Krauklis wave in a trilayer

The Krauklis wave is a slow dispersive wave mode that propagates in a fluid layer bounded by elastic media. The guided properties of this wave and its ability to generate very short wavelengths at seismic frequency range predict possibility of resonances in fluid-filled rock fractures. Study of Krauklis wave properties at laboratory scales requires evaluation of its propagation velocities in models with finite and thin elastic walls. Analysis of an exact solution for a fluid-filled trilayer with equal thickness plates reveals existence of the Krauklis waves in such a model, as well as another mode which propagates mostly in the solid part. Both propagation modes exist at all frequencies. We derived and verified various asymptotic solutions by comparing their dependencies on layer thicknesses and frequency with the exact numerical solution. Analytical and computational results demonstrate that in a 60-cm long model, the first resonant frequency can be below 10 Hz. This result suggests that the Krauklis-wave effects can be studied in a laboratory at seismic range of frequencies avoiding a notorious problem of frequency downscaling. Strong dispersive properties of Krauklis waves and their dominant behavior in fluid-fracture systems are likely phenomena explaining the observed frequency-dependent seismic effects in natural underground reservoirs.