►
From YouTube: EOSC 350 Lecture 11: Seismic 3. Doug Oldenburg
Description
Third lecture on seismic. Lecture notes available at https://github.com/ubcgif/eosc350website/raw/master/assets/3_Seismology/Seismology.pdf
A
Briefly
kind
of
go
over
where
we
were
last
time,
so
what
we're
doing
is
we're
looking
at
the
seismic
refraction
survey,
which
allows
you
to
try
to
find
out-
and
this
is
I-
think
the
main-
a
petition
for
engineering.
You
know
what
the
thicknesses
of
some
upper
layer
of
the
bedrock
and
you
have
the
situations
where
you've
got
a
v1
and
the
p2
with
the
speed
to
be
the
bedrock
being
greater
than
p1.
So
what
we're
going
to
do
is
is
to
first
of
all
generate
the
travel
time
curves.
A
A
A
Right,
so
this
is
going
to
be
1
over
the
speed
of
t1
good.
So
that's
that's!
This
guy
is
coming
along
here,
so
we
just
have
to
measure.
We
just
have
to
make
sure
that
we've
got
some
arrivals
that
are
coming
from
here
and
pick
off
those
first
arrivals.
Then,
okay.
Now
that
gives
us
that
gives
us
already
the
velocity
at
the
top
layer.
A
A
Speed
what
oh
yeah
a
speedy
one
of
you
to
anybody
else
do
so.
This
way
travels
along
here
at
a
speed,
V,
2,
okay,
question:
does
this
way
can
I
see
this
refracted
wave
at
this
particular
Gible
know
the
first
location
is
going
to
be
something
so
here's
here's
an
angle,
and
what's
that
angle,
going
to
be
called
that's
going
to
be
called
the
critical
angles
you
could
put
a
C
or
not,
and
so
that
means
that
there's
going
to
be
a
distance
here
and
what
are
we
gonna
call
that.
A
A
A
Once
we
get
to
this
critical
distance
and
that
critical
distance
might
be
here,
okay,
then
there's
going
to
be
an
arrival,
is
that's
going
to
come
in
and
it
is
going
to
travel
like
this
we've
already
said:
that's
going
to
be
speed,
v2,
and
so
this
has
got
a
slope
of
1
over
B
you
go
and
you
look
at
your
seismograms.
You
pick
off
the
first
arrivals
and
those
two
things
are
going
to
form
straight
lines,
one
of
them
just
going
to
tell
you
the
velocity
of
the
top
layer.
A
A
We
have
to
do
some
computations,
which
are
really
simple,
but
they
just
require
that
you
use
Pythagoras
theorem
and
you
know
figure
out
the
lengths
of
the
of
the
lines.
So
what
we're
doing
is
we're
going
to
have
to
compute
what
the
arrival
time
is
for
this
refracted
wave,
and
we
can
show
that
it's
equal
to
something
like
this.
It's
x
over
v2
plus
T
naught
so
this
refracted
wave
comes
in
as
x
over
b2
plus
some
some
constant.
A
A
Not
really
anybody
else,
it's
an
intercept
time
right.
So
if
we
take
this
so
this
is
the
nothing
is
going
to
arrive
till
here.
Okay,
so
we
have
to
be
out
a
certain
distance
before
we
get.
This
is
so
this
point
here
is
X
sub
C,
that's
a
straight
line.
We
could
project
it
back
to
this
point
here,
and
that
is
my
intercept
time
and
now
the
good
thing
about
this
is
I
actually
have
a
formula
for
it.
A
So
I'm
written
in
here
is
x
over
v2
plus
TI,
but
if
I
look
at
it
over
here,
there
is
an
expression
that
you
guys
can
derive
it's
actually
to
ride
in
the
TP.
R
denotes
I.
Don't
want
to
go
through
that
over
here.
I
think
that's
particularly
useful,
but
this
intercept
time
is
given
by
this
thing
here.
So
TI
is
equal
to
2
Zed
v2,
squared
minus
v1,
squared
over
B
1
D
2.
A
A
That's
right
so
I've
got
TI,
but
this
over
here
this
under
here
/,
so
I've
got
an
expression
%
I've
done
good
to
go
the.
How
simple
is
that
right?
You
want
to
try
to
like
I
mean
you
can
imagine
your
outings
if
some
site
characterization
place
and
you
want
to
have
like
okay,
how
deep
the
bedrock
well
you've
got
two
options:
you
could
drill.
