Ascertaining study on the order of Fresnel volume in seismic migration to seismic reflection method
Abstract
An elastic wave propagates in the spatial volume depending on its wavelength, which is called the Fresnel volume. In seismic migration, diffracted waves are propagated back to every secondary seismic source, i.e., diffractors or scatterers that represents detailed underground structures. In the back propagation procedure, the spatial coverage of receivers has been mainly considered in the past although it is possible to accommodate the Fresnel volume. In this study, we consider the Fresnel volume for every portion of received elastic waves. A method using pre-stack depth migration with a restriction to the Fresnel volume is called Fresnel volume migration. In theory, careful selection of the Fresnel volume would surely suppress migration noise in the Fresnel volume migration. Therefore, we think that the Fresnel volume migration could be a powerful tool for seismic data processing when the spatial coverage of receivers is limited with restricted aperture such as the acquisition in tunnels, VSP, etc. To adopt the Fresnel volume migration, we first have to choose the location of the Fresnel volume in every wavepath. In this study, we calculated the incident angles for each receiver using the following two different ways for 2D forward-modeled seismic data: 1) polarization using observed amplitude, 2) polarization using the tau-p transform. In the tau-p space, we can choose the most reliable horizontal and vertical slowness of P-waves for every receiver trace. Given that the incident wave slowness can be estimated in the array of receivers, the incident angles of reflected waves are derived. By the latter method, we can use several receivers’ data for each receiver to estimate incident angles. We find that slant stack method gives better result for the data in which P-P and P-S reflected waves are superposed. Also, we evaluated the signal to noise ratio (S/N) and focused intensity (FI) of the Fresnel volume migration. The conventional Fresnel volume migration is in general applied using upto the second Fresnel volume. After our processing using the Fresnel volumes of different order, e.g. first, first and half, second Fresnel volumes, we confirmed that both S/N and FI depend on the migration aperture, i.e., the order of the Fresnel volume. In particular, the migration processing using the first Fresnel volume aperture gives us the best improvement of S/N ratio. On the other hand, the processing using the widest or the highest order Fresnel volume migration can image the reflection structure with a sharp contrast.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.S33A1738K
- Keywords:
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- 0520 COMPUTATIONAL GEOPHYSICS / Data analysis: algorithms and implementation;
- 0902 EXPLORATION GEOPHYSICS / Computational methods: seismic