Experiment of thrust fault slipping under unloading

The unloading effect induced by coal mining often leads tothe rupture of thrust fault and then causes rock burst.Takingthe F16 thrust fault of Yimamining area as an example, the experiment of thrust fault slipping was conducted under unloading.Based on the experiment result, the differential stress variation, the evolution of displacement and strain field along the fault were studied.Furthermore, the transient slip displacement and acoustic emission characteristics were analyzed and the process of thrust fault slipping was discussed. The results show that① the differential stress jumps repeatedly when the fault slips, among which the first “jump”, 0.36MPa, is the biggest one. ②Different points along the fault have different slippages. The slippage of the lower part is larger than that in the middle and upper part, so asthe slippage in the far field of footwall is larger than that in the near field and the upper wall.③The normal strain and shear strain monitored by the strain gauges arranged along the fault line change as "decline-surge-fluctuate-stable" during the fault slipping. Also, the strain field differentiates as the fault's monitoring points change. The differentiation is that the normal strain's rupture at the lower part of the fault is larger than that at the middle and lower part, while the shear strain's rupture at both ends of the fault is larger than that at the middle.④When the fault ruptures, three phrasesincluding sliding initiation, main earthquake and aftershock occur, along with the main earthquake releasing most energy, which is the energy source of fault rock-burst. The whole course of thrust fault unloading contains four phrases, linearly increasing, nonlinearly increasing, meta-stable and rupture. When the fault ruptures, shear strain first suddenly drops, then rebounds and becomes stable at last. In practice, the unloading effect causes different patterns of the F16 fault slipping, namely the upper part of the F16 fault slips anticlockwise and the deeper part ruptures clockwise.