A Comparison of Mine Seismic Discriminators Based on Features of Source Parameters to Waveform Characteristics

Table 1

Guidelines for mine seismic events classification manually.

Characteristics	Description
The presence of delays of the blast	Blasts, especially stope firings, have multiple delays, which are expressed in the seismogram as similar signals repeating closely within a short time interval. The practice of decides whether an event is a blast or a microseismic event is based on the repetition feature. Besides, seismograms capturing a blast will have a monotonically decreasing tail commonly. For the waveform of a microseismic signal, a large amplitude difference exists between the maximum peak and the peak closest behind, without a gradual decrease.
The steeper rise in the energy curve of the normal event	Seismograms capturing a microseismic event usually associated with shear fracturing and have an S-wave arrival more obvious than in the cases of blasts due to the source of the latter are usually in the focal mechanism of expansion and compression. Furthermore, blasting events will typically have a consistent gradual rise in their energy curve while seismic events will tend to have a steeper, more distinct, rise in the energy curve, and the energy curves for blasting events can be loosely compared to a positive sloping flat line.
The time of occurrence	Another way to eliminate blasts from the microseismic catalogue is to apply the time filters (i.e., generally mines have prescribed blasting times, and the events that does not occur at the blasting time are marked as microseismic events). Two main daily blasting shifts are observed from the typical diurnal chart of Chinese mines, hours between 10~16 (stope firings) and 23~1 (development firings), each of which triggers an increase in seismicity. It has to be classified referring to other features for the cases that recorded during the blasting time and located close to the blasting area.
The dominant frequency	A large number of actual observations and analysis show that blasts or explosions usually radiate higher frequency waves compared to normal microseismic events. The statistics show that the value of the dominant frequency of the microseismic events varies from 10 to 100 Hz and from 70 to 260 Hz for blasts. In addition, blasting events will typically not be well matched to the Brune’s model curve as plotted in the Stacked Spectra Plot within TRACE (the software provided by IMS). Spectral analysis is often considered as a relative effective method to distinguish blasts from microseismic events.
The maximum amplitude	The maximum amplitude of the waveform, which characterizes the size of energy released, is also considered as an important reference for the recognition of blasts and microseismic events. Generally the maximum vibration velocity of microseismic events is about 10^−5 m·s^−1 far less than 10^−3 m·s^−1 of the blasting. However, this approach cannot be considered as universally applicable since it is possible to have a scenario where a blast triggers shear fracturing that radiates stronger seismic signals than the blast itself.