Effects of Earthquake

The destructive effects of an earthquake can be classified into primary and secondary effects.

Primary effects are the immediate damage caused by the quake, such as collapsing buildings, roads and bridges, which may kill many people. Those lucky enough to survive can suffer badly from shock and panic.

Secondary effects are the after-effects of the earthquake, such as fires, tsunami, landslides and disease.

•   Fire - earthquakes destroy gas pipes and electric cables, causing fires to spread. Broken water mains prevent the Fires being extinguished. Fires spread very quickly in cities, especially in poor-quality housing areas where wooden buildings are common.

•   Tsunamis - an earthquake on the sea floor or close to the coast may cause huge waves.

•   Landslides - earthquakes often cause landslides, especially in steep river valleys and areas of weak rocks.

•   Disease and famine - fresh water supplies are often cut off causing typhoid and cholera. Lack of shelter and food causes much suffering.

•   soil liquefaction when soils with a high water content are violently shaken they lose their mechanical strength and behave like a fluid and so buildings can literally sink.

•   Fukushima nuclear power station

Shaking: Seismic waves vibrate the ground causing collapse of building and other structures, as well all trees and other plants. Faulting and Ground Rupture

Fires

Fires, often associated with broken electrical and gas lines, is one of the common side effects of earthquakes. Gas is set free as gas lines are broken and a spark will start bringing "inferno". To complicate things water lines are broken and so there is no water to extinguish the fire. The San Francisco earthquake of 1906 caused 90% of damage by fire.

Tsunamis

For sure, one of the most dangerous effects of an earthquake is a Tsunami. Tsunamis are giant waves that can cause floods and in some cases may reach up to 100 feet in height. These deadly waves strike a great distance from the epicentre. Tsunamis often result from sub-sea faulting of ocean floor sending seismic shocks through the water and creating large waves of low amplitude but of long period, moving at 500-700 mph.

Figure 1 http://www.sms-tsunami-warning.com/pages/earthquake-effects#.WCYE-2ViZ7Y

Landslides and ground subsidence

Avalanches, landslides, rockslides are triggered by ground shaking. These landslides are often more destructive than the earthquakes as they plough through villages and other developments. Often unstable regions of hillsides or mountains fail. In addition landslides can cause problems when they block roads, which makes it difficult for emergency and rescue operations.

Liquefaction of water-laden sediments: A process by which water-saturated sediment temporarily loses strength and acts as a fluid.

Groundwater, sand and soil combine during seismic shaking to form liquefaction during a moderate to powerful earthquake. A quicksand like soil is the result of this process. When liquefaction takes place under buildings the foundations sink and the building collapse. After the earthquake has passed, the soil firms again and the water settles deeper in the ground. Areas with sandy soil and groundwater close to the surface are far more at risk of liquefaction.

Ground Rupture: The movement of the ground along one side of a Fault relative to the other side, caused by an earthquake. When an earthquake event occurs, ground rupture is only where the fault zone moves. Those constructions built adjacent to the fault will survive while structures built across these zones will collapse.