Irish Weather Online, June 20, 2011
2011 is on target to record the largest number of earthquakes in a single year for at least 12 years.
Research by Irish Weather Online, using data from the US Geological Survey (USGS), has found that earthquake activity (5.0-9.9 magnitude) from 01 January to 19 June 2011 is already exceeding the total annual seismic activity for the years 2001, 2002 and 2003. 2011’s total number of recorded earthquakes is also expected to exceed the most seismically active year of the past 12 years, 2007.
A total of 1,445 earthquakes, ranging in magnitude from 5.0 to 9.9, have been recorded in the year up to 19 June. The total number of earthquakes recorded globally for the entire of 2007 was 2,270.
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 5.0 magntiude to 7.9 magnitude is rising. In particular there has been a sharp rise during the past 12 years of moderate earthquakes in the range 5-6.9.
While considered moderate to strong on the Richter Scale and far less severe than 7+ 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).
In the last 24 hours alone earthquakes ranging 5 magnitude or more have hit Tonga, Fiji, Panama, the South Sandwich Islands, Japan, Papua New Guinea, Peru and Indonesia.
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.”