of 32
Bulletin
of
the
Seismological
Society
of
America
VOL.
25
JANUARY,
1935
No.
1
AN
INSTRUMENTAL EARTHQUAKE MAGNITUDE
SCALE*
BY CHARLES
F.
RICHTER
In
the
course
of
historical
or
statistical
study
of earthquakes
in
any
given
region
it
is
frequently
desirable
to
have
a
scale
for
rating
these
shocks
in
terms
of
their
original
energy,
independently
of
the
effects
which
may
be
produced
at
any
particular
point of
observation.
On
the
suggestion
of
Mr.
H.
O.
Wood,
it
is
here
proposed
to
refer
to
such
a
scale as
a "magnitude"
scale.
This
terminology
is
offered
in
distinction
from
the
name
"intensity"
scale,
now
in
general
use
for
such
scales
as
the
Rossi-Forel
and
Mercalli-Cancani
scales,
which
refer
primarily
to
the
local
intensity
of
shock
manifestation.
The
writer
is
not
aware of
any
previous
approach
to this
problem
along
the
course
taken
in
this
paper,
except
for
the
work
of
Wadati
cited
below.
Total
original energies
have
been
calchlated
for
a
number
of
shocks,
using
seismometric
and
other
data
; but
such
a procedure
is
prac-
ticable
only
for
a limited
number
of
cases,
whereas
it is
desired
to
apply
a
magnitude
scale
to
all
or
nearly
all
of
the
shocks
occurring.
Mr.
Maxwell
W.
Allen
states
that
he
has
for
some
time
'employed
an
arbitrary
scale
for
rating
large
earthquakes,
based
on
the
amplitudes
of
earth
motion
calculated
from
the
reports
of
distant
stations.
This
labori-
ous
procedure
is
not
far
removed
in
principle
from
that
adopted
in
the
following
discussion.
Doubtless
it has
also
occurred
to
others,
but
has
failed
of
general
application
because
of
its
paucity
of
dependable
results.
In
the
absence
of
any
accepted
magnitude
scale,
earthquakes have
oc-
casionally
been
compared
in
terms
of
the
intensity
on
the
Rossi-Forel
or
some
similar
scale,
as
manifested
near
the
epicenter.
Even
when
reliable
information
is
Obtainable,
this
method
is
obviously
exposed
to
uncertain-
ties
arising
from
variations
in
the
character
of
the
ground,
the
depth of
the
focus,
and
other
circumstances
not
easily
allowed
for.
In
a
region
such
as
Southern
California,
where
a large
proportion
of
the
shocks
occur
* [Received'for publication June
17,
1934.]
BULLETIN
OF
THE
SEISMOLOGICAL
SOCIETY
OF
AMERICA
in
almost
unpopulated
districts,
while
still
others
are
submarine
in
origin,
any
general
procedure
of
this
kind
is
out
of
the
question.
Despite
the
evident
difficulties
the
requirements
of
research,
as
well
as
the
public
interest,
call
for
some
estimate
of
the
magnitude,
in
the
sense
here
used,
of
each
important
shock
in
the
California
region.
This
led
to
an
attempt
at
constructing
a
magnitude
scale
based
on
instrumen-
tally
recorded
amplitudes
at
the
seven
stations
of
the
Southern
California
group.
Precision
in
this
matter
was
neither
expected
nor
required.
What
was
looked
for
was
a
method
of
segregating
large,
moderate,
and
small
shocks,
which
should
be
based
directly
on
instrumental
indications,
and
thus
might
be
freed
from
the
uncertainties
of
personal
estimates
or
the
accidental
circumstances
of
reported
effects.
The
method
used
proved
to
be
much
more
selective
than
had
been
anticipated,
assigning
observed
earthquakes
to
as
many
as
fifteen
well-defined
scale
numbers,
with
pos-
sibilities
of
further
extension
and
finer
subdivision.
The
procedure
used
was
suggested
by
a
device
of
Wadati,
1
who
plotted
the
calculated
earth
amplitudes
in
microns
for
various
Japanese
stations
against
their
epicentral
distances.
He
employed
the
resulting
curves
to
distinguish
between
shallow
and
deep
earthquakes,
to
calculate
the
coefficient
of
absorption
for
surface
waves,
and
to
make
a
rough
com-
parison
between
the
magnitudes
of
several
strong
shocks.
On
Certain
assumptions,
which
cannot
hold
to
any
high
accuracy,
it
is
possible
to
derive
a
quantitative
magnitude
scale
from
curves
plotted
in
this
way.
