Low frequency signal spectrum analysis for strong earthquakes

We examined changes in the spectral composition of the low frequency (LF) subionospheric signals from the NRK transmitter (37.5 kHz) in Iceland that were received in Bari (Italy) relative to the earthquake that occurred in L’Aquila on April 6, 2009. In our previous studies, we have reported the occu...

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Published in:Annals of Geophysics
Main Authors: Masashi Hayakawa, Konrad Schwingenschuh, Pier Francesco Biagi, Maria Solovieva, Alexander Rozhnoi
Format: Article in Journal/Newspaper
Language:English
Published: Istituto Nazionale di Geofisica e Vulcanologia (INGV) 2012
Subjects:
Online Access:https://doi.org/10.4401/ag-5076
https://doaj.org/article/c2482e0fd9144067bfb00305e5c6e227
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spelling ftdoajarticles:oai:doaj.org/article:c2482e0fd9144067bfb00305e5c6e227 2023-05-15T16:52:23+02:00 Low frequency signal spectrum analysis for strong earthquakes Masashi Hayakawa Konrad Schwingenschuh Pier Francesco Biagi Maria Solovieva Alexander Rozhnoi 2012-04-01T00:00:00Z https://doi.org/10.4401/ag-5076 https://doaj.org/article/c2482e0fd9144067bfb00305e5c6e227 EN eng Istituto Nazionale di Geofisica e Vulcanologia (INGV) http://www.annalsofgeophysics.eu/index.php/annals/article/view/5076 https://doaj.org/toc/1593-5213 https://doaj.org/toc/2037-416X doi:10.4401/ag-5076 1593-5213 2037-416X https://doaj.org/article/c2482e0fd9144067bfb00305e5c6e227 Annals of Geophysics, Vol 55, Iss 1 (2012) VLF/LF signal propagation. eartquake precursors Meteorology. Climatology QC851-999 Geophysics. Cosmic physics QC801-809 article 2012 ftdoajarticles https://doi.org/10.4401/ag-5076 2022-12-31T11:35:08Z We examined changes in the spectral composition of the low frequency (LF) subionospheric signals from the NRK transmitter (37.5 kHz) in Iceland that were received in Bari (Italy) relative to the earthquake that occurred in L’Aquila on April 6, 2009. In our previous studies, we have reported the occurrence of preseismic night-time anomalies using observations from three receivers located in Bari, Graz (Austria) and Moscow (Russia). The strongest anomalies in the signals were observed in the NRK-Bari propagation path during the period 5-6 days before the L’Aquila earthquake, as well as during the series of aftershocks. During this period, similar very low frequency (VLF)/LF amplitude anomalies were also observed along several other propagation paths that crossed the L’Aquila seismogenic zone. Spectral analysis of the LF signals filtered in the frequency range 0.28 mHz to 15 mHz shows differences in the spectra for seismo-disturbed days when compared to those for either quiet or geomagnetically disturbed days. These spectral anomalies, which are only observed in the propagation path between NRK and Bari, contain signals with periods of about 10 min to 20 min. These periodic signals are absent both in the spectra of the undisturbed signals for the control paths, and in the spectra of the signals received during geomagnetic storms. The same changes in the spectral composition were observed in the analysis of LF (40 kHz) signals from the JJY transmitter in Japan that were received in Petropavlovsk-Kamchatsky (Russia) during the occurrence of three strong earthquakes with M ≥7.0. The results of this study support the theoretical prediction that the possible mechanism for energy penetration from the origin of an earthquake through the atmosphere and into the ionosphere is based on the excitation and upward propagation of internal gravity waves. Article in Journal/Newspaper Iceland Directory of Open Access Journals: DOAJ Articles Petropavlovsk ENVELOPE(158.626,158.626,53.067,53.067) Petropavlovsk-Kamchatsky ENVELOPE(158.651,158.651,53.044,53.044) Annals of Geophysics 55 1
institution Open Polar
collection Directory of Open Access Journals: DOAJ Articles
op_collection_id ftdoajarticles
language English
