Constraints on Crustal P Wave Structure With Leaking Mode Dispersion Curves

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.