Reason why mountains are not vulnerable to earthquake

Introduction

Natural disasters are very frequent nowadays in the whole world. Earthquakes are the phenomena which has been very frequent in recent times specially in the Asian region. Even the biggest and strongest structure of the world are always prone to earthquake.

But have you ever wondered why the mountains having a height of few kilometres are never vulnerable to earthquake ? Why Burj Khalifa having the height of only around 600 metres is prone to earthquake. But Mount Everest having a height of around 9 km is safe from earthquake ?

This reason can be explained through the theory of isostasy. It is a very complex theory but I will try to explain it in the simplest words.

Theory of Isostasy

As we know the earth's crust is divided into two layers. The upper layer comprises of silica and Aluminium ( SiAl ). The lower layer comprises of silica and magnesium ( SiMa ).  The  depth of SiAl and SiMa layer variates from place to place. This variation depends upon the rock structure of that particular place. It is very uneven all over the surface of Earth. The depth of SiAl and SiMa variates according to the rock structure of the landform and also the height of the landform.



For example if the landform is a mountain and is made up of lighter rock materials then it will have a greater depth of SiAl. And if the landform is a depression then it will have a greater depth of SiMa.

Reason

Now I will try to explain the reason in the most simplest form. As we know we construct basements in the large structures to make it more stable and make it earthquake safe. But how does the basment protect the structure from earthquake​ ?

The reason is that when the basement is constructed below the Earth surface, the centre of gravity of the structure is lowered down. The centre of gravity comes closer to the surface which makes it safe from the earthquake. Similar condition is with the mountains the upper layer of the crust that is SiAl is its basement. The height of basement in the case of mountains is more than the height of the Mountain above the surface. For example in case of Mount Everest the height of the mountain is 8850 metre where as the height of its basement is around 40 kilometres. This makes it very stable as its centre of gravity is very much inside the Earth surface.

This is the reason why Mountains are not vulnerable to earthquakes and remain steady in disastrous scenarios too.