The INFREP Network: Present Situation and Recent Results

Abstract

VLF/LF (20-300 kHz) radio waves propagation is affected by different factors such as meteorological conditions, solar bursts and geomagnetic activity. At the same time, variations of some parameters in the ground, in the atmosphere and in the ionosphere occurring during the preparatory phase of earthquakes can produce disturbances in the propagation of the previous signals along their radio paths: these disturbances are the radio precursors. Since 2009, several VLF/LF radio receivers have been installed throughout Europe in order to realize a European (VLF/LF) radio network for studying the VLF/LF radio precursors of earthquakes, called the INFREP network. In this paper, at first the description of the present situation of the INFREP network is presented, that is: the location of the receivers, the location of the VLF/LF transmitters whose signal is sampled, the daily download of the data collected by the receivers on the INFREP server and the method of data analysis used in order to individuate possible radio precursors. Then the results obtained on the occasion of recent (2016-2017) seismic activities which occurred in the "sensitive" zone of the INFREP network are presented. The first case examined is the October 30, 2016 earthquake with M w = 6.5, which occurred in Central Italy, near Norcia small town; this earthquake was preceded by a strong shock (M w = 5.9) which occurred 4 days before. The second case presented is the strong (M w = 6.7) offshore earthquake which occurred on July 20, 2017, near the coast of Turkey and Kos island (Greece) and the third case is the August 8, 2017 earthquake with M w = 5.0, which also occurred near the coast of Turkey and Kos island (Greece). In all the previous cases radio anomalies were revealed in some radio signals collected by the receiver lo

Earthquake Prediction Evaluation Based on VLF Data Using a Novel Intersection-Union Method

“…Wavelet transform is used to detect any anomaly in radio data (Torrence and Compo, 1998). Earthquake temporal prediction (Wavelet analysis) has been used in many case studies related to radio wave perturbations and their relationship with earthquakes (Biagi et al, 2019;Righetti et al, 2012). Changes in VLF/LF amplitude data are very different from one path to another, so we need to analyse and compare data from different propagation paths in some ways.…”

“…Righetti et al (2012) investigated the relationship between LF radio signals received in the European VLF/LF network from July 2009 to April 2011 with earthquakes greater than M=5 using wavelet analysis. Biagi et al (2019) investigated the seismic activities occurring within the European VLF/LF network from 2016 to 2017 by wavelet analysis. Most of the previous research have been based on one or some limited transmitter-receiver VLF/LF wave paths (Asano and Hayakawa, 2018).…”

Satellite Measured Ionospheric Magnetic Field Variations over Natural Hazards Sites

“…The wave propagation between narrowband very low frequency (VLF; f = 3-30 kHz) and low frequency (LF; f = 30-300 kHz) transmitter and receiver stations is confined in this cavity, e.g., [19]. In a network configuration with several VLF/LF propagation paths it is possible to sample larger areas, e.g., over Southern Europe [20]. The upper waveguide boundary could be externally driven, e.g., through solar X-ray flares [21], but significant internal drivers can be acoustic waves (AW) and atmospheric gravity waves (AGW) [22].…”

Earthquake Predicting and Tectonic Stress Reducing Possibilities

“…Among geophysical anomalies, specific attention has been given to the electromagnetic emissions (very low frequency (VLF), low frequency (LF), and ultralow frequency (ULF)) recorded before earthquakes, with an interesting correlation between seismic activity and disturbances to radiobroadcasts (1,2,3,4,5,6,7,8,9,11,15,20,21,23,32,35,42,44,45).…”

“…To collect VLF/LF radio signals and study the electromagnetic field variations associated with seismogenic processes, since the 2000s VLF radio networks were established by Japanese researchers (Japanese-Pacific VLF/LF Network) (22) and a European network (5,6) by Japanese, Russian, and Italian teams cooperation. It is worth underling that there are examples of large earthquakes when no radiation has been detected (4,8).…”