AN EXPERIMENTAL STUDY OF EVOLUTION OF PHYSICAL FIELD AND THE ALTERNATIVE ACTIVITIES DURING STICK-SLIP OF 5°|BEND FAULT

doi:10.3969/j.issn.0253-4967.2011.02.009

Abstract

Abstract:

The spatial-temporal evolution process of strain field and acoustic emission(AE)events was investigated during the deformation of 5° bend faults,with 96-channels strain acquisition system and 16-channels distributed AE acquisition system in the laboratory.The loading was applied by controlling the Y-displacement and holding the X-load in a biaxial servo-control loading system, and the Y-loading rate was altered by 0.5μm/s,1μm/s,0.5μm/s and 0.1μm/s in sequence.The observation results show that: (1)quasi-periodic stick-slip always occurred under different loading rates, and the smaller the loading rate,the greater the period and stress drop; (2)low energy AE events increased before faults slid,but high energy AE events appeared as faults slid.AE events distributed near the bends and the upper and lower fault segments which were located by arrival time of AE wave.From the AE location results,AE sources mostly scattered in bend zones,and upper and lower fault segments,and the fault instability appeared first near bend point,then the alternative activities happened between upper and lower fault segments.Large instability took place in the lower fault segment,finally; (3)High strain concentration zone located near bend point and fault segment.And it is significantly different that mean strain and maximum shear strain increment changed alternately at the inside and outside of bend during strain accumulation and release stage; (4)Strain observation results illustrate that mean strain release first occurred near the bend,then released in the whole fault.It would be a critical instability condition for a bend fault.The observation to bend faults is important and helpful to investigate fault activity state.

Key words: bend fault, acoustic emission, strain field, alternative activities of fault

摘要：

在实验室利用96通道应变记录采集系统和分布式多通道瞬态信号采集系统,观测了预切5°拐折断层的标本在变形失稳过程中应变场和声发射事件的时空演化。实验在双轴伺服加载系统上进行。在Y方向按位移控制方式加载,位移速率先后取0.5μm/s、1μm/s、0.5μm/s和0.1μm/s。观测得到: 1)标本沿断层发生周期性的黏滑失稳,不同加载速率下黏滑事件表现出不同的特点,加载速率越小,周期越大,应力降也越大。2)断层失稳错动时伴随高能级的声发射事件,之前只发生能级很小的事件。定位结果显示,声发射事件主要分布在拐折部位周围、上断层中部和下断层中下部。断层失稳前声发射事件的迁移过程是: 开始发生在拐折部位,随后在上、下断层段间交替活动,最终在下断层段发生失稳大事件。3)应变观测结果显示拐点和断层带附近是高应变集中部位。在应变积累阶段和释放阶段,应变增量场的分布有显著差异,表现为拐点内外侧平均应变和最大剪应变的增减交替。4)平均应变在拐点和断层段先后释放可能是断层失稳的条件之一。对拐折构造部位进行观测十分重要,有利于判断断层活动状态的转变。

关键词: 拐折断层, 声发射, 应变场, 断层交替活动

CLC Number:

P313

YUN Long, GUO Yan-shuang, MA Jin. AN EXPERIMENTAL STUDY OF EVOLUTION OF PHYSICAL FIELD AND THE ALTERNATIVE ACTIVITIES DURING STICK-SLIP OF 5°|BEND FAULT[J]. SEISMOLOGY AND GEOLOGY, 2011, 33(2): 356-368.

云龙, 郭彦双, 马瑾. 5°拐折断层在黏滑过程中物理场演化与交替活动的实验研究[J]. 地震地质, 2011, 33(2): 356-368.

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