Skip to main content

Broadband P waves transmitting through fracturing Westerly granite before and after the peak stress under a triaxial compressive condition


We analyzed temporal changes in the velocity and amplitude of P waves transmitted through a granite sample during a triaxial compression test, with the goal of monitoring the fault formation process associated with open and shear cracking. We used newly developed transducer assemblies for the broadband recording, and we continued to record transmitting waves even after the peak stress occurred. For transmitting P waves with paths parallel to the maximum compressive axis, we found that both the first wave amplitude and the velocity decreased after dilatancy started, and they kept decreasing even after the peak stress. In addition, the large nonlinear decrease in amplitude was associated with a rapid decrease in differential stress, whereas the rate of decrease in velocity remained almost constant. Thus, before the rapid decrease of differential stress, when both the amplitude and the velocity gradually decreased, open cracking was indicated to be dominant. Thereafter, shear cracking was indicated to become dominant in synchronization with the rapid decrease in differential stress. It is suggested that a main fault started to grow around the sample surface and then progressed into the sample interior; this corresponded to the rapid stress decrease. This fault acts as a strong scatterer for P waves that are parallel to the maximum compressive axis.


  1. Kawakata, H., A. Cho, T. Kiyama, T. Yanagidani, K. Kusunose, and M. Shimada, Three-dimensional observations of faulting process in Westerly granite under uniaxial and triaxial conditions by X-ray CT scan, Tectonophys., 313, 293–305, 1999.

    Article  Google Scholar 

  2. Kitagawa, G., FORTRAN 77 programming for time series analysis, 350 pp, Iwanami Publishing Company, Japan, 1993 (in Japanese).

    Google Scholar 

  3. Lei, X.-L., K. Kusunose, M. V. M. S. Rao, O. Nishizawa, and T. Satoh, Quasi-static fault growth and cracking in homogeneous brittle rock under triaxial compression using acoustic emission monitoring, J. Geophys. Res., 105, 6127–6139, 2000.

    Article  Google Scholar 

  4. Lockner, D. A., J. B. Walsh, and J. D. Byerlee, Changes in seismic velocity and attenuation during deformation of granite, J. Geophys. Res., 82, 5374–5378, 1977.

    Article  Google Scholar 

  5. Lockner, D. A., J. D. Byerlee, V. Kukscnko, A. Ponomarev, and A. Sidorin, Observations of quasi-static fault growth from acoustic emissions, in Fault Mechanics and Transport Properties of Rocks, edited by B. Evans, T.-F. Wong, 3–31, Academic Press, San Diego, 1992.

    Google Scholar 

  6. Moore, D. E. and D. A. Lockner, The role of microcracking in shear fracture propagation in granite, J. Struct. Geol., 17, 95–114, 1995.

    Article  Google Scholar 

  7. Pyrak-Nolte, L. J., L. R. Myer, and N. G. W. Cook, Transmission of seismic waves across single natural fractures, J. Geophys. Res., 95, 8617–8638, 1990.

    Article  Google Scholar 

  8. Reches, Z. and D. A. Lockner, Nucleation and growth of faults in brittle rocks, J. Geophys. Res., 99(B9), 18,159–18,173, 1994.

    Article  Google Scholar 

  9. Sellers, J. E., M. O. Kataka, and L. M. Linzer, Source parameters of acoustic emission events and scaling with mining-induced seismicity, J. Geophys. Res., 108(B9), doi:10.1029/2001JB000670, 2003.

    Google Scholar 

  10. Thompson, B. D., R. P. Young, and D. A. Lockner, Fracture in Westerly granite under AE feedback and constant strain rate loading: nucleation, quasi-static propagation, and the transition to unstable fracture propagation, Pure Appl. Geophys., 163, 995–1019, 2006.

    Article  Google Scholar 

  11. Yukutake, H., Fracturing process of granite inferred from measurements of spatial and temporal variations in velocity during triaxial deformations, J. Geophys. Res., 94, 15,639–15,651, 1989.

    Article  Google Scholar 

Download references

Author information



Corresponding author

Correspondence to Nana Yoshimitsu.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Yoshimitsu, N., Kawakata, H. & Takahashi, N. Broadband P waves transmitting through fracturing Westerly granite before and after the peak stress under a triaxial compressive condition. Earth Planet Sp 61, e21–e24 (2009).

Download citation

Key words

  • Broadband recording
  • fracturing Westerly granite
  • triaxial compression test
  • post-peak stress
  • transmitting P wave
  • amplitude change
  • velocity change
  • fault formation process