Japan Earthquake: part of an increasing trend?

This is an update of the blog I posted last year

Are earthquakes becoming more frequent? What are the long term trends?

 I find an interesting page here, with this graph showing a pretty convincing increase since the 1980's.

But this increase could be due to better instrumentation - wider distribution of more sensitive seismographs. However, this explanation does not accord with the recent downward trend.

The writer also collects all  earthquakes >6.9 magnitude, which would be recorded by less widespread, less sensitive instruments. 

Again, a trend is apparent:

  DATES FROM & TO      PERIOD            NO. EARTHQUAKES (Mag. > 6.99) 
  ---------------------------         -----------             ------------------------------
 1863 to 1900 incl            38 yrs                   12
 1901 to 1938 incl            38 yrs                   53                                                                   Reference list 1901 to 1938
 1939 to 1976 incl            38 yrs                   71                                                                   Reference list 1939 to 1976
 1977 to 2014 incl *          38 yrs                 144 (to Sept. 2009) predict >180 in total. 

So here we have evidence that the earthquake frequency is rising.

I decided to do my own plot, using data from here , choosing earthquakes >7.0 magnitude between 1900 and 2011.

Again there is a convincing upward trend.

But these were only magnitude 7.0.  Maybe the early seismographs weren't picking them up. (There must be a time when instruments could pick up evidence of large earthquakes occurring anywhere in the world).

So I went to the ANSS data catalogue here and searched for earthquakes >8.0 from 1900 - 2011.
To minimise data manipulation, I just calculated the number of years between these quakes. The greater the number of years, the fewer quakes. When the value hits the zero, there are more than one quakes that year. So the graph is the inverse of the earthquake rate.

Here's the picture:

  

The timeline runs from 1900-2011 (sorry, I'm not very good with Excel, no education)

We are very clearly getting more frequent earthquake recordings in the last few decades.

However, we find the opposite view here on the US Geological Survey. They say, "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".

By "This century", they mean the 21st century. Not a very large dataset. This reminds us of the methods used by climate change deniers, who try to use a few years' data to contradict much longer data series.

The USGS seems at pains to reassure people that earthquakes are not increasing.  They quote several factors that boost the perception, but do not do what they are supposed to do - look at the data, clean it up, and address the core question of whether earthquakes are increasing.

Unless and until someone comes up with some hard data to smooth out the graphs presented here, I will nurture the strong suspicion that earthquakes are increasing.

Why should this be?

The match between earthquake activity and global temperatures is interesting - right down to the recent easing up of both temperature and earthquakes.

Don't forget that the earth has a hot core, and this heat has to escape through the surface.
If the surface is warmer, the heat escape will be diminished.
Hotter rocks expand more, which would mean more seismic activity.

The claim that global warming is causing increasing earthquake activity is a reasonable hypothesis for seismologists and earth scientists to test.

The New Scientist examines whether large earthquakes come in clusters. 
 "What is clear is that for the 6.2 years since 2004, there have been more great earthquakes around the world than in any 6.2-year period throughout the 110-year history of seismic recordings," says Thorne Lay at the University of California."


More here:

Volcanoes

If earthquakes are increasing, what are volcanoes up to?

Here is a page on volcano activity trends. It shows an increase over 200 years, but puts it down to better reporting. However it is generally agreed that if global warming causes glaciers and icecaps to melt, the "unloading" (reduced pressure on earth's mantle) will cause an increase in volcanism. Which will help to reduce global warming, by reflecting more sunlight back into space.

It is argued by Prof Ben  McGuire of UCL that unloading of land-based ice due to global warming could affect the earth's crust, triggering earthquakes and volcanoes.

[Update 22.12.12] Confirmation from long term GEOMAR study, who find positive correlation between rapid warming, ice melt, and increased volcanic activity.

So there is evidence that both earthquakes and volcanoes are increasingly common, and there are plausible mechanisms to relate them to observed global warming. The relationship at the moment is speculative, and it will take many years for scientists to come to a consensus on the question. In the meantime we should set about decarbonising the world economy.

See also: Earthquake resistant buildings
Controlling the Fukushima radiation spread at source