Another strong earthquake claimed many victims in Myanmar. The interesting thing now is that the earthquake is 1000 kilometers away. What caused the buildings to fall… Eng. Ivan Kirmin spoke on the topic to FAKTII.
- Eng. Kirmin, the earthquake with a magnitude of 7.7 on the Richter scale that hit Myanmar on March 28 took the lives of over 3500 people. It turns out that the earthquake was of a rare type, called supershear. Let's explain what this is?
- Unfortunately, due to the political situation in Myanmar, data is scarce. Some sources already cite over 5,000 victims, others suggest over 10,000. There have been reports that in recent years, the devices that record earthquake data have also been drastically reduced due to budget cuts. Regarding the type of earthquake, it is important to say that the earthquake in Turkey in February 2023 was of a similar type. Unlike Turkey, the earthquake now occurs during the day and this is one of the reasons why the expected number of victims is lower. Also, unfortunately, it was cold in Turkey and many people took shelter in dangerous buildings that collapsed under the impact of the weaker, but still strong enough earthquakes, known as aftershocks. It seems to me that the economic aspect of such disasters is quite far behind, and the economic damage affects huge regions and many people in different countries. Without downplaying the tragedy of the loss of life, I would like to draw attention to the fact that if the damage is limited to a smaller area around the epicenter, if there is no damage from the weaker seismic effects, and they decrease with distance from the epicenter, then there will be more resources and it will be much easier to restore the affected region and help the population. Since, due to the civil war and the military junta in Myanmar, we do not have much information about the damage there, we can look at what happened in neighboring Thailand.
- The earthquake was 1000 km from Bangkok, and we can see the destruction. Why?
- Yes, I think this is quite impressive. Moreover, according to information from representatives of the insurance business, this concerns damage to tall new buildings that meet modern standards, while old low-rise buildings that were built before Bangkok even had requirements for anti-seismic construction were not damaged. The estimated amount that insurers in Thailand will pay out in compensation exceeds 2 billion euros, and this is for an earthquake with an epicenter 1000 km away. The quick answer is that in some cases the existing standards significantly underestimate the impact of earthquakes on tall buildings. In recent years, scientific studies have been conducted on the impact of earthquakes on buildings in Bangkok, which show serious deviations from the models that are embedded in the standards. I will try to briefly and simply explain this complex matter by analogy with the swing. I hope that colleagues will understand that in simplifying, I will miss some important details. I suppose everyone knows that in order for a swing to swing, you have to push it at a precisely specific moment, at a precisely specific interval. The same is true for buildings - each building has its own frequency and period, and if the impact coincides with them, then we have the greatest effect. Low buildings have short periods, high ones - long ones. In addition to the period, the force also matters - that is, in order to swing the swing maximally, you must apply the greatest force in a certain period. The standards stipulate that the energy of the earthquake is mainly in high frequencies, waves with short periods are several times stronger than those with long periods. Designers calculate on the assumption that low or medium-high buildings (6-7 floors) will be hit approximately 3 times harder than a 20-story building. However, in a 2023 study for the Bangkok area, peaks were found not up to 0.6 seconds, but from 2 to 10 seconds, which are the periods of high and very high buildings. Approximately over 20 floors. A similar effect - a discrepancy between the standard and the impact over long periods - has occurred in other places in recent years, as well as in the earthquake in Turkey. This was the reason why the damage in some cities was much greater than in other places.
- We saw footage of tall buildings connected by thermal connections breaking but not falling. How do they hold up?
- The problem is different. Why is there any damage at all in this earthquake, which is 1000 kilometers from the epicenter? These buildings should not have any problems, and the damage is in billions of euros. In my opinion, this is mainly due to the above-described problems with soft soils and there is no one to blame. As they say - we continue to learn.
- And we saw how a building collapsed… Why?
- This is extremely shocking and is the only case in history that I know of a collapsed structure 1000 kilometers from the epicenter. The way in which this building is being destroyed shows that in addition to the above-mentioned inconsistencies in the impact with the standards, there are also some gross errors in design and execution. A new building, even if it collapses in an earthquake, should not collapse like this, but should deform in a way that leaves spaces to increase the chance of survival of the people in it. There is also something sinister in the fact that it is the new building of the Court of Auditors of Thailand under construction.
- If such an earthquake occurs in our country…
- I am more worried about milder earthquakes, because they are more likely and cause only material damage. The probability of an earthquake with the strength of the Pernik earthquake in 2012 with an epicenter in Sofia is not negligible, but then we will have significant material damage and hopefully without human casualties. As I mentioned, I prefer to focus on economic damage. Sofia is located on soft soils, which is a kind of analogy with Bangkok and in order to rank at least with Thailand and Turkey, this issue must be studied. Moreover, in 2012 - during the Pernik earthquake, higher than expected impacts were registered in the long periods and scientists from the Bulgarian Academy of Sciences in a report “SEISMIC IMPACT OF THE EARTHQUAKE OF 22.05.2012 ON THE CITY OF SOFIA – ANALYSIS AND ASSESSMENT BASED ON INSTRUMENTAL REGISTRATIONS“ make the following conclusions, I quote: “Special attention should be paid to the specific type of spectrum for the NS component of the SGFI station. A plateau of almost identical response is observed for a very wide interval - periods from 0.2 seconds to about 2 seconds (frequencies from 0.5 Hz to 5 Hz). This essentially means that buildings with radically different dynamic characteristics have suffered almost the same seismic forces.”
And the scientists from the Bulgarian Academy of Sciences call for financial resources to be provided for the study of this phenomenon. Since 2012, of course, none have been provided.
Few people realize that seismic risk is paid for today and now, and not only after an earthquake. The price of insurance for earthquake damage is determined based on this risk. Ultimately, insurers are reinsured in several global insurers, which determine the price based on research by international teams. The World Bank has prepared a report on seismic risk in Bulgaria in 2021, in which direct damage, depending on the strength of the earthquake, is estimated at up to 9 billion euros. And the lack of action, including on the above-mentioned problem, leads to higher insurance prices. They are paid not by the construction entrepreneur, but mainly by people with mortgages, i.e. by the young, active, knowledgeable and capable Bulgarian.
I think that we are too worried about disrupting the comfort of investors and the indiscriminate construction of high-rise buildings in Sofia, without adequate requirements for them, which would make construction more expensive. In this way, in fact, we are picking the pockets of our most valuable resource - the young. Maybe it is time to rethink our priorities.