Low-frequency Earthquakes in the Continental Plate and Their Seismological and Tectonic Implications

IF 0.2 Q4 GEOGRAPHY, PHYSICAL Journal of Geography-Chigaku Zasshi Pub Date : 2022-06-25 DOI:10.5026/jgeography.131.289
A. Hasegawa, J. Nakajima
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Abstract

Low-frequency earthquakes ( LFEs ) occurring in the continental plate are reviewed. Most LFEs in the continental plate occur at depths of ~15 ­ 45 km in the uppermost mantle to the lower crust beneath volcanoes, but they also occur within the same depth range beneath non-volcanic areas. Because they occur at greater depths than the typical depth limit for shallow regular earthquakes, they are called “deep low-frequency earthquakes ( deep LFE ) .” However, a recent study reveals that LFEs also occur at depths shallower than 15 km in the upper crust where many regular earthquakes occur. This indicates that LFEs occur over the entire depth range from the uppermost mantle to the upper crust. In the upper crust, LFEs and regular earthquakes coexist and occur in close proximity. Focal mechanisms and activity patterns of LFEs show that tensile-shear crack is the dominant mechanism generating LFEs. In addition, the long duration of waveforms is probably caused by resonance in the fluid-filled crack. Distributions of peak frequency ( fp ) and frequency index ( FI ) values of waveforms, both of which are expected to be significantly small for LFEs and large for regular earthquakes, show that there is no clear boundary for fp and FI values between LFEs and regular earthquakes; rather, they are distrib-uted continuously. It is presumed that the distribution of high and low pore fluid pressures in source faults creates such distributions of small and large fp and FI values, respectively, and a LFE occurs when the pore pressure is extremely high. This indicates that pore pressure is direct-ly related also to the genesis of regular earthquakes. In source areas of recent large inland earthquakes, LFEs are activated by the mainshock, and FI and fp
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大陆板块低频地震及其地震学和构造意义
综述了大陆板块发生的低频地震。大陆板块中的大多数LFE发生在火山下方最上层地幔至下地壳的约15­45公里深处,但它们也发生在非火山区域下方的相同深度范围内。由于它们发生的深度大于浅层规则地震的典型深度限制,因此被称为“深低频地震(深LFE)”。然而,最近的一项研究表明,LFE也发生在发生许多规则地震的上地壳中浅于15公里的深度。这表明LFE发生在从最上层地幔到上层地壳的整个深度范围内。在上地壳中,LFE和常规地震共存并发生在很近的地方。LFEs的焦点机制和活动模式表明,拉伸剪切裂纹是LFEs产生的主要机制。此外,波形持续时间长可能是由充满液体的裂纹中的共振引起的。波形的峰值频率(fp)和频率指数(FI)值的分布表明,LFE和常规地震之间的fp和FI值没有明确的边界;相反,它们是连续分布的。据推测,源断层中高孔隙流体压力和低孔隙流体压力的分布分别产生了小的和大的fp和FI值的分布,并且当孔隙压力极高时会发生LFE。这表明孔隙压力与常规地震的发生也有直接关系。在最近内陆大地震的震源区,LFE被主震激活,FI和fp
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来源期刊
CiteScore
1.50
自引率
33.30%
发文量
28
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