Source duration of stress and water-pressure induced seismicity derived from experimental analysis of P wave pulse width in granite

Authors

  • Koji Masuda

    Corresponding author
    1. Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
    • Corresponding author: K. Masuda, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, AIST, Tsukuba Central 7, Tsukuba 305–8567, Japan. (koji.masuda@aist.go.jp)

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Abstract

[1] Pulse widths of P waves in granite, measured in the laboratory, were analyzed to investigate source durations of rupture processes for water-pressure induced and stress-induced microseismicity. Water was injected into a dry granite sample under constant axial stress of about 70% of fracture strength and a confining pressure of 40 MPa. After the effects of event size and hypocentral distance were removed from observed pulse widths, the ratio of the scaled source durations of water-pressure induced and stress-induced microseismicity was 0.52. The difference in the scaled source durations between water-pressure induced and stress-induced microseismicity suggests that water-pressure induced microseismicity involves a greater rupture velocity or a more equidimensional fault geometry than stress-induced microseismicity. These results suggest that pulse width analysis of P waveforms can be used to distinguish water-pressure induced events from those induced by regional stress and to characterize the faulting process.