不同温压条件下声发射应变能释放特征——加速模型参数物理含义的初步讨论
关键词 应变加速释放模型，m值，岩石变形实验，声发射，温度，围压
DOI:10.3969/j. issn. 0001-5733.2009.08.015中图分类号P315 ;收稿8期2008-11-26 ,2009-01-04收修定稿
Behaviors of AE strain release under the different temperature and pressure condition :discussion on the physical meanings of ASR model parameter
Abstract Using the data of granite deformation experiments under different temperature and confining pressure, the strain release features of acoustice mission events have been studied, and the relationship between m-value, the parameter of the accelerating strain release ( ASR) model, with the temperature and pressure environmental condition have been discussed. In room temperature,the AE strain shows a certain ASR, but the m-value does not show the tendential variety, this expresses that the m-value does not interrelate to the rock strength tightly. When confining pressure be fixed, m-value increases with the temperature, and the AE strain release changes gradually from accelerating pattern to the linear pattern. This means that the different microfracture modes inside the rock sample during the process of the rock deformation under the different temperature condition probably leads to the different strain release pattern (i. e.different m-values). To simulate the temperature and confining pressure condition in differentdepths of the crust, a certain accelerating feature had been checked before the rock failure forshallow crust and m-value is smaller than 1. In progressive failure range of the crust, the strainshows a gradual decelerating release and m-value is greater than 1 obviously. For the HT-HP .condition in deep crust, the accelerating feature is remarkable and m-value is very small. Besides ,the rock status has a big influence on the m-value, the accelerating feature is obvious before thefracture of the symmetrical and integrated rock sample, but it is linear before the stick-slip of the .rock sample with macro-cracks.
1 引言
大地震前的矩释放加速现象(AMR)被越来越多的研究者所关注[1~4]，矩释放加速现象可以通过幂指数关系进行定量描述[3，5]，进一步的研究表明，用Benioff应变对加速模型进行拟合，以构造Benioff应变的加速释放模型(Accelerating Strain Release,ASR),比用地震矩释放能更准确地对目标地震发生时间及震级进行预测[3]。AMR或ASR之所以引起广泛关注，一个重要的原因是，正如各种介质中的破裂过程那样，地震被看作是一种典型的临界现象[6，7],而强震前的AMR或ASR则是地震临界点模型的一个有力的观测证据近期的研究表明[8~10]，较大临界区范围内地震应变加速释放的同时，在较小的孕震区范围内还存在地震应变释放减弱的现象( Deeelerating Strain Release,DSR) ,据此提出了作为地震前兆的DA模式(Patterns of"Decelerating In Accderating Out Seismic Strain")。其含义是，大震前临界区范围内地震活动呈加速释放态势，同一时期,在较小的孕震区范围内则出现地震活动的减弱蒋长胜等利用中国大陆1978年以来109例Ms5.7以上地震对ASR的普遍性进行检验,发现具有加速和减速特征的震例分别是55例和23例。震前孕震区范困内地震活动的减弱，被归因于由于震前滑移所导致的应力松他过程[12,13]。
ASR模型参数m值表征Benioff应变释放状态。以及释放速率的大小。通常取m=0.3及m=3.0以分别拟合中小地震累积应变释放的加速及减速特征门对应变释放加速,m=0.3有较多的统计证据支持[14]，同时也开展了一些理论探讨[6,15]。但总的来说，上述现象学层面上的统计模型研究，并未涉及m值究竟与什么物埋因素有关这一基本问题 ;
加速模型着重研究大震前中小地震的应变释放状态，而地震是地下岩体的破裂或粘滑失稳已有研究表明，在温压环境、加载速率环境刚度等诸多影响地下岩体破坏与失稳的因素中，温压环境对岩体变形破坏具有十分重要的影响[16]。已有作者在实验室条件下模拟地壳深部温压环境，分析花岗岩在不同湿压条件下的变形及破坏[17],讨论微破裂声发射时序特征[18-20]。并对地震活动的增强-平静、b值变化、空区图像等地震学现象的可能机理进行了初步讨论[21]。
在此基础上，本文将利用不同温、压条件下岩石变形过程中的声发射数据[17-20]，研究不同温、压条件下声发射应变释放特征，着重讨论模型参数m值与微破裂发生环境温.压条件的关系，探讨m值物理含义。由于岩石破裂过程的尺度无关性质[22,23],这一工作有助于地震应变加、减速释放过程物理含义的深入认识。
