Thousands of tiny earthquakes went unnoticed beneath Alaska for years

Rep ese tative
image
of
the
li ea
cluste
of
ea thquakes
t aci g
the
edge
of
the
Yakutat
mic oplate
i
south-ce t al
Alaska
(AI
ge e ated).

Be eath
the
towe i g
peaks
of
the
Alaska
Ra ge,
home
to
De ali,
No th
Ame ica’s
tallest
mou tai ,
scie tists
have
u cove ed
a
hidde
geological
featu e
that
had
go e
completely
u oticed
u til
ow.
Usi g
a
machi e
lea i g
system
to
sift
th ough
yea s
of
seismic
data,
esea che s
built
a
expa ded
ea thquake
catalogue
fo
the
egio
a d,
withi
it,
ide tified
a
disti ct
cluste
of
oughly
1,750
small,
p eviously
u detected
ea thquakes
a a ged
i
a
almost
pe fectly
st aight
li e,
st etchi g
250
kilomet es
f om
o thwest
to
southeast
be eath
south
ce t al
Alaska.
That
azo
sha p
li e
t aces
the
p ecise
edge
of
the
Yakutat
mic oplate,
a
thick
slab
of
ocea ic
c ust
wedged
i to
a
al eady
co gested
collisio
zo e
whe e
the
Pacific
a d
No th
Ame ica
plates
meet.
The
discove y
gives
scie tists
thei
clea est
pictu e
yet
of
a
plate
bou da y
lo g
suspected
to
exist
but
eve
mapped
i
this
ki d
of
detail,
a d
it
may
help
explai
what
t igge ed
o e
of
Alaska’s
most
powe ful
ea thquakes
i
ece t
histo y.

Why
the
collisio
betwee
the
Pacific
plate,
the
Yakutat
mic oplate
a d
the
De ali
fault
made
this
egio
so
ha d
to
map

South
ce t al
Alaska
sits
at
the
ce t e
of
what
esea che s
desc ibe
as
a
ge ui e
tecto ic
t affic
jam,
a
locatio
whe e
multiple
la ge
geological
featu es
co ve ge
a d
compete
fo
space
be eath
the
su face.

The
Pacific
plate
is
actively
subducti g
be eath
the
No th
Ame ica
plate
i
this
egio ,
while
the
Yakutat
ocea ic
plateau,
a
u usually
thick
slab
of
c ust
caught
up
i
the
same
collisio ,
is
bei g
d agged
alo g
a d
fo ced
be eath
the
co ti e t
as
well.
Laye ed
o
top
of
that
c owded
subductio
zo e
u s
the
De ali
fault,
the
majo
co ti e tal
fault
system
espo sible
fo
the
mag itude
7.9
ea thquake
that
st uck
the
Alaska
i te io
i
2002,
the
st o gest
eve
eco ded
the e.
To
map
the
egio
i
fi e
detail,
a
esea ch
team
led
by
seismologist
Megha
Mille
of
the
Aust alia
Natio al
U ive sity
d ew
o
data
collected
f om
pe ma e t
seismic
statio s
alo gside
a
tempo a y
a ay
the
team
deployed
ac oss
the
egio
betwee
2018
a d
2021,
the
built
a
machi e
lea i g
wo kflow
capable
of
su faci g
ea thquakes
too
small
a d
subtle
to
appea
i
existi g
catalogues.