A
A
If
you
have
a
layer
that
looks
like
this
okay,
which
you
might
have,
then
if
you
have
a
other
source
out
here,
then
as
long
as
things
don't
get
too
crazy.
Okay,
that
energy
comes
along
here
and
it
gets
traveling
through
this.
So
it'll
it's
over
here.
It's
sort
of
putting
up
already
here
here
so
always
at
the
critical
distance
with
respect
to
the
normal,
and
it
certainly
looks
energy.
A
So
it's
going
to
make
so,
instead
of
just
being
a
nice
straight
line,
it's
going
to
be
a
little
bit
of
fluctuations,
but
then
you
know:
there's
codes
up
there
that
can
start
to
handle
now
the
most
complicated
thing
that
we're
going
to
look
at
and
we're
only
going
to
do
it
briefly,
because
we
simply
don't
have
very
much
time
is
the
following
one.
Where
now
my
interface
might
actually
look
like
that,
so
suppose,
I
have
a
dipping
interface.
A
A
One
thing
because
I
would
actually
like
you
guys
to
go
through
the
key
key
key
and
actually
derive
this
guy
I.
Just
it
just
requires
to
use
some
geometry
and
you'll
find
the
lengths
of
lines
and
every
time
you
know
the
length
of
line
divided
by
velocity.
You
know
give
me
the
time,
but
there's
this
I
wrote
this
funny
thing
up
here.
It's
called
a
velocity
triangle
and
I'm
wondering
if
anybody
has
looked
through
the
new
feature,
T
and
B.
A
A
A
A
A
A
A
Okay,
that
is
the
basics
of
refraction,
as
I
said,
there's
only
going
to
be
a
couple
extra
complications
that
come
in
because
of
things
that
look
work
that
we're
under
lading
or
a
few
other
things
we'll
take
account
of
them
a
little
bit
towards
you,
but
I
want
to
now
it's
kind
of
go
fast.
We
haven't
caught
the
whole
deal
right.
We
haven't
really
talked
about
the
sources
we
haven't
really
talked
about.
A
So
a
source
is
anything
that
can
shake
the
ground,
so
it
could
be
a
natural
source.
So
we
could
everybody's
familiar
with
earthquakes,
so
you
see.
No
so
that's
possibility
could
be
man-made
oceans,
anything
and
then
the
receivers
can
be
anything
to
measure
something,
so
it
could
measure
a
velocity
or
could
measure
an
acceleration
or
so
those
are
going
to
be
the
two
guys
and
let's
just
look
at
a
couple
of
sources
so
on
a
global
scale,
we've
got
earthquakes,
so
you
guys
are
all
familiar
with
this.
A
So
here's
map
of
the
world,
here's-
you
can
sort
of
see
the
plates
that
are
going
on
here.
You've
got
these
big
subduction
zones,
so
we
get
different
kinds
of
earthquakes
in
different
locations.
So
we
could
have
a
normal
fault
of
thrust.
Faults
obvious
coming
up
like
this.
We
can
also
have
a
strike-slip
fault
going
down
into
the
you
know
into
here.
We've
got
these
big
thrust
faults
as
the
Pacific
plate
goes
down
right,
so
the
the
plates
going
down,
it's
sort
of
binding
elastically
with
a
plate.
A
That's
up
here
everything
gets
deformed
and
then
energy
gets
released.
You
get
bigger!
That's
one
way
over
here:
we
stand
in
various
we've,
got
sort
of
strength
footballs
and
on
the
ocean.
Ridges
you're
basically
got
tension,
so
we've
got
all
kinds
of
ways
of
moving
rocks
each
one
of
them
is
going
to
give
rise
to
different
types
of
motion,
but.
A
So
it's
it's
just
a
big
massive
truck
and
underneath
there
they
have
a
plate
and
that
plate
just
sort
of
oscillates
up
and
down.
Actually
it's
the
truck,
that's
oscillating
up
and
down,
and
that's
pumping
energy
into
the
ground,
because
hydrocarbon
deserve
I'm,
pretty
deep.
You
need
to
get
a
lot
of
energy
in
so
your
line,
all
these
guys
up
and
you
get
a
whole
bunch
of
them,
they're
all
in
sync
and
they're,
trying
to
vibrate
up
and
down
shake
it
round
enough
that
you
get
weight
inside
here.
A
I
could
also
do
this.
This
is
not
a
good
idea,
but
you
know
dynamite
gives
one
way
of
doing
things.
If
you
do
use
dynamite,
you
try
to
bury
it.
