22 research outputs found
Evidence for tidal triggering for the earthquakes of the Ionian geological zone, Greece
No full text<p>We here investigate the evidence for tidal triggering of the earthquakes of the seismic area of the Ionian geological zone in Greece, using the cumulative histogram method that was introduced recently by Cadicheanu et al. (Nat. Hazards Earth Syst. Sci., 2007, 7, 733-740). We analyzed the series of earthquakes that occurred in the area bounded by 19°E # { # 22°E and 36°N # m # 40°N from 1964 to 2006. Over this time, there were 19.916 shallow and intermediate depth earthquakes with magnitudes ranging between 2.5 and 6.2. The great majority of these earthquakes, including those with M ≥ 5.0, were shallow. The results of our analysis indicate that the monthly variations in the frequencies of the earthquake occurrence are in agreement with the period of the tidal lunar monthly variations. The same is true for the corresponding daily variations of the frequencies of earthquake occurrence and the diurnal lunisolar (K1) and semidiurnal lunar (M2) tidal variations. In addition, the confidence levels for the identification of such periodical agreement between the frequency of earthquake occurrence and the tidal periods varies according to the seismic activity; i.e. the higher confidence levels correspond to the periods with stronger seismic activity. These results are in favor of a tidal triggering process of earthquakes when the stress in the focal area is near the critical level.</p><p> </p>
Wavelet analysis of the LF radio signals collected by the European VLF/LF network from July 2009 to April 2011
No full text<p>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.</p><p> </p>
The spatial-temporal total friction coefficient of the fault viewed from the seismo-electromagnetic theory. By Patricio Venegas-Aravena , Enrique G. Cordaro , David Laroze
No full textPreface
No full textOver the last several years, a lot of evidence has indicated that the earthquake generation process is a critical phenomenon, which culminates in a large event that corresponds to a critical point. A fundamental prediction of this hypothesis is that before the event reaches this critical point, a regional system of faults goes through a period of accelerating seismicity and seismic energy release, which forms the signature of the approach to the critical state. By the end of this stage, the critical point has been attained, and the stress exerted by friction on the shear zone, as well as the strain caused by an avalanche of fusing cracks, lead to irreversible instability and rupture. As a consequence of the processes prior to an event, changes in the physical/chemical state of the earth precede earthquakes. These variations can be called the ground precursors. There are a variety of such precursors, that are evident in their genesis, such as ground uplift and tilt, gas emissions, underground water-level fluctuations, changes in groundwater chemistry, and changes in electrical resistivity of the rock. [...]<br />
Lower Ionospheric turbulence variations during the intense tectonic activity in Eastern Aegean area
No full textThis 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
Variation of the Earth tide-seismicity compliance parameter during the recent seismic activity in Fthiotida, central Greece
No full textBased on the results of our previous studies concerning the tidal triggering effect on the seismicity in Greece, we consider the confidence level of earthquake occurrence - tidal period accordance as an index of tectonic stress criticality, associated with earthquake occurrence. Then, we investigate whether the recent increase in the seismic activity at Fthiotida in Greek mainland indicates faulting maturity and the possible production a stronger earthquake. In this paper we present the results of this investigation
Total electron content variations over southern Europe before and during the M 6.3 Abruzzo earthquake of April 6, 2009
No full text<p>Total electron content (TEC) data of 14 global positioning system (GPS) stations of the EUREF network were provided by the IONOLAB. These were analyzed using wavelet analysis and discrete Fourier analysis to investigate the TEC variations over southern Europe in the month before the catastrophic Abruzzo earthquake of M 6.3 of April 6, 2009. The main conclusions of this analysis are: (a) TEC oscillations in a broad range of frequencies occurred randomly over a broad area of several hundred kilometers from the earthquake; (b) Morning and evening extensions of the day-time TEC values were seen for all of the EUREF stations of this program shortly before, during and shortly after the main earthquake period; (c) High frequency oscillations (f <span> </span>0.0003 Hz, period T <span> </span>60 m) appear to indicate the location of the earthquake, although with questionable accuracy, while the fractal characteristics of the frequency distribution indicates the locus of the earthquake with relatively greater accuracy. We conclude that the lithosphere-atmosphere-ionosphere coupling mechanism through acoustic or gravity waves might explain this phenomenology.</p>
