Posted on September 28, 2012 by thetruthbehindthescenes|
You may not have felt it, but the whole world shuddered on 11 April, as Earth’s crust began the difficult process of breaking a tectonic plate.
When two huge earthquakes ripped through the floor of the Indian Ocean,
they triggered large aftershocks on faults the world over, and provided
the best evidence yet that the vast Indo-Australian plate is being torn
Geologists have spent five months puzzling over the twin quakes - of magnitude 8.6 and 8.2
– which took place off the coast of North Sumatra. Events that large
normally occur at the boundary between tectonic plates, where one chunk
of Earth’s crust slides beneath another, but these were more than 100
kilometres from such a subduction zone. What’s more, both involved rocks
grinding past each other sideways with very little vertical movement –
what geologists call strike-slip earthquakes. Yet strike-slip quakes
this large had never been reported before.
Matthias Delescluse at the École Normale Supérieure in Paris, France,
and his colleagues have an explanation. They analysed quakes in the
area since December 2004, when a magnitude-9.1 quake in a subduction
zone near Sumatra triggered a devastating tsunami. They found
earthquakes during this period were nearly 10 times more frequent
compared with the previous eight years. What’s more, 26 of the quakes
that happened between December 2004 and April 2011 were similar to the
11 April quakes in that they involved rocks being pushed and pulled in
the same directions.
Taken together, the events suggest that the Indo-Australian plate is
breaking up along a new plate boundary, say the researchers, and that
may account for both the location and the size of April’s quakes .
Although both are currently on the same plate, Australia is moving
faster than India. This is causing a broad area in the centre of the
Indo-Australian plate to buckle. As a result, the plate may be splitting
John McCloskey at the University of Ulster in Coleraine, UK, is not
yet convinced, saying the evidence from the April events is still too
weak to support such a bold claim. But Lingsen Meng at the University of
California, Berkeley, who studied the rupture pattern of the larger 11
April quake, is more confident. “I think it’s a fair argument that the
11 April earthquakes may mark the birth of a plate boundary,” he says.
Things should become clearer as more earthquakes shake the region.
If they are anything like the 11 April events, the rest of the world
may shake too. In another new study, Fred Pollitz at the US Geological Survey in
Menlo Park, California, and his colleagues found that the global rate
of quakes with a magnitude of 5.5 or greater increased almost fivefold
in the six days after 11 April – something that has never been seen
before, even after very large earthquakes .
“This was the most powerful event (ever recorded) in terms of putting
stress on other fault zones around the world,” Pollitz says.
Source and author: newscientists tectonic plate
Thanks to: http://www.thetruthbehindthescenes.org