Are mega quakes becoming more frequent?

The twin Indonesian quakes on Wednesday represented the sixth and seventh in the series of mega quakes being recorded around the world in almost as many years.

These have measured in excess of 8 on the Richter scale (classified as ‘great') and have originated from as far afield as Sumatra in Indonesia to Maule, Chile.

The M9.1 Sumatran event of 2004 and M9.0 of Sendai, Japan, have been the strongest in terms of intensity.

AXIS TILTERS

These quakes are associated with such massive intensity that they are able to even nudge the tilt of Earth's axis, especially in the case of the M9 ones.

According to a New Scientist report, large earthquakes generate tectonic waves that ripple around the world's surface and trigger smaller quakes on distant faults.

The Indonesian archipelago has been particularly active after the M9.1 event of 2004 that sent down a giant tsunami wave killing more than two lakh people.

Large quakes can cluster locally: aftershocks are common in the wake of a large quake, and occasionally they can be as large as the primary shock.

CLUSTERING EVENTS

This was brought home in good measure on Wednesday when the Indonesian seabed rocked twice with an intensity of above M8.

New Scientist quoted geologists saying that the number of mega quakes is too small to be able to make a statistically convincing case for a link.

A handful, however, feel there must be a link between recent events.

In the 6.2 years since 2004, there have been more great earthquakes than in any 6.2-year period throughout the 110-year history of seismic recordings.

The recent spurt of magnitude-8-plus earthquakes may be an extended aftershock sequence of the 2004 Sumatra earthquake.

RARE BUT ROARING

One of the few consolations is that quakes of magnitude 8.5 and above are rare: Sendai is in the top 10 of the highest-magnitude quakes of the last 100 years.

Yet three of these – the December 2004 Sumatra quake, the February 2010 Chile quake, and now Sendai – have struck in just over six years.

This presents a horrifying possibility: that there is a link between these mega quakes and that, as a result, more could strike, the New Scientist said.

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