Earthquakes Shake, rattle and roll Year 9 Science – Seaview High School

Tremors from below Movement in the Earth’s crust result in earthquakes. These can originate as far as 700 km below the surface. We call the resultant vibrations at the surface, tremors. Some tremors are too weak to be felt When they are sudden and strong, we call them earthquakes. http://www.geolsoc.org.uk/~/link.aspx?_id=BE183F53-A742-434C-A874-06DA51386914&_z=z

Earthquakes Major quakes occur at or near plate boundaries. Plates can be: Pushing against each other in subduction zones Spreading apart to form ocean ridges and new underwater volcanoes and volcanic islands Slipping and sliding against each other causing sudden jolts

Location Wherever there is a weakness in the Earth’s crust, tremors are likely to occur. Faults provide such weaknesses Write this in your book now: The epicentre of an earthquake is directly above the point below the surface where the movement in the crust began. The point where the earthquake begins is called the focus.

Measuring earthquakes Movements are recorded with a seismograph. There are a number of ways the strength of an earthquake can be measured The most well-known way is using the Richter scale A modern seismometer Seismograph of the 2004 earthquake which resulted in the devastating Boxing Day tsunami

Richter scale The Richter scale measures the energy released during an earthquake A measurement of less than 2.0 is called a microquake and is rarely detected by people. Measurements greater than 5.0 are detectable and may cause objects on shelves to move or rattle Every increase of 1.0 on the Richter scale represents an increase of 30 times as much energy So a 6.0 releases 30 times as much energy as a 5.0 A 7.0 releases 900 times as much as a 5.0 (30x30) http://earthquake.usgs.gov/earthquakes/map/

The Richter scale

The Richter scale Richter scale measurments are not always good indicators of destructive power. A small earthquake with an epicentre in or near a city may cause many deaths, injuries and a lot of damage (cut of water, electricity, gas supplies). Large earthquakes in remote areas often have little affect causing few injuries and little damage. Earthquake damage to a rail line Damage caused by the 2010 Haiti quake, which measured 7.0 on the Richter scale with at least 52 after shocks over 4.5

Destructive power Destructive power depends on the distance from the epicentre In 1988 a 6.7 magnitude earthquake in Tennant Creek, NT, resulted in damage to 2 buildings and a gas pipeline. In 1989 a 5.6 magnitude earthquake in Newcastle, NSW, killed 13 people, hospitalised 160 others, demolished 300 buildings and damaged lots more. The difference was the distance from the epicentre Tennant Creek was 40 km from the epicentre Newcastle was only 5 km from the epicentre

1989 Newcastle quake

Living on the edge For people living near plate boundaries, the ability of scientists (seismologists) to predict earthquakes and tsunamis is critical. This is particularly the case for people living around the Pacific Ocean. While the exact location, time and size of a quake is very hard to predict, sensors can monitor movement along plate boundaries and fault lines. These monitors can inform seismologists about pressure build ups and warn of the likelihood of a quake. No reliable early warning system currently exists.

Deep-ocean Assessment and Reporting of Tsunamis Seismologists are experimenting with a variety of methods including satellites, sensors and even animal behaviour. Tsunami early warning systems are reliant on the early detection of earthquakes. There is a system of buoys around the Pacific and Atlantic Oceans to assist with early detection. The DART system. This system detects sudden rises in sea level and sends alerts to tsunami warning centres.

DART locations

Waves of destruction If an earthquake occurs beneath the ocean, tsunami waves can be generated. These waves travel at speeds of up to 900 km/h As the waves approach the land and the water gets shallower, the waves slow down and build in height (up to around 40m have been recorded).

Recent tsunamis The potential for damage was made obvious by two recent tsunamis. The Boxing Day tsunami of 2004 The Sendai (Japan) tsunami of 2011

Boxing Day tsunami of 2004 The Sumatra-Andaman tsunami Around 300,000 people across South-East Asia, southern Asia and eastern Africa died. Millions lost their homes. 250 km from the coast of Sumatra, Indonesia. 9.0 on the Richter scale. Pushed a 1000 km long strip of ocean floor up around 30 metres. Damage occurred up to around 5000 km from the epicentre of the earthquake (Somalia, Kenya and Tanzania).

Sendai tsunami, March 2011 Magnitude of 9.0 on Richter scale Epicentre was 70 km off the Japanese coast. In the city of Sendai alone, at least 670 people were killed and 2200 injured. Around 6900 homes were totally destroyed and many more damaged. Waves of up to 40 metres high recorded. Reached as far as 10 km inland in some places. The unfortunate proximity to the Fukushima nuclear plant compounded the problem with damage causing meltdowns in three of the reactors at the Fukushima Daiichi Power Plant.