A deadly combination of earthquake properties and regional characteristics resulted in one of the worst disasters in Afghan history
It is already one of the worst earthquake disasters in the country's history, although the exact extent is still not fully understood. At least 1045 dead, hundreds injured and villages that no longer exist. The nightly earthquake in south-east Afghanistan took people by surprise and claimed many lives. More than one would normally expect from an earthquake of this magnitude. There are many reasons for this fatal outcome. So many that, looking back, one can say: It was the perfect disaster.
Magnitude 5.9 to 6.1. There is some uncertainty in the final earthquake magnitude determination, mainly due to the patchy seismic monitoring network in Central and South Asia. But magnitude, regardless of the exact number, is rarely the primary cause of catastrophic impact. It is much more the interaction of different properties of the earthquake and in the affected region. In Khost and Paktika, the affected provinces, many, if not all, of the crucial factors came together: .
The closer an earthquake hypocentre is to the surface, the stronger the shaking. If it originates in only a few kilometres depth, there is less rock in between that could dampen the earthquake waves than at from depth of 100 kilometres. The Khost earthquake occurred at a depth of about seven kilometres. There is some uncertainty, but that's less than an average earthquake. The intensity of the shocks was therefore higher than in most other cases.
Where people live, people can die. Of course, if many people live in the immediate vicinity of the epicentre, the probability of fatalities is higher. Although Khost and adjacent areas are not the most densely populated areas of the country, they still have a relatively high population density, comparable to more rural regions in Central Europe. In addition, the lower population density is also an influencing factor for the next point.
The mud houses and structures built in large parts of the country are not match to withstand such magnitude earthquakes. These houses dont adhere to the building code. They are simply reduced to rubble, resulting in precious loss of life. pic.twitter.com/S6z7EYqDwm— BILAL SARWARY (@bsarwary) June 22, 2022
In many rural regions of Asia (but also in southern Europe) buildings are traditionally built and often relatively old. In Afghanistan, it is the classic adobe houses that are constructed to suit the climatic and natural conditions but offer no protection in case of an earthquake. Even comparatively weak earthquakes can bring these buildings down and endanger people who are inside. How many people are at risk usually depends on the…
If an earthquake hits during the day, many people are usually outside. The current one, however, happened at night and thus at a time when pretty much everyone was asleep in bed. So, collapsing buildings were full of people.
“One family lost 17 male and female members in Gayan.” Source : https://t.co/3qL2u7dpR3— BILAL SARWARY (@bsarwary) June 22, 2022
In Afghanistan, many people live in the same household and often sleep in the same room. Ten or more residents per household are not uncommon. One collapsing building alone can claim many lives there. In the current case, there are reports that even a whole family of 17 living in one house was killed. In addition, the escape time increases with the number of people if there is only one door or window. Time that didn't exist here anyway.
Seismological evaluations showed that the earthquake itself, the rupture process, lasted only three seconds. Three seconds in which a huge block of rock has shifted by ten centimetres. On average, magnitude 6 earthquakes take about five to ten seconds. What may seem positive at first glance becomes the complete opposite if you take the energy into account. (Note: The duration of the noticeable tremors increases with distance from the epicenter due to reflections within the rock layers. Testimonies that describe a duration of more than 30 seconds therefore do not contradict the measurements.)
Magnitude 6.1 #earthquake in southern #Afghanistan exactly one hour ago (2022-06-21Z20:54). Absolutely extraordinary signal on station IU.KBL (Kabul, Afghanistan - obtained via @IRIS_EPO). Hopefully not too deadly or damaging.https://t.co/iCHAqFFBJ2 pic.twitter.com/V3Ng4oz2gQ— Dr. Steven J. Gibbons (@stevenjgibbons) June 21, 2022
It is not the duration of the earthquake that determines the magnitude (on this scale), but the energy released. Two earthquakes of the same magnitude release the same energy. If an earthquake lasts longer, this means that the energy can unfold over a longer time, so the individual waves are weaker. However, the Khost earthquake was very brief, meaning that all of the energy was released within a few seconds. Or with other words: It was the first wave that has already caused houses to collapse. Escape time, already extended by points 4 and 5 anyway, almost 0. Hardly anyone was able to save themselves in time.
Anything that can go bad has gone bad. A very shallow earthquake hit a densely populated region where most houses are vulnerable. The time to rescue, which is hardly realistic anyway due to the high number of residents and night time, was reduced to 0 by the physical properties and at the same time the potential for destruction, which was already there, was further increased. An earthquake like out of a movie. A real horror movie that thousands of people didn't survive.