75 research outputs found
Recent results of the research for preseismic phenomena on the underground water and temperature in Pieria, northern Greece
International audienceThe recent results of the research for earthquake precursory phenomena on the underground water level and temperature at the area Pieria of northern Greece are presented. The analysis of our observations in relation to the local microseismicity indicate that underground water level variations may be considered as precursory phenomena connected to the local microseismic activity in the area of Pieria. Base on these results, it can be supported that monitoring the shallow underground water level and temperature for detecting earthquake precursory phenomena may be proved to be a useful method in the framework of an interdisciplinary research for earthquake prediction
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
A catalogue of rotation and activity in early-M stars
We present a catalogue of rotation and chromospheric activity in a sample of
334 M dwarfs of spectral types M0--M4.5 populating the parameter space around
the boundary to full convection. We obtained high-resolution optical spectra
for 206 targets and determined projected rotational velocity, vsini, and Halpha
emission. The data are combined with measurements of vsini in field stars of
the same spectral type from the literature. Our sample adds 157 new rotation
measurements to the existing literature and almost doubles the sample of
available vsini. The final sample provides a statistically meaningful picture
of rotation and activity at the transition to full convection in the solar
neighborhood. We confirm the steep rise in the fraction of active stars at the
transition to full convection known from earlier work. In addition, we see a
clear rise in rotational velocity in the same stars. In very few stars, no
chromospheric activity but a detection of rotational broadening was reported.
We argue that all of them are probably spurious detections; we conclude that in
our sample all significantly rotating stars are active, and all active stars
are significantly rotating. The rotation-activity relation is valid in
partially and in fully convective stars. Thus, we do not observe any evidence
for a transition from a rotationally dominated dynamo in partially convective
stars to a rotation-independent turbulent dynamo in fully convective stars;
turbulent dynamos in fully convective stars of spectral types around M4 are
still driven by rotation. Finally, we compare projected rotational velocities
of 33 stars to rotational periods derived from photometry in the literature and
determine inclinations for a few of them.Comment: accepted for publication in A
Statistical Analysis and the OPEA Model of the White-Light Flares Occurring on Kr\"uger 60B (DO Cep)
In this study, new observations and some results of statistical analyses are
presented. The largest flare data set of DO Cep in the literature has been
obtained with 89 flares detected in 67.61 hours of U-band flare patrol. First
of all, the observations demonstrated that the star is one of the most active
flare stars in respect to the computed flare frequency. Secondly, using the
independent samples t-test, the detected flares were classified into two
subtypes, and then they were modelled. Analysing the models demonstrated that
the fast and slow flares occurring on the star can be separated with a critical
value of the ratio of their decay time to rise time. The critical value was
computed as 3.40. According to this value, the fast flare rate is 20.22%, while
the slow flare rate is 79.78%. Besides, there is a 39.282 times difference
between the energies of these two types of flares. However, the flare
equivalent durations versus the flare rise times increase in similar ways for
both groups. In addition, all all the flares were modelled with the one-phase
exponential association function. Analysing this model, the plateau value was
found to be 2.810. Moreover, the half-life value was computed as 433.1s from
the model. The maximum flare rise time was found to be 1164s, while the maximum
flare total duration was found to be 3472s. The results of the flare timescales
indicate that the geometry of the flaring loop on the surface of the star might
be similar to those seen on analogues of DO Cep. Consequently, considering both
the half-life value and flare timescales, the flares detected on the surface of
DO Cep get maximum energy in longer times, while the geometries of the flaring
loops or areas get smaller.Comment: 18 pages, 8 figures, 5 tables, 2011PASA...28..365D. arXiv admin note:
substantial text overlap with arXiv:1206.579
Present status and preliminary results of the VLF/LF radio recording European network installed in 2009.
In January 2009 a European network of receivers able to measure the electric field intensity from various VLF/LF
broadcasting stations located throughout Europe, was installed. Five new receivers constructed by an Italian
enterprise have been delivered to Greece, Romania, Turkey and to the Italian team. The motivation of this effort
is to study the possible connections between the preparatory phase of earthquakes and perturbations in the
transmitted radio signals.
The receivers can be reached via ftp and gsm mobile connection, thus allowing a real time data collection. We
present here the status of the network and the various testing steps performed in order to achieve a correct set up.
We show how antennas variations, receivers locations and changes of selected frequencies affect the performances
of the whole network.
After this necessary testing period, several LF/VLF radio signals are now simultaneously and continuously being
sampled by the five receivers.
As a preliminary result we inspect also specific cases in which an anomaly in the radio signals is clearly related to
the transmitter or to the receiver (e.g. meteorological conditions around the sampling site). At a basic level, the
analysis adopted consists in a simple statistical evaluation of the signals by comparing the instantaneous values to
the trend of the signal
Wavelet analysis applied on temporal data sets in order to reveal possible pre-seismic radio anomalies and comparison with the trend of the raw data
Since 2009, several radio receivers have been installed throughout Europe in order to realize the INFREP European radio network for studying the VLF (10-50 kHz) and LF (150-300 kHz) radio precursors of earthquakes. Precursors can be related to “anomalies” in the night-time behavior of VLF signals. A suitable method of analysis is the use of the Wavelet spectra. Using the “Morlet function”, the Wavelet transform of a time signal is a complex series that can be usefully represented by its square amplitude, i.e. considering the so-called Wavelet power spectrum.
The power spectrum is a 2D diagram that, once properly normalized with respect to the power of the white noise, gives information on the strength and precise time of occurrence of the various Fourier components, which are present in the original time series. The main difference between the Wavelet power spectra and the Fourier power spectra for the time series is that the former identifies the frequency content along the operational time, which cannot be done with the latter. Anomalies are identified as regions of the Wavelet spectrogram characterized by a sudden increase in the power strength.
On January 30, 2020 an earthquake with Mw= 6.0 occurred in Dodecanese Islands. The results of the Wavelet analysis carried out on data collected some INFREP receivers is compared with the trends of the raw data. The time series from January 24, 2020 till January 31, 2000 was analyzed. The Wavelet spectrogram shows a peak corresponding to a period of 1 day on the days before January 30. This anomaly was found for signals transmitted at the frequencies 19,58 kHz, 20, 27 kHz, 23,40 kHz with an energy in the peak increasing from 19,58 kHz to 23,40 kHz. In particular, the
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signal at the frequency 19,58 kHz, shows a peak on January 29, while the frequencies 20,27 kHz and 23,40 kHz are characterized by a peak starting on January 28 and continuing to January 29. The results presented in this work shows the perspective use of the Wavelet spectrum analysis as an operational tool for the detection of anomalies in VLF and LF signal potentially related to EQ precursors
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