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The epicenter of the earthquake that plagued Plovdiv and was experienced in much of the country is located in the industrial area of the city of Rakovski. This is derived from the first official data published on the website of the Bulgarian Academy of Sciences.
According to the European Seismological Center, the magnitude of the earthquake is 4.5 Richter. Its epicenter is 135 kilometers east of Sofia and 13 kilometers northeast of Plovdiv. According to BAS, however, the magnitude of the earthquake is 4.1 and it is 2.7 kilometers deep.
Director of Seismology of the National Institute of Geophysics, Geography and Geodesy (NIGGG) of the Bulgarian Academy of Sciences (BAS) Emil Botev in an interview with the Focus Agency on the earthquake in Plovdiv on May 1.
– Mr Botev, yesterday there was an earthquake in the Plovdiv area. What seismic zone was the earthquake in?
-This is the Maritsa Seismic Zone or the Upper Thracian Plain. In this case, it was not the Marishka fracture line, but the fracture line separating the upper Thracian plain from the middle mountains. We call it the Chirpan fracture line, because to say 30-40 kilometers east of yesterday’s earthquake is the epicenter of a very powerful earthquake of April 14, 1928, magnitude 6.8, when just over 20 people die and hundreds are killed. wounds. , with total destruction in Chirpan and the surrounding villages. This is the same fault line that runs west of the city of Rakovski. They know that the epicenter of this earthquake yesterday, which is much smaller than the great earthquakes of 1928, we define this epicenter as in the villages of Stryama and Momino selo.
What does the experience in the Mariska Seismic Zone show? How strong can an earthquake be?
– The earthquakes are related to the contacts of the Thracian High Plain, or the Mariska Seismic Zone, with the surrounding mountain ranges to the north with the Middle Mountains, to the south with the Rhodopes. These contacts have caused very strong earthquakes. They are Richter 7 magnitude and greater. For example, we have already said about April 14, 1928. 4 days later, on April 18, a 7.1 magnitude earthquake in Richter became the epicenter around Popovitsa.
This earthquake kills 100 people and perhaps thousands were injured. In 1928, earthquakes were superficial. At the surface there are such fissures in the earth’s surface that they reach up to a meter and a half in height on both sides of the fault. Compared to previous earthquakes, yesterday, as in most cases, it is very weak.
Now we can say that it has a slightly more serious impact on the city of Plovdiv, despite the fact that the epicenter is located 20 km northeast of Plovdiv. The rift itself is 18 km deep. The break is along this fault line, which limits the upper Thracian plain. The Plovdiv region is on a very low surface. It is a decaying lowland for millennia, and in fact, two fords rise: the Middle Mountains to the north and the Rhodope Mountains to the south.
Apart from these two very strong earthquakes of magnitude 7 and greater than 1928, there were no earthquakes of magnitude greater than 6, and in the last four decades, we have several thousand micro earthquakes of magnitude less than 3 Richter and dozens like yesterday. These earthquakes in the Thracian High Plain are three to four years old. The last 4.7 magnitude earthquake was on February 21, 2018. But it was on the southern board of the upper Thracian plain in contact with the lowlands with the Rhodopes, from Plovdiv to Assenovgrad.
Ten years ago, there was also an earthquake towards Krumovo, which was quite shallow, not like yesterday at 18 km depth, but 2-3 km depth. Then ruptures occur on the surface itself and there the displacements are greater and the impact specifically at the site of the rupture in the epicentral zone is much more severe.
At that time it was around Krumovo and had a very serious series after the earthquake with great impact on the settlements. This earthquake, which occurred yesterday, in fact as a result of the collapse of the Upper Thracian Plain along the sloping contact of the Middle Mountains to the south, is a mechanism to direct initial seismic energy to Plovdiv. Therefore, in the city of Plovdiv there was a slightly more severe impact on the surface.
– Easy, people. Are more secondary earthquakes expected?
-No earthquake in the Thracian High Plains, of the same magnitude as yesterday, in any of the tenths of four decades has a major earthquake followed. Usually, as before, they are followed by a serious series of post-concussion micro earthquakes. As of yesterday, we have more than 50 micro earthquakes, most of them are registered only at the Plovdiv station. They have a magnitude of about 1 and a little larger. The strongest of all earthquakes has a magnitude of 2.7 Richter.
-What are your tips for earthquakes? What should be the first thing we do?
The first thing is not to think what to do when the earthquake occurs, but to avoid it. The exact time of future earthquakes is known worldwide in extremely rare cases. Far below 1%, strong earthquakes are forecast. Therefore, they roughly know where these earthquakes occur and people who know the maximum power of the earthquakes expected near them will simply prepare in advance. It is a good idea not to have objects so easily moved on shelves that they can easily fall under any influence.
The building stock must be maintained with the required resistance, and not as it turned out in Plovdiv, many of the old houses were not maintained and suffered damage. Preliminary preparation is very important. You must know what are the healthiest places, what walls are they supporting, to be able to adapt to them and to know and have the exact preparation of where to stop. It is best to deal with some very sturdy furniture when the earthquake strikes, so that if something falls from above it gets hit. It’s also best to stand under some kind of metal frame, which is usually the front door, so that you can stabilize yourself in the event of a very strong earthquake. The most important condition for a person not to panic.
We affirm that we are safe at the moment in the event of a very severe earthquake, which can have a devastating effect on people’s homes, especially newer homes. Six of these earthquakes occurred at the beginning of the last century, and the frequency of these earthquakes is very high. He is 250 years old on average. We accept that at this time there is no evidence of high voltages that may again cause such earthquakes.
Rather, they are loosened. We believe that the tension has eased in the coming decades. The upper Thracian plain is, in another episode, a standard for the area of seismicity, not bottom. As mentioned, on average, 3-4 such an earthquake necessarily occurs without a major earthquake affecting the infrastructure.
Not so for nearby seismic zones, which have a much higher frequency, outside our country, but with impact. They have a much higher frequency of very strong magnitude earthquakes for 7 years and long ago colleagues in Turkey expected an earthquake near Istanbul. Already in the Sea of Marmara, unlike the Sea of Smyrna, at the beginning of the century, remember, in 1999 and 2000 there were two earthquakes of magnitude greater than 7 and larger that caused devastation and up to 20,000 casualties.
Also in Vrancea, Romania, which is one hundred kilometers north of our territory. The seismic source is deep there and the frequency of catastrophic earthquakes is 30-40 years. One of them was on March 4, 1977, when 125 people died in Svishtov from the fall of two large buildings: a hostel and a large apartment block.
The interview was taken by Theodora Patronova
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