Underground cavern opening can cause the surrounding rock tangential compressive stress to raise rapidly. Such high compressive stress increase can result in some original pre-existing cracks growing parallelly to the free surface of the remaining rock. This paper presents a model of crack stable or unstable propagation under compressive stress in thin layers that are separated from the main rock mass due to crack growth. Based on this analysis of flat plate buckling,a rock burst mechanism is presented. Immediate and delayed rock burst mechanism are proposed to explain time dependency in brittle rock sub-critical crack growth under compression. Influence of free surface on the surface-parallel crack growth is also discussed.