On the man-made contamination on ULF measurements: evidence for disturbances related to an electrified DC railway
An analysis of measurements performed at L'Aquila (Italy) during a deep minimum of solar and magnetospheric activity (2008–2010) allowed for the evaluation of possible contamination of the ultralow-frequency (ULF) spectrum (<i>f</i> ≈ 1–500 mHz) from artificial distur...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-09-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/32/1153/2014/angeo-32-1153-2014.pdf |
| Summary: | An analysis of measurements performed at L'Aquila (Italy) during a deep
minimum of solar and magnetospheric activity (2008–2010) allowed for the
evaluation of possible contamination of the ultralow-frequency (ULF) spectrum (<i>f</i> ≈
1–500 mHz) from artificial disturbances, practically in absence of natural
signals. In addition, the city evacuation and the interruption of all
industrial and social activities after the strong earthquake of 6 April 2009
allowed also for the examination of possible changes of the contamination level under
remarkably changed environmental conditions. Our analysis reveals a
persistent, season-independent, artificial signal, with the same
characteristics in the <i>H</i> and <i>Z</i> components, that affects during daytime
hours the entire spectrum; such contamination persists after the city
evacuation. We speculate that the DC electrified railway (located ≈
33 km from the Geomagnetic Observatory of L'Aquila, it maintained the same train traffic after
the earthquake) is responsible for the observed disturbances. |
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| ISSN: | 0992-7689 1432-0576 |