Suppose
two
shocks
of
different
magnitude
were
to
take
place
at
exactly
the
same
focus,
all
other
circumstances
being
identical
in
the
two
cases.
Then
any
seismograph
at
a
particular
station
should
write
two
records,
one
of
which
should
be
very
closely
an
enlarged
copy
of
the
other.
The
ratio
of
this
enlargement
should
be
the
same
for
all
seismo-
graphs,
provided
of
course
that
the
constants
remain
unaltered
between
the
two
events,
and
that
the
response
of
the
registering
apparatus
is
linear.
This
ratio
could
then
be
used
to
measure
the
relative
magnitudes
of
the
two
shocks.
With
the
given
assumption
that
the
mechanism
of
shock
production
is
the
same
in
the
two
cases,
the
ratio
of
the
seismometric
amplitudes
is
the
square
root
of
the
ratio
of
the
energies
liberated.
In
practice
we
have
to
compareshocks
from
different
foci,
and
prob-
ably
different
also
in
the
mechanism
of
occurrence.
Comparison
is
thus
rendered
very
inexact.
However,
useful
results
can
be
obtained
by
corn-
1
K.
Wadati,
Geophysical
Magazine
(Tokyo),
4,
231,
1931.
AN
INSTRUMENTAL
EARTHQUAKE
MAGNITUDE
SCALE
3
parison
of
the
records
at
several
stations.
It
is
necessary
to
establish
empirically
a
relation
between
the
maximum
seismographic
amplitudes
of
a
given
shock
at
various
distances
;
this
is
done
by
assuming
that
the
ratio
of
the
maximum
amplitudes
of
two
given
shocks,
as
registered
by
similar
instruments
at
equal
epicentral
distances,
is
a
constant.
That
is,
if
shock
~/
is
registered
with
maximum
amplitude
5
millimeters
at
75
kilometers
and
2
millimeters
at
200
kilometers,
while
shock
B
registers
with
maximum
amplitude
15
millimeters
at
75
kilometers,
then
shock
B
should
register
6
millimeters
at
200
kilometers.
The
precision
of
magnitudes
based
on
such
an
assumption
is
evidently
impaired
by
a
variety
of
conditions.
The
most
obvious
of
these
are
the
effects
of
inhomogeneity
in
the
propagation
of
elastic
waves,
of
varying
depth
of
focus,
of
difference
in
mechanism
of
shock
production,
of
the
ground
at
the
several
stations,
and
of
the
instrumental
constants.
The
most
serious
of
these
difficulties
is
the
first.
In
most
cases
energy
appears
to
be
radiated
unequally
in
different
azimuths
from
the
point
of
origin.
This
may
arise
from
the
circumstances
of
origination
of
the
shock
(strike
of
the
fault,
nature
of
displacement
on
the
fault)
or
from
differences
in
geological
structure
along
the
various
wave
paths.
When
the
records
of
a
number
of
stations
surrounding
the
epicenter
are
avail-
able,
this
effect
can
be
allowed
for
to
some
extent;
but
it
remains
an
obstacle
in
the
way
of
any
precise
determination
of
earthquake
magni--
tudes,
which
can
only
be
overcome
with
the
advent
of
a
more
detailed
understanding
of
the
dynamics
of
shock
production,
and
more
complete
information
as
to
the
various
local
structures.
Variation
in
depth
of
focus
is
less
important.
The
majority
of
shocks
in
this
region
appear
to
originate
at
depths
not
far
different
from
15
kilo-
meters.
The
effect
of
even
considerable
departures
from
this
level
can
be
reduced,
for
all
but
the
smallest
shocks,
by
using
the
records
at
sta-
tions
distant
100
kilometers
or
over.
It
is
nearly
certain
that
in
most,
though
not
all,
of
the
stronger
shocks
the
distribution
of
energy
among
various
frequencies
is
not
the
same
as
for
weaker
shocks.
Especially
when
there
is
evidence
of
extended
move-
ment
along
a
fault,
a
high
proportion
of
energy
appears
to
go
into
waves
of
long
period.
As
the
maximum
phase
on
the
seismograms
usually
ex-
hibits
longer
periods
than
the
beginning
of
the
record,
the
effect
is
to
exaggerate
the
maxima.
Comparison
with
the
recorded
maxima
of
a
smaller
shock
then
leads
to
an
overestimate
of
the
difference
in
magni-
tude.
