rayleigh-wave velocity that generates the diffraction curve. We used four two-dimensional square voids to demonstrate the feasibility of detecting a void with Rayleigh-wave diffractions: a 2 m by 2 m with a depth to the top of the void of 2 m, 4 m by 4 m with a depth to the top of the void of 7 m, and 6 m by 6 m with depths to the top of the void 12 m and 17 m. We also modeled surface waves due to a vertical fault. Rayleigh-wave diffractions were recognizable for all these models after FK filtering was applied to the synthetic data. The Rayleigh-wave diffraction traveltime equation was verified by the modeled data. Modeling results suggested that FK filtering is critical to enhance diffracted surface waves. A real-world example is presented to show how to utilize the derived equation of surface-wave diffractions. © 2006 Elsevier B.V All rights reserved.

Abstract Seismic waves are elastic waves that propagate in the earth. Specifically, seismic waves induce elastic deformation of particles, represented by an infinitesimally small volume around a point, within the soil and rock column along the propagation path in the subsurface. The term elastic refers to the type of deformation that vanishes upon removal of the stress that has caused it.

Abstract Seismic waves induce elastic deformation along the propagation path in the subsurface. The term elastic refers to the type of deformation that vanishes upon removal of the stress which has caused it. In exploration seismology, we are primarily interested in compressional and shear waves which travel through the interior of solid layers, and thus are characterized as body waves. Whereas in engineering seismology, we also make use of Love and Rayleigh waves which travel along the free surface, and thus are characterized as surface waves.

Abstract In engineering seismology, for site investigations required for civil engineering structures, we most commonly use Rayleigh-wave and rarely Love-wave dispersion curves to estimate an S-wave velocity-depth model for the soil column. We use first-arrival times associated with mostly refracted waves to estimate a P-wave velocity-depth model and shallow reflections to derive a seismic image for the near-surface. By using the velocity-depth model and the seismic image, we delineate the geometry of the layers and faults within the soil column, and the geometry of the soil-bedrock interface.

Abstract The design and location of civil engineering structures at a project site require, aside from investigation of the site geology and geotechnical field and laboratory tests, knowledge of the soil-column shear-wave velocities and the geometry of the layers within the soil column and that of the soil-bedrock interface. We shall present case studies for seismic, geotechnical, and earthquake engineering site characterization.

Abstract When the gravity-induced shear stress on a potential slip (failure) surface exceeds the shear resistance, then the soil mass above the slip surface moves downslope. This occurs when the slip surface composed of a clay layer is saturated by water as a result of a heavy rainfall. The land mass may also be set into motion as a result of an earthquake. Factors that control shear stress on the slip surface include the volume of the soil mass above the slip surface, the dip of the slip surface, and the magnitude of the earthquake.

Abstract Active fault investigations are imperative for major infrastructures – nuclear power plants, refineries, tunnels, and dams. An active fault is defined as a fault that has a history of tectonic activity, at least within the past several tens of thousands of years, and will give rise to an earthquake in the future.