September 17, 2012 – Global Earthquakes From 1973 to 2011 – Are They on the Increase? The charts above reflect global earthquakes, greater than or equal to 6.0 magnitude – quantity and USGS 32X strength rating – by year.
Global earthquakes appear to be increasing, in both quantity and strength over the 39 year period. This is especially true of the quantity of quakes. The USGS strength rating of those quakes clearly point out the two 21st century mega-quakes in Sumatra, Indonesia in December, 2004 and Japan in March, 2011.
Are global earthquakes really increasing in quantity and strength or, does it appear so because of the increased reporting and monitoring capabilities? Below is the current seismic reporting station global map:
In 1931 there were 350 seismic monitoring stations. Now there are 19,000.
The USGS is continually asked if earthquakes are on the increase. Although it may seem that we are having more earthquakes, earthquakes of magnitude 7.0 or greater have remained fairly constant.
A partial explanation may lie in the fact that in the last twenty years, we have definitely had an increase in the number of earthquakes we have been able to locate each year. This is because of the tremendous increase in the number of seismograph stations in the world and the many improvements in global communications. In 1931, there were about 350 stations operating in the world; today, there are 19,000 stations and the data now comes in rapidly from these stations by electronic mail, internet and satellite. This increase in the number of stations and the more timely receipt of data has allowed the USGS and other seismological centers to locate earthquakes more rapidly and to locate many small earthquakes which were undetected in earlier years. The NEIC (National Earthquake Information Center) now locates about 20,000 earthquakes each year or approximately 50 per day. Also, because of the improvements in communications and the increased interest in the environment and natural disasters, the public now learns about more earthquakes.
According to long-term records (since about 1900), the USGS expects about 17 major earthquakes (7.0 – 7.9) and one great earthquake (8.0 or above) in any given year.
Using a straight line increase in the number of seismic reporting stations from 1931 to 2012 and comparing that figure to the number of yearly number of earthquakes, there is a 73.8% correlation. In other words, about three-quarters of the earthquake quantity increase over the 39 year period from 1973 to 2011 can be explained by the increase in seismic reporting stations.
The Master of Disaster