地震不稳定破裂扩展与前兆过程

本文讨论了地震的深部滑动破裂扩展过程模型和它的前兆意义。结果表明：该模型预示着一个失稳加速破裂扩展的阶段；这个阶段的时间尺度（前兆时间）很大程度上依赖于地震孕育的介质环境和应力环境；由此产生的地表应力—应变场在空间上出现反向发展变化，可能是一种非常有意义的前兆特征。

水热条件下白云石的摩擦滑动稳定性实验研究以及对潜在地震风险的启示

为了探讨含白云石断层的摩擦滑动稳定性,我们使用白云石断层泥开展了水热条件下的摩擦滑动实验研究。实验的有效正应力为60MPa,孔隙流体压力为20MPa,温度范围为25~150℃。实验过程中为了得到白云石摩擦强度系数的速度依赖性,我们将轴向加载速率在5μm/s、1μm/s、0.2μm/s和0.04μm/s之间进行切换。在本研究的温度和压力条件下,我们发现白云石断层泥表现出低温的稳定的速度强化的摩擦滑动行为向高温不稳定黏滑的转变。白云石摩擦强度系数为0.65~0.7,没有表现出显著的温度依赖性。在25~50℃的温度范围,白云石表现出稳定的速度强化的摩擦滑动行为。当温度升高到100℃时,在0.2~0.04μm/s加载速率范围内表现出速度弱化并伴随着黏滑现象,而在1~5μm/s的加载速率下表现出显著的速度强化的摩擦滑动行为。白云石的速率依赖性参数(a-b)值随温度和有效正压力的升高和加载速率的降低表现出有稳定的滑动向不稳定地震成核的转变趋势。因此,对油气储层而言,当其上覆的白云岩岩层被断层穿过时,其在较低的温度范围内(<100℃)也具备了发生不稳定地震成核的条件,需要防范其发生诱发地震的风险。

Seismological method for prediction of areal rockbursts in deep mine with seismic source mechanism and unstable failure theory

The research on the rock burst prediction was made on the basis of seismology,rock mechanics and the data from Dongguashan Copper Mine(DCM) ,the deepest metal mine in China.The seismic responses to mining in DCM were investigated through the analyses of the spatio-temporal distribution of hypocenters,apparent stress and displacement of seismic events,and the process of the generation of hazardous seismicity in DCM was studied in the framework of the theory of asperity in the seismic source mechanism.A method of locating areas with hazardous seismicity and a conceptual model of hazardous seismic nucleation in DCM were proposed.A criterion of rockburst prediction was analyzed theoretically in the framework of unstable failure theories,and consequently,the rate of change in the ratio of the seismic stiffness of rock in a seismic nucleation area to that in surrounding area,dS/dt,is defined as an index of the rockburst prediction.The possibility of a rockburst will increase if dS/dt>0,and the possibility of rock burst will decrease if dS/dt<0.The correctness of these methods is demonstrated by analyses of rock failure cases in DCM.

Βedrock instability of underground storage systems in the Czech Republic, Central Europe

Underground storage systems are currently being used worldwide for the geological storage of natural gas （CH4）, the geological disposal of CO2, in geothermal energy, or radioactive waste disposal. We introduce a complex approach to the risks posed by induced bedrock instabilities in deep geological underground storage sites. Bedrock instability owing to underground openings has been studied and discussed for many years. The Bohemian Massif in the Czech Republic （Central Europe） is geologically and tectonically complex. However, this setting is ideal for leaming about the instability state of rock masses. Longterm geological and mining studies, natural and induced seismicity, radon emanations, and granite properties as potential storage sites for disposal of radioactive waste in the Czech Republic have provided useful information. In addition, the Czech Republic, with an average concentration radon of 140 Bq m-3, has the highest average radon concentrations in the world. Bedrock instabilities might emerge from microscale features, such as grain size and mineral orientation, and microfracturing. Any underground storage facility construction has to consider the stored substance and the geological settings. In the Czech Republic, granites and granitoids are the best underground storage sites. Microcrack networks and migration properties are rock specific and vary considerably. Moreover, the matrix porosity also affects the mechanical properties of the rocks. Any underground storage site has to be selected carefully. The authors suggest to study the complex set of parameters from micro to macroscale for a particular place and type of rock to ensure that the storage remains safe and stable during construction, operation, and after closure.

Pseudo-dynamic analysis of seismic stability of reinforced slopes considering non-associated flow rule

The required reinforcement force to prevent instability and the yield acceleration of reinforced slopes are computed under seismic loading by applying the kinematic approach of limit analysis in conjunction with the pseudo-dynamic method for a wide range of soil cohesion, friction angle, dilation angle and horizontal and vertical seismic coefficients. Each parameter threatening the stability of the slope enhances the magnitude of the required reinforcement force and vice versa. Moreover, the yield acceleration increases with the increase in soil shear strength parameters but decreases with the increase in the slope angle. The comparison of the present work with some of the available solutions in the literatures shows a reasonable agreement.

Post-earthquake Rainfall-triggered Slope Stability Analysis in the Lushan Area

The ＂4.20＂ Lushan earthquake in Sichuan province, China has induced a large amount of geological hazards and produced abundant loose materials which are prone to post-earthquake rainfall- triggered landslides. A detailed landslide inventory was acquired through post-earthquake emergent field investigation and high resolution remote sensing interpretation. The rainfall analysis was conducted using historical rainfall records during the period from 1951 to 2010. Results indicate that the average annual rainfall distribution is heterogeneous and the largest average annual rainfall occurs in Yucheng district. The Stability Index MAPping （SINMAP） model was adopted to assess and analyze the post- earthquake slope stability under different rainfall scenarios （light rainfall, moderate rainfall, heavy rainfall, and rainstorm）. The model parameters were calibrated to reflect the significant influence of strong earthquakes on geological settings. The slope stability maps triggered by different rainfall scenarios were produced at a regional scale. The effect of different rainfall conditions on the slope stability is discussed. The expanding trend of the unstable area was quantitatively assessed with the different critical rainfall intensity. They provide a new insight into the spatial distribution and characteristics of post- earthquake rainfall-triggered landslides in the Lushan seismic area. An increase of rainfall intensity results in a significant increase heterogeneous distribution strongly correlated with of unstable area. The of slope instability is the distribution of earthquake intensity in spite of different rainfall conditions. The results suggest that the both seismic intensity and rainfall are two crucial factors for post- earthquake slope stability. This study provides important references for landslide prevention and mitigation in the Lushan area after earthquake.

A Simple Model for Earthquake Instability

Based on the heterogeneity of fault plane strength,the macro rupture process of a fault plane can be treated as the rupture accumulation process of local micro-elements in the fault surface.Assuming that the strength of the local micro-elements follows the Weibull probability distribution,the macro-fault constitutive relationship of the complete load-deformation process is derived from a statistical mechanics viewpoint.Applying a one-dimensional earthquake mechanics model and using far-field displacement a as the control variable,the problem of earthquake instability is investigated by employing the stability theory.The results show that the system stiffness ratio(stiffness ratio of fault to surroun-ding rock) β is the important parameter that affects the occurrence of earthquakes.Earthquake instability occurs only when β < 1,and the sudden stress jump appears at the displacement turning point of the equilibrium path curve.The expression of three important parameters for earthquakes(fault half-dislocation distance after earthquake,earthquake stress drop and elastic energy release) is also given.When β≥1,the earthquake does not occur and the fault only slips slowly without an earthquake.