ONE-STATION, DOUBLE-STATION AND ARRAY ANALYSIS OF RAYLEIGH SURFACE WAVES APPLIED TO A COMMON-SHOT GATHER: A PROGRAMMED TECHNIQUE DESCRIBED THROUGH SYNTHETIC SEISMOGRAMS IN NEAR-SURFACE

The knowledge of near-surface shear-vibration speed (i.e., V_S30) is crucial to properly define the dynamic characteristic of shallow subsurface in the earthquake mitigation efforts. In this respect, we propose a programmed technique in which the Rayleigh surface vibrations are solved for the determination of two-dimensional (2D) speed structure (vertically polarized shear-vibration – V_SV) in terms of fundamental mode (FM) dispersal curves (both group and phase speeds). The synthetic seismograms are calculated to simulate the real Earth and then the three data processing procedures, i.e., the weighted preconditioned linear radon transform (WPLRT), one-station (OS) approach and double-station (DS) approach, are sequentially applied to these synthetics. The common-shot gather (CSG) is assumed as data collection geometry. The WPLRT is first used to produce a phase speed dispersal curve from which the one-dimensional (1D) V_SV structure corresponding to the average structure underneath the CSG is inverted. The average 1D V_SV structure between the source and receiver is next inverted using the OS group speed dispersal curve where the number of OS curves is proportional to the number of geophones. In the third step, the average 1D V_SV structure corresponding to the DS pathway is inverted utilizing the group and phase speed curves where the number of DS curves is proportional to the number of inter-station pathways. Hundreds of dispersal curves (both group and phase speeds) take place in each step of the proposed technique. To select the associated dispersal curve, a programmed scheme is established. The studied area is described in terms of grid points and then the OS and DS dispersal curves are transferred into unique dispersal curves at these grid points for which a set of linear systems defined through travel times are solved. A pseudo 2D cross-section beneath the studied area is eventually established by merging the 1D V_SV structures found by the inversion of dispersal curves at grid points.