The time—frequency characteristics of quarry blasts and calibration explosions recorded in Kazakhstan, USSR

Abstract

In this paper we consider two fundamentally different processes that can be responsible for the organization of energy in seismic coda into discrete time‐independent frequency bands. One process involves the resonance of energy in low velocity horizons and the other requires the interaction of time offset wavefields produced by subevents within multiple‐event mine explosions (ripple‐fired quarry blasts). We examined data collected by high frequency seismometers in Kazakhstan, USSR, and observed regular time‐independent spectral modulations in coda resulting from events strongly suspected to be Soviet quarry blasts, but not in the coda from single event calibration explosions detonated at similar ranges. We conclude these modulations are a source effect and due to ripple‐firing. This modulation is independent of the source‐receiver azimuth and we infer that the spatial array of subshots in each event must be small. We demonstrate that simple linear superposition theory can be used to reproduce effectively the spectral modulation observed in real quarry blasts. On the basis of these observations we attempt to discriminate between the two types of events using a spectral pattern‐based algorithm that seeks time‐independent features. We consider the detrimental effect that resonant energy in low velocity horizons can have on the successful application of our algorithm. Copyright © 1989, Wiley Blackwell. All rights reserved