断层亚失稳阶段变形场时空演化的实验研究

发布时间：2018-11-28 20:43

【摘要】：断层粘滑过程的差应力-时间曲线可以分成线性、偏离线性、亚失稳和失稳四个阶段。亚失稳阶段是指差应力从峰值时刻到产生快速应力降起始时刻之间的阶段,也是断层失稳之前的最后阶段。利用在实验室既能通过压机观测到标本应力状态,又能使用多物理场观测手段获取标本表面变形信息的优势,通过分析标本表面全场变形的时空演化,寻找识别标本进入亚失稳阶段的标志,有助于分析野外断层所处的应力状态,进而判断地震危险时刻是否临近。本文以断层粘滑过程变形场的时空演化作为研究对象,采用高速相机采集标本变形图像,运用数字图像相关方法为主要分析手段,结合其他物理场观测手段(如应变片、声发射等),研究了不同加载速率下含平直断层的花岗闪长岩标本的变形时空演化特征。此外,基于粘土材料对基底断层活动引起盖层变形场演化的过程进行了模拟。取得的主要认识如下：(1)断层局部预滑区的加速扩展是断层进入亚失稳阶段的标志之一。标本通过断层局部预滑释放应力,在偏离线性阶段标本应力以积累为主释放为辅,局部预滑区开始出现,进入亚失稳阶段后标本以应力释放为主并从平稳释放向加速释放转变,局部预滑区也同时出现明显的加速扩展。采用断层局部预滑区归一化长度(W)随时间的变化对局部预滑区的扩展程度进行定量分析,结果表明W的曲率峰值时刻可作为断层进入亚失稳阶段的近似识别标志。(2)断层各部位位移方向趋向一致过程的加速是断层进入亚失稳阶段的另一标志。采用度量断层位移方向空间分布无序程度的断层位移方向归一化信息熵(S)随时间的变化进行定量分析,结果表明S的曲率峰值时刻可作为断层进入亚失稳阶段的另一近似识别标志。(3)亚失稳阶段后期观测到应变的条带状分布和动态传递过程。通过对样品的全场应变高速采样观测(空间分辨率0.15mm,时间分辨率1ms),发现亚失稳阶段后期平行于断层的应变和体应变呈条带状分布和动态传递的现象。结合早期应变片观测结果,分析此类应变波随着失稳的临近存在频率加快、幅度增大并向震源初始破裂位置传递的特点。对这个现象的进一步研究将有助于认识人们在地震前发现并讨论的前兆波现象。(4)盖层变形模式受基底断层活动方式控制。基底断层活动引起上覆盖层中出现盆地系,这些盆地变形过程可分为初始的独立扩展与后期的相互作用两个阶段。通过分析盖层变形了解基底断层的活动性质,有助于进一步通过盖层变形研究基底断层的亚失稳阶段。
[Abstract]:The stress-time curves of the slip process can be divided into four stages: linear, deviating from linearity, sub-instability and instability. The metastable phase is the phase from the peak moment to the beginning of the rapid stress drop, and the last stage before the fault instability. Using the advantage that the stress state of the specimen can be observed by the press in the laboratory and the deformation information of the specimen surface can be obtained by the means of multi-physical field observation, the space-time evolution of the full-field deformation of the specimen surface is analyzed. It is helpful to analyze the stress state of the field fault and to judge whether the seismic danger time is approaching or not. In this paper, the spatiotemporal evolution of the deformation field in the process of fault stick-slip is taken as the research object, the deformation images of the specimen are collected by high-speed camera, the digital image correlation method is used as the main analysis means, and other physical field observation methods (such as strain gauge) are combined. The temporal and spatial evolution characteristics of deformation of granodiorite specimens with flat faults at different loading rates were studied. In addition, the evolution process of deformation field of caprock caused by basement fault activity is simulated based on clay material. The main results are as follows: (1) the accelerated expansion of the local preslip zone is one of the indicators of the fault entering the stage of sub-instability. The specimen was released by local pre-slip through the fault, the stress was mainly released by accumulation in deviation from the linear phase, and the local preslip began to appear. After entering the sub-unstable stage, the specimen mainly released stress and changed from steady release to accelerated release. At the same time, the local preslip area also appears obvious acceleration expansion. The extension degree of local preslip zone is quantitatively analyzed by using the variation of normalized length (W) with time in the local preslip zone of fault. The results show that the peak moment of curvature of W can be used as an approximate identification marker for the fault to enter the stage of sub-instability. (2) the acceleration of the direction of displacement in each part of the fault is another sign for the fault to enter the stage of sub-instability. The normalized information entropy (S) of fault displacement direction, which is used to measure the disordered degree of spatial distribution of fault displacement direction, is used to quantitatively analyze the change of information entropy with time. The results show that the curvature peak time of S can be used as another approximate identification marker for the fault to enter the stage of sub-instability. (3) the strip distribution and dynamic transfer process of strain are observed in the later stage of sub-instability. Based on the high speed sampling of the whole field strain (spatial resolution 0. 15 mm, time resolution 1ms), it is found that the strain and volume strain parallel to the fault in the later stage of subinstability are striped and dynamically transmitted. Based on the results of early strain gauge observations, the characteristics of such a strain wave are analyzed as the frequency of instability approaches to accelerate, the amplitude increases and the strain wave propagates to the initial rupture location of the source. Further study of this phenomenon will be helpful to understand the phenomenon of precursor wave discovered and discussed before the earthquake. (4) the deformation model of caprock is controlled by the mode of basement fault activity. The basin system appears in the overburden caused by the basement fault activity. These basin deformation processes can be divided into two stages: the initial independent extension and the late interaction. By analyzing the deformation of the caprock to understand the active properties of the basement fault, it is helpful to study the sub-instability stage of the basement fault through the deformation of the caprock.
【学位授予单位】：中国地震局地质研究所
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P315.2

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