Retrieving shallow shear-wave velocity profiles from 2D seismic-reflection data with severely aliased surface waves

ONNIS, L.E.; OSELLA, A.; CARCIONE, J.M.

JOURNAL OF APPLIED GEOPHYSICS

ELSEVIER SCIENCE BV

Año: 2019 vol. 161 p. 15 - 25

0926-9851

The inversion of surface-wave phase-velocity dispersion curves provides a reliablemethod to derive near-surfaceshear-wave velocity profiles. In thiswork,we invert phase-velocity dispersion curves estimated from2D seismicreflectiondata. These data cannot be used to image the first 50m with seismic-reflection processing techniquesdue to the presence of indistinct first breaks and significant NMO-stretching of the shallowreflections. A surfacewaveanalysis was proposed to derive information about the near surface in order to complement the seismicreflectionstacked sections, which are satisfactory for depths between 50 and 700 m. In order to perform theanalysis, we had to overcome some problems, such as the short acquisition time and the large receiver spacing,which resulted in severe spatial aliasing. The analysis consists of spatial partitioning of each line in segments,picking of the phase-velocity dispersion curves for each segment in the f-k domain, and inversion of the pickedcurves using the neighborhood algorithm. The spatial aliasing is successfully circumvented by continuouslytracking the surface-wavemodal curves in the f-k domain. This enables us to sample the curves up to a frequencyof 40 Hz, even though most components beyond 10 Hz are spatially aliased. The inverted 2D VS sections featuresmooth horizontal layers, and a sensitivity analysis yields a penetration depth of 20?25 m. The results suggestthat long profilesmay be more efficiently surveyed by using a large receiver separation and dealingwith the spatialaliasing in the described way, rather than ensuring that no spatially aliased surface waves are acquired.