Estimation of debris-flow discharge by monitoring ground tremor

Abstract

Boulder rich type of debris flow is known to generate strong ground tremor. Discharge of 34 debris-flow surges and ground tremor due to the surges have been observed at the Kamikamihori Gully of Mount Yakedake, Japan. Analysis of the relationship between peak discharge of the surge and peak acceleration of the tremor shows a positively high correlation with a correlation coefficient of R=0.90. This relationship results from the fact that a larger momentum of boulder may be expected with the larger peak discharge of the surge, and that the larger the momentum, the higher the intensity of the ground tremor. Another relationship between the volume obtained by integrating the discharge over the duration time of a surge and the integral of acceleration amplitude of the tremor over the same period shows a positively very high correlation with a correlation coefficient of R=0.98. This relationship may be roughly understood by a conceptual analogy, in which the volume should be a substitute of momentum of a surge, and the integral of tremor-acceleration amplitude should be an alternate of impulse which is equivalent to momentum. The result suggests that peak discharge of the surge can be roughly estimated from peak acceleration of the tremor, and volume of the surge can be precisely estimated from the integral of acceleration amplitude of the tremor.