topic VLF/LF signal propagation. eartquake precursors
Meteorology. Climatology
QC851-999
Geophysics. Cosmic physics
QC801-809
spellingShingle VLF/LF signal propagation. eartquake precursors
Meteorology. Climatology
QC851-999
Geophysics. Cosmic physics
QC801-809
Masashi Hayakawa
Konrad Schwingenschuh
Pier Francesco Biagi
Maria Solovieva
Alexander Rozhnoi
Low frequency signal spectrum analysis for strong earthquakes
topic_facet VLF/LF signal propagation. eartquake precursors
Meteorology. Climatology
QC851-999
Geophysics. Cosmic physics
QC801-809
description We examined changes in the spectral composition of the low frequency (LF) subionospheric signals from the NRK transmitter (37.5 kHz) in Iceland that were received in Bari (Italy) relative to the earthquake that occurred in L’Aquila on April 6, 2009. In our previous studies, we have reported the occurrence of preseismic night-time anomalies using observations from three receivers located in Bari, Graz (Austria) and Moscow (Russia). The strongest anomalies in the signals were observed in the NRK-Bari propagation path during the period 5-6 days before the L’Aquila earthquake, as well as during the series of aftershocks. During this period, similar very low frequency (VLF)/LF amplitude anomalies were also observed along several other propagation paths that crossed the L’Aquila seismogenic zone. Spectral analysis of the LF signals filtered in the frequency range 0.28 mHz to 15 mHz shows differences in the spectra for seismo-disturbed days when compared to those for either quiet or geomagnetically disturbed days. These spectral anomalies, which are only observed in the propagation path between NRK and Bari, contain signals with periods of about 10 min to 20 min. These periodic signals are absent both in the spectra of the undisturbed signals for the control paths, and in the spectra of the signals received during geomagnetic storms. The same changes in the spectral composition were observed in the analysis of LF (40 kHz) signals from the JJY transmitter in Japan that were received in Petropavlovsk-Kamchatsky (Russia) during the occurrence of three strong earthquakes with M ≥7.0. The results of this study support the theoretical prediction that the possible mechanism for energy penetration from the origin of an earthquake through the atmosphere and into the ionosphere is based on the excitation and upward propagation of internal gravity waves.
format Article in Journal/Newspaper
author Masashi Hayakawa
Konrad Schwingenschuh
Pier Francesco Biagi
Maria Solovieva
Alexander Rozhnoi
author_facet Masashi Hayakawa
Konrad Schwingenschuh
Pier Francesco Biagi
Maria Solovieva
Alexander Rozhnoi
author_sort Masashi Hayakawa
title Low frequency signal spectrum analysis for strong earthquakes
title_short Low frequency signal spectrum analysis for strong earthquakes
title_full Low frequency signal spectrum analysis for strong earthquakes
title_fullStr Low frequency signal spectrum analysis for strong earthquakes
title_full_unstemmed Low frequency signal spectrum analysis for strong earthquakes
title_sort low frequency signal spectrum analysis for strong earthquakes
publisher Istituto Nazionale di Geofisica e Vulcanologia (INGV)
publishDate 2012
url https://doi.org/10.4401/ag-5076
https://doaj.org/article/c2482e0fd9144067bfb00305e5c6e227
long_lat ENVELOPE(158.626,158.626,53.067,53.067)
ENVELOPE(158.651,158.651,53.044,53.044)
geographic Petropavlovsk
Petropavlovsk-Kamchatsky
geographic_facet Petropavlovsk
Petropavlovsk-Kamchatsky
genre Iceland
genre_facet Iceland
op_source Annals of Geophysics, Vol 55, Iss 1 (2012)
op_relation http://www.annalsofgeophysics.eu/index.php/annals/article/view/5076
https://doaj.org/toc/1593-5213
https://doaj.org/toc/2037-416X
doi:10.4401/ag-5076
1593-5213
2037-416X
https://doaj.org/article/c2482e0fd9144067bfb00305e5c6e227
op_doi https://doi.org/10.4401/ag-5076
container_title Annals of Geophysics
container_volume 55
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