What is an earthquake and what causes them to happen? An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel. In California there are two plates - the Pacific Plate and the North American Plate. The Pacific Plate consists of most of the Pacific Ocean floor and the California Coast line. The Pacific Plate grinds northwestward past the North American Plate at a rate of about two inches per year.Parts of the San Andreas Fault system adapt to this movement by constant "creep" resulting in many tiny shocks and a few moderate earth tremors. Learn more: "Earthquakes".
History of deadly earthquakes Image copyright Getty Images Earthquakes have claimed hundreds of thousands of lives in the last 100 years, and improvements in technology have only slightly reduced the death toll. 25 April 2015 A 7.8-magnitude earthquake kills more than 8,000 people and leaves hundreds of thousands homeless, in the worst natural disaster to strike Nepal since 1934. In some parts of the country, the quake flattens 98% of all homes in hillside villages. 3 August 2014 Approximately 600 people are killed in a 6.1-magnitude earthquake that strikes Yunnan province in China. 15 October 2013 More than 200 people are reported to have died after a magnitude 7.2 earthquake strikes centrally-located Bohol and Cebu in the Philippines. 25 September 2013 More than 300 people are killed as a 7.7-magnitude quake flattens entire villages in Pakistan's remote south-western province of Balochistan, mainly in the district of Awaran. 20 April 2013 11 August 2012 23 October 2011 11 March 2011 22 February 2011 14 April 2010 6 April 2009
KS3 Bitesize Geography - Plate tectonics : Revision, Page 5 How Are Earthquake Magnitudes Measured? Unfortunately, many scales, such as the Richter scale, do not provide accurate estimates for large magnitude earthquakes. Today the moment magnitude scale, abbreviated MW, is preferred because it works over a wider range of earthquake sizes and is applicable globally. The moment magnitude scale is based on the total moment release of the earthquake. Moment is a product of the distance a fault moved and the force required to move it. It is derived from modeling recordings of the earthquake at multiple stations. Magnitudes are based on a logarithmic scale (base 10). Magnitude scales can be used to desribe earthquakes so small that they are expressed in negative numbers. Here's a table describing the magnitudes of earthquakes, their effects, and the estimated number of those earthquakes that occur each year. Some things that affect the amount of damage that occurs are: Figures 1 and 2 from Walker, 1982.
BBC Nature - How animals predict earthquakes 1 December 2011Last updated at 01:53 By Victoria Gill Science reporter, BBC Nature Can pond-dwelling animals pick up pre-earthquake signals? Animals may sense chemical changes in groundwater that occur when an earthquake is about to strike. This, scientists say, could be the cause of bizarre earthquake-associated animal behaviour. Researchers began to investigate these chemical effects after seeing a colony of toads abandon its pond in L'Aquila, Italy, in 2009 - days before a quake. They suggest that animal behaviour could be incorporated into earthquake forecasting. Continue reading the main story “Start Quote When you think of all of the many things that are happening to these rocks, it would be weird if the animals weren't affected in some way” End QuoteRachel GrantThe Open University The team's findings are published in the International Journal of Environmental Research and Public Health. Strange behaviour Continue reading the main story Toad exodus "It was very dramatic," she recalled.
Shaking Intensity It is a modern human tendency to focus on the number of an earthquake—specifically, the magnitude, or what people used to call the “Richter scale.” But the destruction from a quake usually has more to do with location and timing. Such was the case with the earthquake in Christchurch, New Zealand, on February 22, 2011. A September 2010 earthquake centered 40 kilometers (25 miles) west of Christchurch, in the plains near Darfield, struck at 4:35 a.m., had a magnitude of 7.1, and caused some structural damage and one death (by heart attack). The earthquake in February 2011 occurred at 12:51 p.m. and just 10 kilometers (6 miles) from the center of Christchurch. The natural-color image above was captured on March 4, 2011, by the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite. The deeper the red color of the circle, the more intense the “peak ground acceleration,” or shaking of the earth. There are two forms of energy that cause the shaking in an earthquake.
Papua New Guinea hit by 7.2-magnitude earthquake A powerful earthquake has struck the South Pacific nation of Papua New Guinea, the fourth strong quake to hit the South Pacific island nation in a week. A local tsunami warning was issued but it was lifted shortly afterward with no reports of damage. The 7.2-magnitude quake struck about 150 kilometres south-west of the town of Panguna on Bougainville Island at a depth of 22 kilometres, the US Geological Survey reported. The Pacific Tsunami Warning Center said tsunami waves of up to 1 metre were possible within 300 kilometres of the epicenter on the coast of Papua New Guinea. There were no reports of damage, said Chris McKee, assistant director of the Geophysical Observatory in the capital, Port Moresby. “The earthquake appears to have not been as big as first estimated,” McKee said. Thursday’s quake was located in a different area of Papua New Guinea than the previous three tremors that rattled the region over the past week, and was therefore an unrelated event, McKee said.
