Abstract
Velocity of guided waves which propagate along a subsurface fracture is estimated by means of a wave detection technique based on time-frequency representations. Propagation characteristics of the guided waves depend on not only geometric features of the interface but also mechanical properties on it. These interface conditions sensitively affect the propagation characteristics because their energy concentrates on the interface and they propagate along the interface. Measurement of the guided waves, therefore, has an advantage to characterize the interface condition. This energy distribution, however, makes it difficult to use an array sensor in velocity measurement. Number of sensors which can be arranged near the interface is limited, in particular, in a field measurement.
We examine a wave detection technique based on the time-frequency representations. The time-frequency representations combine time-domain and frequency-domain analyses to distinguish the guided waves from other waves and detect an arrival of each frequency component. This technique is applied to the estimation of the guided waves trapped in an artificial subsurface fracture. Specific patterns of both a wave source and detected guided waves are analyzed in the time-frequency representations. A result by the time-frequency representation analysis shows a typical dispersion pattern of the fundamental symmetric mode of the guided waves.