Fortunately,
this
effect
does
not
appear
to
be
larger
than
the
other
sources
of
error
;
and
with
long
experience,
or
with
more
precise
theories
BULLETIN
OF
THE
SEISMOLOGICAL
SOCIETY
OF
AMERICA
of
shock
production,
it
should
be
possible
to
take
it
into
account
quanti-
tatively.
In
comparing
records
from
different
stations,
conclusions
are
affected
by
differences
in
ground
and
in
the
instrumental
constants.
If
the
latter
are
known
with
precision,
the
periods
of
the
seismographic
maxima
may
be
measured,
and
the
actual
amplitudes
of
earth
displacement
calculated
and
used
for
estimating
magnitudes.
The
procedure
is
somewhat
labori-
ous
;
and,
as
will
appear
presently,
it
can
be
dispensed
with
if
the
constants
of
the
various
instruments
are
approximately
the
same.
The
short
period
torsion
seismometers
installed
at
the
Southern
California
stations
are
designed
to
have
identical
constants
;
but,
owing
to
unavoidable
irregulari-
ties
in
manufacture,
some
differences
exist.
It
is
not
convenient
to
de-
termine
the
constants
from
time
to
time;
however,
it
is
known
that
the
constants
of
any
one
instrument
remain
relatively
fixed
over
periods
of
years.
Determination
of
constants
would
make
it
possible
to
separate
the
purely
instrumental
effects
from
those
due
to
ground
;
but,
because
of
the
uncertain
elements
in
the
latter,
no
great
access
of
precision
in
estimating
magnitudes
would
follow.
In
practice
it
is
considered
that
the
effect
of
ground
and
that
of
the
instrument
combine
in
each
case
into
a
fairly
uniform
deviation
from
the
mean
registered
amplitudes
for
all
stations
and
instruments
;
so
that
statistical
study
of
a
group
of
shocks
will
lead
to
average
corrections
applicable
to
the
amplitudes
registered
by
each
indi-
vidual
instrument.
These
corrections
turn
out
to
be
small,
and
of
the
same
order
as
fluctuations
due
to
other
causes.
For
precise
purposes,
it
would
be
desirable
to
identify
the
phases
of
each
seismogram,
and
to
compare
amplitudes
of
the
same
wave
or
set
of
waves
at
the
various
distances.
Such
identification
is
difficult
and
ques-
tionable
for
marly
of
the
smaller
shocks,
and
is
too
time-consuming
for
use
in
routine
work
where
hundreds
or
thousands
of
shocks
must
lie
dealt
with.
Thus
the
scale
has
been
set
up
on
the
basis
of
measurements
of
the
maximum
recorded
amplitude.
This
maximum
will
of
course
not
always
correspond
to
the
same
wave-group
or
phase.
It
will
change
especially
with
distance,
coinciding
with
S
or
Q
for
very
near
shocks,
at
intermediate
distances
with
some
member
of
the
complicated
S
series
of
phases,
and
at
the
larger
distances
with
a
slow
surface
wave.
However,
if
the
magnitude
scale
is
set
up
empirically
for
the
measured
maximum
amplitudes,
these
considerations
do
not
directly
affect
its
precision.
If
it
were
strictly
true
that
all
seismograms
written
by
identical
instruments
at
any
one
distance
were
simply
enlarged
or
reduced
copies
of
one
another,
AN
INSTRUMENTAL
EARTHQUAKE
MAGNITUDE.
SCALE
such
an
empirical
scale
would
apply
perfectly,
and
magnitudes
derived
from
it
would
be
exact.
The
foregoing
considerations
are
preliminary
to
the
actual
setting
up
of
a
workable
empirical
scale
of
magnitudes.
To
derive
such
a
scale,
a
representative
group
of
shocks
(those
of
January,
1932)
was
carefully
studied,
and
the
logarithm
of
the
recorded
amplitude
in
each
case
plotted
against
the
epicentral
distance.
Curves
were
drawn
through
the
several
points
referring
to
each
shock,
and
were
seen
to
be
roughly
parallel,
as
the
hypothesis
of
proportional
amplitudes
requires.
These
were
then
combined
into
a
single
curve,
parallel
to
the
indi-ddual
shock
curves,
and
passing
through
an
arbitrarily
selected
point.
From
this
composite
curve
were
read
off
the
numerical
values
presented
in
Table
I.
