29. Integrated Approach for Surface-Wave Analysis from near Surface to Bedrock

Abstract

A study of surface-wave analysis can be divided into two main parts. In the first stage, dispersive Rayleigh waves are extracted using multichannel analysis of surface waves (MASW) and then are inverted using a genetic-algorithm (GA) method to obtain shear-wave velocity profiles of the investigated site. A new interactive-based inversion algorithm that includes both GA and surface-wave inversion schemes was used in an MASW study. A special type of seismic source (SR-II, or Kangaroo) proved to be very effective in surface-wave studies. The standard-penetration-test data (SPT) and the shear-modulus distribution map derived from MASW data are compared with borehole results aimed for geotechnical applications. In the second stage, a microtremor survey carried out parallel to the MASW survey estimated lateral variations in sedimentary-basin depths up to bedrock. A shear-wave velocity profile of basin sediments is estimated from the GA inversion of the microtremor horizontal-to-vertical (H/V) spectrum based on surface waves from seismic noise at each site. Average shear-wave velocities estimated from the MASW survey are given as constraints in the microtremor inversion process. A new relationship between the resonance frequency f(0) and the thickness of the overlaying layer H is derived. A combination of active- and passive-source surface-wave analysis methods is proposed to obtain the optimum shear-wave velocity model from near surface to bedrock.