Earthquake
You might have faced sudden movement of earth.This sudden movement is called earthquake which occur when energy stored in elastically strained rocks is suddenly released.This release of energy causes intense ground shaking in the area near the source of earthquakes and sends waves called Seismic waves.
Earthquake can be categorized as a geological hazard for the persons residing in earthquake prone areas. But, these seismic waves are an important source for studying the interior of the earth.
Natural earthquakes are caused by sudden slippage along a fault. Faults occur when brittle rocks fracture and there is displacement of one side of the fracture relative to the other side.
The amount of displacement in a single slippage event is rarely 10 to 20 meter for large displacement.
Eartquake effects:
Earthquakes produce several effects that cause damage and destruction. Some of these effects are the direct result of the ground shaking produced by the arrival of seismic waves and others are secondary effects.
The earthquake effects are as follows:
Ground Shaking-
Shaking of the ground caused by the passage of seismic waves near the epicentre of the earthquake is responsible for the collapse of most structures.
The intensity of ground shaking depends on distance from the epicentre ,nd on the type of bedrock underlying the area.
In general loose unconsolidated sediment is subject to more intense shaking than solid bedrock.
Damage to structures from shaking depends on the type of construction. Concrete and masonry structures, because they are brittle and are more susceptible to damage than wood and steel structures, which are more flexible.
Ground Rupture
It occurs along the fault zone that move during the earthquake. Thus, structures that are built across fault zones may collapse, whereas structures built adjacent to, but not crossing the fault may survive.
Fire
It is a secondary effect. It can occur because of the knocked down power lines and rupture of natural gas lines. The problem can be severe if water lines are also broke. As , there is no water to extinguish fire.In 1906 San Francisco earthquake more than 90% of the damage to buildings was caused by fire.
Landslides and Rock fall
Earthquake in mountainous region can trigger rapid mass wasting events like landslides, rock and debris falls, slumps, and debris avalanches.
Liquefaction
It is a process that occurs in water saturated unconsolidated sediment due to shaking. The ground shaking causes the grains to loose grain to grain contact, and thus the material tends to flow.
Aftershocks
The stress state in rocks can be changed due to an earthquake near the hypocentre. This may induce numerous earthquakes that occur after the main earthquake. These are almost always smaller than the main earthquake. But, these aftershocks can be dangerous as they can last for many months and further damages to already damaged structure and make it harder for any rescue operations.
Tsunami
Tsunami are giant ocean waves that can rapidly travel across oceans. Earthquake is one of the cause for tsunami to take place. Earthquake that occur along coastal areas can generate tsunami, which can damage thousands of kilometers away on the other side of the ocean.