Saturday 18 February 2012
|
Costa
Rica News.
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Can
Diving
Mountains
Stop,
or
Start,
Earthquakes?
What
happens
when
inexorable
geological
forces
shove
a
giant
seafloor
mountain
beneath
a
continent?
This
is
not
the
improbable
premise
of a
bad
eco-disaster
movie,
but
a
serious
area
of
inquiry
—
and
a
question
with
few
clear-cut
answers,
scientists
say.
A
spot
off
the
coast
of
Costa
Rica
where
seamounts
have
burrowed
into
the
continental
plate.
Two
seamounts
at
the
edge
of
the
frame
are
headed
in
the
same
direction.
However,
new
technology
is
allowing
researchers
improved
glimpses
of
what
happens
when
a
seafloor
mountain
crashes
into
and
under
a
continental
plate,
and
what
role
the
slow-motion
collision
plays
in
earthquakes.
These
collisions
occur
out
of
sight,
along
subduction
zones,
where
oceanic
plates
subduct,
or
dive
under,
overlying
continental
plates.
As
the
oceanic
plate
goes,
so
goes
the
mountain
that
sits
atop
it,
slowly
burrowing
into
the
side
of
the
continental
plate,
and
then
deeper
and
deeper
beneath
it.
Tunneling
mountains
Yet
these
subduction
zones
aren't
always
slow
movers.
When
the
oceanic
plate
suddenly
slips,
it
generates
an
earthquake
—
sometimes
a
massive
one,
such
as
last
year's
devastating
Tohoku
earthquake
in
Japan.
Some
research
has
cast
seafloor
mountains
(called
seamounts
) as
heroes,
suggesting
the
peaks
are
capable
of
halting
a
subduction
earthquake
in
its
tracks.
"To
get
a
super-big
quake
you
need
to
break
a
large
portion
of
the
plate
boundary
in
one
shot,
and
subducting
seamounts
may
segment
the
plane
in
big
earthquakes
— so
it
doesn't
all
go
at
once,"
said
Anne
Trehu,
a
geophysicist
at
Oregon
State
University.
Yet
new
research
suggests
these
burrowing
mountains
can
also
play
the
villain.
"They
could
form
a
barrier
to a
giant
earthquake
—
and
they
could
also
easily
trigger
a
giant
earthquake,"
said
Roland
von
Huene,
a
veteran
geophysicist
who
has
studied
subducting
seamounts
for
more
than
30
years.
Good
mountain,
bad
mountain
New
research
has
tied
a
spate
of
earthquakes
in
Oregon
to a
tunneling
seamount
scientists
estimate
is
about
16,000
feet
(5,000
meters)
high
—
taller
than
the
Alps.
Dubbed
M2,
the
buried
seamount
lies
about
19
miles
(30
kilometers)
off
the
Oregon
coastline.
Over
millennia,
the
mountain
has
tunneled
about
28
miles
(45
km)
eastward
into
the
North
American
plate,
and
is
buried
beneath
about
7
miles
(12
km)
of
rock.
Another
view
of
the
tunnels
left
behind
by
subducting
seamounts
off
Costa
Rica.
It's
impossible
to
get
such
clear
images
of
the
tracks
left
by
tunneling
mountains
off
the
Oregon
coast,
because
the
region
is
choked
with
unusually
large
amounts
of
sediment.
The
mountain
is
likely
behind
a
magnitude
4.8
earthquake
in
2004,
which
was
felt
on
land,
along
with
a
series
of
smaller
quakes.
So
why
is
it
acting
up
now?
It's
likely
because
the
mountain
is
now
facing
much
harder
rocks
in
the
overlying
continental
plate
than
it
has
yet
encountered,
said
Trehu,
who
led
research
on
the
quakes
published
in
the
Dec.
16
issue
of
the
journal
Geology.
"You
have
seismicity
concentrated
there
because
you
have
a
seamount
hitting
up
against
crystalline
rocks,"
Trehu
said
—
which
are
far
harder
than
the
sedimentary
rocks
the
mountain
plowed
through
on
the
first
leg
of
its
subterranean
journey.
However,
Trehu
cautioned,
that
is
simply
an
interpretation
of
compelling
data,
and
the
idea
is
controversial.
"Some
people
argue
it's
just
chance
that
you
have
earthquakes
there
now,"
she
said.
Nearby
menace
The
Cascadia
subduction
zone,
where
the
seamount
is
subducting,
stretches
from
Vancouver
to
northern
California,
and
has
produced
colossal
earthquakes
in
the
past.
In
1700,
the
subduction
zone
unleashed
a
powerful
earthquake,
likely
a
magnitude
9.0,
which
sent
a
damaging
tsunami
ashore
in
Japan.
And
although
the
Cascadia
hasn't
produced
a
massive
earthquake
in
more
than
300
years,
it
will
undoubtedly
do
so
again.
There's
just
no
telling
when
or
why,
Trehu
said.
It's
not
at
all
clear
what
relationship
the
small
earthquakes
likely
produced
by
the
burrowing
seamounts
would
have
to a
massive,
dangerous
quake,
Trehu
said.
However,
she
said,
technology
that
allows
for
better
imaging
of
the
buried
mountains,
and
the
reams
of
data
gathered
on
the
devastating
subduction
quakes
that
struck
in
Chile
in
2010
and
in
Japan
in
2011
are
helping
scientists
develop
better
theories
about
what
role
seafloor
topography
plays
in
earthquakes.
"We're
looking
for
causative
relationships
between
structure
and
slip,"
she
said.
"So
we're
using
the
lessons
from
Japan
and
Chile
to
better
anticipate
what
could
happen
here."
By
Andrea
Mustain,
OurAmazingPlanet
Costa Rica's Daily English News
Source
Apdo. 2133-1000, San José, Costa
Rica
Tel: (506) 8399
9642
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