Time-average velocity estimation through surface-wave analysis: Part 1 — S-wave velocity

Abstract

In some areas, the estimation of static corrections for land seismic data is a critical step of the processing workflow. It often requires the execution of additional surveys and data analyses. Surface waves (SWs) in seismic records can be processed to extract local dispersion curves (DCs) that can be used to estimate near-surface S-wave velocity models. Here we focus on the direct estimation of time-average S-wave velocity models from SW DCs without the need to invert the data. Time-average velocity directly provides the value of one-way time, given a datum plan depth. The method requires the knowledge of one 1D S-wave velocity model along the seismic line, together with the relevant DC, to estimate a relationship between SW wavelength and investigation depth on the time-average velocity model. This wavelength/depth relationship is then used to estimate all the other time-average S-wave velocity models along the line directly from the DCs by means of a data transformation. This approach removes the need for extensive data inversion and provides a simple method suitable for industrial workflows. We tested the method on synthetic and field data and found that it is possible to retrieve the time-average velocity models with uncertainties less than 10% in sites with laterally varying velocities. The error on one-way times at various depths of the datum plan retrieved by the time-average velocity models is mostly less than 5 ms for synthetic and field data.

First application of a new seismo‐electric streamer for combined resistivity and seismic measurements along linearly extended earth structures

“…A combined 2D reconstruction of seismic and electric models from seismo‐electric streamer data was performed along the studied sector of the embankment, down to a depth of 10 m from its top. The shear wave velocity model, processed by means of the wavelength of the Rayleigh wave fundamental mode and the investigation depth procedure (Socco and Comina, 2017; Socco et al ., 2017), is reported in Figure 11(a). The electrical resistivity model, obtained by an inversion performed with the Res2DInv software, is reported in Figure 11(b).…”

“…The acquired seismic and electric data are processed and interpreted in order to offer a combined seismic and electric 2D reconstruction of the studied earth structure along the surveying length. Seismic data interpretation is based on the application of a new procedure (Socco and Comina, 2017; Socco et al ., 2017) for the analysis of the Rayleigh wave fundamental mode dispersion curve. This processing procedure relies on the use of a site‐dependent relationship between the wavelength of the Rayleigh wave fundamental mode and the investigation depth (W/D relationship).…”

Numerical comparison of Rayleigh and Love full waveform inversion in characterizing soil spatial variability for near‐surface engineering applications

“…The other solution is to use an initial model that better matches the true model (e.g. Pan et al, 2016;Socco et al 2017;Teodor et al, 2018), which would prove to be a challenging task in the absence of a priori information about the subsurface. Cycle skipping during FWI: (a) occurrence in high-frequency components when the phase lag between the synthetic and observed waveforms is greater than half-period; and (b) mitigation of cycle skipping by using low-frequency content that reduces the phase lag.…”

Time-average velocity estimation through surface-wave analysis: Part 2 — P-wave velocity

“…For the north zone, an abrupt variation in the estimated apparent Poisson's ratio at shallow depths can be observed. This can be related to the frequency gap contained in the reference DC (see Figure 10 in Socco et al, 2017).…”

“…The present paper is the companion paper of Socco et al (2017), which will be referred to as paper 1. In paper 1, we outline the use of surface waves (SWs) in seismic exploration records to directly estimate the S-wave time-average velocity that can be used to directly compute V S static corrections.…”