Measurement of rise times of seismic pulses in rock

Abstract

Rise times for seismic pulses in rock are discussed for both nearly constant Q (NCQ) and constant Q (CQ) theories of pulse attenuation. The frequency content of the NCQ pulse is examined in detail. Frequencies close to the megahertz region are shown to have a significant contribution to the rise time of pulses a meter or so from an impulsive source. Hence, the measurement of such rise times is significantly influenced by the frequency response of the measurement system itself. In giving a numerical assessment of the system influence, I propose a model for a general system transfer function. The effect of such a system on the measurement of rise times of seismic pulses is then obtained by convolving the system impulse response with the given seismic pulse. For even the most broad‐band seismic measurement systems presently available, rise time measurements made especially within 10 m or so of an impulsive source show a large contribution dependent upon the rise time of the measurement system itself.