10.03.10 The Day the Earth moved

The recent earthquakes in Haiti and Chile and their aftermaths have been widely reported in the global media. The Haiti earthquake, which struck on January 12, 2010, had a magnitude of 7.0 on the moment movement scale. Earthquakes of this magnitude occur on average, around 17 times a year. The Chile earthquake occurred off the coast of the Maule Region of Chile on February 27, 2010.

It rated a magnitude of 8.8 on the moment magnitude scale and lasted about three minutes. On average, only one earthquake of this magnitude occurs each year. Although earthquakes of these magnitudes are rare, and their effects devastating in terms of loss of life and destruction of property, earthquakes themselves are a fairly common event. The United States Geological Survey estimates that that several million earthquakes occur in the world each year, however many go undetected because they hit remote areas or have very small magnitudes.

Much of science’s understanding of the occurrence of earthquakes is thanks to space technology. Satellites equipped with high resolution sensors are capable of photographing the aftermath of an earthquake in detail, as shown in the images from the Quickbird satellite (courtesy of Digital Globe). These show Concepción Oil Refinery on February 12 and 27, 2010 before and after the quake. Perhaps of more important to scientists are data from the global positioning system (GPS), the same system your SatNav uses to get from A to B. GPS is a constellation of 24 satellites continuously orbiting the Earth at an altitude of 20,000km and a speed of 17,000km/h.
 
Highly sensitive and accurate GPS receivers are capable of measuring movements in the Earth’s crust. For instance, GPS data have revealed that the Chile earthquake moved the entire city of Concepcion 3 metres (10 feet) to the west. However, GPS data collected by the Institute of Engineering Surveying and Space Geodesy at the University of Nottingham over the past 20 years, have shown that the UK is also on the move,  drifting about 2-3 cm each year in a north-easterly direction, and rising and falling slightly each day due to the effect of the tides. In addition, GPS measurements can reveal other changes in sea levels around our coasts.
 
Dr Richard Bingley, from the IESSG, explains: “GPS measurements have shown the land in Scotland is rising by about one or two millimetres a year, while the land in England's south is slowly ‘sinking’. Essentially the country is tilting. By comparing this land movement and sea level measurements provided by the Proudman Oceanograqphic Laboratory, it appears that sea level has risen 10-20 cm over the last century,"