7 research outputs found
Anomalies Observed in VLF and LF Radio Signals on the Occasion of the Western Turkey Earthquake (Mw = 5.7) on May 19, 2011
VLF radio signals lie in the 10 - 60 kHz frequency band. These radio signals are used for worldwide navigation support, time signals and for military purposes. They are propagated in the earth-ionosphere wave-guide mode along great circle propagation paths. So, their propaga-tion is strongly affected by the ionosphere conditions. LF signals lie in 150 - 300 kHz frequency band. They are used for long way broadcasting by the few (this type of broadcasting is going into disuse) transmitters located in the world. These radio signals are characterized by the ground wave and the sky wave propagation modes [1]. The first generates a stable signal that propagates in the channel Earth-troposphere and is affected by the surface ground and troposphere condition. The second instead gives rise to a signal which varies greatly between day and night, and between summer and winter, and which propagates using the lower ionosphere as a reflector; its propagation is mainly affected by the ionosphere condi-tion, particularly in the zone located in the middle of the transmitter-receiver path. The propagation of the VLF/LF radio signals is affected by different factors such as the meteorological condition, the solar bursts and the geo-magnetic 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 above men-tioned signals. As already reported by many previous studies [2-18] the disturbances are classified as anoma-lies and different methods of analysis as the residual dA/ dP [15], the terminator time TT [9], the Wavelet spectra and the Principal Component Analysis have been used [6,7].
Here the analysis carried out on LF and VLF radio signals using three different methods on the occasion of a strong earthquake occurred recently in Turkey is pre-sented
Wavelet analysis of the LF radio signals collected by the European VLF/LF network from July 2009 to April 2011
In 2008, a radio receiver that works in very low frequency (VLF; 20-60 kHz) and LF (150-300 kHz) bands was developed by an Italian factory. The
receiver can monitor 10 frequencies distributed in these bands, with the measurement for each of them of the electric field intensity. Since 2009, to
date, six of these radio receivers have been installed throughout Europe to establish a ‘European VLF/LF Network’. At present, two of these are into
operation in Italy, and the remaining four are located in Greece, Turkey, Portugal and Romania. For the present study, the LF radio data collected
over about two years were analysed. At first, the day-time data and the night-time data were separated for each radio signal. Taking into account
that the LF signals are characterized by ground-wave and sky-wave propagation modes, the day-time data are related to the ground wave and
the night-time data to the sky wave. In this framework, the effects of solar activity and storm activity were defined in the different trends. Then, the
earthquakes with M ≥5.0 that occurred over the same period were selected, as those located in a 300-km radius around each receiver/transmitter and
within the 5th Fresnel zone related to each transmitter-receiver path. Where possible, the wavelet analysis was applied on the time series of the radio
signal intensity, and some anomalies related to previous earthquakes were revealed. Except for some doubt in one case, success appears to have been obtained in all of the cases related to the 300 km circles in for the ground waves and the sky waves. For the Fresnel cases, success in two cases and one
failure were seen in analysing the sky waves. The failure occurred in August/September, and might be related to the disturbed conditions of the ionosphere in summer
The European VLF/LF radio network to search for earthquake precursors: setting up and natural/man-made disturbances
In the last years disturbances in VLF/LF radio signals related to seismic activity have been presented. The radio data were collected by receivers located on the ground or on satellites. The ground-based research implies systematic data collection by a network of receivers. Since 2000 the “Pacific VLF network”, conducted by Japanese researchers, has been in operation. During 2008 a radio receiver was developed by the Italian factory Elettronika (Palo del Colle, Bari). The receiver is equipment working in VLF and LF bands. It can monitor 10 frequencies distributed in these bands and, for each of them, it saves the power level. At the beginning of 2009, five receivers were made for the realization of the “European VLF/LF Network”; two were planned for Italy and one for Greece, Turkey and Romania, respectively. In 2010 the network was enlarged to include a new receiver installed in Portugal. In this work, first the receiver and its setting up in the different places are described. Then, several disturbances in the radio signals related to the transmitters, receivers, meteorological/geomagnetic conditions are presented and described
The European Network for studying the radio precursors of earthquakes: Principal Component Analysis of LF radio signals collected during July 2009 - April 2011
Since 2009 a network of VLF (20-60 kHz) and LF (150-300 kHz) radio receivers was put into operation in Europe
in order to study the disturbances produced by the earthquakes on the propagation of these signals. In 2011 the
network for LF signals was formed by six receivers located two in Italy and one in Greece, Portugal, Romania,
and Turkey. The LF radio data collected during about two years have been analysed. Each radio signal has been
split in day-time and night-time data; then, the earthquakes with M 5.0, occurred in the same period, located in a
300 km radius around each receiver/transmitter and within the 5th Fresnel zone related to each transmitter-receiver
path, have been selected. In this study we adopt the Principal Component Analysis (PCA) to study the radio signal
anomalies possibly related to earthquake activity. A detailed comparison with similar studies that use wavelet
analysis is done and advantages or drawback of the two methods are pointed out
Lower ionospheric turbulence variations during the intense tectonic activity in eastern aegean area
This paper may be considered as an additional approval of the way the tectonic activity affects the lower Ionosphere. The results of our investigation, on the occasion of the recent East Aegean tectonic activity, indicate that the High-Frequency limit, fo, of the ionospheric turbulence content, increases as the site and the time of the earthquake occurrence is approaching, pointing to the earthquake location.We conclude that the Lithosphere Atmosphere Ionosphere Coupling (LAIC) mechanism through acoustic or gravity wave could explain this phenomenology, as a result of a the frequency differential damping of the propagating turbulent in the ionosphere. Proper use of this result may lead to a method of earthquake hazard mitigation using the byproducts of the Global Positioning Network (actually Total Electron Contain, TEC, estimations) which are available freely. © 2020 the Istituto Nazionale di Geofisica e Vulcanologia. All rights reserved
Coordinated observations of the red dwarf flare star EV Lac in 1998
The results of photometric studies of the flare star EV Lac obtained in the course of cooperative observations in 1998 are presented. No significant brightness variations in IR were found from simultaneous observations of the star in UBVRI and H bands, in coincidence with the observed optical flares. Within the framework of the zonal spottedness model of stars the EV Lac surface inhomogeneity parameters are estimated