Spectral characteristics of micro-seismic signals obtained during the rupture of coal

This study was performed to investigate the spectral characteristics of micro-seismic signals observed during the rupture of coal.Coal rupture micro-seismic observations were obtained on a test system that included an electro-hydraulic servo pressure tester controlled by a YAW microcomputer,a micro-seismic sensor,a loading system,and a signal collection system.The results show that the micro-seismic signal increases with increasing compressive stress at the beginning of coal rupture.The signal remains stable for a period at this stage.A large number of micro-seismic signals appear immediately before the main rupture event.The frequency of micro-seismic events reaches a maximum immediately after the coal ruptures.Micro-seismic signals were decomposed into several Intrinsic Mode Functions (IMF's) by the empirical mode decomposition (EMD) method using a Hilbert-Huang transform (HHT).The main frequency band of the micro-seismic signals was found to range from 10 to 100 Hz in the Hilbert energy spectrum and from marginal spectrum calculations.The advantage of applying an HHT is that this can extract the main features of the signal.This fact was confirmed by an HHT analysis of the coal micro-seismic signals that shows the technique is useful in the field of coal rupture.