What
the
ewly
mapped
fault
li e
evealed
about
the
plate’s
t ue
shape
a d
Alaska’s
volca ic
gap

The
esultig
pictu e
was
st iki gly
p ecise.
Acco di g
to
a
stateme t
eleased
by
the
Seismological
Society
of
Ame ica,
the
machi e
lea i g
p ocess
evealed
a
li ea
cluste
of
oughly
1,750
small
ea thquakes
t aci g
the
exact
edge
of
the
subducted
Yakutat
mic oplate
a d
ma ki g
the
poi t
whe e
the
slab’s
i te al
st uctu e
shifts
to
eflect
cha gi g
st ess
i
the
egio .
Acco di g
to
the
study
itself,
titled

Razo -Sha p
Edge,
the
Yakutat
Slab
Dissecti g
South-Ce t al
Alaska
a d
published
i
the
jou al
The
Seismic
Reco d,
this
ewly
defi ed
edge
exte ds
the
k ow
each
of
the
Yakutat
plate
much
fu the
be eath
the
co ti e t
tha
ea lie
studies
had
show ,
placi g
it
di ectly
be eath
the
cu ved
sectio
of
the
De ali
fault.
The
li e
of
ea thquakes
also
alig ed
closely
with
a
se ies
of
small
volca ic
co es
a d
cha ges
i
u de lyi g
ock
type,
a d
the
esea che s
fou d
this
sectio
of
the
plate
bou da y
lacks
a
i te ve i g
ma tle
wedge,
the
laye
of
pa tially
molte
ock
typically
espo sible
fo
feedi g
volca ic
activity
above
a
subductio
zo e,
offe i g
a
st uctu al
expla atio
fo
the
lo g
puzzli g
abse ce
of
active
volca oes
alo g
this
st etch
of
the
fault,
k ow
as
the
De ali
volca ic
gap.

How
this
hidde
edge
may
co ect
to
the
2002
De ali
ea thquake

Pe haps
the
most
st iki g
implicatio
i volves
the
2002
De ali
ea thquake
itself.
The
esea ch
team
p oposes
that
the
ewly
mapped
edge
of
the
Yakutat
mic oplate,
positio ed
di ectly
be eath
the
cu ved
sectio
of
the
fault,
may
have
i flue ced
whe e
that
ea thquake
actually
bega .
Acco di g
to
Mille ,
the
plate’s
locatio
alig s
closely
with
the
i itiatio
poi t
of
the
2002
uptu e,
aisi g
the
possibility
that
st ess
ge e ated
by
the
o goi g
collisio
betwee
the
Yakutat
plate
a d
the
No th
Ame ica
plate
p opagated
upwa d
a d
helped
t igge
the
quake
alo g
a
ea by
sectio
of
the
De ali
fault.
Co fi mi g
that
co ectio
mo e
defi itively,
Mille
has
oted,
will
equi e
fu the
computatio al
modelli g
wo k
buildi g
o
this
ewly
detailed
st uctu al
pictu e,
si ce
the
cu e t
fi di gs
establish
a
compelli g
spatial
alig me t
athe
tha
di ect
p oof
of
cause
a d
effect.

Why
this
discove y
could
cha ge
how
scie tists
assess
ea thquake
isk
elsewhe e

Beyo d
explai i g
past
seismic
activity,
the
discove y
gives
scie tists
a
fa
mo e
detailed
map
to
wo k
f om
whe
assessi g
how
futu e
ea thquakes
might
behave
i
this
de sely
laye ed
tecto ic
egio .
Because
the
study
demo st ates
that
a
ta geted
cluste
of
small,
p eviously
i visible
ea thquakes
ca
eveal
st uctu al
bou da ies
missed
by
decades
of
co ve tio al
mo ito i g,
esea che s
say
the
same
machi e
lea i g
app oach
could
be
applied
to
othe
complex
fault
systems
wo ldwide
whe e
multiple
tecto ic
featu es
ove lap
i
simila ly
complicated
ways.
Fo
a
egio
al eady
k ow
to
p oduce
some
of
No th
Ame ica’s
la gest
ea thquakes,
a
clea e
pictu e
of
what
lies
hidde
be eath
the
su face
offe s
scie tists
a
st o ge
fou datio
fo
u de sta di g
ot
just
how
Alaska’s
la dscape
fo med,
but
whe e
its
ext
majo
seismic
eve t
might
o igi ate.
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