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Scientists from the VAN group are warning for a strong earthquake of 6 on the Richter scale

08 August 2011 / 20:08:05  GRReporter
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Specialists are paying particular attention to the seismic activity in the region around the Gulf of Patras. The yesterday's earthquake 4.7 on the Richter scale in Navpaktos raised their concern. According to the seismologist from the National Observatory of Athens Dr. Yerassimos Houliaras, the epicentre of the earthquake was about two kilometers southwest of Navpaktos and its focal depth was 5 km.

The residents of the city felt the quake but there was no panic. Deep cracks formed on a three-storey building, which housed 40 people until yesterday. The residents of the 14 flats now are staying at a hotel at the expense of the municipality in order to ensure their safety.

An earthquake of 4.1 on the Richter scale was recorded in the sea area around Chalkidiki peninsula a little earlier. Experts said its epicentre was located 86 km east of Larissa, and its focal depth was 10 km.

According to Yerassimos Houliaras, on June 24 the Professor in the Department of Physics at the Athens University and the head of VAN group Panagiotis Varotsos published a report in the University of Cornwall on the high seismicity of the region, making conclusions based on signals received from the station in Pyrgos. The so-called VAN group for predicting earthquakes even received a signal that an earthquake of over 6 on the Richter scale could be anticipated.

The VAN group, which was named after the first letters of the families of the scientists involved in it Panagiotis Varotsos, Caesar Aleksopoulos and Konstantinos Nomikos makes its predictions using the eponymous test method which is based on the detection of seismic electric signals.

Seismic electric signals appear during the mechanical loading of the rocks in a tectonic cleft that forms before the seismic waves. They are the result of the piezoelectric behaviour of many minerals such as quartz or the migration of defects in the crystal lattice. The width of the electrical seismic waves is directly related to the magnitude of the impending earthquake.

Devices, which consist of electrodes placed in the soil, amplifiers and filters capture the seismic electric signals and telemetrically transmit them through telephone lines to the headquarters of the VAN group, which registers them.

In order to separate the specific signals from any electromagnetic interference, each station of the group has at least two perpendicular pairs of electrodes with a length of several kilometers and several other pairs of electrodes of smaller length.

The method of the VAN group is adopted as a tool for studying the earthquakes and seismic activity in Japan. Recently, scientists have studied the magnetic field that follows the electric field of seismic electric signals. It is believed that the monitoring of magnetic disturbances could be a preliminary warning for underwater earthquakes. Although the signal from the magnetic interference is weaker than that of seismic electric signals the time difference between them helps to calculate the distance to the epicentre.

From its very appearance in the early 1990s until today, the VAN group is the subject of sharp criticism from Greek seismologists. Often, the hot disputes took place on the TV and had no particularly positive audience response. Most of the seismologists deny the method, while some others are positive about the findings of the scientists group.

The reliability, accuracy and the use of the VAN method continue to be the subject of lively scientific debate abroad. Today, the group is housed in the Institute of Solid State Physics at the Athens University.

Tags: SocietyEarthquakeMagnitudePredictionSeismic electric signalsVAN group
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