Time to go, step by step, into some explanations of
different terms I used in the previous posts like Trench, Richter Scale,
Convergence Boundaries, Subduction zone, etc. To do that a simple question
comes into mind : "Why on Earth do we have Earthquakes?"
No but frankly. As if it was not enough to face killer weirdos
around the world, we also have to deal with our own planet's periods, and in
both cases a lot of blood is shed. So Ma'am Earth as its own bad times and we,
poor humans, have to deal with it. Its not fair, she's stronger than us... But
hey, whatever. We are here, let's deal with it.
So really, "Why Do We Have Earthquakes" after all?
Usually, the first thing popping to mind is Plate Tectonic,
but, as a matter of fact, the real beginning of Earthquakes begins way down in
the depth of our planet.
Let's define what Plate Tectonic is all about first.
Although most of us think that the earth surface we live on is
a solid rocky place, it so happen that our planet's surface is not as solid as
it looks. It is made up of many pieces called Plates which interact with each
other. Those interactions are mostly unnoticed, but when we take notice of them
we feel it through what we call an Earthquake. And if that interaction between
the Plates is violent, the ensuing Earthquake is violent (and destructive as
well).
If you prefer a dictionary definition of what Plate Tectonic
is, here it is
PLATE TECTONIC noun.
A theory explaining the structure of the earth's crust and many associated phenomena as resulting from the interaction of rigid lithospheric plates that move slowly over the underlying mantle.
The best image of Plate Tectonic is the image of a gigantic Jigsaw
Puzzle in which each pieces fits with each other forming our Globe. The difference
with the Jigsaw Puzzle is that the Plates are always on the move.
Ok. Then arise another logical question - Why is it on the move?
To answer that one let's go down, deep inside the Earth.
Our planet is made up of 4 main layers (from center to
surface order).
Future posts will go in detail for each of those layers in another
post. For this post I will just establish the overall picture.
The Inner Core of our planet produces an enormous amount of
heat travelling through the Outer Core and the Mantle finally reaching Earth's
Crust (on the surface of which we live). On its way up, that heat generates
convection currents, and those currents are what makes the Plates move on the
surface as a consequence.
(Courtesy of peter-mulroy.squarespace.com)
A little Illustration of Convection at Work
As a simple illustration of what convection current are,
you can look at a casserole full of water on which you have poured some oil or like in the illustration blocks of light wood.
I will stick with oil since it is something usually present in any kitchen. Oil
and water unable to mix, the oil will float at the surface. Take the oil as the
Plates on Earth's Surface, and the water as what is under the Plate (i.e. the
depth between the Crust and the Inner Core). The fire under the casserole will
be our source of heat representing the heat coming from the Inner Core.
When you heat it up you will be able to see an increase of
bubbles forming at the bottom and raising toward the surface and reaching the
oil from underneath. As a result of the push of the bubbles against the oil,
the oil will move further from where the bubble raised to the surface, and
further, and further, and further after each bubble.
Each bubble is accompanied by heated water coming from the
bottom going toward the surface. That water loses heat once it reaches the
surface, and because it is colder it goes back toward the bottom to be
re-heated, again, and again in the same cycle. At the surface, the oil is
continuously on the move as a result. That's in bold strokes how things are
going on under our feet. Now just imagine that you are really tiny and living
on that moving oil, and you will have a basic idea of what we, humans, are on the
Surface of the Planet.
Now you have an idea of WHY the Plates on Earth's Surface
are moving. Considering that the Plates constantly under pressure from below
because of the Convection Currents are able to move, you have a prime reason
for the Earthquakes to happen at the Surface. And that's WHY basically we have
Earthquakes.
What I presented here is the very extremely super simplified
version of cause and effect of underground activity. In the futures posts I
will go a little bit deeper in details.
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