The location of almost all earthquakes in the
Earth is related to the movement of large
lithospheric plates. This is the theory of
The mountain belt that runs along the long axis of
Italy is called the
The Apennines are there because one
plate is sliding beneath another along the axis of
these mountains. In fact that is why there are
mountains and uplift. The earthquake is due to the
sliding of one plate beneath the other. The
CRUSH ZONE is the mountain chain.
The earthquake in Italy on 8/24 was a 6.2
magnitude, normal faulting earthquake. Basically,
it happened due to east-west extension in this
area, which means that the region is being
pulled apart in a east-west direction due to the
plate tectonics there. While a 6.2 magnitude
earthquake might not be considered very large by
some standards, the amount of shaking (and
resulting damage) has a lot to do with the
geology of the area (i.e. what type of rocks
the ground is made of) and what the buildings are
The Mercalli Intensity scale is a scale
used to measure the shaking from an earthquake,
from 1 (no shaking felt, no potential damage) up
to 10+ (extreme shaking, very heavy damage). The
shaking nearest to the epicenter of the Italy
earthquake was rated 8, or severe shaking and
moderate/heavy damage. This, coupled with the fact
that many of the buildings appear to be made out
of stone bricks, would cause a lot of damage.
If you are trying to make a building that is
earthquake proof, building it out of stone bricks
is one of the worst materials, it does not hold up
well when shaken and twisted. Brick walls will not
bend or sway when met with seismic waves, instead
they will just break and fall over. That is why
there are so few brick buildings in southern
California. This is likely the reason that there
was so much damage from the 6.2M earthquake. The
buildings were just not made to withstand an
earthquake of that size.
As blocks of crust slowly move against each other,
the stress that builds up is occasionally released
very quickly along a fault to produce an
earthquake. The earthquake in central Italy
happened along a fault in the Apennines Mountains
and had a hypocenter of 10 km (6.2 miles). That
means that the location of the fault that ruptured
was 10 km below Earth’s surface. The surface
experienced stronger ground motion because the
earthquake originated at a relatively shallow
Buildings and roads that are older or less
‘earthquake proof’ generally receive more
than newer buildings that are designed to
withstand earthquakes. Many of the buildings
damaged during the earthquake were built hundreds
of years ago, when construction of buildings was
very different than today.
The earth is covered with huge rocky plates that
float on the hot stuff in the center of the earth.
When two of these plates bump into each other,
there's an earthquake; but we don't know when
earthquakes will happen.
Most buildings aren't built strong enough to stand
up in a big earthquake. When I was riding the
train in Japan, I liked the beautiful blue tile
roofs on the houses in the towns; but the blue
tile roofs were heavy, and the houses fell down in
a big earthquake.
People are learning how to build stronger
buildings that can stand up in bigger earthquakes,
but lots of buildings are old; and they were built
before people knew how to build strong buildings.
The short answer is that, through the process
of continental drift, Africa is ramming northward
into Europe creating the Alps and closing up the
Mediterranean, and the strain that this puts on
the ground creates earthquakes at shallow depth.
This earthquake was not actually that powerful
- the 1906 earthquake that devastated San
Francisco for example was probably about a
thousand times stronger. I'm not enough of
an engineer to tell you what made this one so
destructive, beyond the fact that sound waves
(which are basically what earthquake waves are)
can combine in ways that intensify or dampen them
locally, which can increase or decrease damage.
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