1. CHAPTER 4
Earthquakes

2. Waves
Seismic waves or shockwaves are the vibrations of energy created from the plate movement that causes an earthquake.
Primary waves are the first to arrive and can travel through liquids, solids and gases. Despite being the fastest travelling wave, they do not have much energy and do not cause any damage
Secondary waves arrive after primary waves and have much more energy. Secondary waves cause the crust to move up and down, making the ground shake more noticeably than the primary waves do.
Surface waves arrive after secondary waves and are responsible for almost all damage caused during an earthquake. The waves move slowly along the surface, moving it up and down as well as from side to side.

3. Parts of an earthquake
Earthquakes into the following four parts: fault line, focus, epicentre and seismic waves
The fault line refers to the gap between two tectonic plates, or fractures in rock caused by plate movement.
The focus is the point where the earthquake begins. The focus can be deep in the fault line or at a shallow depth.

4. Parts of an earthquake
The epicentre is the point on the surface, directly above the focus. The epicentre is the shortest distance from the focus for shockwaves to travel before reaching the surface.
Seismic waves or shockwaves are the vibrations caused by the earthquake. These are strongest at the epicentre. The further from the epicentre that seismic waves travel, the less energy they will have.

5. Measuring Earthquakes
Seismologists use an instrument called a seismograph or seismometer to record the waves of energy released by an earthquake. The data collected is then expressed on three different scales.

6. Measuring Earthquakes
Richter scale: Readings from an seismograph can be recorded on a Richter scale. The scale measures the magnitude of earthquakes. The scale begins at 0 and has no upper limit, although the highest magnitude ever recorded on the scale was 9.5, from the Chilean earthquake of 1960.
Moment magnitude scale: The moment magnitude scale (MMS) combines seismograph readings with the amount of rock movement at a fault. MMS readings are considered to be more accurate than the Richter scale for earthquakes above 7.0 and usually record a higher reading. Modified Mercalli scale: The Modified Mercalli scale is an older form of assessing the power of an earthquake. The scale does not use any mathematical formula for measurement, instead relying on the visual damage caused as an indication of strength. There are 12 grades on the Mercalli scale with I representing little damage and XII represent the total destruction of an area hit.

7. Locations of Earthquakes
Nearly all earthquakes across the globe occur at plate boundaries, with 80 per cent of all seismic activity occurring along the Pacific Ocean’s subduction zones.

8. Predicting Earthquakes
Despite large amounts of time and money being spent on the prediction of earthquakes, it remains an almost impossible task.
Generally, there are three methods of earthquake prediction, none of which is universally accepted as being accurate. They are: monitoring the behavior of animals, researching historical records and measuring rock stress. Monitoring stress levels in rock along fault lines is seen as the most reliable form of earthquake prediction.

9. Effects of Earthquakes (Infrastructure)
Earthquakes can cause damage to infrastructure. The vibrations in the crust cause buildings and bridges to sway and crumble. This falling debris is very dangerous and causes many deaths.
The Haitian earthquake of 2010 caused widespread damage to infrastructure in the capital Port- au-Prince. The buildings in Port-au-Prince were poorly built, meaning that the 7.0 magnitude earthquake caused them to collapse.

10. Effects of Earthquakes (Tsunami)
When earthquakes occur beneath the sea, they can produce huge waves known as tsunamis.
As one plate subducts, the overlying plate can be forced upwards in a sudden movement. The uplifting of the plate causes an excess hump of water on the surface of the ocean. If, for example, the plate is uplifted by 4 m, a 4 m hump of water is created on the ocean’s surface. This excess water radiates (spreads) outwards in all directions/
Most tsunamis are created by uplifts of less than 1 m. However, more powerful earthquakes, such as those that occurred in Indonesia in 2004 or in Japan in 2011, create much larger waves.

11. Effects of Earthquakes (Liquefaction)
During an earthquake, the intense shaking of the crust can cause soil to become saturated with groundwater. When this occurs, soil takes on the properties of a liquid (like quicksand). This process referred to as liquefaction.

12. Reducing the Effects of an Earthquake
Although earthquakes are nearly impossible to predict, the damage caused can be greatly reduced through the correct planning and response. Three such methods are:
Earthquake-proof infrastructure: In earthquake zones such as California and Japan, strict building regulations have reduced the damage caused to infrastructure, saving countless lives.
Efficient Urban Planning: In earthquake zones such as California and Japan, strict building regulations have reduced the damage caused to infrastructure, saving countless lives.
Early Warning Systems alert people to seismic activity before it arrives. They work by receiving messages from a network of seismographs that detect primary waves. The length of time between the alarm warning and the arrival of the destructive secondary and surface waves depends on the distance of the epicentre from the area.

13. Japan 2011
On 11 March 2011, an earthquake measuring 9.0 on the Richter scale struck off the coast of Japan. Then earthquake occurred on a subduction zone along the Eurasian Plate and Pacific Plate boundary. Japan has the most advanced earthquake/tsunami warning system in the world. The system delivered warning to the Japanese a full minute before the tremors reached land. All residents also received a text message to their phones warning them of the earthquake and tsunami. The earthquake triggered a 39 m high tsunami that devastated the eastern coast of Japan

14. Japan 2011
The waves were so high that they breached Japan’s tsunami defense system. The waves rushed as far as 10 km inland, destroying buildings and other infrastructure. Many buildings that were destroyed contained people who had fled to the higher floors for safety.
The waves also destroyed the cooling system for the Fukushima Daiichi Nuclear Power Plant, causing a catastrophic meltdown. Radioactive waste still leaks from the power plant into the Pacific Ocean every day. This has destroyed marine habitats and made the surrounding area uninhabitable. In total, over people were killed, most of whom were drowned by the tsunami. Some buildings were completely destroyed, while a further 1 million buildings were damaged.