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Instructions on using the earthquake pages

2.3.2008

  • Earthquakes during the last 48 hours
Earthquake data on the web-site are derived from the SIL seismic network, which automatically detects and locates earthquakes in Iceland and the surrounding offshore region. Because the data are displayed in near-real-time, they should be considered preliminary. Both the map and the corresponding graph are updated every five minutes.
  • Earthquake maps

Earthquakes occur due to sudden slip along a fault-plane within the crust. The position where this slip occurs is known as the hypocentre; the epicentre is the location on the Earth's surface directly above the hypocentre.

The symbols on the maps denote earthquake epicentres registered during the last 48 hours. The colour of the symbol signifies the number of hours since the earthquake occurred, as shown on the colour scale on the maps. The most recent events are displayed in red, and the oldest in blue. A green star signifies an earthquake larger than magnitude 3 in size. The list to the left of the earthquake map contains maps from other regions within the country. In the regional-scale maps, SIL seismic stations are represented by black triangles. Additionally, some maps contain circular outlines; these features represent volcanic calderas and central volcanoes (Einarsson and Sæmundsson, 1987). Mapped faults and fissures are also shown on some regional maps.

  • Earthquake graphs
The graphs show the timing and size of the earthquakes depicted in the map above the graph. The same colour-coding applies to the graphs as to the maps (see above). The size of each earthquake is measured on a local magnitude scale, which is a logarithmic measure of earthquake size. For two earthquakes in the same location, the level of shaking due to a magnitude 5 earthquake would be about 10 times larger than a magnitude 4 event. However, in terms of energy release, the larger earthquake would radiate 32 times more energy than the smaller event.
  • Earthquake table
The table displays the map and graph data in tabulated form. The first two columns denote the date and GMT time of the earthquake, respectively. Columns 3 and 4 detail the location of the epicentre in decimal units of latitude and longitude. Columns 5 and 6 approximate the focal depth (the distance from the hypocenter to the epicentre) and the magnitude of the earthquake, respectively. Column 7 contains a measure of earthquake ‘quality’, based on several calculated parameters. The higher the quality value, the more accurate the positioning of the epicentre. Lastly, column 8 describes the location of the epicentre in relation to a nearby landmark.



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