Earthquake expo

Today, we will talk about the earthquakes

1 - What is an earthquake

An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.

2 - Where do they happen?

Earthquakes at plate boundaries

Most earthquakes occur in a few narrow bands that stretch across the planet. These narrow bands are where plates meet and push, pull and grind past each other.

More than 80 per cent of the planet’s earthquakes are caused by just one plate. The Pacific Ocean Plate, as it knocks and scrapes the other plates around it.

Intraplate earthquakes

While most earthquakes occur at plate edges, some happen towards their centre. When plates collide, land either side of the boundary can crumple up for hundreds of kilometres causing earthquakes far from the plate edges.

These intraplate earthquakes are rare. There can be hundreds even thousands of years between them. During this time, cities can grow, and the inhabitants may be unaware of the dangers.

3 - Dangers after the quake

Dangers after the quake

The danger doesn’t stop once the ground has stopped shaking. Fires, landslides and even liquefaction can all cause further damage and loss of life:

The biggest threat comes from the sea. If an earthquake strikes underwater, it can trigger a giant wave called a tsunami. As the wave speeds towards the coastline, it grows taller. When it finally reaches the shore, it can flood inland for many kilometers.

I will explain the dangers more specifically :

Landslides

The shaking of an earthquake can causer ground on steep slopes or on weak sediment to give way-a landslide, they can destroy everything in their way and bury homes, roads and people.

Liquefaction

Earthquakes can do strange things to soil. They can turn it into liquid, a process called liquefaction. Usually clay-rich soil sticks together, trapping water in its pores. But during an earthquake the shaking destabilizes the clay and releases the water.

      Fire

The shaking experienced during an earthquake can lead to fire. Cooking stoves fall over. Electrical wires spark and gas pipelines rupture Fire-fighters can’t always reach these fires.

4 Impact Scale

There are different ways of measuring earthquakes. Unlike the Richter scale, which measures the magnitude of the shaking, the Mercalli scale measures the amount of damage caused – the loss of life and damage to buildings.

The higher an earthquake’s magnitude the greater the devastation, especially when it strikes near populated areas. But you also must factor in the depth of the earthquake, and how well people have prepared. A big earthquake could have a low Mercalli value if it happens deep underground or if buildings have been properly supported.

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