A laboratory nanoseismological study on deep-focus earthquake micromechanics.
A laboratory nanoseismological study on deep-focus earthquake micromechanics.
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DOI：
10.1126/sciadv.1601896
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发表时间：
2017-07
期刊：
影响因子：
13.6
通讯作者：
Brunet F
中科院分区：
文献类型：
--
作者：
Wang Y;Zhu L;Shi F;Schubnel A;Hilairet N;Yu T;Rivers M;Gasc J;Addad A;Deldicque D;Li Z;Brunet F
在受控条件下对实验室地震的纳米地震学分析为深源地震的机制提供了新的线索。全球地震发生率在300 km以下呈指数衰减，在550 ~ 600 km附近达到峰值，在700 km附近突然终止。裂缝如何在这些深度开始，成核和传播仍然是地球科学中最大的难题之一，因为增加的压力抑制了裂缝的传播。我们报告nanoseisological分析高分辨率的声发射（AE）记录在断裂过程中触发的部分转变从橄榄石尖晶石的Mg 2GeO 4，一个类似的主要矿物（Mg，Fe）2SiO 4橄榄石在上地幔，使用国家的最先进的地震技术，在实验室。分析了声发射的震源机制及其在变形过程中的时空分布。显微结构分析表明，声发射是由纳米晶尖晶石组成的剪切带的动态传播产生的。这些纳米剪切带具有接近恒定的厚度（~100 nm），但在变形期间具有变化的长度和自组织。这一不规则的地震过程导致试样最终的宏观破坏。从记录的波形中提取了AE事件的几个源参数，从而可以密切跟踪整个变形/转变过程中的事件启动、聚类和传播。AE遵循Gutenberg-Richter统计，在三个阶矩量级上定义良好的B值为1.5，表明实验室失效过程是自仿射的。震级和破裂面积之间的地震关系正确地预测了毫米尺度的AE震级。提出了一种基于应变局部化理论的断裂扩展模型。未来的数值分析可能有助于解决实验室AE事件和深源地震之间的标度问题。
Nanoseismological analyses on labquakes under controlled conditions shed new lights on mechanisms of deep-focus earthquakes. Global earthquake occurring rate displays an exponential decay down to ~300 km and then peaks around 550 to 600 km before terminating abruptly near 700 km. How fractures initiate, nucleate, and propagate at these depths remains one of the greatest puzzles in earth science, as increasing pressure inhibits fracture propagation. We report nanoseismological analysis on high-resolution acoustic emission (AE) records obtained during ruptures triggered by partial transformation from olivine to spinel in Mg2GeO4, an analog to the dominant mineral (Mg,Fe)2SiO4 olivine in the upper mantle, using state-of-the-art seismological techniques, in the laboratory. AEs’ focal mechanisms, as well as their distribution in both space and time during deformation, are carefully analyzed. Microstructure analysis shows that AEs are produced by the dynamic propagation of shear bands consisting of nanograined spinel. These nanoshear bands have a near constant thickness (~100 nm) but varying lengths and self-organize during deformation. This precursory seismic process leads to ultimate macroscopic failure of the samples. Several source parameters of AE events were extracted from the recorded waveforms, allowing close tracking of event initiation, clustering, and propagation throughout the deformation/transformation process. AEs follow the Gutenberg-Richter statistics with a well-defined b value of 1.5 over three orders of moment magnitudes, suggesting that laboratory failure processes are self-affine. The seismic relation between magnitude and rupture area correctly predicts AE magnitude at millimeter scales. A rupture propagation model based on strain localization theory is proposed. Future numerical analyses may help resolve scaling issues between laboratory AE events and deep-focus earthquakes.
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