© UnknownSeismic chart of the 11 March 2011 Japan earthquake
By analysing data from the US Geological Survey (USGS), IWO was able to determine that earthquake activity (6.0-9.9 magnitude) during the period 01 January to 12 October 2011 reached its highest level in 20 years. The 2011 data was compared with data for the corresponding period in each of the 19 previous years since 1992.
A total of 177 earthquakes in the range 6.0 to 10 magnitude on the Richter Scale have been recorded so far in 2011, compared to 149 for the same period in 2010 and 119 in 2009.
Recent earthquakes exceeding 6 magnitude on the Richter Scale have occurred in Tonga (08 Oct), northern Argentina (06 Oct), India/Nepal (18 Oct), Cuba (15 Sept), northern Sumatra (05 Sept), Vanuatu (03 Sept), Alaska (02 Sept), and East Timor (30 Aug).
Interestingly, the total number of earthquakes (magnitude 0-9.9 magnitude) recorded in 2011 is dramatically lower than the previous four years since 2007.
The highest number of earthquakes recorded in the period 01 January to 12 October during these years was 23,980 (2008). Only 9,506 earthquakes have been detected by the USGS in 2011 to date.
© iWeather Online/USGSGraph showing 6-10 magnitude earthquakes during the period 1992-2011
© NEIC-USGSLocation of 6-10 magnitude earthquakes in 2011.
© iWeather Online/USGSTotal earthquakes (0-10 magnitude) for the period 01 Jan to 12 Oct 2007-11
- More than 10,000 earthquakes have been detected by Spain's Instituto Geográfico Nacional (IGN) around the island of El Hierro since 17 July.
- In late August/early September, the Geophysical Institute, Academy of Sciences of the Czech Republic recorded 10,000 earthquakes in the Nový Kostel area of the Cheb District, a region located close to the Czech Republic's western border with Germany.
- The Atlantic region of Bermuda, which was hit by its first earthquake in over a decade in April, was rattled by two moderate quakes in early October
- A rare moderate earthquake struck the Northwest Territories region of Canada on 26 September
- Ottawa was shaken by a rare 4 magnitude earthquake on 18 September
- Holland experienced a 4.3 magnitude quake on 08 September
- One of the strongest earthquakes to strike the U.S. East Coast in decades rocked buildings as far as North Carolina and Canada on 23 August, causing damage to buildings and a number of injuries.
- A magnitude 2.9 earthquake, followed by at least six earth tremors, was recorded in western Scotland on 21 August.
- Georgia was struck by a magnitude 5.1 earthquake on 18 August, the strongest earthquake to hit the eastern European nation in almost two years.
- A relatively rare, moderate earthquake struck near the coast of Israel and the Gaza Strip on 07 August.
- A 4.8 magnitude earthquake shook the northern Italian city of Turin, as well as parts of neighbouring France, Monaco and Switzerland, on 25 July.
- A moderate earthquake struck in the English Channel on 14 July. The shallow 4.5 magnitude earthquake struck at 6:59 a.m. GMT. at a depth of 15km in waters between Portsmouth, England, and Le Harve France.
- A moderate earthquake struck near the Nabro volcano in Eritrea on 17 July, five days after the stratovolcano erupted for the first time in recorded history.
- A rare 4.6 magnitude earthquake struck Australia, just 97 km southeast of Melbourne and 24 km SW of Warragul, on 05 July.
- A 5.5 magnitude earthquake struck the South Sandwich Islands region, situated around 750km south east of South Georgia, in the South Atlantic on 19 June. It was the latest in a series of quakes to hit the Antarctic Region during a 24-hour period.
- Two moderate earthquakes, measuring 5.2 and 4.5 on the Richter Scale, struck Spain on 11 May, killing 10 people.
- 2011 also has been a very active year for the Pacific Ring of Fire
The massive earthquakes in Japan (2011), Chile (2010), Sichuan (2008), Sumatra (2005 and 2008) and Indonesia (2004) have served to remind us of the devastating impact of earthquakes on life and property.
While the number of earthquakes ranging between 8.0 magnitude and 9.9 magnitude have shown no significant increases in recent years, the number of earthquakes ranging 6.0 magnitude to 7.9 magnitude is rising and reached a 20-year high in 2011.
While considered moderate to strong on the Richter Scale and far less severe than 5-6 magnitude quakes, earthquakes in this range can still cause widespread damage and loss of life. Some well known examples include Haiti in 2010 (7 mag), San Francisco Bay, California, USA, in 1989 (6.9 mag), Caracas, Venezuela, in 1965 (6.5 mag), Christchurch, New Zealand, in 2011 (6.3 mag), L'Aquila, Italy in 2009 (5.8 mag), and Newcastle , Australia, in 1989 (5.6 mag).
Increase in recorded earthquakes
Seismologists argue that an increase in detected earthquakes does not necessarily represent an increase in actual earthquakes. The USGS, for example, says improved global communication and enhancements in detection technology have both contributed to higher earthquake numbers being recorded over time.
According to the USGS: "Although it may seem that we are having more earthquakes, earthquakes of magnitude 7.0 or greater have remained fairly constant throughout this century and, according to our records, have actually seemed to decrease in recent years."
Commenting on swarm earth activity in a specific geographical area, the USGS said :" A temporal increase in earthquake activity does not mean that a large earthquake is about to happen. Similarly, quiescence, or the lack of seismicity, does not mean a large earthquake is going to happen. A temporary increase or decrease in the seismicity rate is usually just part of the natural variation in the seismicity. There is no way for us to know whether or not this time it will lead to a larger earthquake. Swarms of small events, especially in geothermal areas, are common, and moderate-large magnitude earthquakes will typically have an aftershock sequence that follows. All that is normal and expected earthquake activity."
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