Perpustakaan Digital ITB

The inversion of surface-wave phase-velocity dispersion curves provides a reliablemethod to derive near-surface shear-wave velocity profiles. In thiswork,we invert phase-velocity dispersion curves estimated from2D seismicreflection data. These data cannot be used to image the first 50m with seismic-reflection processing techniques due to the presence of indistinct first breaks and significant NMO-stretching of the shallowreflections. A surfacewave analysis was proposed to derive information about the near surface in order to complement the seismicreflection stacked sections, which are satisfactory for depths between 50 and 700 m. In order to perform the analysis, 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 picked curves using the neighborhood algorithm. The spatial aliasing is successfully circumvented by continuously tracking the surface-wavemodal curves in the f-k domain. This enables us to sample the curves up to a frequency of 40 Hz, even though most components beyond 10 Hz are spatially aliased. The inverted 2D VS sections feature smooth horizontal layers, and a sensitivity analysis yields a penetration depth of 20–25 m. The results suggest that long profilesmay be more efficiently surveyed by using a large receiver separation and dealingwith the spatial aliasing in the described way, rather than ensuring that no spatially aliased surface waves are acquired.