K Leslie Graves Show So
You Cannot Sleep Tell Why
DAILY GLOBAL UPDATE - The K. Leslie Graves Show
Recently
Keeping you abreast so
that no victims are forgotten and no community stands alone.
Please contribute $1 to
keep this show on the air
All contributions are
appreciated!
FAIR USE: Visit these
great links
6.3-quake hits off Indonesia's Sumatra: USGS
AFP | Sep 14, 2012,
11.50AM IST
JAKARTA: A 6.3-magnitude quake struck off Indonesia's Sumatra island today, the US Geological Survey said, but no tsunami warning was issued and there were no immediate
reports of damage or injuries.
The epicentre of the quake, which struck at 11:51 am (0451 GMT) at a depth of 25 kilometres, was 190 kilometres northwest of the town of Bengkulu.
Indonesia's Meteorology, Climatology and Geophysics Agency measured the magnitude at 6.1.
"There are no reports of damage so far. The quake happened in the sea close to Mentawai island, but no tsunami warning has been issued," the agency's duty officer, Koko Widyatmoko, told AFP.
Indonesia sits on the Pacific "Ring of Fire" where continental plates collide, causing frequent seismic and volcanic activity.
The epicentre of the quake, which struck at 11:51 am (0451 GMT) at a depth of 25 kilometres, was 190 kilometres northwest of the town of Bengkulu.
Indonesia's Meteorology, Climatology and Geophysics Agency measured the magnitude at 6.1.
"There are no reports of damage so far. The quake happened in the sea close to Mentawai island, but no tsunami warning has been issued," the agency's duty officer, Koko Widyatmoko, told AFP.
Indonesia sits on the Pacific "Ring of Fire" where continental plates collide, causing frequent seismic and volcanic activity.
Business in now worried
Global
Warming: Top Firms 'Fear Climate Change'
Major companies are increasingly
concerned that they are at risk from climate change in the face of recent
extreme weather events such as drought and floods, according to a report.
More than a third (37%) see the
physical risks of a changing climate such as extreme weather, rising sea levels
and water scarcity as a real and present danger, up from just 10% two years
ago, says the latest Carbon Disclosure Project (CDP) survey of top global companies.
Four-fifths (81%) identify climate
change risks to their business operations, supply chains and plans, up from 71%
last year.
Of the 379 of the 500 companies
who responded to the CDP's request for information about climate strategies and
emissions data, 78% say they are now integrating climate change into their
business strategy, up from 68% last year, the annual CDP Global 500 report
said.
K Leslie Graves Show So You Cannot Sleep Tell Why
Our Archives
|
8/30/2012 6:30 PM
|
1249
|
1
|
1
|
||
|
8/15/2012 11:00 PM
|
1092
|
2
|
3
|
||
|
8/12/2012 8:30 PM
|
307
|
0
|
1
|
||
|
8/9/2012 11:00 PM
|
547
|
0
|
1
|
||
|
8/7/2012 11:00 PM
|
300
|
0
|
1
|
||
|
8/6/2012 11:30 PM
|
169
|
7
|
6
|
||
|
7/30/2012 11:30 PM
|
2518
|
4
|
2
|
Worldwide Recent, Significant
Historical
Tsunami Generation from the 2004 M=9.2 Sumatra-Andaman
Earthquake
Tectonics of Sumatra-Andaman Islands
Indonesia's Sumatra alive to quake and tsunami risks
There is no doubting
the people of Sumatra are alive to the risks of earthquakes and the possibility
of a tsunami.
News video of panic
and shock emerging from Banda Aceh, the provincial capital and largest city in
the island's northern province, spoke volumes.
Wednesday's major tremor (M8.6) occurred in a similar location, although much
further offshore (some 400km), at 15:38 local time (08:38 GMT). It was followed
by an aftershock of M8.2 just a couple of hours later.
Tsunami alerts were
issued for the entire Indian Ocean basin but, mercifully, the scale of the wave
action appears to have been small - on the order of a few tens of cm in height.
"Our tide gauges
and buoys recorded small tsunamis," Said Kristiawan, of Indonesia's
Meteorology and Geophysics Agency, said.
Underwater
landslide
Geologists reported
quickly that the quake was "predominantly strike-slip" - that is to
say, the movement of rock at the site of fracture was horizontal in nature.
