震后松弛阶段地壳岩石非稳态蠕变实验研究

The layer of major seismic events occurred in continental crust was so-called seismogenic zone or Schizosphere, which is termed to brittle plastic transition of quartz. The deformation in this zone was effect not only by temperature, strain rate and stress also play an important role during seismic cycle. The major deformation mechanism is steady creep during inter-seismic deformation, but it changes to rupture at coseismic loading and transient creep at postseismic relaxation. However, most of studies focused on ductile deformation in natural fault and steady creep tests under high temperature in past time. The project plans to study transient creep related postseismic relaxation based on geological survey for brittle plastic transition of fault and experiemts under high temperature and pressure. To identify microstructural indications of seismogenic zone deformation during rapid coseismic loading to high stress, transient creep at postseismic relaxation and inter-seismic steady creep, we try to study the fossil record deformation in exhumed rocks related brittle plastic transition of red river fault and boundary faults of Fenhe and Weihe basin. We will perform creep tests in gas medium and solid medium traxial mechine under high temperature and high stress conditions using quartz, feldspar and granite samples, and get the semiquantitative empirical equation of transient creep related postseismic relaxation. Based on the micristructures analyzed under SEM, EBSD, TEM for natural and experimental deformed samples, the microfabrics mode can be setup related to transient creep at postseismic relaxation, which developed in the experiments are expected to correspond to those formed in nature. The project can supply essential experimental data and method for GPS data analysis about postseismic deformation and seismogenic environment study.

大陆浅源地震密集分布层称为地震层，该深度处于石英脆塑性转化带，其变形除受温度控制外，地震周期各阶段变形随应变速率和应力发生变化，从间震期的稳态蠕变转化为同震破裂和震后松弛阶段非稳态蠕变。以往研究主要关注韧性变形和高温稳态流变实验。本项目拟通过高温高压实验，结合野外断层脆塑性转化带变形分析，研究震后松弛阶段非稳态蠕变。通过研究红河断裂和汾渭盆地边缘断层中构造岩记录的脆塑性转化带变形，识别间震期、同震加载、震后松弛各阶段震源深度的典型变形特征。在气体介质和固体介质三轴高温流变仪上，采用石英、长石、花岗岩样品，开展中温高应力条件下的非稳态蠕变实验，初步建立非稳态蠕变半定量经验方程。利用SEM, EBSD, TEM对野外与实验变形样品进行微观结构分析，归纳两者类似的变形机制，建立震后松弛阶段非稳态蠕变的变形模式。本研究为GPS观测到的震后地壳形变分析和强震孕育环境研究提供必要的数据和方法。

受应变速率和应力影响，处于石英脆塑性转化带的大陆浅源地震层从间震期的稳态流变转化为同震破裂和震后松弛阶段非稳态流变。以往研究主要关注稳态流变，本项目研究震后松弛阶段脆塑性转化带非稳态流变。.本项目在总结非稳态流变研究进展基础上，通过对红河断裂构造岩记录的脆塑性转化带变形，识别了间震期、同震、震后松弛阶段震源深度的变形特征，建立了脆塑性转化带非稳态流变与地震孕育模型;在固体介质三轴高温流变仪上开展花岗岩岩非稳态流变实验，并研究了汶川地震孕育机制;在气体介质高温流变仪上开展了大理岩非稳态流变实验和简单剪切实验，建立非稳态流变方程。.红河断裂构造岩研究表明，脆塑性转化带在间震期变形为低温位错流变与长石水解反应，形成糜棱岩，同震变形为脆性破裂与摩擦熔融，在糜棱岩中形成碎裂岩和假玄武玻璃，震后松弛阶段变形为脆性碎裂与裂隙愈合。.采用彭灌杂岩中典型花岗岩，按照龙门山断层带5-30km深度对应的温度和压力设定实验条件开展非稳态流变实验。花岗岩在10-20km深度处于脆性破裂-脆塑性转化域，具有很高的强度，在20-30km进入塑性流变域。以花岗岩为代表的彭灌杂岩在15-20km深度不仅强度达到最大值，而且表现为不稳定滑动，具备地震成核条件，这是汶川地震孕育和发生的必要条件。.大理岩非稳态流变实验的力学数据、微观结构表明，在200-400℃，样品强度高，具有硬化特征，应力指数大于25，属于半脆性非稳态流变；在600-650℃，强度逐渐降低，应力指数在13左右，属于低温高应力非稳态流变；在700-800℃，样品强度低，没有硬化特征，应力指数在6-9之间，属于高温非稳态流变。.大理岩简单剪切实验力学数据及微观结构表明，在20℃/30MPa，样品没有沿预制45°断层滑动，而是产生了30-35°的新破裂；在20℃/50MPa，主变形沿着45°预切面滑动，预制断层两侧出现脆性-塑性变形；在300℃/30MPa，出现粘滑；在600℃/30MPa，预制断层没有起到任何作用，样品出现均匀半脆性-塑性变形。.本项目为认识震后非稳态流变与强震孕育提供必要的数据和方法。