- Open Access
A numerical analysis of seismic waves for an anisotropic fault zone
Earth, Planets and Space volume 58, pages569–582(2006)
In this study we examine the effects of anisotropy on the seismic wavefield in a fault zone from computation of the synthetic seismograms for a simple fault zone model and a variety of seismic wave sources. The fault zone is modeled by a homogeneous vertical layer with transverse isotropy, induced by cracks, sandwiched between isotropic half-spaces (host rocks). The symmetry axis of the transverse isotropy is horizontal and perpendicular to the fault zone strike. We calculate the synthetic seismograms for this anisotropic fault zone model using a semianalytical method, the propagator matrix method. The synthetic seismograms show a later phase arriving after the main shear-wave in the horizontal component perpendicular to the fault zone strike at most stations near the fault zone. It is the slower shear-wave (qS2) and its reverberation. The amplitude of this phase and the time delay from the main shear-wave arrival are proportional to the degree of anisotropy, which suggests that observing such phase in field measurements may imply the presence of an anisotropic fault zone. We also perform the shear-wave splitting measurements by applying the cross-correlation method to the synthetic seismograms for various sources. For a strike-slip source, the synthetic seismograms show that the wavefield is more affected by the velocity structure than by the degree of anisotropy, which makes it difficult to estimate the anisotropic (shearwave splitting) parameters. For normal and dip-slip fault sources with the strike parallel to or striking against the fault zone, the effects of anisotropy is so dominant that the anisotropic fault zone can be detected. These results suggest that the determination of the anisotropic properties in the fault zone would require an appropriate station deployment and the source type information.
Anderson, D. L. and A. M. Dziewonski, Upper mantle anisotropy: evidence from free oscillations, Geophys. J. Roy. Astr. Soc., 69, 383–404, 1982.
Ben-Menahem, A, Source mechanism of the 1906 San Francisco earthquake, Phys. Earth Planet. Inter., 17, 163–181, 1978.
Booth, D. C. and S. Crampin, Shear-wave polarizations on a curved wavefront at an isotropic free-surface, Geophys. J. Roy. Astr, Soc., 83, 31–45, 1985.
Bowman, J. R. and M. Ando, Shear-wave splitting in the uppermantle wedge above the Tonga subduction zone, Geophys. J. Roy. Astr. Soc., 88, 25–41, 1987.
Chester, F. M., J. P. Evans, and R. L. Biegel, Internal structure and weakening mechanisms of the San Andreas fault, J. Geophys. Res., 98, 771–786, 1993.
Cochran, E. S., J. E. Vidale, and Y. G. Li, Near-fault anisotropy following the Hector Mine earthquake, J. Geophys. Res., 108, 2436, doi:10.1029/ 2002JB002352, 2003.
Crampin, S., Seismic wave propagation through a cracked solid: polarization as a possible dilatancy diagnostic, Geophys. J. Roy. Astr. Soc., 53, 467–496, 1978.
Crampin, S. and S. Peacock, A review of shear-wave splitting in the compliant crack-critical anisotropic Earth, Wave Motion, 41, 59–77, 2005.
Crampin, S., R. Evans, B. Üçer, M. Doyle, J. P. Davis, G. V. Yegorkina, and A. Miller, Observations of dilatancy-induced polarization anomalies and earthquake prediction, Nature, 286, 874–877, 1980.
Evans, R., Effects of the free surface on shear wavetrains, Geophys. J. Roy. Astr. Soc., 76, 165–172, 1984.
Gilbert, F. and G. Backus, Propagator matrices in elastic wave and vibration problems, Geophysics, 31, 326–332, 1966.
Haskell, N. A., The dispersion of surface waves in multilayered media, Bull. Seism. Soc. Am., 43, 17–34, 1953.
Herrmann, R. B., SH-wave generation by dislocation sources—A numerical study, Bull. Seism. Soc. Am., 69, 1–15, 1979.
Hough, S. E., Y. Ben-Zion, and P. C. Leary, Fault-zone waves observed at the southern Joshua Tree earthquake rupture zone, Bull. Seism. Soc. Am., 84, 761–767, 1994.
Hudson, J. A., Overall properties of a cracked solid, Math. Proc. Camb. Phil. Soc., 88, 371–384, 1980.
Hudson, J. A., Wave speeds and attenuation of elastic waves in material containing cracks, Geophys. J. Roy. Astr. Soc., 64, 133–150, 1981.
