Several magnetic measurements and theoretical developments from different research groups have shown certain relationships with worldwide geological processes. Secular variation in geomagnetic cutoff rigidity, magnetic frequencies, or magnetic anomalies have been linked with spatial properties of active convergent tectonic margins or earthquake occurrences during recent years. These include the rise in similar fundamental frequencies in the range of microhertz before the Maule 2010, Tōhoku 2011, and Sumatra–Andaman 2004 earthquakes and the dramatic rise in the cumulative number of magnetic anomalous peaks before several earthquakes such as Nepal 2015 and Mexico (Puebla) 2017. Currently, all of these measurements have been physically explained by the microcrack generation due to uniaxial stress change in rock experiments. The basic physics of these experiments have been used to describe the lithospheric behavior in the context of the seismo-electromagnetic theory. Due to the dramatic increase in experimental evidence, physical mechanisms, and the theoretical framework, this paper analyzes vertical magnetic behavior close to the three latest main earthquakes in Chile: Maule 2010 (M_w 8.8), Iquique 2014 (M_w 8.2), and Illapel 2015 (M_w 8.3). The fast Fourier transform (FFT), wavelet transform, and daily cumulative number of anomalies methods were used during quiet space weather time during 1 year before and after each earthquake in order to filter space influence. The FFT method confirms the rise in the power spectral density in the millihertz range 1 month before each earthquake, which decreases to lower values some months after earthquake occurrence. The cumulative anomaly method exhibited an increase prior to each Chilean earthquake (50–90 d prior to earthquakes) similar to those found for Nepal 2015 and Mexico 2017. The wavelet analyses also show similar properties to FFT analysis. However, the lack of physics-based constraints in the wavelet analysis does not allow conclusions that are as strong as those made by FFT and cumulative methods. By using these results and previous research, it could be stated that these magnetic features could give seismic information about impending events. Additionally, these results could be related to the lithosphere–atmosphere–ionosphere coupling (LAIC effect) and the growth of microcracks and electrification in rocks described by the seismo-electromagnetic theory.

中文翻译：

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长期磁异常及其与最近的智利大地震在地震电磁理论背景下的可能关系

来自不同研究小组的一些磁测量和理论发展表明与全球地质过程存在某些关系。近年来，地磁截止刚度、磁频率或磁异常的长期变化与活动收敛构造边缘的空间特性或地震发生有关。其中包括在 Maule 2010、Tōhoku 2011 和 Sumatra-Andaman 2004 地震之前微赫兹范围内类似基频的上升，以及在尼泊尔 2015 和墨西哥 (Puebla ) 2017. 目前，所有这些测量结果都可以通过岩石实验中单轴应力变化产生的微裂纹来物理解释。这些实验的基础物理学已被用来描述地震电磁理论背景下的岩石圈行为。由于实验证据、物理机制和理论框架的急剧增加，本文分析了智利最近三个主要地震附近的垂直磁行为：Maule 2010 (M _w  8.8)、Iquique 2014 ( M _w  8.2) 和 Illapel 2015 ( M _w 8.3)。采用快速傅里叶变换(FFT)、小波变换和日累积异常数方法在每次地震前后1年的安静空间天气时间段内过滤空间影响。FFT 方法证实，每次地震前 1 个月，功率谱密度在毫赫兹范围内上升，而在地震发生后几个月，功率谱密度下降到较低值。累积异常方法在每次智利地震之前（地震前 50-90 天）都表现出增加，类似于 2015 年尼泊尔和 2017 年墨西哥的发现。小波分析也显示出与 FFT 分析相似的特性。然而，由于小波分析中缺乏基于物理的约束，因此无法得出与 FFT 和累积方法一样强的结论。通过使用这些结果和先前的研究，可以说这些磁特征可以提供有关即将发生的事件的地震信息。此外，这些结果可能与岩石圈-大气-电离层耦合（LAIC 效应）以及地震-电磁理论描述的岩石中微裂纹的生长和带电有关。