Earthquakes / Tsunami

Earthquakes / Tsunami

An earthquake also known as a quake, tremor or trembler is simply a shaking of the ground.

This is caused by the sudden breaking and movement of large sections (tectonic plates) of the earth's rocky outermost crust. The edges of the tectonic plates are marked by faults (or fractures). Most earthquakes occur along the fault lines when the plates slide past each other or collide against each other.

As the large plates shift, shock waves powerful enough to change the surface of the Earth are generated and these alter the surface of the Earth, thrusting up cliffs and opening great cracks in the ground and cause great damage ... collapse of buildings and other man-made structures, broken power and gas lines (and the consequent fire), landslides, snow avalanches, tsunamis (giant sea waves) and volcanic eruptions.

​How Do Earthquakes Occur? ​

Earthquakes send vibrations through the earth in much the same way as the ripples formed when pebbles are dropped into a pond. An earthquake occurs when rigid and brittle rocks near the earth's surface break suddenly. Vibrations known as seismic waves spread out from the point of fracture, known as the focus.

These shock waves spread upwards as well as outwards. On the surface of the earth, directly above where the earthquake has occurred, is the epicentre. This is where the greatest damage occurs.

The line along which the break occurs is called the fracture zone or fault. The break begins at a point and then runs along the fracture zone. This is called a rupture.

When the ground cracks/ breaks up and then relaxes again, buildings collapse, gas and water mains fracture, flooding occurs as rivers and lakes overflow and tsunamis (giant waves) may form at sea.

Some earthquakes only last a few minutes but others will have aftershocks that will occur for days or weeks afterwards. Scientists estimate that about a million earthquakes occur every year.

Often accompanies an earthquake. What happens in this process if the strength and stiffness of a soil is affected by the shaking of the ground caused by the earthquake.

It is responsible for a tremendous amount of damage that is done to structures – buildings and bridges, etc.

Liquefaction occurs in saturated soils. Sand usually contains water so the grains of soils and water are loosely packed. The shaking of the ground makes the grains of sand settle down more densely. The water cannot get out and so the soil turns

How a Tsunami Occurs ​ ​

​ A Tsunami is a series of waves, or "wave trains," usually triggered by an earthquake.

A. Between Earthquakes Stuck to the subducting plate, the overriding plate gets squeezed. Its leading edge is dragged down, while an area behind bulges upward. This movement goes on for decades or centuries, slowly building up stress.

Vertical Slice Through a Subduction Zone One of the many tectonic plates that make up Earth's outer shell descends, or "subducts," under an adjacent plate. This kind of boundary between plates is called a "subduction zone." When the plates move suddenly in an area where they are usually stuck, an earthquake happens.