Abstract
Classic surface wave imaging relies mainly on the dispersion of Rayleigh
waves or Love waves. In addition to these types of waves, waveforms that
arrive prior to the S wave also exhibit dispersion. These early
dispersed waves are controlled mainly by the leaking modes and are
rarely used for imaging. We applied the frequency-Bessel transform
method to waveforms that arrive before the S wave and successfully
extracted multiple leaking mode dispersion curves. The extracted “0th”
mode shows continuous sensitivity to S-wave velocity (Vs) and mass
density structure whereas the “higher” modes behave more like surface
waves that are sensitive to P-wave velocity (Vp) structure in the crust.
Thus, the “higher” modes can be used to invert the Vp structure, which
can compensate for the fact that conventional surface wave imaging
methods are mainly sensitive to Vs structure.