Krauklis Wave Initiation in Fluid-Filled Fractures by a Passing Body Wave

Abstract

Krauklis waves are a special wave mode bound to and propagating along fluid-filled fractures. They are of great interest because when propagating back and forth a fracture, they may fall into resonance and emit seismic signals with a characteristic frequency. This resonant behavior can lead to strongly frequencydependent propagation effects for seismic waves and may explain seismic tremor generation in volcanos or affect micro-seismic signals in fractured fluid reservoirs. All existing studies assume a Krauklis wave initiation inside a fracture, for example by hydro-fracturing. Here, Krauklis wave initiation by an incident plane P-wave is studied. The P-wave is scattered at the fracture, but also, two Krauklis waves are initiated, one at each fracture tip (i.e., diffraction-points of the fracture). The initiation of Krauklis waves strongly depends on the fracture orientation with respect to the incident P-wave. High-amplitude Krauklis waves are initiated at moderate (12°–40°) and high (>65°) incident angles with a distinct gap at around 50°. The initiated Krauklis waves are only visible within, but not outside the fracture. Nevertheless, the fact that P-waves can initiate Krauklis waves has important implications for earthquake signals propagating through fluid-bearing fractured rocks (volcanic areas, fluid-reservoirs) or for active seismic surveys in fractured reservoir situations.