"Tsunami can be
caused in a number of ways, but typically it is where the seafloor can be moved
vertically, and that displaces a large amount of water that travels outward
from that source toward land," observed Bruce Pressgrave, from the US
Geological Survey (USGS).
"One of the ways
that strike-slip earthquakes can cause tsunami is if the shaking itself causes
some kind of underwater landslide that then produces the movement in the water
column," he told BBC News.
Nonetheless, the
alerts stayed in place for several hours as the authorities attempted to get on
top of the latest information, and there is now a lot more of it.
This is one of the big
changes since 2004. There is now a tsunami monitoring system dedicated to the
Indian Ocean, put in place through the leadership of [UN scientific agency]
Unesco in 2006.
Pressure sensors on
the ocean floor detect anomalous behaviour in the water column and signal that
information to surface buoys, which then relay the data, via satellite, to
onshore control centres.
The system is much
needed, particularly in Indonesia. Its Sumatra island lies close to an active
subduction zone, where the Indian-Australian tectonic plate presses into and
under the Eurasian plate.
This monumental
collision is evident on the ocean floor by a huge depression known as the Sunda
Trench.
The slab of cold,
dense rock that descends into the Earth at this point gets stuck, and strain
builds up that has to be released at some stage in the form of an earthquake.
More
aftershocks
But what was key to
Wednesday's outcome was that the main event occurred some distance to the west
of the Sunda Trench, and so did not produce the very big megathrust action
capable of deforming the seafloor in a way likely to generate large tsunamis.
"This is not one
of those; it was the seafloor moving horizontally - one part moving relative to
the other," explained Dr Richard Luckett, a seismologist with the British
Geological Survey.
"What we think
this is, is some kind of correction to do with all the massive earthquakes that
have happened in the Sunda trench in the last 10 years.
"And so this kind
of earthquake, although very big and widely felt, is much less likely to cause
a serious tsunami," he told the BBC.
"We're unlikely
to get another aftershock as big as the M8.2, although it can happen. But there
will be aftershocks - fives, sixes, maybe even sevens, going on for several
months."
To put these
magnitudes in context: one would expect about two or three quakes a year
greater than M8.0 to occur somewhere on Earth. On Wednesday, they had a pair of
big ones off the coast of Sumatra.
Already a curiosity for its sheer
size, the 8.6-magnitude earthquake that shook the seafloor west of the Indonesian
island of Sumatra on April 11 appears to have been even weirder than scientists
thought.
A
new study reveals the quake zigzagged along four faults, three of which are set
perpendicular to each other. From above, the layout looks like a city street grid.
"We call it an earthquake in a maze," said Lingsen Meng, lead author
of the study and a graduate student in seismology at Caltech.
"We
were very excited to see this because an earthquake this large, involving this
complicated a fault system, does not happen very often," Meng told
OurAmazingPlanet. "This may be the only one I will see in my
lifetime."
The April Sumatra shaker was a strike-slip earthquake, in which two parts of the
Earth's crust slide past each other horizontally. The quake was not only the
11th largest quakerecorded by seismometers, it's also the largest strike-slip
quake on the books. It's also one of the rare big intraplate earthquakes ; that is, it happened away from a plate
boundary, where two plates of the Earth's crust meet and where most of the world's largest earthquakes occur.
The
results of the new study, detailed in tomorrow's (July 20) issue of the journal
Science, provide the first in-depth picture of the rupture. The study also
offers intriguing clues about the physics of extremely large
earthquakes, and the properties of oceanic plates. The observations
could shed new light on intraplate quakes and how tectonic plate boundaries
evolve.
This
earthquake "provides an exceptional opportunity to probe the mechanical
properties of Earth’s materials deep beneath the oceans," Meng said. [ April 2012 Sumatra Quake (Infographic) ]
Seismic back-tracking
To better understand how the Earth unzipped during this quake, Meng and his Caltech colleagues applied a technique called back-projection imaging to seismic waves recorded from the Sumatra quake. The imaging process is similar to how our brain uses sound to determine the position of moving objects.
To better understand how the Earth unzipped during this quake, Meng and his Caltech colleagues applied a technique called back-projection imaging to seismic waves recorded from the Sumatra quake. The imaging process is similar to how our brain uses sound to determine the position of moving objects.
