Tuesday, April 20, 2010

Are earthquakes increasing in frequency?

This post has been updated with a new graph here.

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.
However, we find the opposite view here "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. Reminds me of the methods used by climate change deniers, who try to use a few years' data to contradict much longer data series.

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

Hotter rocks expand more, which would mean more seismic activity.

Emphatically, this is not a claim that global warming is causing increasing earthquake activity. But that is a reasonable hypothesis for seismologists to pore over for a few decades.

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.

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
Earthquakes may be connected.


Vote Clegg said...

That's a huge claim using the data available and there are reasons too numerous to go through as to why your conclusions are erroneous.

DocRichard said...

Which is why I wrote "Emphatically, this is not a claim that global warming is causing increasing earthquake activity. But that is a reasonable hypothesis for seismologists to pore over for a few decades."

Anonymous said...

Please check out my website http://www.tectonicplates.ca/ that contains my theory on the increase in earthquakes world wide; but primarily in the South China Sea regeon. My theaory in a nutshell is that the warming water of the planet is resulting in thermal expansion of the tectonic plates in the south china sea regeon: Scroll way down to the bottom of the very long page and there is a chart indicating the increase of earthquakes in the area of indonesia due to the very shallow south china sea warming and causing thermal expansion of the plate. Check it out! It is the one stop you need for all your tectonic plate info. Note: This is a new theory that I am hoping will be accepted, although my website was created in a hurry and looks a bit unprofessional, the theory I believe to be sound. Cheers… and please email your thoughts to the adress at the top of the website.
Best Regards

DocRichard said...

Hi Kevin
I had a quick look at your page, and found it very interesting and not flaky. The figure on the number of earthquakes in the South China Sea is very interesting.

I wonder whether the thermal expansion of the Earth would actually have a diminishing influence in sea level rise, just as old glass thermometers were said to have an initial fall when placed into a warming environment, because the glass container expanded before the heat got through to the fluid.

However, I am not a geologist, and I would guess you are having difficulty getting a hearing from professional geologists, who would demand peer-reviewed data in the right journals for about 20 years before you can claim respectability. I believe the guy that came up with plate tectonics was self-taught, and had a big struggle to gain acceptance. So - good luck, and be persistent. Thanks for commenting.

fpteditors said...

What about ice on land melting and raising sea level. Would not the change in sea-water weight have an effect? Has it not already been shown that the moon and tides have an impact?

DocRichard said...

Ice melting is a known factor because the relief of weight causes the plates to move upwards.

I do not know what effect the change in sea levels have. I guess there must again be pressure changes.

Every change in physical forces acting on the planet must have an impact, but it is going to take a while for seismologists to arrange the forces in a reliable well-understood system.

Thanks for commenting.

DocRichard said...

Notice the update: confirmation from a long term correlation between volcanic activity and rapid warming: http://www.sciencedaily.com/releases/2012/12/121219133551.htm