Development and application of new imaging methods for small-scale heterogeneities in the crust and estimation of their physical properties

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With array analysis of high-frequency seismic wave records scattered by small-scale heterogeneities in the crust, researchers have imaged their spatial distributions in the past. We show it possible to estimate some of their physical properties based on wave phenomena. In addition, we pay attention to the fact that there are both phase delay and advance, corresponding to scatterings of low-and high-velocity heterogeneities, respectively, which is in contrast with phase delay only in other research fields such as optics, electromagnetism and acoustic waves. In such a case, scattered waves are not always caustic but it can be explained by the concept of time-reversed phases depending on velocity anomalies of heterogeneities.