5 days after the earthquake, the devastating earthquake in Myanmar of 28 March of magnitude 7.7 He caused not only destruction but also over 2700 victims and 4500 injured in the ex-birma (but the balance is still temporary), in addition to the collapse of a skyscraper in Bangkok, Thailand, more than 1000 km away: a 26-year-old young man has recently been extracted alive from the rubble and believed there are many other people trapped among the remains of the fallen buildings. But how is it possible from a geological point of view that an earthquake causes so much damage? Let’s analyze the features of fault sagaing, The responsible of this disaster, taking a recent Ingv publication as its main reference.
The characteristics of the sagaing fault that caused the earthquake in the ex-wheery
There sagaing fault It belongs to a complex fault system that runs in the north-south direction in the central portion of the country. This system allows the sliding between the Burma plate and that of Probe: Just this movement is responsible for activating the sagaing fault. From a geological point of view, it is a spending fault about 1200 km long, even if in the case of the earthquake in question they are a stretch went against a break.
At first, the length of the breakdown of the fault was calculated using data from distant seismometers – such as those USGS in the USA. These first models have returned a length of about 200 kmfor a total duration of about 90 seconds.
The March 29th A second model was produced which provided for a value of 350 km and, finally, on March 31 a last model that hypothesizes an even longer and equal breakage 400 km. It is therefore a double value compared to what was initially hypothesized.
With these two data – length and time – it is also possible to estimate the speed to which the rupture took place which, in this case, is equal to 4.4 km/s. This is a value more than double Compared to what could be expected normally, and therefore it is believed that this event is part of a special class of breaks of fault called “supershear“. With this term all those phenomena are indicated in which the breakdown of the fault is faster than s wavesi.e. the cutting waves (or secondary) that we warn during an earthquake. The name “secondary” is linked to the fact that they are the second waves that we warn after an earthquake, since the former, the P waves are much faster and have a speed that is often over 7 km/s.
Having said that, what are the practical implications of a break of fault of this type?
Because the earthquake in Myanmar has caused so many victims and damage
A break supershear generates ashock wave towards the break. This means that some areas will be affected simultaneously by a series of Overlapping S waves and linked to the different moments of the break, going to generate amplified shaking and, consequently, More damage to things and people.
Below is an image that summarizes the main earthquakes in the last few days in the area. The size of the circles indicates their magnitude, while the color indicates the day they took place. As we can see the main earthquake has reached magnitude 7.7, while the consequent shocks related to the seismic sequence are mostly between magnitude 3.0 And 5.5.
A great question of this earthquake is how he did to cause so much damage to Bangkok, to over 1000 km away from the epicenter. As we have seen, the breakdown of the fault is 400 km long and therefore the distance between the shocks and the Thai city, in reality, is of “Just” 600 km. Obviously this does not completely clarify how he has made a whole skyscraper under construction: probably in addition to this closeness, a phenomenon of amplification given by the local geological, linked to the presence of alluvial sediments.
To learn more, here is an ad hoc video on the subject:
