The honor of greatest earthquake of all time goes to the 1960 Chile
earthquake because scientists were able to 'catch this one on tape'.
In other words, there have been a lot of really big earthquakes throughout
human history (and even greater ones before we came on the scene),
but this one they were able to measure, record and verify its ground
motion strength. The instruments that seismologists use to measure
earthquake magnitudes are designed to detect the amount of energy
released by the movement of the ground during a quake. In the case
of the Chile earthquake, the amount of energy released during the
quake, not the number of human deaths and damage to structures, earned
it the title of greatest.
The epicenter
of the earthquake (the point on the earth's surface directly above
the focus of an earthquake) was 60 meters down below the ocean floor
about 100 miles off the coast of Chile out in the Pacific. The nearby
towns of Valdivia and Puerto Montt suffered devastating damage because
of their closeness to the center of such a massive quake. The loss
of human life was not as bad as it could have been because there
were large foreshocks that sent people into the streets talking.
About 30 minutes after
the foreshocks, when the main jolt came, many people were still
outside calming their jitters from the first shock. The buildings
and homes that fell had pretty much vacated. However, damage cost
estimates were over a half billion dollars.
Not only
was there damage to man-made structures during the quake, but the
earth itself was forever changed by the enormous amount of energy
released from below. Huge landslides, massive flows of earthen debris
and rock, were sent tumbling down mountain slopes. Some landslides
were so enormous they changed the course of major rivers or dammed
them up creating new lakes. The land along the coast of Chile, particularly
in the Port city of Peurto Montt, subsided
(sunk downward) as a result of the movement of the ground during
the quake and the coastal city was flooded with ocean water.
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Flooding of village streets was
due to subsidence of coastal land as a result of the 1960
earthquake.
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The damage
from the quake was not limited to the nearby shores of Chile. Enormous
waves or tsunamis
(read about the world's biggest), traveled
for thousands of miles across the vast expanse of the Pacific Ocean,
reaching the shores of Hawaii, the Philippines, and even Japan devastating
everything in their path. The tsunamis were created by the shifting
of the sea floor that generated the huge temblor. It was as though
someone had dropped a huge boulder in the ocean right over the epicenter
of the quake, sending enormous ripples in every direction, traveling
at speeds up to 200 miles per hour!
Deep Rumblings
So what caused
the earthquake? Whenever an earthquake of any size happens anywhere
in the world the same basic thing happens; the ground along either
side of a fault
(a fracture or crack in the ground) moves.
Faults are
cracks in the earth caused by buckling and stress from the
movement of the tectonic
plates.
Movement along faultlines tends to happen along plate boundaries (where
the edges of the tectonic plates meet) See
the page on Ocean's Deep for more information.
In the case of this enormous earthquake, the subduction (downward
movement) of the Nazca plate under the the South American continent
is what caused the major quake back in 1960 (see
the page on Plate Tectonics). In
fact, the Nazca plate continues to dive down below the continent and
it's this constant slow movement (with some occasional rapid shifts
leading to big jolts) that creates earthquakes throughout that region.
Chile has
seen many earthquakes both before the 1960 record-setting temblor
and after. Two very large contenders have happened on March 3, 1985,
and another on July 30, 1995. These earthquakes both had a magnitude
of about 8. Chilean earthquakes are not rare nor are they small. Large
earthquakes in Chile seem, through history, to occur about every 25
to 100 years. They'll continue as long as the Pacific plate continues
subducting.
