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论地震发生机制
On the mechanism of earthquake

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陆坤权 1 *   曹则贤 1 *   厚美瑛 1   姜泽辉 2   沈容 1   王强 1   孙刚 1   刘寄星 3  
文摘 地震发生的物理机理和过程是还没有认识清楚的问题. 此前人们将浅源地震归因于弹性回跳,根据这一观点和岩石实验结果计算得到的地震能量与实际观测结果有很大矛盾,被称之为“热流佯谬”. 中源和深源地震发生在地幔区域,其成因也没有合理的解释. 考虑到地壳和地幔是离散集合态物质体系及其慢动力学运动行为的基本特点,本文根据物理学原理,特别是近年凝聚态物理发展出来的相关新观念,并依据已有观测事实,从新的视角探究地震发生的物理机制. 1)关于地壳岩石层中的应力分布:在不考虑构造力时,依据万物皆流的流变学原理,原始地壳岩石在自重压强长时间作用下,纵向和横向应力相同,没有差应力. 大地构造力推动岩块滞滑移动挤压断层泥,施加于其他岩块,逐渐传递和积累. 这种附加的横向构造力与原始岩石中应力叠加,形成地壳岩石层中的实时应力. 由于断层泥属于颗粒物质体系,具有与岩石不同的力学特征,其弹性模量比岩石小得多,且随压强而增大,导致构造作用力随深度非线性增大. 给出了地壳中构造应力分布及其变化规律. 2)关于地壳岩石层强度:地壳岩石的自重会使岩石发生弹性-塑性转变. 通过对弹性-塑性转变深度的计算,并根据实际情况分析,给出了地壳岩石弹性、部分塑性和完全塑性三个区域的典型深度范围. 在部分塑性区,塑性体比例达到约10%以上时,发生塑性连通,这时岩石剪切强度由塑性特征决定. 塑性滑移的等效摩擦系数比脆性破裂小一个数量级以上,致使塑性滑移时岩石剪切强度比脆性破裂小得多. 同时,随深度增大,有多种因素使得岩石剪切屈服强度减小. 另一方面,地震是大范围岩石破坏,破坏必然沿薄弱路径发生. 因此,浅源地震岩石的实际破坏强度必定比通常观测到的岩石剪切强度值低. 给出了地壳岩石平均强度和实际破坏强度典型值随深度的分布规律. 3)关于地震发生的条件和机制:地震发生必定产生体积膨胀,只有突破阻挡才可膨胀. 地震发生的条件是:大地构造力超过岩石破坏强度、断层边界摩擦力以及所受阻挡力之和. 因此,浅源地震是岩石突破阻挡发生的塑性滑移. 在此基础上提出了浅源地震发生的四种可能模式. 深源地震是冲破阻挡发生的大范围岩块流. 浅源地震和深源地震都是堵塞-解堵塞转变,是解堵塞后岩石层块滑移或流动造成的能量释放. 4)关于地震能量和临震前兆信息:地震能量即为堵塞-解堵塞转变过程释放的动能. 以实例估算表明,地震岩石滑移动能与使岩块剪切破坏和克服周围摩擦阻力所需做的功相一致,不会出现热流佯谬. 同时指出,通过观测地震发生前构造力的积累过程、局域地区地质变迁以及岩石状态变化等所产生的效应,均可能获得有价值的地震前兆信息.
其他语种文摘 The physical mechanism of earthquake remains a challenging issue to be clarified. Seismologists used to attribute shallow earthquake to the elastic rebound of crustal rocks. The seismic energy calculated following the elastic rebound theory and on the basis of experimental results of rocks, however, shows a large discrepancy with measurement-a fact that has been dubbed “the heat flow paradox”. For the intermediate-focus and deep-focus earthquakes, both occurring in the region of the mantle, there is not any reasonable explanation yet. The current article will discuss the physical mechanism of earthquake from a new perspective, starting from the fact that both the crust and the mantle are discrete collective systems of matters with slow dynamics, as well as from the basic principles of physics, especially some new concepts of condensed matter physics emerging in recent years. 1. Stross distribution in earth's crust: Without taking the tectonic force into account, according to the rheological principle that “everything flows”, the vertical and the horizontal strosses must be in balance due to the effect of gravitational pressure over a long period of time, thus no differential stross in the original crustal rocks is to be expected. The tectonic force is successively transferred and accumulated via stick-slip motions of rocky blocks to squeeze the fault gouges, and then applied to other rocky blocks. The superposition of such additional horizontal tectonic force and the original stross gives rise to the real-time stross in crustal rocks. The mechanical characteristics of fault gouge are different from rocks as it consists of granular matters. Thus the elastic modulus of the fault gouge is much lower than that of rocks, and will become larger with increasing pressure. This character of the fault gouge leads to a tectonic force that increases with depth in a nonlinear fashion. The distribution and variation of tectonic stross in the crust are then specified. 2. Strength of crust rocks: The gravitational pressure can initiate the transition from elasticity to plasticity in crust rocks. A method for calculating the depth dependence of elasticity-plasticity transition is formulated, and demonstrated by exemplar systems. According to the actual situation analysis the behaviors of crust rocks fall into three typical zones: elastic, partially plastic and fully plastic. As the proportion of plastic parts in the partially plastic zone reaches about 10%, plastic interconnection may occur and the variation of shear strength of rocks is mainly characterized by plastic behavior. The equivalent coefficient of friction for the plastic slip is smaller by an order of magnitude, or even less, than that for brittle fracture, thus the shear strength of the rocks for plastic sliding is much less than that for brittle breaking. Moreover, with increasing depth a number of other factors can further reduce the shear yield strength of rocks. On the other hand, since earthquake is a large-scale damage, the rock breaking must occur along a weakest path.
来源 物理学报 ,2014,63(21):219101-1-219101-23 【核心库】
DOI 10.7498/aps.63.219101
关键词 地震发生机制 ; 热流佯谬 ; 地壳岩石应力和强度 ; 堵塞-解堵塞转变
地址

1. 中国科学院物理研究所, 北京凝聚态物理国家实验室, 北京, 100190  

2. 哈尔滨工业大学物理系, 哈尔滨, 150001  

3. 中国科学院理论物理研究所, 北京, 100190

语种 中文
文献类型 研究性论文
ISSN 1000-3290
学科 地球物理学;地质学
基金 中国科学院知识创新工程项目 ;  国家自然科学基金 ;  中国地震局地震行业科研专项经费项目
文献收藏号 CSCD:5279673

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1 许宏 层状材料褶皱对几种地质活动机理研究的启示 物理学报,2020,69(2):026101
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