Some Practical Aspects of MASW Analysis and Processing

Abstract

We use multi-channel analysis of surface waves (MASW) on seismic data in an attempt to test data acquisition parameters and compare those results to reaffirm existing general theoretical recommendations and rules of thumb. Of particular interest were optimum seismic receiver spread size, minimum and maximum receiver offsets and dominant geophone frequency for best-case fundamentalmode dispersion-curve evaluation of the Rayleigh wave. Recommended MASW parameter selection criteria are tested on seismic data collected at various sites, such as desert setting, river sediments, and glacier, for which shear-wave properties were estimated. Presented MASW results demonstrate that observing optimal parameter selection can improve the resolution and quality of the fundamental-mode dispersion-curve images of the surface wave and the final 2D Vs section. After comparing the optimal parameter selection approach with the general theoretical recommendations it was concluded that the rules of thumb are s a good starting point, especially when applying the MASW method at a site with unknown seismic characteristics. However, optimal acquisition and processing MASW parameter selection can be best achieved using field site tests and is the preferred approach over theoretical recommendations. Specifically testing a selected brand of geophones, it is expected that, in general, frequencies as low as one octave and a half bellow the natural geophone frequency can be recommended used for most MASW analysis.

Resolution enhancement in shallow 3D-PS seismic reflection

“…It is also of interest that, despite the much higher natural frequency (28 Hz) of the 1C geophones, it is possible to obtain dispersion results well below the natural frequency. This is due to the relatively gentle low-cut (12 dB/octave) on the phones and agrees with similar results presented by Ivanov et al (2008). However, the low-frequency portion of the curve is more difficult to pick on these 1C data, leading to reduced confidence in the deeper part of the inversion.…”

“…The natural frequency of the geophones, while also important, is not specifically investigated here, although the previous finite-difference modelling provided some insight into the problem. Ivanov et al (2008) provided an example comparing 4.5 Hz, 10 Hz and 40 Hz geophones showing near identical results on the 4.5 Hz and 10 Hz geophones. The dispersion curves on the 40 Hz geophones were restricted to > 15 Hz.…”

“…Liner, 2012;Lin et al, 2005) and acquisition parameters (e.g. Ivanov et al, 2008;Zeng et al, 2007). In this chapter we revisit this style of sensitivity analysis, but with a particular emphasis on how the properties of exploration-scale surveys affect the resolution of ground-roll dispersion curves.…”

Tool for analysis of multichannel analysis of surface waves (MASW) field data and evaluation of shear wave velocity profiles of soils

“…The analysis of the multichannel surface wave records is based on the assumption that the wave front of the Rayleigh wave is plane. Hence, propagation of nonplanar surface waves and interference of body waves near the impact load point, referred to as near-field effects, can bias the experimental dispersion curve estimate (Ivanov et al 2008;Park and Carnevale 2010;Yoon and Rix 2009). In general, the length of the source offset (x 1 ) has to be sufficient to assure plane wave propagation of surface wave components.…”

“…An overly long source offset, however, risks excessive attenuation of fundamental-mode components at higher frequencies. A simple, widely accepted rule-of-thumb indicates that the investigation depth of the survey is around the same as the receiver spread length (L) and that the minimum source offset is in the range of 0.25L-L (Ivanov et al 2008). However, it should be noted that such empirical rules-of-thumb might not be applicable at specific sites.…”