Theoretical Issues with Rayleigh Surface Waves and Geoelectrical Method Used for the Inversion of Near Surface Geophysical Structure

Abstract

We numerically simulate the field measurements of Rayleigh surface waves and electrical resistivity in which the target depth is set to be less than 50-m. The Rayleigh surface waves are simulated in terms of fundamental mode group and phase velocities. The seismic field data is assumed to be collected through a conventional shot-gather. The group velocities are found from the application of the multiple filter technique in a single-station fashion while for the phase velocities the slant stacking, or linear radon transform are applied in fashion of multichannel analysis of surface waves (MASW). The average seismic structure from the source to the receiver (or geophone) is represented by the group velocity curve while the average seismic structure underneath the geophone array is represented by the phase velocity curve. The single-station group velocity curves are transformed into local group velocity curves by setting a linear system through grid points. The shear-wave velocity cross section underneath the examined area is constructed by inverting these local group velocity curves. The electrical resistivity structure of the underground is similarly studied. The field compilation of the resistivity data is assumed to be completed by the application of the multiple electrode Pole-Pole array. The actual resistivity assemble underneath the analyzed area is inverted by considering the apparent (measured) resistivity values. Unique forms such as ore body, cavity, sinkhole, melt, salt, and fluid within the Earth may be examined by joint interpretation of electrical resistivities and seismic velocities. These formations may be better outlined by following their distinct signs such as high/low resistivities and high/low seismic velocities. Doi: 10.28991/HEF-2021-02-03-01 Full Text: PDF

Dispersion of Rayleigh Surface Waves and Electrical Resistivities Utilized to Invert Near Surface Structural Heterogeneities

“…In real applications, the single-station (observed) group velocity curve can be obtained from the MFT (Multiple Filter Technique) analysis applied on the observed waveforms [14,55]. Herein we do not apply the MFT, but rather simulate the observed slowness (𝑆 ̅ 𝑖 ) by forward solving the system in Equation 2.…”

“…There exist structural discontinuities in the horizontal and vertical directions. In the simplest case of one-dimensional (1D) multi-layered Earth media, the structural discontinuities occur mainly in the vertical direction [14]. In a fold-and-thrust belt (i.e., subduction and collision zones), the layer boundaries are folded and are displaced over some distances, creating discontinuities in the lateral direction, i.e., faults, nappes, and transitional slopes.…”

“…We follow a similar scheme to the surface waves for the electrical resistivity inversion. The apparent resistivity pseudo-section is computed based on a resistivity Earth model [14,43], which is then inverted to estimate the underground (2D) resistivity-depth formation. Herein we are primarily interested in estimating the size and shape of near-surface buried objects (i.e., ore body and cavity) using Rayleigh surface waves and electrical resistivities in manner of cooperative inversion.…”

Seismic Hazard Evaluation of the North and Northwest Iranian Plate Considering the Bayesian Perspective

“…Since 2013, the area's crustal deformation has been monitored by a dense GNSS network (PPGNet), consisting of five stations, equipped with Leica and Septentrio receivers [21]. e group velocities are found from the application of the multiple filter technique in a single-station fashion, while for the phase velocities, slant stacking or linear radon transform are applied in the fashion of multichannel analysis of surface waves (MASW) [22]. Soil's potential against liquefaction for 45 locations has been carried out using PGASUR results so obtained.…”