Three destructive mining shocks successively occurred nearby the seismic Station No.6 located in a shaft of the Fangshan Coal Mine of Beijing Mining Service in 4 minutes at 19 o′clock of May 15, 1993. The largest sho...Three destructive mining shocks successively occurred nearby the seismic Station No.6 located in a shaft of the Fangshan Coal Mine of Beijing Mining Service in 4 minutes at 19 o′clock of May 15, 1993. The largest shock is of M =2.3 ( M 0=1.5×10 11 N·m). Analysis of synthetic seismogram provides that the three shocks exhibited predominantly a dip slip movement mode, which is consistent with the collapse of coal mass from the coal bed at high dip angle, as observed by those who were present at the site. The near field records of the main shock and a series of events prior to it made at the Station No.6 are different from normal records, it had not only high frequency vibration, but also low frequency vibration. By using elastic wave theory and nucleation theory of seismic fracture during recent years, analysis of the data indicates that the low frequency vibration maybe long period wave as the subcritical extension is pushing forward. It is an unrecovered deformation. The high frequency vibration is just the mining shock event, exhibiting a wave field of brittle fracture radiation. From the dominant frequency of low frequency vibration in the records of M =2.3 event and the records of foreshocks at 5.4 s before it, it is inferred that the volume of dilatation zone at the termination of shock generating fracture has rapidly enlarged during the occurrence of the main shock. In 20 or more days before the main shock, the source process was of the following characteristics: the subcritical extension occurred for many times; during this period the volume of dilatation zone at the termination of shock generating fracture little changed. The subcritical extension not only exits long period waves, but also induced small events at the same time. The dominant orientation of subcritical extension is basically consistent with the direction of slip movement during main shock.展开更多
文摘Three destructive mining shocks successively occurred nearby the seismic Station No.6 located in a shaft of the Fangshan Coal Mine of Beijing Mining Service in 4 minutes at 19 o′clock of May 15, 1993. The largest shock is of M =2.3 ( M 0=1.5×10 11 N·m). Analysis of synthetic seismogram provides that the three shocks exhibited predominantly a dip slip movement mode, which is consistent with the collapse of coal mass from the coal bed at high dip angle, as observed by those who were present at the site. The near field records of the main shock and a series of events prior to it made at the Station No.6 are different from normal records, it had not only high frequency vibration, but also low frequency vibration. By using elastic wave theory and nucleation theory of seismic fracture during recent years, analysis of the data indicates that the low frequency vibration maybe long period wave as the subcritical extension is pushing forward. It is an unrecovered deformation. The high frequency vibration is just the mining shock event, exhibiting a wave field of brittle fracture radiation. From the dominant frequency of low frequency vibration in the records of M =2.3 event and the records of foreshocks at 5.4 s before it, it is inferred that the volume of dilatation zone at the termination of shock generating fracture has rapidly enlarged during the occurrence of the main shock. In 20 or more days before the main shock, the source process was of the following characteristics: the subcritical extension occurred for many times; during this period the volume of dilatation zone at the termination of shock generating fracture little changed. The subcritical extension not only exits long period waves, but also induced small events at the same time. The dominant orientation of subcritical extension is basically consistent with the direction of slip movement during main shock.