So
it
doesn't
explode
in
the
oceans.
You
can
get
job
ships
that
have
a
source
behind
them,
or
in
this
case
you
can't
see
it
very
well,
but
here
you've
got
four
ships
and
each
of
them
has
got
an
array
of
receivers.
That's
coming
out
and
ultimately,
those
data
are
being
combined
to
generate
a
picture
of
the
near
subsurface.
A
A
Geotechnical
work,
actually
a
lot
of
the
things
that
you
do
are
sometimes
like
this.
It's
still
not
uncommon
to
actually
have
a
let's
a
hammer
seismograph.
So
this
guy
gal
swinging
a
hammer,
see
we
equal-opportunity
she's
she's
swinging
a
hammer,
this
guy's
on
a
little
bit
pitches,
you
a
little
bit
of
a
thumper
truck,
and
this
guy
is
got
a
little
bit
of
a
dynamite
explosion,
one
of
the
ones
that
this
is
this
one's
very
commonly
used
by
geotechnical
Golder,
for
instance,
or
to
your
geosciences
use
these
guys
a
lot
they're,
basically
right.
A
A
And
one
thing
about
hammer
seismograph
is
that
standard
sizing
is
you
can
take
it
all
kinds
of
places?
What's
interesting
here.
Is
that
so
here's
the
hammer
and
you
notice
that
there's
a
chord
it
extends
from
here
into
a
box,
and
the
reason
for
that
is
that
it's
very
important
to
know
the
tiny
of
when
you
put
a
signal
in,
and
so
you
therefore
watt
to
you
know
as
you're
striking
a
base
plate
and
there
that's
what
happens
here.
A
There's
usually
some
kind
of
a
metal
plate
under
here,
that's
coupled
to
the
ground
so
that
when
you
hit
it
that
energy
couples
in
you
want
to
know
exactly
when
that
hits,
and
so
you
record
the
moment
that
hits
and
that
everything
else
from
these
other
geophones
is
then
sync
to
that.
So
you
know
exactly
how
long
it
took
the
signals
would
leave
from
here
to
even
the
first
tooth,
and
then
you
string
these
guys
out
along
a
line,
and
you
can
go
to
all
kinds
of
places
that
are.
A
A
So,
let's
go
take
some
place
here
on
the
earth
and
here's
the
moon
and
you
had
a
cord
that
was
running
down
for
the
moon
and
it
was
attached
to
an
instrument
here
and
you
could
then
measure
okay
when
the
earth
moved
okay
up
and
down
just
how
much
this
guy
has
been
moving.
We
can't
do
that,
but
we
can
do
something.
That's
similar
to
that.
We
have
a
contraption
that
looks
like
this,
so
it's
got
a
frame
and
then
there's
a
spring.
That's
attached
to
it,
and
sometimes
you'll
hear
the
word.
A
Zero
light
spring
because
it's
kind
of
carefully
carefully
tuned
and
the
idea
is
that
this
is
sort
of
sitting
here
and
we've
got
attached
to
the
spring,
some
kind
of
usually
it's
kind
of
like
a
copper
coil
of
wire.
That's
what
this
guy
is,
so
you
can
see
that
there's
just
a
whole
bunch
of
wire.
That's
that's
in
here,
and
these
out
guys
outside
guys
are
magnets.
A
When
the
earth
moves
up,
then
from
an
inertial
perspective,
this
guy
is
kind
of
staying
staying
in
the
same
position,
so
it's
just
like
the
coil
is
there
and
this
magnet
kind
of
goes
up
and
down,
not
the
nut.
So
that's
what
you
would
ideally
like
like
to
have,
and
my
first
question
is
so:
if
I
had
a
device
like
that,
why
would
it
measure
anything.
A
So
you've
all
at
some
point
then
introduced
to
how
a
generator
works
right.
So
so,
basically,
if
you've
got
a
any
kind
of
a
moving
conductor
in
a
magnetic
field,
then
we
build
out
the
current,
and
once
we
have
a
current,
that's
flowing
in
everything
that
we
can
measure
the
current.
So
as
this
as
this
magnet
moves
up
and
down,
okay
with
respect
to
this.
A
A
A
Okay
did:
did
you
ever
get
out
in
the
field
or
no
anybody
has
got
a
colloquial
name,
for
these
guys
are
often
called
jugs.
