When the earth shakes…

• Earthquakes involve the powerful movement of rocks in the Earth’s crust. The rapid release of energy creates seismic waves that travel through the earth. • Scientists use the different speeds of seismic waves to locate the epicentre (the point on the surface directly above the place where the earthquake originated) of earthquakes. • Seismometers are used to measure the magnitude of earthquakes. You are unlikely to feel a magnitude 3 earthquake, but a magnitude 6 earthquake could potentially cause considerable damage. • The damage caused by earthquakes also depends on their depth and fault type. • It is estimated that there are 500,000 detectable earthquakes in the world each year. 100,000 of those can be felt, and 100 of them cause damage. • The interior of Antarctica has ice quakes which, although they are much smaller, are perhaps more frequent than earthquakes in Antarctica. The ice quakes are similar to earthquakes, but occur within the ice sheet itself instead of the land underneath the ice. Some of our polar observers have told us they can hear the ice quakes and see them on the South Pole seismograph station, but they are much too small to be seen on enough stations to obtain a location.

Some famous earthquakes

• On April 16, 2013, Iran was struck by its most powerful earthquake in more than 50 years, with tremors felt across Pakistan, India and the Middle East. The epicentre of the 7.8-magnitude quake was near the south-eastern city of Khash, close to Pakistan. • The earthquake that hit the Tohoku region of Japan on March 11, 2011, had a magnitude of 9.0 and killed over 15,000 people. • The destruction caused by the Tohoku earthquake was made much worse by powerful tsunamis that were triggered due to the earthquake’s epicentre being located offshore. A tsunami is a sea wave caused by an underwater earthquake or landslide (usually triggered by an earthquake) displacing the ocean water. • The 2004 earthquake that occurred in the Indian Ocean near Sumatra, Indonesia, triggered a series of tsunamis that killed over 200,000 people in 14 countries. • The February 2011 earthquake in Christchurch, New Zealand, followed nearly six months after a magnitude 7.1 earthquake shook the region. The earthquake killed 181 people and significantly damaged the central city. • An earthquake that hit Haiti in January 2010 with a magnitude of 7.0 killed over 200,000 people according to Haitian sources. • The most powerful earthquake ever recorded on Earth was in Valdivia, Chile. Occurring in 1960, it had a magnitude of 9.5. When the Chilean earthquake occurred in 1960, seismographs recorded seismic waves that travelled all around the Earth. These seismic waves shook the entire earth for many days! This phenomenon is called the free oscillation of the Earth. • The world’s deadliest recorded earthquake occurred in 1556 in central China. It struck a region where most people lived in caves carved from soft rock. These dwellings collapsed during the earthquake, killing an estimated 830,000 people. • It is important in earthquake prone countries such as Japan to build houses and buildings that react well to earthquakes. Good engineering practices can help stop buildings collapsing under the stress of large earthquakes.

— Compiled by The Surfer