安庆4.8级地震序列的地震波谱变化研究

采用安徽区域数字地震台网记录的安庆4.8级地震序列波形资料,开展地震波谱研究,求取了零频位移谱值、应力降和地震矩等震源参数。分析了纵、横波零频谱值比和应力降随时间的变化趋势,并讨论了震源参数之间的关系。结果表明,安庆4.8级主震后,纵、横波零频位移谱值比和应力降呈现一定的变化规律,可为主震—余震序列的最大余震的预测提供一定的参考依据,同时发现震源参数与震级有一定相关。     

利用非均匀细胞自动机模拟震级与应力降关系

为解释实际观测资料震源破裂过程与自相似(分形)模型的不一致性, 本文基于观测结果, 构建了由81×81个细胞单元组成二维非均匀断层模型, 并通过设计的细胞自动机模拟程序进行了模拟试验。 研究结果表明: 断层结构非均匀性是影响孕震过程特征的重要因素, 而且地震强度分布并非简单的自相似。 随着断层非匀质性增加, 破裂过程出现由相对的脆性破坏向塑性破坏特征变化的趋势。 利用细胞自动机不仅能较好地解释震级-频度关系中的大、 小震级段低头现象, 而且也可解释大震级事件具有相对恒定的应力降, 得到了与实际观测研究相一致的结果。     

沂沭断裂带构造区光弹实验与地震危险区判定研究

在对沂沭断裂带的地质构造环境、断裂带分布特征进行详细分析的基础上,采用聚碳酸酯材料制成沂沭断裂带构造区域的地质模型,分别运用集中、2点和均布等加载方式,使用光弹实验方法模拟特定构造框架下应力、应变场的变化特征。通过对光弹实验数据的分析,在对比不同加载方式下应力积累区域和地震危险区的基础上判定沂沭断裂带构造区中的地震危险区域。     

An experiment on temperature variations in sandstone during biaxial loading

The temperature response to stress–strain variations in rock is useful in developing an understanding of the thermodynamic property of crust. In this study, the temperature of sandstone during loading was investigated using laboratory biaxial testing. By changing the loading patterns, the deformation of a specimen was controlled to produce two distinct modes of strain: volume strain only and shear strain only. These strain modes were produced separately such that the temperature variation associated with the different deformation modes could be analysed. Experimental results indicate that temperature, as a scalar quantity, is notably sensitive to rock deformation. In the case of the volume strain, the temperature variation is positively correlated with the variation in the bulk stress. The temperature rises with the increase in hydrostatic pressure, and vice versa. In the case of the shear strain, experimental results repeatedly show two characteristics: firstly, there appears obvious increase in temperature in the area of pure shear strain, which is most likely related to local plastic deformation; secondly, the temperature drops in the area of tension during loading, whereas the temperature rises within the area of compression. This is to say, the state of crustal stress–strain should be obtained through the measurement of rock temperature.     

Dynamic responses of a saturated poroelastic half-space generated by a moving truck on the uneven pavement

A truck–pavement–ground coupling model was established to study the dynamic responses of a saturated poroelastic half-space generated by a moving heavy truck on the uneven pavement. The ground was simulated as a fully saturated poroelastic half-space governed by Biot’s theory. The overlying pavement was simplified as a Kirchhoff thin plate. With the assumption of a sinusoidal pavement surface, the dynamic wheel–pavement force was obtained through a linear Hertizian contact model. The numerical results showed that this dynamic load could make considerable contributions to the stress and excess pore water pressure responses in the ground. Furthermore, the effective stress path of the soil unit beneath the pavement caused by the moving truck was firstly calculated and presented. It was found that the differences between the total stress path and the effective stress path became significant as the truck speed increased, thus the effective stress path was more suitable than total stress path to reflect the stress history of soil elements in the saturated ground during the passage of high-speed traffics.     

