断层发震时应力释放的温度响应

The friction coefficient of the seismic fault during slip controls earthquake dynamics. The coseismic temperature anomaly of fault, which can be identified and obtained by analyzing borehole temperature after earthquake, provides an unique idea and an effective mean for friction features of fault and basic research seismogenic mechanism. For a long time, the friction heat generated during earthquake faulting is considered to be the only reason for the coseismic temperature anomaly. But coseismic stress release instantaneously can lead internal energy decreasing which results in the temperature decrease. This effect can be not only supported by the theory of adiabatic decompression, but also proved to be correct in experiment about the temperature response test when pressure loading and unloading to rock and in borehole temperature data after earthquake.Thus, coseismic temperature anomaly can be caused by the combined impact of the friction heating and coseismic stress releasing instantaneously. For this reason, this application of the research project based on the borehole temperature data from TCDP hole in Chelongpu fault zone, WFSD hole in longmenshan fault zone and the JFAST hole-C0019 in Japan Trench subduction zone, through the establishment of finite element numerical model of coseismic stress release and temperature response, we can understand better about the mechanism study on coseismic temperature response and identify the temperature anomalies caused by coseismic stress release and frictional heat. And we can accurately estimate seismogenic friction heat and coefficient of dynamic friction of fault zone during slip. This work provide theoretical basis for better understanding friction features , the seismogenic mechanism and seismic energy distribution which has guiding significance for protecting against and mitigating earthquake disasters in the future.

摩擦系数是研究断层发震机制的基础参数.而断层同震温度异常,因可在震后钻孔测温中识别并获得,从而为断层摩擦特性和发震机制等基础研究提供了非常独特的思路和有效手段.一直以来,摩擦生热被认为是断层同震温度异常的唯一原因.但同震应力瞬间释放,定会引起内能减小,导致温度降低.这一效应,不仅有绝热减压理论支持,且在岩石加/卸压与温度响应试验和断裂带震后钻孔温度数据中都得到证实.因此,同震温度异常受摩擦生热和应力释放致温度降低的共同影响.为此,本申请拟基于车笼埔断裂带TCDP钻孔、龙门山断裂带WFSD钻孔及日本海沟俯冲带JFAST钻孔测温数据,通过建立同震应力释放和温度响应的有限元数值模型,深入开展断层同震温度响应机制研究,将摩擦热和同震应力释放导致的温度异常加以区分,以便准确估算各断裂带发震时摩擦热和摩擦系数.这为深入了解断裂带摩擦特性、发震机制及地震能量分配提供理论依据,对今后防震减灾具有指导意义.

断裂带同震温度响应,可在震后钻孔测温中获得并识别,为发震断层摩擦特性与发震机制等基础研究提供了非常独特的思路和有效手段.集集、汶川及日本东北大地震后,实施了TCDP、WFSD及JFAST钻探及测温,结果表明:滑移面上下5-20 m范围内存在温度正异常,这是同震摩擦生热所致,该机制已被广泛认识和接受；而距滑移面20-60 m范围内存在明显的温度负异常,其峰值虽只有正异常的1/4-1/3,但分布范围却为正异常的3-4倍,即正、负温度异常区对应的总能量基本相当,不容忽视.但震后钻孔测温中的负异常成因机制几乎还未被真正关注和认识..为此,本项目1)通过自主设计并组建岩石应力快速加卸载系统,对采自龙门山和车笼埔断裂带典型岩样开展应力-温度响应实验及综合物性测试,结果表明:常见地壳岩石应力加载时温度升高、应力卸载时温度降低；在干燥条件下,其绝热应力-温度响应系数(β)为1.5-6.2 mK/MPa,其中沉积岩为3.5-6.2 mK/MPa,而火成岩和变质岩较低(2.5-3.2 mK/MPa),且与体积模量K存在较好的线性关系:β=(-0.068*K+5.69)±0.4, R2=0.85.2)通过单轴慢速加载直至岩样破裂温度响应实验,发现:在破裂面上及邻近出现温度升高,而远离破裂面则出现温度降低现象,且正负异常的比值大致为1/3,这与震后地层温度异常特征基本一致.3)通过在数值模型中同时考虑摩擦生热和应力释放导致温度降低两种机制,模拟结果能较好的反映钻孔实测温度中的正异常和负异常分布特征.4)依据GPS、震源机制解及地震波波形等数据获得的同震剪切应力降,估算同震平均主应力降,结合本项目最新实验结果,估算集集和日本东北地震导致的温度降分别达13-44 mK、59-150 mK,这与TCDP和JFAST钻孔中~20 mK和~75 mK的温度负异常,在量级上基本吻合.因此,利用震后钻孔测温研究断层摩擦强度时,不可忽略同震应力释放导致的温度降..由此可知,本项目基础工作,为深入发震断层同震应力与温度响应机制研究提供了新视角；同时,也为进一步了解这些活动断裂带的摩擦特性、发震机制及地震能量分配提供理论依据,对今后防震减灾工作具有实际指导意义.