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Ultra Low Frequency (ULF) European multi station magnetic field analysis before and during the 2009 earthquake at L'Aquila regarding regional geotechnical information

机译：2009年L'Aquila地震之前和之中的超低频（ULF）欧洲多站磁场分析，涉及区域岩土信息

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摘要

This work presents ground based Ultra Low Frequency (ULF) magnetic field measurements in the frequency range from 10-15 mHz from 1 January 2008 to 14 April 2009. In this time period a strong earthquake series hit the Italian Abruzzo region around L'Aquila with the main stroke of magnitude M = 6.3 on 6 April 2009. In the frame of the South European Geomagnetic Array (SEGMA), a European collaboration runs ULF fluxgate instruments providing continuously magnetic field data recorded in mid- and south Europe. The main scientific objective is the investigation of signal variations due to seismic activity and the discrimination between other natural and human influences. The SEGMA station closest to the L'Aquila earthquake epicenter is L'Aquila observatory located in the epicenter region. For the scientific analysis we extract the nighttime period from 22:00-02:00 UT and determine the power spectral density (PSD) of the horizontal (H) and vertical (Z) magnetic field components and the standardized polarization ratio (Z) over (H). To discriminate local emissions from global geomagnetic effects, data from three SEGMA stations in distances up to 630 km from the epicenter region are analyzed and further compared to the independent global geomagnetic ∑ Kp index. Apart from indirect ionospheric effects, electromagnetic noise could be originated in the lithosphere due to tectonic mechanisms in the earthquake focus. To estimate the amplitude of assumed lithospheric electromagnetic noise emissions causing anomalies in the PSD of the (Z) component, we consider magnetotelluric calculations of the electric crust conductivity in the L'Aquila region. Results found at L'Aquila observatory are interpreted with respect to the lithosphere electrical conductivity in the local observatory region, the ∑ Kp index, and further in a multi station analysis. Possible seismic related ULF anomalies occur ～2 weeks before the main stroke.
机译：这项工作提出了从2008年1月1日至2009年4月14日在10-15 mHz频率范围内的地面超低频（ULF）磁场测量。在此期间，强烈地震序列袭击了拉奎拉附近的意大利阿布鲁佐地区，在2009年4月6日，主震级M = 6.3。在南欧地磁阵列（SEGMA）的框架内，欧洲合作组织运行了ULF磁通门仪器，提供了在中欧和南欧记录的连续磁场数据。主要的科学目的是研究由于地震活动引起的信号变化以及其他自然和人为影响之间的区别。最靠近拉奎拉地震震中的SEGMA站是位于震中地区的拉奎拉天文台。为了进行科学分析，我们从UT的22：00-02：00提取了夜间时段，并确定了水平（H）和垂直（Z）磁场分量的功率谱密度（PSD）以及标准的极化率（Z） （H）。为了将局部排放物与全球地磁效应区分开来，分析了三个SEGMA台站距震中区最远630 km的数据，并与独立的全球地磁∑ Kp指数进行了比较。除了间接电离层效应外，由于地震震源的构造机制，电磁噪声可能起源于岩石圈。为了估计造成（Z）分量PSD异常的假设岩石圈电磁噪声发射的幅度，我们考虑对拉奎拉地区电壳电导率的大地电磁计算。 L'Aquila天文台发现的结果将根据当地天文台区域的岩石圈电导率，∑ Kp指数以及进一步的多站分析进行解释。与地震有关的ULF异常可能发生在中风前约2周。

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