应力增量触发断层岩体能量释放模拟与地震成因探讨——以龙门山断裂带为例

Simulation on energy release of fault rock mass triggered by stress increment and discussion on seismogenesis:Taking Longmenshan fault zone as an example

本文以龙门山断裂带为背景,基于岩体应变能基本理论,使用FLAC软件模拟地震能量源和能量释放形式,计算结果显示:在0.01 MPa水平应力增量作用下,龙门山断裂带及附近区域可释放的应变能约为3.24×1013 J;使得断层面之间发生滑移,克服断层面滑动摩擦所需消耗的能量约为2.10×1013 J;岩体在重力方向上产生位移,克服重力做功所消耗的能量约为1.14×1013 J。由此可推断:在一定区域内,应力触发释放能量值与克服断层面滑动摩擦和克服重力做功所消耗的能量之和大致相当;应变能可能会在某一区域范围内集中释放,形成地震效应。本次应力增量触发断层周围岩体能量释放事件中,在映秀—北川断裂与灌县—安县断裂之间的局部区域集中释放的能量为7.67×1012 J,相当于一次MS5.39地震发生所释放的能量。

Taking Longmenshan fault zone as the research background,basing on theory of strain energy of rock mass,this paper simulated energy source and energy release form of a simulated earthquake by using the software FLAC.Calculation results show that the total strain energy that can be released from the Longmenshan fault zone and its vicinity is approximately3.24×1013 J under the action of horizontal stress increment 0.01 MPa.When stress triggering causes slip between fault planes,energy consumption for overcoming sliding friction on the surface is about 2.10×1013 J on fault plane.When the rock mass moves in the direction of gravity,energy consumption for overcoming gravity is 1.14×1013 J.Therefore it is deduced that,in a certain region,the energy released by stress triggering is approximately equal to the sum of consumption energy for overcoming the friction on fault surface and that for overcoming the gravity of regional rock mass.Strain energy may be released in a certain range,resulting in seismic effect.In the event of energy release of rock mass around fault triggered by stress increment,as for the the local region between the Yingxiu-Beichuan fault and Guanxian-Anxian fault in this paper,energy released centrally is about 7.67×1012 J,equivalent to that for occurrence of an earthquake with MS5.39.