Indonesia quake a record, risks for Aceh grow
(Reuters) - The powerful undersea earthquake off the
Indonesian island of Sumatra this week was a once in 2,000 years event, and
although it resulted in only a few deaths, it increases the risks of a killer
quake in the region, a leading seismologist said.
Wednesday's 8.6
magnitude quake and a powerful aftershock were "strike-slip" quakes
and the largest of that type recorded, Kerry Sieh, director of the Earth
Observatory of Singapore, told Reuters.
"It's a really an
exceptionally large and rare event," he said.
"Besides it being the
biggest strike-slip earthquake ever recorded, the aftershock is the second
biggest as far as we can tell," said Sieh, who has studied the seismically
active, and deadly, fault zones around Sumatra for years.
Strike-slip quakes involve the
horizontal movement of colliding earth plates, and are typically less powerful
than those where there is vertical movement. They are also less likely to
trigger big tsunamis, or tidal waves.
A magnitude 9.1 quake in roughly
the same region on Boxing Day in 2004 decimated Aceh province on Sumatra and
killed over 230,000 people in 13 countries around the Indian Ocean.
Sumatra, the westernmost island
in the sprawling Indonesian archipelago, has a history of powerful quakes and
tsunamis, most triggered by an offshore zone along its entire length, where the
Indian-Australian tectonic plate is forced under the Eurasian plate.
This creates a deep ocean trench
as one plate slides under the other at a rate of several centimeters a year. In
this zone, called the Sunda megathrust, stress builds up when the subducting
Indian-Australian plate bends the Eurasian plate like a spring board as it
moves down into the Earth's crust.
Eventually enough stress builds
up that the edge of Eurasian plate suddenly jolts upward, triggering an
earthquake. The sudden uplift of the seafloor and huge pulse of seawater
triggers a tsunami.
Over the centuries, repeated
magnitude 8 and 9 quakes have struck along portions of the megathrust zone off
the coast of Sumatra, flattening towns and killing thousands of people.
STING IN THE TALE
Wednesday's event was different,
Sieh said, because it occurred further west from the megathrust zone in a fault
that runs north-south. This strike-slip fault involved a sudden horizontal
movement of the Indian and Australian plates along hundreds of kilometers,
preliminary data suggest.
Sieh said the Indian plate and
Australian plate are moving relative to each other horizontally at about 1 cm a
year.
"If all of that ... is taken
up on this one fault and if you make some crude calculations about how much
slip occurred during this earthquake, say 20 meters. It means that this
earthquake shouldn't happen more than once every 2,000 years."
Wednesday's quake caused few
casualties and triggered very small waves, despite its magnitude. But the sting
in the tale is that it likely to have increased stress on the plate boundaries
near Aceh, increasing the risks of another major earthquake in the same area as
the 2004 disaster.
In addition, research by Sieh and
colleagues published in 2010 showed that the 2004 Aceh quake only relieved
about half the stress that has built up over the centuries along a 400 km
portion of the megathrust faultline.
That makes another major quake in
the area a matter of time.
Adding to concerns, further south
along another 700 km portion of the megathrust fault under the Mentawai
islands, Sieh and colleagues in a separate 2008 research said so much stress
was building up on this section that one or more major quakes were likely
within years.
The Mentawai islands, a popular
surfing destination, are a chain of about 70 islands off the western coast of
Sumatra. They face the city of Padang on Sumatra, home to about one million
people and likely to be in the path of any tsunami that is triggered.
"I am very confident that we
are very likely to have within the next few decades to have this great Mentawai
earthquake that will have a magnitude at least as big as yesterday's,"
said Sieh.
And when it does, history shows
there will be more than one quake within a few years.
He said a magnitude 8.4 quake in
2007 that struck this part of the megathrust relieved only a small portion of
the pent-up pressure. The last time it ruptured was a magnitude 9 quake in 1833
and an 8.4 quake in 1797.
"We've had so many big
earthquakes around in Sumatra in the past few years that it seems like an awful
lot of the faults around there seem ready to go."
Panic in
Indonesia as 8.6 quake hits off Sumatra (PHOTOS, VIDEO)
A massive quake off the
west coast of Indonesia sent fears across the country, prompting residents in
coastal cities to rush to higher ground. A tsunami that followed a similar
quake in 2004 killed nearly 230,000 people, most of them in Indonesia.
No comments:
Post a Comment