I ran a 60 m line intended for surficial seismic refraction. Energization with hammer. 12 (10 hz vertical 5 m spaced) geophones and 5 shots (15 m spaced). Record length 0.5 s. Thanks to a borehole near a strata of man-made gravelly silt (0.40 m) and very soft silty clay (to 5 m) and then clay improves its consistency deeper were identified. My seismic traces seemed to be ok, but at office the principal wave train gives 200 m/s and first arrivals refractions are so weak that they cannot be easily identified. I think the principal train wave shadows them.

My question: What is the meaning of a 200 m/s train wave?

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    $\begingroup$ That's pretty slow... slower than air velocity (300m/s). Are you sure about your measurement? $\endgroup$
    – Antonio
    Aug 4 '19 at 23:38
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    $\begingroup$ Question edited to clarify point. $\endgroup$ Aug 9 '19 at 19:04

I've seen data like this before. My research focused on acquiring/processing both vertical and horizontal component data in subsurface environments characterized mainly by saturated and/or unconsolidated facies. So, it's entirely possible even for a that kind of surface-wave to display such low apparent velocities.

What I think you are seeing at that particular offset and traveltime is the Rayleigh-wave beginning to 'disperse' - AKA seismic dispersion beginning to manifests itself as a results of the wavefield convolving with layering and near-surface heterogeneity.

As for a refraction arrival, if it's indeed present, it should be extremely weak and probably only discernible via some kind of gain (e.g. AGC).

  • $\begingroup$ would it be possible that you can share your research's paper? $\endgroup$ Nov 5 '19 at 12:36
  • $\begingroup$ Absolutely, please visit this web-page and go to my thesis link (subsurfacesee.org). Be advised that particular research and paper concentrated on only SH- and Love-waves. $\endgroup$
    – nate
    Nov 5 '19 at 15:14

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