How earthquakes generate tsunamis How do earthquakes generate tsunamis? Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. Large vertical movements of the earth's crust can occur at plate boundaries. This simulation (2 MB) of the 1993 Hokkaido earthquake-generated tsunami, developed by Takeyuki Takahashi of the Disaster Control Research Center, Tohoku University, Japan, shows the initial water-surface profile over the source area and the subsequent wave propagation away from the source.
Earthquakes & Tsunamis: Causes & Information Almost every year, a large earthquake occurs somewhere in the world and captures the public's attention. Meanwhile, every day thousands of smaller tremors often go unnoticed by most people. Although we usually consider the ground to be solid and stable, the earth is, in fact, constantly shifting under our feet. What causes earthquakes? Earth's crust ranges from 3 to 45 miles deep (5 to 70 kilometers). The crust is a thin, hard shell that floats on the denser, hotter rock of the mantle. As they slide past one another, the tectonic plates snag on rough patches of rock. An earthquake occurs when the pressure built up along a fault becomes stronger than the pressure holding the rocks together. Even though the tectonic plates slide at a regular rate over time, the way that faults release stored energy is different with each earthquake, said Shimon Wdowinski, a geophysicist at the University of Miami's Rosentiel School of Marine & Atmospheric Sciences. Tsunamis Measuring earthquakes
Why do Some Earthquakes Cause Tsunamis When Others Don't? Damage caused by the 2011 Japanese tsunami. Photo by Tamaki Seto In the past decade, the devastating impact of major tsunamis has made the news on a number of occasions, most notably the 2011 Japanese tsunami and the notorious Boxing Day tsunami of 2004. But the earth experiences very many earthquakes each day, and each year sees on average around 15 major earthquakes of at least magnitude 7 (M7.0) and one of ≥M8.0 – and in this context, damaging tsunamis are few. What Causes a Tsunami? Tsunamis are not just large waves: they are generated by vertical displacement of sea water by some kind of submarine activity. The devastating impact of a major tsunami comes from the fact that, unlike the waves we normally see, they travel through the whole depth of the ocean. Which Earthquakes Cause Tsunamis? How a tsunami is generated. For an earthquake to cause a tsunami, certain conditions must be satisfied; size, depth of water, and type of movement must all be right to generate the huge waves.
Canterbury earthquake facts and figures 29 November 2010 What are earthquakes? New Zealand lies on the boundary of the Pacific and Australian tectonic plates. Tectonic plates are large plates of rock, about 100km in thickness, that make up the foundation of the earth's crust and the shape of the continents (like pieces of a giant jigsaw puzzle). There are ten major plates and many more minor ones. Tension builds up as they scrape over, under or past each other. Most (though not all) earthquakes occur at faults, which are breaks extending deep within the earth, caused by the movement of these plates. The fault that caused the Canterbury earthquake on 4 September 2010 has been named the Greendale Fault. Scientists from the Institute of Geological and Nuclear Sciences (GNS) think it is the first time this fault has moved in several thousand years, and it is unlikely that it will move again for another few thousand years. Measuring earthquakes The magnitude is a measure of the amount of energy released by the earthquake. Aftershocks
When solid ground is shaken to mush - Science Large tracts of silty, low-lying land compounded the effects of Saturday's earthquake in Canterbury, as whole streets were transformed from firm land to sludge. In what's known as liquefaction, Christchurch's sandy soil was shaken violently, causing water to rise through its pores. Scientists compared it to jumping on wet sand at the beach - it soon turns to a murky soup. Professor Michael Pender from the University of Auckland geology department said the Canterbury quake was one of the most significant cases of liquefaction in New Zealand history. He said the process could affect any town or city near a river, estuary or coastline. Coastal developments which encroached on sand dunes, such as Mt Maunganui and some North Shore beaches, were also susceptible during a major earthquake. Large sections of Christchurch were built on soft sediments which remained saturated after a wet winter. As many as nine out of 10 homes on the city's flat have been damaged by the quicksand-like effect.
Earthquakes / Hot topics / Themes As aftershocks continue in the Wellington and Central NZ Regions following with earthquakes, it would be a good time to look at this topic and understand what we all need to do in the event of a big one. Ed, Wiki, and I are learning to keep safe in the event of an earthquake. We have discovered some things that might be of interest to you. Have a look through some of the links and resources below and you too may be learn how to stay safe when earthquakes occur. Try this wickED Challenge! What causes earthquakes in New Zealand? We have checked out the Internet and found some places to help you with your research. Back to top Find out about earthquakes Activities you can do about earthquakes Have a go at these activities that can give you some helpful information and support during tough times.