Stress spatial evolution law and rockburst danger induced by coal mining in fault zone

In order to explore the influence of coal mining disturbance on the rockburst occurring in fault zone, this research constructed a mechanical model for the evolution of fault stress, and analyzed the influence of the ratio of horizontal stress to vertical stress on the stability of fault, and the spatial distribution of the stress in fault zone as well as its evolution rule. Furthermore, the rockburst danger at different spatial areas of fault zone was predicated. Results show that: when both sides of the working face are mined out, the fault zone in the working face presents greater horizontal and vertical stresses at its boundaries but exhibits smaller stresses in its middle section; however, the ratio of horizontal stress to vertical stress is found to be greater at middle section and smaller at boundaries. As the working face advances towards the fault, the horizontal and vertical stresses of the fault firstly increases and then decreases; conversely,the ratio of horizontal stress to vertical stress keeps decreasing all the time. Therefore, if the fault zones are closer to the goaf and the coal wall, the stress ratio will be smaller, and the fault slip will be more prone to occur, therefore rockburst danger will be greater. This research results provide guidance for the rockburst prevention and hazard control of the coal mining in fault zone.

Research on Frequency of the Aftershock Sequence of the Wenchuan Earthquake Based on Coseismic Coulomb Stress Change

By the aftershock frequency estimation method based on the calculation of coseismic static Coulomb stress changes and rate-and state-dependent fault constitutive law,we calculate the frequency of "direct "aftershocks of the Wenchuan earthquake related to coseismic static Coulomb stress changes in its aftershock zone and the areas nearby.It shows that the frequency is significantly lower than the truth in the main rupture zone,especially in the southern rupture zone,due to the decrease of stress level on the rupture plane of the main shock resulting from coseismic Coulomb stress change.The study also shows that the effect of the Coulomb stress change on the duration of aftershock activity is associated with the lower limit magnitude.The duration is about 15-16 months for aftershocks above ML4.0,and close to 60 months for aftershocks above ML3.5.In this period,the ratio of the"direct"aftershocks caused by coseismic Coulomb stress change ranges between 44.7% to48.6%,which suggests that,even in the "effective"period of coseismic Coulomb stress changes,about half of the aftershocks on the main shock rupture plane are independent of coseismic Coulomb stress changes.It is pointed out that those aftershocks may be related to the afterslip or the viscoelastic relaxation,which are time dependent cases.