2008年盈江地震序列的震源参数和震源机制相关系数研究

基于云南数字地震台网记录的2008年盈江地震序列的数字波形资料,采用波谱分析方法和Brune震源模型,得到盈江地震序列的震源参数。利用两次地震事件的相同台站的震源谱参数（零频振幅）计算谱振幅相关系数,据此对地震的震源机制进行聚类分组,并收集和对比地震序列已知的震源机制解结果,发现每组内震源机制解P轴的相关性较好,且相关系数越大,P轴的方位角就越接近。将盈江地区划分为三个研究区,联合震源参数的应力降和聚类分组中每组的平均震源机制解结果研究地震序列发生过程中应力的释放水平和应力场方向变化特征。结果表明：不同阶段震源机制解类型的变化和转化特征一定程度上反映了孕震过程中区域应力场随时间的变化特征,并且地震震源机制解类型在时间段上的集中并向区域构造应力场方向转换的现象可能是发生强震的标志。震源机制解分组类型和对应类型的地震的应力降有一定依赖关系,震源机制解类型反映的应力场与区域应力场接近的地震应力降高,震源机制解类型反映的应力场与区域应力场差距较大的地震应力降普遍较低。     

Numerical simulation of fracture path and nonlinear closure for simultaneous and sequential fracturing in a horizontal well

Reservoir stimulation requires a model to evaluate the fracture path and closure for the simultaneous or sequential propagation of the hydraulic fracture (HF). This paper presents a fluid-solid coupled model to simulate multi-stage HF propagation. A non-linear joint model is proposed to evaluate the fracture closure when the created fractures are elastically propped. HF closure continues until the balance of external stress matches the proppant's resistance. The reservoir along the horizontal wellbore is not stimulated equally by the multi-stage fracturing. The HFs in the subsequent stage are ‘repelled’ and restrained by the HFs in the previous stage.     

山西地区应力场变化与地震的关系

收集了1970～2006年37年的小震初动符号建立了震源机制解数据库,研究了山西断陷带小震综合机制解时空演化特征.结果表明:山西断陷带小震综合机制解以走滑正断层为主,断陷带两端以拉张作用为主,中部地区以剪切作用为主,忻定盆地、太原盆地的区域应力场与华北区域应力场差异较大.利用沿山西断裂带布设的GPS监测网1996～2007年12期复测资料,分析了山西断裂带水平运动与地震活动的关系.结果表明:山西断裂带现主要受NWW-SEE向压应力场、NNE-SSW向张应力场的控制.1998～1999年有一次较为明显的应力扰动,空间上表现为北强南弱,接着发生了1999年11月1日大同-阳高5.6级地震.     

华北盆地强震孕育的动力学机制研究

强震活跃区通常出现在地壳变形剧烈的地区.但是,华北盆地地壳变形速率小,而破坏性强震却十分频繁.文中利用有限元方法对华北盆地发震断层下方可能存在的速度异常体进行了力学分析,计算结果显示：无论这个异常区是低速异常还是高速异常,在水平构造力的作用下（无论是挤压还是引张力作用）,应力及应变能密度都在空间某些区域积聚.根据本文的工作及前人的研究结果,认为华北盆地强震孕育的物理机制如下：华北克拉通在减薄、破坏过程中,浸入的岩浆或上涌的地幔物质经过漫长的地质时期演化,成为低速异常体.当断裂带下面存在这种低速异常体时,水平向构造力的作用,会使异常体上方应力集中、应变能积聚.当异常体上方的应力水平达到某种限度,介质发生破坏.在破坏过程中,异常体释放的能量,使断裂带上的应变能集聚速度加快;另一方面,异常体的破坏使断层的闭锁面积减小.随着外部构造应力的持续加载,当发震断层上的应力及能量积累达到一定极限,断层产生错动,发生强震.同时,文中结果还显示,断层在从闭锁、积累能量到解锁、发生强震的过程中,其下方的低速异常体起着重要的推进作用.     

2014年鲁甸MS6.5地震前后介质波速变化特征分析

本文利用研究区内13个地震台站2014年1月至12月的连续波形数据, 采用背景噪声互相关方法, 提取了2014年8月3日鲁甸M_S6.5地震的同震波速变化。 结果表明, 鲁甸地震对介质波速的影响具有明显的空间差异性, 较大幅度的同震波速变化主要集中于则木河断裂—小江断裂及莲峰断裂区域。 其中, 莲峰断裂SW段和则木河断裂NW段区域的波速出现了较为明显的同震降低, 则木河断裂和小江断裂交界处则出现了明显的波速升高。 通过对比研究区内介质波速的同震变化与鲁甸地震对周边主要活动断裂应力积累的影响后发现, 波速变化与应力变化在空间分布上具有较高的一致性, 且两者的变化幅度也成正相关关系。 由此可以看出, 鲁甸地震造成的应力变化可能是地下介质波速变化的主要原因。 采用相同的方法对2014年4月5日永善M_S5.1地震研究后发现, 永善地震后鲁甸地震震源区及其附近区域波速明显升高。