The plates of the earth move due to the movement of convectional currents in the mantle below the crust. This is called as the endogenetic force as the energy comes from within the earth. At a destructive plate boundary (convergent boundaries) the plates push against each other or slide past each other. This action causes a build up of pressure over time.
Sometimes one of the plates will slip to release the pressure that has built up. The central location of this activity is called the focus of an earthquake. Tremors or shockwaves travel from the focus and causes the ground to shake. Buildings or structures that are above the focus of an earthquake may be heavily damaged or may collapse. The region directly above the focus receives most power from the earthquake and is called as the epicentre.
Earthquakes that occur on the sea floor could cause tsunamis.
Damage caused by Earthquakes
The shockwaves of an earthquake are measured using a seismograph. The Richter Scale is then used to classify the size/energy/magnitude of the earthquake. The Richter Scale has values ranging from 1 to 10, where 3 is a minor earthquake and 7 is a major earthquake. The size of an earthquake of 7 on the Richter Scale is ten times more powerful than one of 6 and 100 times more powerful than one of 5.
The damage caused by an earthquake depends on a number of factors:
- The magnitude (size) of an earthquake.
- The depth of the focus.
- They type rocks and soil through which the waves travel.
- How close the epicentre is to a city.
The Mercalli Scale is used to measure the the damage/effects caused by the earthquake. It has values ranging from 1 to 12, where 1 means no damage and 12 indicated complete devastation.
Reducing the effects of earthquakes
- The damage caused by earthquakes could be reduced by enforcing the construction of earthquake proof buildings at risk zones.
- Use shock absorbers in buildings to withstand the effects of earthquakes.
- Have an emergency plan to cope with earthquake disasters.
Plate tectonics tells us where earthquakes and volcanic eruptions are likely to occur but is is more difficult to predict or forecast when earthquakes are likely to occur. Earthquakes may be predicted by the using some of the following methods:
- Observing animal behaviour. Animals are more sensitive to tremors in the crust.
- Monitoring of seismic activity using the reading from seismographs to indicate the build-up of stress in the crust.