Igel, H., Y. Ben-Zion, and P. C. Leary, Simulation of SH- and P-SV-wave propagation in fault zones, Geophys. J. Int., 128, 533–546, 1997.
Kawasaki, I. and T. Tanimoto, Radiation patterns of body waves due to the seismic dislocation occurring in an anisotropic source medium, Bull. Seism. Soc. Am., 71, 37–50, 1981.
Li, Y. G., P. C. Leary, K. Aki, and P. E. Malin, Seismic trapped modes in the Oroville and San Andreas fault zones, Science, 249, 763–766, 1990.
Li, Y. G., W. L. Ellsworth, C. H. Thurber, P. E. Malin, and K. Aki, Faultzone guided waves from explosions in the San Andreas fault at Parkfield and Cienega Valley, California, Bull. Seism. Soc. Am., 87, 210–221, 1997.
Liu, E. and S. Crampin, Effects of the internal shear wave window: Comparison with anisotropy induced splitting, J. Geophys. Res., 95, 11275–11281, 1
Mandal, B. and B. J. Mitchell, Complete seismogram synthesis for transversely isotropic media, J. Geophys., 59, 149–156, 1986.
Mizuno, T., K. Yomogida, H. Ito, and Y. Kuwahara, Spatial distribution of shear wave anisotropy in the crust of the southern Hyogo region by borehole observation, Geophys. J. Int., 147, 528–542, 2001.
Nakamura, T. and H. Takenaka, Influence of anisotropy in the fault zone on the seismic wave, Zisin 2 (J. Seism. Soc. Jpn.), 57, 331–342, 2005 (in Japanese with English abstract).
Nakamura, T., H. Takenaka, and S. Suzuki, Strong S-wave anisotropy in the aftershock region of the 2000 Tottori-ken Seibu, Japan, earthquake (Mw6.6), Earth Planets Space, 57, 1055–1062, 2005.
O’Connell, R. and B. Budiansky, Seismic velocities in dry and saturated cracked solids, J. Geophys. Res., 79, 5412–5426, 1974.
Peacock, S., S. Crampin, D. C. Booth, and J. B. Fletcher, Shear-wave splitting in the Anza seismic gap, Southern California: temporal variations as possible precursors, J. Geophys. Res., 93, 3339–3356, 1988.
Peng, Z. and Y. Ben-Zion, Systematic analysis of crustal anisotropy along the Karadere-Düzce branch of the north Anatolian fault, Geophys. J. Int., 159, 253–274, 2004.
Savage, M. K., Seismic anisotropy and mantle deformation: What have we learned from shear wave splitting?, Rev. Geophys, 37, 65–106, 1999.
Shih, X. R., R. P. Meyer, and J. F. Schneider, An automated, analytical method to determine shear-wave splitting, Tectonophysics, 165, 271–278, 1989.
Takeuchi, H. and M. Saito, Seismic surface waves, in Methods in Computational Physics, Vol. 11, pp. 217–295, edited by B. A. Bolt, Academic Press, New York, 1972.
Vavryčcuk, V., Inversion for anisotropy from non-double-couple components of moment tensors, J. Geophys. Res., 109, B07306, doi:10.1029/2003JB002926, 2004.
Wang, C. Y. and R. B. Herrmann. A numerical study of P-, SV-, and SHwave generation in a plane layered medium, Bull. Seism. Soc. Am., 70, 1015–1036, 1980.
Watanabe, A., H. Takenaka, and S. Suzuki, Spatial variation of shear wave anisotropy in the focal region of the 1997 northwestern Kagoshima earthquakes, Abstr. Jpn. Earth Planet. Sci. Joint Meeting, Sz-P003, 2001.
Wessel, P. and W. H. F. Smith, Free software helps map and display data, EOS Trans. Am. Geophys. Union, 72, 441–446, 1991.
Yamanaka, H., Y. Hiramatsu, and H. Katao, Spatial distribution of atypical aftershocks of the 1995 Hyogo-ken Nanbu earthquake, Earth Planets Space, 54, 933–945, 2002.
About this article
Cite this article
Nakamura, T., Takenaka, H. A numerical analysis of seismic waves for an anisotropic fault zone. Earth Planet Sp 58, 569–582 (2006). https://doi.org/10.1186/BF03351954
- Seismic anisotropy
- shear-wave splitting
- synthetic seismogram
- fault zone