Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Kelner, S. Articles by Coutant, O. Search for Related Content GeoRef GeoRef Citation

Characterization of fractures in shallow granite from the modeling of the anisotropy and attenuation of seismic waves

Laboratoire de Géophysique Interne et Tectonophysique Université Joseph Fourier, B.P. 53, 38041 Grenoble Cédex 9, France

Abstract

We try to characterize the fracturing of the anisotropic shallow granite (<250 m) present at Garner Valley, southern California. The shear-wave splitting observed on a downhole seismic array installed there (Archuleta et al., 1992) is modeled by performing numerical simulations of propagation of P and SV waves in 2D fractured media. The calculations are performed using a boundary integral equation method, which takes into account multiple scattering and full crack diffraction. The value of the time delay measured at Garner Valley between the fast S wave and the slow S wave is well reproduced for different models of fractured media. In order to differentiate between these models, we also measure and calculate the attenuation of the transmitted S waves. From the comparison between the observations and the numerical simulations, we conclude and infer the following: (1) The presence of fractures in granite explains the seismic anisotropy and attenuation observed at Garner Valley. (2) The cracks and fractures are nearly vertical and are oriented in a north-south direction. (3) There is no characteristic crack length, but rather, the crack length distribution seems to be fractal. (4) The density of fractures present in the shallow granite at Garner Valley is about 10^–4 representing the total volume of the fractures over the total volume of the fractured zone.

Footnotes

^* Present address: Compagnie Générale de Géophysique, 1 rue Léon Migaux, 91341 Massy, France.

This article has been cited by other articles:

				A. Rodriguez-Castellanos, F. J. Sanchez-Sesma, F. Luzon, and R. Martin Multiple Scattering of Elastic Waves by Subsurface Fractures and Cavities Bulletin of the Seismological Society of America, August 1, 2006; 96(4A): 1359 - 1374. [Abstract] [Full Text] [PDF]

				Borehole Response Studies at the Garner Valley Downhole Array, Southern California Bulletin of the Seismological Society of America, December 1, 2002; 92(8): 3165 - 3179.