Civil Engineering Association

Utilization of multimode Love wave dispersion curve inversion for geotechnical site investigation

Inversion codes based on a modified genetic algorithm (GA) have been developed to invert multimode Love wave dispersion curves. The multimode Love wave dispersion curves were synthesized from the profile representing shear-wave velocity reversal using a full SH (shear horizontal) waveform. In this study, we used a frequency–slowness transform to extract the dispersion curve from the full SH waveform. Dispersion curves overlain in dispersion images were picked manually. These curves were then inverted using the modified GA. To assess the accuracy of the inversion results, differences between the true and inverted shear-wave velocity profile were quantified in terms of shear-wave velocity and thickness errors, ES and EH. Our numerical modeling showed that the inversion of multimode dispersion curves can significantly provide the better assessment of a shear-wave velocity structure, especially with a velocity reversal profile at typical geotechnical site investigations. This approach has been applied on field data acquired at a site in Niigata prefecture, Japan. In these field data, our inversion results show good agreement between the calculated and experimental dispersion curves and accurately detect low velocity layer targets.

Attenuation measurements on shallow seismic refraction data in the Kocaeli region, Turkey

Attenuation of P-waves (Qp) in different geologic units in the Kocaeli region, NW of Turkey, was determined using both the pulse-broadening and the spectral amplitude ratio techniques. With that aim, shallow seismic refraction data were conducted at total 97 points at the Sirintepe, Akveren, Izmit, Korucu, Arslanbey, Sopalı, Peksimet and the Çınarlıdere formation sites, which are generally in dry states located in the vicinity of the North Anatolia Fault within the Kocaeli segment. The Qp values determined from both techniques were correlated. The wide variation of the computed Qp values indicated that the spectral technique can found to be generally slightly better than the pulse-broadening method. In addition to these studies, the dynamic elastic properties were figured out using P and velocities determined from seismic refraction studies, and the natural water content and density of the subsoil layers were determined from the soil samples collected from total 36 boreholes drilled in the formations to observe their variation with Qp values. The dynamic elastic properties determined using P- and S-wave velocities in empirical equations were correlated with the quality factors. Generally, the physical parameters did not represent any linear relations with the quality factors which demonstrated that the attenuation characteristics of seismic waves cannot be used to derive dynamic elastic parameters of the subsurface sediments.

Statistical correlations of shear wave velocity and penetration resistance for soils