Fri, 27 Jun 2014 14:54 UTC
"We have recently experienced a period that has had one of the highest rates of great earthquakes ever recorded," said lead study author Tom Parsons, a research geophysicist with the U.S. Geological Survey (USGS) in Menlo Park, California.
But even though the global earthquake rate is on the rise, the number of quakes can still be explained by random chance, said Parsons and co-author Eric Geist, also a USGS researcher. Their findings were published online June 21 in the journal Geophysical Research Letters.
With so many earthquakes rattling the planet in 2014, Parsons actually hoped he might find the opposite - that the increase in big earthquakes comes from one large quake setting off another huge shaker. Earlier research has shown that seismic waves from one earthquake can travel around the world and trigger tiny temblors elsewhere.
"As our group has been interested in the ability of an earthquake to affect others at a global scale, we wondered if we were seeing it happening. I really expected we would see evidence of something we couldn't explain by randomness," Parsons told Live Science's Our Amazing Planet in an email interview.
The new study isn't the first time researchers have tried and failed to link one earthquake to another in time and across distance. Earlier studies found that the biggest earthquakes on the planet - the magnitude-8 and magnitude-9 quakes - typically trigger much smaller jolts, tiny magnitude-2 and magnitude-3 rumblers. Yet, no one has ever proven that large quakes unleash other large quakes. Finding a statistical connection between big earthquakes is a step toward proving such connections takes place.
But despite the recent earthquake storm, the world's great earthquakes still seem to strike at random, the new study found.
The average rate of big earthquakes - those larger than magnitude 7 - has been 10 per year since 1979, the study reports. That rate rose to 12.5 per year starting in 1992, and then jumped to 16.7 per year starting in 2010 - a 65 percent increase compared to the rate since 1979. This increase accelerated in the first three months of 2014 to more than double the average since 1979, the researchers report.
The rise in earthquakes is statistically similar to the results of flipping a coin, Parsons said: Sometimes heads or tails will repeat several times in a row, even though the process is random.
"Basically, we can't prove that what we saw during the first part of 2014, as well as since 2010, isn't simply a similar thing to getting six tails in a row," he said.
But Parsons said the statistical findings don't rule out the possibility that the largest earthquakes may trigger one another across great distances. Researchers may simply lack the data to understand such global "communication," he said.
"It's possible that global-level communications happen so infrequently that we haven't seen enough to find it among the larger, rarer events," Parsons said.
However, earthquakes smaller than magnitude-5.6 do cluster on a global scale, the researchers found. This suggests these less-powerful quakes are more likely to be influenced by others - a finding borne out by previous research.
For example, the number of magnitude-5 earthquakes surged after the catastrophic magnitude-9 earthquakes in Japan and Sumatra, even at distances greater than 620 miles (1,000 kilometers), earlier studies found.
Comment: To understand why this is happening, read Earth Changes and the Human-Cosmic Connection. Here's a relevant excerpt:
From 1973 to 1996, earthquake and eruption frequencies were almost stable, increasing only slightly year after year, but from 1996 onwards, an acceleration is noticeable. Volcanic eruptions show an increase from about 59 eruptions per year at the end of the 1990s to roughly 75 eruptions per year in the period 2007 - 2010 (+30%).
Today, the increase in volcanic activity has reached such a level that, by late November 2013, 35 volcanoes were actively erupting , including volcanoes that had been dormant for decades.
It could be argued that the increase in both the frequency and intensity of earthquakes and volcanic eruptions is, at least partly, a result of the slowdown and 'opening up' processes:
1) The Earth's minute slowdown exerts mechanical stress on the crust (compression at low latitudes and extension at high latitude). This stress deforms the crust. This deformation is more pronounced and can even lead to partial ruptures around the weakest spots of the crust, i.e. the fault lines (boundaries between tectonic plates) which are the typical location of seismic and volcanic activity.
2) The mantle has a higher density than the crust and therefore has a higher momentum and won't slow down as fast as the crust. The difference in rotation between the crust and the mantle is equal to the crustal slippage. The fluidity of the mantle enables slippage induced by the different momentum carried by the crust, the upper mantle and the core.
This speed difference can cause friction at the interface between the crust and the mantle. This friction can locally deform the crust and cause earthquakes and eruptions.
3) The decrease in the surface - core E-field reduces the binding force and loosens the tectonic plates relative to each other. The plates are then free to move relative to each other. It is this very relative movement (divergence, convergence or sliding) which is one of the main causes for earthquakes and volcanic eruptions:[Change] in Earth's speed of rotation would induce changes in the magma tide as it adjusted to the new equator or altered rotational speed. Such changes, however, might not be uniform throughout, owing to a 'drag' factor deep in the magma itself, although, overall, they would certainly impose terrible strains on the lithosphere generally.4) A final factor involved in earthquakes and volcanic eruptions is electromagnetism:Some scientists have become aware of a correlation between sunspots and earthquakes and want to use sunspot data to help predict earthquakes. The theory is that an intensification of the magnetic field can cause changes in the geosphere [i.e. crust]. NASA and the European Geosciences Union have already put their stamp of approval on the sunspot hypothesis, which suggests that certain changes in the Sun-Earth environment affect the magnetic field of the Earth, which can then trigger earthquakes in areas prone to them. It is not clear how such a trigger might work.