CAUSE OF EARTHQUAKE

 

CAUSE OF EARTHQUAKE

 The Earth and its Interior

Long tome ago, a large collection of material masses coalesced to form the Earth. Large amount of heat was generated by this fusion and slowly as the earth cooled down, the heavier and denser materials sank to the centre and the lighter ones rose to the top. The differentiated earth,  consists of four elements:

       i.          The inner core of radius Ω 1290 km

     ii.          The outer core of thickness Ω  220 km

   iii.          The mantle of thickness Ω 2900 km and

   iv.          The crust, of thickness Ω 5 to 40 km

The inner core is solid and consists of heavy metals (e.g. nickel and iron) while in the crust consists of light materials (e.g. basalts and granites). The outer core is liquid in form and the mantle has the ability to flow. At the core, the temperature is estimated to be 25000 C, the pressure 4 million atmospheres and density 13.5 gm/ce: this is in contrast to 25° C, 1 atmosphere and 1.5 gm/ce respectively, on the surface of the earth..

The Circulations

Convection currents develop in the viscous mantle, because of prevailing high temperature and pressure gradients between the crust and the core, like the convective . The energy for the above circulations is derived from the heat produced from the incessant decay of radioactive elements in the rocks throughout the earth's interior. These convection currents result in a circulation of the earth's mass; hot molten lava comes out and the cold rock mass goes in the earth. The mass absorbed eventually melts under high temperature and pressure and becomes a part of the mantle, only to come out again from another location, some day.

Tectonic Plates:

The convective flows of Mantle material cause the Crust and some portion of the Mantle, to slide on the hot molten outer core. This sliding of Earth's mass takes place in pieces called Tectonic Plates. The surface of the Earth consists of seven major tectonic plates and many smaller ones These plates move in different directions and at different speeds from those of the neighboring ones. Sometimes, the plate in the front is slower, then, the plate behind it comes and collides and mountains are formed. On the other hand, sometimes two plates move away from one another and rifts are created. In another case, two plates move side-by-side, along the same direction or in opposite directions. These three types of inter-plate interactions are the convergent, divergent and transform boundaries, respectively. The convergent boundary has a peculiarity (like at the Himalayas) that sometimes neither of the colliding plates wants to sink. The relative movement of these plate boundaries varies across the Earth; on an average, it is of the order of a couple to tens of centimeters per year.