May 25, 2006 — The "Rim of Fire" that girdles the Pacific has recently unleashed dozens of shocking earthquakes and a volcanic eruption, but scientists suggest these shows of ill temper may be no more than coincidence.
From Jan. 3, when a huge quake occurred between Fiji and Tonga, to May 23, when a temblor shook Kamchatka, in Russia's Far East, there have been 33 earthquakes on the Rim measuring 6.0 or more on the Richter Scale.
Adding to the tableau is the angry awakening of the volcano Mount Merapi on the Indonesian island of Java.
Twenty-nine of the quakes have occurred on the western side of the Rim, in an arc running from Kamchatka to New Zealand.
Six of the quakes measured greater than 7.0, topped by a 7.9 behemoth off Tonga on May 3. Six took place in Kamchatka and three near Tonga.
The activity has led some to wonder whether the series of quakes be the harbinger of something nastier. But seismologists are generally reassuring.
They say there can be clusters of quakes triggered in domino fashion. The energy released by one quake puts additional stress on adjacent weak spots, and it may take only a small extra push for that point to rip open.
"Almost all the systems in the major faults that we know behave in the same way," said Paul Tapponnier of France's Institute for the Physics of the Globe in Paris (IPGP). "It's a bit like a shirt that you unbutton. If you suddenly release one button, you place more pressure on the others and they quickly pop, one after another."
But this phenomenon has only been seen along short lengths of a big fault over a few hundred kilometres (miles) -- not thousands.
There have been two outstanding examples of this "domino" effect in recent years. In northwestern Turkey, two quakes occurred in August and November 1999, killing around 20,000 people.
And the 9.3-magnitude Dec. 26, 2004, quake, which unleashed a tsunami in the Indian Ocean that killed more than 200,000 people, was followed by an 8.7 quake just 160 kilometres (100 miles) to the south on March 28, 2005, killing 900.
According to the US Geological Survey (USGS), since 1900 there have been on average 19.4 quakes measuring 7.0 or higher on the Rim each year, though only 11 occurred in 2005. So this year's activity may not prove to be all that exceptional.
"The Pacific Ocean rim is studded with subduction zones that are constantly active," said Mustapha Meghraoui, of Institute for the Physics of the Globe in Strasbourg (IPGS), eastern France. A subduction zone is where one plate slides under the other, rather than bumps or grinds alongside, and it produces the most powerful, dreaded earthquakes of all.
"But most of the activity never makes the headlines, because many quakes occur deep beneath the Pacific or in very sparsely populated areas and the toll is light," said Meghraoui.
