Earthquakes on the Increase

There was another large earthquake off the East coast of Honshu, Japan today. It measured magnitude 7. This coincides with a general increase in the number of all magnitude earthquakes over recent years.

The trend is in part due to the increase in seismographs, which have helped seismological centres to locate many small earthquakes which were undetected in earlier decades.

Therefore, an upward trend is not unexpected in the graph. The rise in the number of large earthquakes is more significant to the assessment of the trend of increasing tectonic activity.

Source Data: Report produced by R Webb Ó 2008

DATES FROM - TO      PERIOD            NO. EARTHQUAKES (Mag +6.99) 
1863 to 1900 incl            38 yrs               12
1901 to 1938 incl            38 yrs               53
1939 to 1976 incl            38 yrs               71
1977 to 2011 incl            34 yrs              164

By limiting the range of earthquakes being counted to magnitude 7 or above, it means these earthquakes can easily be identified by a limited number of seismographs, ensuring that any increase in frequency for larger earthquakes cannot be down to the increase in overall detection rates, as all these larger earthquakes are able to be easily detected with fewer seismograph stations.

References

1. The number and energy intensity of earthquakes in any given period are based upon records from USGS and other sources, including those recorded at http://earthquake.usgs.gov/
2. Earthquake details used here may also be available at http://en.wikipedia.org/wiki/List_of_earthquakes
3. Graph plot for "all magnitude" earthquakes reproduced from DL Research paper http://www.dlindquist.com/