000
bridges
strength
eggshell
property
shake
unnoticed
700
tremor
000
moving
000
ruins
shift
gives
fault
damage
way
motion
piece
terrifying
seismograph
changing
snaps
core
buildings
1
devastating
hit
grind
plates
grade
waves
trembling
trembling
chasm
safe
release
rupture
100
10
highways
floor
rumble
ground
waves
waves
April
18
,
1906
,
California
San
Andreas
____________________
____________________
,
shaking
San
Francisco
for
nearly
60
____________________
seconds
.
When
the
____________________
stops
,
the
disaster
is
only
beginning
.
Gas
lines
____________________
setting
off
massive
fires
.
Some
____________________
people
die
.
Most
of
the
city
is
reduced
to
____________________
.
This
____________________
of
the
____________________
caused
when
masses
of
rocks
suddenly
____________________
below
the
earth's
surface
is
called
an
earthquake
.
Hundreds
of
little
earthquakes
____________________
the
planet
every
day
but
most
pass
____________________
.
They
usually
occur
along
the
boundaries
of
the
thin
____________________
that
cover
the
Earth
like
an
____________________
.
Driven
by
the
heat
deep
within
the
Earth's
____________________
,
the
plates
____________________
against
each
other
along
lines
called
?
faults
?
.
When
a
plate's
____________________
is
blocked
,
stress
builds
up
.
Finally
the
fault
____________________
____________________
.
The
released
energy
races
through
the
Earth
in
the
form
of
seismic
____________________
.
Scientists
record
these
____________________
on
a
device
called
a
____________________
.
These
zigzag
lines
show
the
____________________
of
various
seismic
____________________
.
Using
the
lines
scientists
____________________
the
earthquake
on
the
Richter
scale
.
For
a
quake
to
measure
one
number
higher
on
the
Richter
scale
it
must
____________________
about
30
times
as
much
energy
as
the
number
below
it
.
Every
year
,
about
____________________
,
____________________
earthquakes
____________________
through
the
ground
hard
enough
for
people
to
feel
them
.
Of
these
,
only
about
____________________
,
____________________
are
strong
enough
to
____________________
____________________
.
But
a
powerful
earthquake
can
be
____________________
.
On
average
,
about
____________________
,
____________________
people
die
each
year
as
a
result
of
earthquakes
.
The
greatest
recorded
earthquake
ever
to
____________________
North
America
measured
a
massive
9
.
2
.
The
____________________
struck
Alaska
on
March
28
,
1964
.
A
camera
on
board
a
ship
docked
in
Valdez
recorded
the
draining
of
the
entire
harbor
as
a
____________________
opened
up
on
the
sea
____________________
.
There's
no
stopping
the
surface
of
the
Earth
from
____________________
and
____________________
so
engineers
are
focusing
on
ways
to
create
better
____________________
,
____________________
and
____________________
,
structures
that
will
remain
____________________
and
stay
in
one
____________________
the
next
time
the
Earth
begins
to
shake
.