There's no saying when this could happen, say researchers. It
could be tomorrow, or 500 years from now.
A
monster earthquake, possibly with a magnitude 8.2 to 9 on the Richter scale, is
brewing beneath Bangladesh, Myanmar and Northeast India, imperilling 140
million people within 99 km of its potential epicentre, according to a new paper in the journal Nature
Geoscience.
When that might
happen is unclear. It could be 500 years from now or it could be tomorrow, but
the researchers said an earthquake is inevitable.
The 62,159-sq-km
area, along what is called the “Indo-Burmese arc”, which runs through India,
Bangladesh and Myanmar, is where the Indian tectonic plate – a raft of the
earth’s crust that bears the subcontinent – is diving obliquely under the Sunda
plate in Myanmar, at around 46 mm a year. The two plates have been stuck for
400 years, and a growing strain could eventually liberate itself in a large
earthquake, researchers said.
The evidence
comes from the first detailed picture of the region’s tectonic motion. A team
of scientists from the US, Singapore and Bangladesh analysed the combined data
over 13 years from global positioning system – a network of satellites around
the earth used to locate positions, in this case plates that form the planet’s
crust–stations in Bangladesh, with additional data from India and Myanmar.
“This is the
first regional GPS study that uses data from across the entire plate-boundary
region (locations where two tectonic plates meet),” Michael Steckler, the lead
author of the study and a geophysicist at Columbia University’s Lamont-Doherty
Earth Observatory told IndiaSpend.
“This is a great
work,” Vineet Gahalaut, Director, National Centre for Seismology, New Delhi,
told IndiaSpend.
“Lots of groups and people are working on the Himalayan region, not in this
region. Considering the lives involved, the study brings much-needed attention
to the seismology of the region.” Gahalaut is not involved with the study.
As many as 107
Indian towns and cities lie in areas prone to earthquakes, with 60% of the
subcontinental landmass vulnerable, IndiaSpend reported in April 2016.
Steckler said
they have long guessed a megathrust fault – the interface between tectonic
plates – may be lurking underneath Bangladesh, but they did not have the data
or the model. Now, using data from the GPS arrays, which can track the crust’s
movements accurate to within 2 mm each day, “we can see the motion of the
various blocks and across faults over the years”.
The region is unstable below the surface as much as on
the surface, with a daily dose of social, economic and security problems. Fault
lines crisscross the innards and surface. “The presence of a locked megathrust
plate boundary represents an underappreciated hazard in one of the most densely
populated regions of the world,” said the paper.
Great tectonic conflict
The newly
identified subduction zone – where one tectonic plate dives under the other –
yet again illustrates the patchwork of faults in South Asia. As India plows
into Asia, some of the continent is wrapping around the side of the Indian
plate, causing considerable deformation in Asia. The Indian and Eurasian plates
have been in conflict for 50 million years at this collision zone, with the
Indian plate diving, northward, under the Eurasian plate.
“This produces
the combination of mostly sideways and some convergence in this complicated
zone,” Steckler explained.
The world’s
largest earthquakes occur at subduction zones, when slabs of heavy ocean crust
slide under the other plate below the ocean floor or under neighbouring
continental crusts.
In 2004, the 9.3
magnitude Indian Ocean temblor, epicentred in the Indian Ocean off the coast of
Sumatra, triggered a tsunami that killed
2,27,898 people; in 2011, a 9 magnitude earthquake centred off the
coast of Tohoku in Japan setting off a tsunami, killing
15,891 and triggering
the Fukushima nuclear
meltdown.
Wobbly effect
However, this
particular subduction zone in the Indo-Burma region is right under our feet, so
to speak, and its nature has been a bone of contention. Since the motion
between the plates is angled, some researchers thought the two plates were
sliding past each other and that there was no significant coming-together
between the plates and hence no subduction, a more violent affair.
The latest GPS
evidence indicates motion consistent with subduction. “Furthermore,” said
Steckler, “the pattern of deformation indicates that the two plates are locked
– they are stuck together [the Indian plate is stuck to the underside of
mountains in Northeast India and Myanmar] – but will eventually jump in a large
earthquake.”
Another
peculiarity of the region is its sedimentary build-up. As the Himalayas erode,
mud pours into the Ganga and Brahmaputra and finally spills into the Bay of
Bengal. This mud is being scraped off and folded up to form the Indo-Burman
Ranges, like a rug being pushed against a wall, as Steckler put it, further
destabilising the plates. “The largest difference between this and other
subduction zones (not counting zones where continents are in collision) is the
enormous thickness,” said Steckler.
This mud also
feeds the plains of the Ganga and Brahmaputra basin, turning it one of the
world’s most fertile regions. The researchers estimated that sediment disgorged
from the rivers has moved the edge of the continent westward by about 400 km
near Bangladesh.
With the mud
piled up as thick as 19 vertical km, it is challenging for scientists to
pinpoint the contours of a future temblor.
140 million people living on a jelly-like land
In effect, the
region’s 140 million people are living on jelly. In the event of an earthquake,
Steckler said, the thick sediment may reduce “high-frequency shaking” but will
amplify “low-frequency ground shaking”, which refers to violent shaking that
can topple buildings.
“No one has yet
modeled the effect in detail, but overall, I think, it will make the effects of
the earthquake worse,” said Steckler. “There may also be liquefaction, where
the ground can temporarily lose solidity, and buildings can topple.”
The present
study focused on the eastern boundary of the Indian plate, the Indo-Burman
range, but tectonic disquiet grows as well on the northern boundary, on the
Main Himalayan Thrust, as IndiaSpend reported here and here.
There is, as IndiaSpend reported in October 2015, a possibility of a
more severe earthquake in the Himalayas – although it isn’t certain when – than
the 7.8-magnitude temblor that devastated Nepal on April 25, 2015.
Steckler
acknowledged that a study of this nature calls for more data collection and
interpretation. For example, researchers don’t know when the last one was or
how often they repeatedly occur, and so they cannot estimate a time for the
next one. There is not yet robust data on the shape of the fault, how much
strain is taken by the folds and how much at the meeting of the plates, the
megathrust.
Researchers say
they’re working on collaboration, and a tripartite meeting between India,
Bangladesh, and Myanmar scientists –including Steckler and his colleagues – had
been held. Gahalaut said that a “big project” is in the works – with each
country’s researchers seeking funding from their own respective ministries–to
possibly include early warning systems. “We’re going to share data and analyse
it jointly,” he said.
Representative Image
Source: Scroll
To get more such news in feed, like our page ‘Facet’
This is dummy text. It is not meant to be read. Accordingly, it is difficult to figure out when to end it. But then, this is dummy text. It is not meant to be read. Period.
ConversionConversion EmoticonEmoticon