Elsevier

Engineering Geology

Volume 311, 20 December 2022, 106912
Engineering Geology

Differentiating between artificial and natural sources of electromagnetic radiation at a seismogenic fault

https://doi.org/10.1016/j.enggeo.2022.106912Get rights and content
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Highlights

  • ULF to LF electromagnetic radiation was monitored at a seismogenic fault

  • A broadband data logger was installed in a cave to reduce the environmental noise

  • A number of distinct signals were identified in the spectrum

  • The low energy broadband impulses show a clear association with local rock strain

  • Unfortunately, they were overprinted by the larger lightning-related impulses

Abstract

Ultralow frequency (ULF) to low frequency (LF) electromagnetic radiation represents one of the most promising effects of brittle rock strain and microcracking that might be potentially helpful for short term earthquake forecasting. In this study the results of a six month monitoring campaign are presented from Obir Cave in the eastern Alps. Direct experimental observations of electromagnetic radiation have been made using a customised broadband data logger installed next to the Obir Fault - this seismogenic fault near the Periadriatic Lineament is known to be related to at least three large prehistoric earthquakes. On the basis of these measurements it has been possible to characterise a number of distinct signals: artificial constant narrowband signals at discrete frequencies; short serial broadband impulses; high energy broadband impulses; and low energy broadband impulses. The narrowband artificial signals were removed from the electromagnetic radiation time series analysis so that the natural signals were enhanced and could be compared more easily to meteorological parameters and rock strain indicators. Critically, the high energy broadband impulses show a strong correlation with lightning activity across much of central Europe and the eastern Mediterranean while the low energy broadband impulses appear to be associated with local rock strain in and around Obir Cave. Unfortunately, it seems certain that some of the essential strain related impulses are likely to have been overprinted by the larger lightning related impulses.

Keywords

Electromagnetic radiation
Brittle rock strain
Microcracking
Seismogenic fault
Eastern Alps

Data availability

Data will be made available on request.

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