3.
Label
the
curve
that
represents
travel
times
of
P-wave
first
arrivals.
Now
do
the
same
for
the
two
lines/curves
associated
with
S-
and
surface-wave
first-arrivals,
respectively.
4.
Briefly
explain
why
these
points
(and
all
similar
points
from
other
earthquakes)
occur
along
three
discrete
lines
or
curves.
B
Study
the
three
discrete
curves
you
just
drew
in
Fig.
A11.2.1.
Why
is
the
S-wave
travel-time
curve
steeper
than
the
P-wave
curve?
€
Why
do
the
surface
wave
data
points
that
you
plotted
on
Fig.
A11.2.1
form
a
straight
line
whereas
data
points
for
P-waves
and
S-waves
form
curves?
(Hint:
P-
and
S-waves
are
body
waves
that
travel
through
Earth’s
interior,
whereas
surface
waves
travel
along
Earth’s
surface.)
D
Notice
that
the
origin
on
your
graph
(where
travel
time
is
zero
and
distance
is
zero)
represents
the
location
of
the
earthquake
epicenter.
The
time
interval
between
the
first
arrival
of
P-waves
and
the
first
arrival
of
S-waves
at
the
same
recording
station
is
called
the
S-minus-P
time
interval.
How
does
the
S-minus-P
time
interval
change
with
distance
from
the
epicenter?
E
Tmagine
that
an
earthquake
occurred
this
morning.
The
first
P-waves
of
the
earthquake
were
registered
at
a
recording
station
in
Houston
at
11:06:12.6
UTC
(expressed
as
hours:minutes:seconds),
and
the
first
S-waves
arrived
at
the
same
Houston
station
at
11:06:17.1
UTC.
Use
the
travel-time
graph
(Fig.
A11.2.1)
to
answer
each
of
the
following
questions.
1.
What
is
the
S-minus-P
time
interval
of
the
earthquake?
Express
your
answer
in
decimal
minutes.
min
2.
Use
the
curves
you
drew
on
Fig.
A11.2.1
to
estimate
the
distance
from
the
earthquake’s
epicenter
to
the
Houston
seismograph
station.
km
F'
REFLECT
&
DISCUSS
You
have
determined
the
distance
between
Houston
and
the
earthquake
epicenter.
What
additional
data
would
you
require
to
determine
the
location
of
the
earthquake’s
epicenter
on
a
map?
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