I,
don't
really
know
where
that
comes
from,
but
they
another
term
for
these
is
jugs
and
people
who
carry
them
around
are
called
jug
hustlers
and
the
the
great
think
of
these
is
that
you
just
there
you
kind
of
put
them
on
the
ground,
and
then
you
they're
rugged
enough
that
you
can
step
on
the
top.
A
Give
something
a
little
bit
different
in
the
first
lab.
Remember
you
did
that
seismic
experiment.
That
was
a
little
bit
different,
because
I've
got
I've
got
it
stretched
out
here,
but
anybody
know
what
was
happening
there,
because
we
learned
that
was
a
bit
different.
We
didn't
hit
something
at
the
back
and
you
had
this
at
this
machine.
Look
well,
there's
part
of
it
as
your
your
cylinder
was
kind
of
clamped
in.
A
A
Perfect
yeah,
so
it's
it!
It's
a
transformation
from
like
electrical
voltage
to
crystal
and
energy.
So
now
we've
actually
got
so.
We've
got
a
transducer
here
that
takes
a
voltage
and
then
it
changes
shape
a
bit
and
then
now
that
shape
change
can
propagate
through
and
then
another
transducer
back
here
and
then
come
up
here,
which
is
now
that
I'm
thinking
about
not
exactly
sure
it's
what
you
said,
but
it's
we're
pretty
good
we're
pretty
close
yeah.
So
you,
the
point,
is
you
can
take
energy
in
one
form
and
transfer
to
that?
A
A
This
transducer
changes
that
actually
to
now
a
physical
motion
that
propagates
through
a
physical
motion
taken
up
by
this
transducer
changes
it
back
to
electrical
form
and
then
measurements.
So
that's
how
that
that
works
so
there's
quite
a
few
ways
of
sort
of
getting
yeah.
That's
what
you
get
in
the
lab,
and
previously
we
saw
something.
A
A
This
is
actually
kind
of
amazing.
Thank
you.
So
here
is
the
accelerometer
to
a
first-order.
It's
got
that
coil
inside
and
here's
your
magnets
on
the
outside
and
there's
lots
of
other
stuff
too
right,
but
what's
kind
of
amazing
about
this.
Is
they
take
this?
So
it's
just
like
this
guy
that's
coming
around
and
then
you
make
three
of
them,
because
you
can
only
measure
your
motion
or
acceleration
in
one
direction.
A
You
want
to
have
all
three,
so
you
need
three
these
guys,
so
they
take
each
of
those
three
and
they
put
them
on
a
chip.
So
now
you
take
this,
and
now
you
just
got
this
little
chip
right
and
you
put
three
accelerometers
into
there.
You
put
all
that
stuff
in
so
everything
is
like
really
tiny,
yeah,
so
most
of
yeah.
A
So
your
your
accelerometer
is,
you
know,
sitting
someplace
in
here
and
it's
way
smaller
than
and
that's
actually
measuring
all
three
components,
and
there
are
apps
around
that
you
can
download
various
kinds
of
seismic
gap.
So
if
you
just
sign
on
to
you,
know
iTunes
or
wherever
just
Google,
there
will
be
some
that
you
can
download
and
if
we
get
the
airplay
going,
I'll
show
you
them
on
the
screen.
A
A
Yeah,
like
life,
is
like
this
right.
You
get
something.
We
just
showed
that
tough
we've
got
a
situation
that
looks
like
this.
We
got
a
b1
and
b2.
When
we
got
some
kind
of
thickness.
Hey
said
we
can
actually
get
all
those,
but
sometimes
things
get
more
complicated
and
we
might
have
a
situation
that
looks
like
this,
in
which
case
as
long
as
the
velocities
keep
increasing,
there
really
isn't
any
problem.
You
know
we
can
have
a
raid
that
comes
down
like
this,
and
you
know
then
refracts
don't
like
this
comes
along
here.
A
Here's
our
direct
here's,
our
money
for
d1,
cube
and
then
there'd
be
another
guy
coming
in
here
at
1,
upon
B
3.
So
if
we
could
recognize
stamp
with
okay,
but
there's
a
couple
of
times
that
things
don't
work
out
quite
as
nicely
and
one
of
those
is
when
this
velocity
is
either
smaller
than
the
one,
in
which
case
we've
now
got
the
low
velocities
on
or
actually
if
it's
really
quite
fit
and
I
just.
A
So
in
in
this
case,
so
in
this
case
seriously,
I've
got
three
layers:
I've
got
a
refraction
that
comes
along
here,
but
if
this
velocity
that
that
layer
was
low
velocity
that
I
never
have
any
wave
that
comes
across
like
this
right,
so
a
v2
is
less
than
v1.
