Roger Pielke Jr, University of Colorado did a recent plot of earthquakes frequency by strength.
There has been no apparent trend.
Note in this piece on Watts Up with That, Anthony Watts and Steve Goddard show that although an increase over the last century of ‘reported earthquakes’ have occurred, it may be the result of more seismologists and equipment and that major devastating earthquakes in Japan, on the Pacific Ring of Fire are not new.
Really? You had to ask this question?
By Anthony Watts
I’m always amazed at the lack of historical perspective some people have related to natural disasters. It’s doubly amazing when reporters who work in newspapers, who have huge archive resources at their disposal, don’t even bother to look. Here’s some excerpts from the story:
“There is certainly some literature that talks about the increased occurrence of volcanic eruptions and the removing of load from the crust by deglaciation,” said Martin Sharp, a glaciologist at the University of Alberta. “It changes the stress load in the crust and maybe it opens up routes for lava to come to the surface.
“It is conceivable that there would be some increase in earthquake activity during periods of rapid changes on the Earth’s crust.”
Other scientists, however, believe that tectonic movements similar to the one that caused the Japanese quake are too deep in the Earth to be affected by the pressure releases caused by glacier melt.
Some experts claim that jump can be explained by the increased number of seismograph stations — more than 8,000 now, up from 350 in 1931 — allowing scientists to pinpoint earthquakes that would otherwise have been missed.
But this does not explain the recent increase in major earthquakes, which are defined as above 6 on the Richter magnitude scale. Japan’s earthquake was a 9.
Scientists have been tracking these powerful quakes for well over a century and it’s unlikely that they have missed any during at least the last 60 years.
According to data from the U.S. Geological Survey there were 1,085 major earthquakes in the 1980s. This increased in the 1990s by about 50 per cent to 1,492 and to 1,611 from 2000 to 2009. Last year, and up to and including the Japanese quake, there were 247 major earthquakes.
There has been also a noticeable increase in the sort of extreme quakes that hit Japan. In the 1980s, there were four mega-quakes, six in the 1990s and 13 in the last decade. So far this decade we have had two. This increase, however, could be temporary.
h/t to Steve Goddard, who has been doing a lot of historical research here.