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Quick links:
Earthquakes in the South West - case study Historical earthquakes in the South West Historical earthquakes in the UK Useful websites: |
EarthquakesAll information taken from the British Geological Survey (2004) and IDEERS (Intoducing & Demonstrating Earthquake Engineering Research in Schools).. What is an earthquake?An earthquake is the vibration, sometimes violent, of the Earth's surface that follows a suddent release of energy in the Earth's crust. There are a variety of different causes, including:
The most common cause, however, is tectonic plate movement. This is simply when pressire that has built up in tectnonic plates causes the rock to break suddenly - usually occurring at the boundaries of tectonic plats and along existing faults. The point where an earthquake starts is called the focus (or hypocentre), and it may be many kilometres below the earth's surface. The point on the earth's surface that is directly above the focus is called the epicentre. Where do earthquakes occur?Earthquakes occur anywhere. The majority, however, take place at the boundaries of the major crustal plates. The most destructive types of earthquakes happen where the earth's plates collide (called 'interplate earthquakes'), for example the recent Far East tsunami.. Britain is not on a faultline so does not experience these destructive interplate earthquakes. Instead we are often hit by 'intraplate earthquakes'. This type of earthquake occurs within the plate, at weak points in the rock, as it tries to deform (or change its shape). Earthquakes in BritainAlthough the the UK is not usually associated with earthquakes, the British Geological Society actually detect between 200 and 300 every year and predict the following for mainland Britain:
Want to know details about the biggest or most damaging British earthquakes on sea and land then visit the IDEERS website. Earthquakes in the South WestRecording for earth tremors is carried out throughout the region by seismograph stations (marked by the green triangles in the map below). These stations continually record any earth tremors (or seismic events). Seismic monitoring stations in the South West
Source: British Geological Survey Recent and historical records, held on the British Geoological Survey's database, show that over 100 recent and historic earthquakes have hit the South West region and its coastline, the locations of which can be seen in the map below. Although the majority of seismic events in the region are below 2.0 on the Richter scale, the largest measured 3.8 on the Richter scale and hit Penzance in 1996. This event was felt throughout Devon and Cornwall. recent and historical Earthquakes in the South West
Source: British Geological Survey (2005) The most recent seismic events can be viewed on the British Geological Survey's website. Three earth tremors have occurred on Jersey (26th August 2005 - magnitude 0.9, 28th August 2005 - magnitude 0.3 and 9th September 2005 - magnitude 1.2). A larger tremor took place in the English Channel, 50km off Plymouth, on the 24th August which was a magnitude 3.0. See map below for locations: Map of the recent earthquakes in the UK - August - September
Source: British Geological Survey (2005) Earthquakes in the South West - case studyEdinburgh-based seismologists registered 4 earth tremors in and around Bridgwater on the 29th January 2004. These earthquakes, all of which took place within 200m of each other, had an epicenter near North Petherton (between Taunton and Bridgwater). The tremors took place in two clear events - two at 10:56 am and two at 8:23 pm, as can be seen in the table below:
Source: British Geological Survey (2004) A recent case study - 4 earth tremors hit Somerset on 29th January 2004
Source: British Geological Survey (2004) Although all four earthquakes were around the same magnitude, it was the 8:23pm events that people felt - many reporting a loud rumble and feeling the earth tremor (its intensity). The intensity of an earthquake measures how much each event impacts on humans. In terms of the Taunton earthquakes:
Source: On the 18th January 2004, an earthquake also occurred off St Ives in Cornwall. Measuring just 0.9 on the Richter Scale this event took place 7km out to sea. Historical earthquakes in the South West and UKHistorical earthquakes are those recorded pre-1970 (before the start of comprehensive seismic monitoring of the UK and the development of the UK earthquake database). The map below shows the distrbution of historic earthquakes in the UK. There is no evidence to show that earthquakes are becoming more frequent in the UK, however, the British Geological Survey are recording larger numbers, especially of smaller earthquakes. Since 1815 around 38 earthquakes have been recorded in the South West and its coastline. The largest event measured 4.4 on the Richter scale and occurred 1815 with an epicentre near Penzance.
Source: British Geological Survey |