That
I
never
have
that,
and
so
the
only
thing
I
would
have.
Is
this
guy
here,
in
which
case
I?
Don't
have
this
arrival?
So
I
just
have
this
so
I've
got
a
1
over
B
1,
the
1
over
B
3,
but
I.
A
Don't
have
any
indication
that
that
he's
here.
So
if
I
don't
have
anything
from
a
a
second
layer
in
here,
then
I'm
kind
of
kind
of
the
other
thing
is
that
even
if
this,
so,
let's
suppose
I've
got
a
B
want
to
be
too
and
a
v3,
even
if
these
are
progressively
larger
velocities,
so
that
initially
I
might
have.
Something
looks
like
that
if
I
start
to
shrink
this
layer
thickness,
then
what's
going
to
happen,
is
that
this
travel
time
curve
I'm
still
going
to
get
a
refraction
from
that
second
layer.
A
But
the
guy
this
guy,
coming
in
on
the
bottom
of
the
survive,
is
actually
going
to
get
around
quickly
enough.
That
I
don't
see
much
of
a
manifestation
of
him
and
at
some
point
I
could
actually
have
a
low
velocity
zone.
So
there
is,
there
is
even
still
is
a
refraction,
but
he's
not
a
first
arrival,
and
so,
if
I'm,
just
looking
for
first
arrive
as
I
just
see
a
B
1,
&,
2,
B,
3,
and
so
therefore
I've
got
a
hidden
place.
A
A
A
A
A
So,
as
we
come
down
here,
okay,
then
the
length
of
this
is
going
to
increase.
So
it's
always
going
to
look
like
it's
taking
a
bigger
time
right
so
as
I
come
down
here,
the
time
that
it
takes
to
arrive,
there's
actually
going
to
be
progressively
larger
than
it
would
be
from
the
normal,
and
so
that
means
that
this
slope
is
going
to
be.
A
A
Now,
as
I'm
coming
this
way,
the
pathway
is
progressively
shorter,
so
it
just
takes
lesson
last
time.
So
the
result
of
that
is
as
follows:
that
if
I
have
a
shot
that
goes
down
dip,
it
comes
up
here
particular
rate
I'll.
If
I
now
go
back
the
other
way,
so
the
blue
is
starting
from
here
and
going
up
here,
we
can
see
that
they
have
the
same.
A
A
So
it's
called
the
reciprocal
time
and
what
it
says
is
that
I'm
taking
using
my
my
two
shots,
so
I'm
always
I
have
a
shot
and
then
I
put
an
end
receiver
and
then
I
invert.
That
and
I
put
the
shot,
we're
getting.
Receiver
was
and
receiver
wouldn't
for
shot
was,
and
so
I've
got
a
complete
reciprocity,
where
I
have
two
two
waves
going
from
different
directions,
but
they
take
exactly
that
same
time.
A
So,
let's
see
that
down
dip,
we've
got
progressively
farther
to
go.
So
it's
got
a
steeper
slope.
This
has
got
a
shallower
slope.
They
arrive
at
the
same
time,
that's
our
reciprocal
time
and
we
can
call
it
up
dip
and
down
dip,
so
I
get
to
a
pair.
So
these
are
now
apparent.
Velocities
and
I
can
use
that
information
with
a
couple
of
the
formulas.
That
tells
me
what
the
time
is
for
my
initial
shot.
A
Here
so
I
get
an
intercept
T
to
an
intercept
t2
prime
TI
Prime
and
I've
got
formulas
for
these
guys,
and
that
allows
me
to
get
this
depth
underneath
the
reciprocal
shot
and
this
depth
underneath.
So
that
comes
back
to
your
point
earlier.
If
we've
got
something,
that's
that's
varying.
What
actually
do
we
need,
but
by
the
depth
and
with
Yogi's
formula
and
no
knowing
what
my
two
slopes
are
up
get
down
there
and
knowing
what
this
reciprocal
coin
is
and
also
these
intercept
times.
A
Okay,
so
what
we'll
do
next
time
that
just
about
finishes
this
up?
What
we'll
do
next
time
is
start
besides,
if
you're,
flexible,
I'd,
like
you
to
do,
is
to
go
on
to
the
seismic
basics
and
also
to
the
apps
there's
an
app
there
for
generating
a
normal
incident
seismograph,
if
you
can
do
that,
then
you'll
be
kind
of
well-versed
with
what
we
want
to.