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International Journal of Geophysics
Volume 2012, Article ID 101545, 8 pages
http://dx.doi.org/10.1155/2012/101545
Research Article

Crosscorrelation of Earthquake Data Using Stationary Phase Evaluation: Insight into Reflection Structures of Oceanic Crust Surface in the Nankai Trough

1Graduate School of Engineering, Kyoto University, C1 Kyoto-Daigaku Katsura, Nishikyo-ku, Kyoto 6158540, Japan
2International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, Ito Campus, 744 Motooka, Nishi-Ku, Fukuoka 819-0395, Japan
3Japan Agency for Marine-Earth Science and Technology, Institute for Research on Earth Evolution, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001, Japan

Received 6 February 2012; Accepted 27 March 2012

Academic Editor: Yun-tai Chen

Copyright © 2012 Shohei Minato et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Seismic interferometry (SI) has been recently employed to retrieve the reflection response from natural earthquakes. We perform experimental study to apply SI to Ocean Bottom Seismogram (OBS) records in the Nankai Trough, southwest Japan in order to reveal the relatively shallow geological boundaries including surface of oceanic crust. Although the local earthquakes with short raypath we use to retrieve reflection response are expected to contain the higher-frequency components to detect fine-scale structures by SI, they cannot be assumed as plane waves and are inhomogeneously distributed. Since the condition of inhomogeneous source distribution violates the assumption of SI, the conventional processing yields to the deteriorated subsurface images. Here we adopt the raypath calculation for stationary phase evaluation of SI in order to overcome this problem. To find stationary phase, we estimate the raypaths of two reflections: (1) sea-surface P-wave reflection and (2) sea-surface multiple P-wave reflection. From the estimated raypath, we choose the crosscorrelation traces which are expected to produce objective reflections considering the stationary phase points. We use the numerical-modeling data and field data with 6 localized earthquakes and show that choosing the crosscorrelation traces by stationary phase evaluation improves the quality of the reflections of the oceanic crust surface.