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The magnitude 8.6 earthquake that struck North Sumatra, Indonesia, at
2:38 p.m. local time today did not lead to a tsunami comparable to
Indonesia's 2004 disaster for a couple of reasons.
The magnitude 9.1 earthquake that struck in 2004 and triggered a
tsunami that killed more than 200,000 people in 14 countries was a
subduction megathrust earthquake closer to shore (250 kilometers
south-southeast of Banda Aceh). A megathrust earthquake is also the same
type of earthquake that struck off Japan in 2011. These types of
earthquakes do the kind of damage that their name implies, mega
thrusting of the fault.
Today's temblor ripped along an oceanic transform fault, tearing
the seafloor in a strike-slip motion as opposed to popping it apart.
Strike-slip motion carries less of an ability to push up on the entire
water column above it and hence is less likely to form the same kind of
tsunami wave as what hit Indonesia in 2004 and Japan in 2011. Though it
is not without risks. Early calculations showed that the island of
Simeulue might expect waves as high as 6 meters (20 feet).
Thank God it is a Strike slip not a Reverse Dip (Thrust) Slip, which caused havoc in 2004 & 2011 in Indonesia & Japan respectively.
The diagrams explain themselves.
Click Here to go to Wikipedia - Fault Geology
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