Speaker: Zoé Renat
Date: Thursday 2nd of December 2021, 1:15 pm.
Abstract:
The time-reversal method is based on the back-propagation of seismic waveforms recorded at a set of receivers which form a closed surface. When the elastic properties of the medium are correct, the seismic energy focuses at the source location, creating a focal spot. Such a spot is smooth in space, whereas the original wavefield is characterized by a displacement discontinuity at the source. The goal of the present work is to discuss the link between the focal spot and the original source using the concept of homogenized point-source recently proposed by Capdeville (2021). We show that the back-propagated wavefield is equivalent to the sum of two low-wavenumber fields resulting from the homogenization of the original point-source. In other words, the homogenized point-source is the equivalent force for producing the focal spot. In addition to the demonstration in the general
3D heterogeneous case, we present numerical examples in 2D including the case of an extended source made of multiple point-source.