Earthquake Storms - questions and answers
What causes an earthquake?
The crust of the Earth is broken into seven enormous 'tectonic' plates that stretch over entire continents. These plates of solid rock are in constant motion. Where they meet is known as a fault line. As these plates drag past or over each other, huge amounts of stress can build up. When the stress is too great the rocks force apart like an expanding spring.
Where are the most dangerous places for earthquakes?
Major fault lines cross the planet and it is there that major earthquakes take place. Two of the most earthquake-prone faults are the San Andreas in California and the North Anatolian which runs along the north of Turkey. These are both more than 1000km long. Other areas of high earthquake activity are Japan, the Middle East and along the west coast of South America. All lie on the boundaries of the Earth's continental plates.
What is the difference between an earthquake and earthquake storm?
An earthquake is a single isolated event in which the Earth's crust pulls apart due to the build up of stress. The phrase earthquake storm was coined by Stanford Professor of Geophysics, Amos Nur, and describes a series of earthquakes where one triggers another and then another. The phenomenon is based on a scientific theory known as the stress triggering model.
Scientists believe that on some faults, as an earthquake strikes, the stress released does not simply disappear. Instead it must be redistributed to another region of the fault which sets off another earthquake. This series of earthquakes is known as an earthquake storm. Although still in its infancy the stress triggering model has identified possible series of earthquakes in California, Japan and Turkey.
How much stress is needed to trigger an earthquake?
The amount of stress needed to trigger a following quake does not have to be great. Studies of over 20 faults have convinced many scientists that earthquakes can be triggered by as little as one eighth of the pressure required to inflate a car tyre.
Can earthquake storms only happen along fault lines?
The most well known earthquake storm track is along the North Anatolian fault in Turkey where a series of earthquakes migrated along the fault in a westerly direction. There have been other known examples where earthquakes have triggered other earthquakes on different, nearby faults.
What is the difference between an aftershock and an earthquake storm?
All major earthquakes are followed by a series of aftershocks. These are smaller tremors that follow a main event. A series of aftershocks following a large earthquake is not considered to be a storm. An earthquake storm is when large independent earthquakes are triggered over long distances and over long periods of time. However aftershocks have helped scientists identify the mechanism which triggers an earthquake storm and have given them a clearer understanding of how the transfer of stress along a fault takes place.
How many people die a year in earthquakes?
There is no definitive figure for this but every year earthquakes can kill many thousands. In 1999, the Izmit earthquake in Turkey killed over 25,000. In January 2001 the Indian State of Gujarat was struck by a major earthquake killing over 30,000 people. The single most catastrophic quake of recent times was the Tungshan earthquake in China in 1976 - an estimated 650,000 people were killed.
