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Abstract To evaluate and monitor the danger and intensity of roof dynamic fracture by the evolution rules of frequency-spectrum，the research on microseismic(MS) activity rules in the process of roof fracture is presented. With SOS MS monitoring system，the hard and weak roof fracture processes are measured in field. The achieved results are as follows. (1) Before the roof fracture，the amplitude of MS signals in the low-frequency band increases gradually；then it reaches the maximum value at roof fracture and pressurization；after that，the amplitude begins to decrease quickly. Simultaneously，the correlation between precursory signal main frequency and the pressurization intensity is negative. (2) Before the weak roof fracture，the main frequency of MS signals begins to move to the low-frequency band，but the main frequency of precursory signals is larger than 20 Hz. After roof pressurization，the main frequency will move to the high-frequency band. (3) The process of hard roof fracture is transient，and the amplitude of main shock signals is higher，but the main frequency is lower than 5 Hz. Amplitude in the low-frequency band before and after fracturing is lower，and the precursory effect is not obvious. With above rules，the process and intensity of roof fracture and pressurization can be evaluated and predicted effectively.
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Received: 19 October 2009
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