Table
I
gives
the
logarithm
(to
the
base
10)
of
the
calculated
ampli-
tude,
in
millimeters,
with
which
the
standard
short-period
torsion
seis-
mometer
(To
=
0.8
sec.,
V
-=
2,800,
h
=
0.8)
should
register
at
various
distances
an
earthquake
of
standard
magnitude
;
this
is
chosen
so
that
the
calculated
amplitude
of
registration
at
an
epicentral
distance
of
100
kilo-
meters
is
0.001
millimeters
(1
micron).
Note
that
the
logarithms
are
all
negative,
as
all
the
amplitudes
are
less
than
one
millimeter.
However,
they
are
given
as
negative
quan{ities
instead
of
in
the
usual
common-logarithm
form
of
negative
characteristic
and
positive
mantissa.
Thus,
the
tabulated
logarithm
at
65
kilometers
is
--2.79;
in
the
usual
notation
this
would
be
given
as
7.21
--
10
or
3.21.
The
form
used
in
Table
I
is
more
convenient
in
the
actual
calculation
of
magnitude.
Table
I
can
be
applied
to
assign
a
magnitude
scale
number
to
any
shock
for
which
measured
amplitudes
at
known
epicentral
distances
are
available.
The
following
procedure
is
in
routine
use
:
the
measured
ampli-
tude
at
any
station
is
expressed
in
millimeters,
and
the
logarithm
of
the
number
is
taken.
From
this
is
algebraically
subtracted
the
logarithm
appearing
in
Table
I
opposite
the
given
epicentral
distance.
The
result
is
taken
as
the
magnitude
scale
number,
and
is
clearly
the
logarithm
Of
the
ratio
of
the
amplitude
of
the
given
shock
to
that
of
the
standard
shock,
represented
by
Table
I,
at
the
same
epicentral
distance.
As
a
numerical
example,
suppose
a
shock
recorded
with
an
amplitude
of
5
millimeters
at
225
kilometers.
The
logarithm
of
5
is
0.70
;
opposite
225
kilometers
we
find
--3.68
;
hence
the
magnitude
is
0.70
--
(--3.68)
-----
4.38'.
When
this
calculation
is
carried
out
separately
for
each
station
at
which
the
shock
is
recorded,
the
magnitude
scale
numbers
found
at
the
6
BULLETIN
OF
THE
SEISMOLOGICAL
SOCIETY
OF
AMERICA
TABLE
I
LOGARITHMS
OF
THE
AMPLITUDES
(IN
MILLIMXTE°RS)
WITI-I
WHICH
THE
STANDARD
TORSION
SEISMOME2ER
(T
O
=
0.8,
V
--
2,800,
h
=
0.8)
SHOULD
REGISTER
A
S~IOCK
REGISTERED
AT
A
~
100
I~ILOM~TERS
WITIzI
AN
AMPLITUDE
OF
0.001
MILLIMETERS
(1
MICRON)
A(km)
Log
A
A(km)
Log
A
A(km)
Log
A
25
--1.65
205
--3.56
405
--4.48
30
--2.10
210
--3.59
410
--4.50
35
--2.32
215
--3.62
415
--4.51
40
--2.43
220
--3.65
420
--4.52
45
--2.54
225
--3.68
425
--4.54
50
--2.63
230
--3.70
430
--4.56
55
--2.70
235
--3.72
435
--4.57
60
--2.77
240
--3.74
440
--4.59
65
--2.79
245
--3.77
445
--4.61
70
--2.83
250
--3.79
450
--4.62
75
--2.87
255
--3.81
455
--4.63
80
--2.90
260
--3.83
460
--4.64
85
--2.94
265
--3.85
465
--4.66
90
--2.96
270
--3.88
470
--4.68
95
--2.98
275
--3.92
475
--4.69
100
--3.00
280
--3.94
480
--4.70
105
--3.03
285
--3.97
485
--4.71
110
--3.08
290
--3.98
490
--4.72
115
--3.10
295
--4.00
495
--4.73
120
--3.12
300
--4.02
500
--4.74
125
--3.15
305
--4.05
505
--4.75
130
--3.19
310
--4.08
510
--4.76
135
--3.21
315
--4.10
515
--4.77
140
--3.23
320
--4.12
520
--4.78
145
--3.28
325
--4.15
525
--4.79
150
--3.29
330
--4.17
530
--4.80
155
--3.30
335
--4.20
535
--4.81
160
--3.32
340
--4.22
540
--4.82
165
--3.35
345
--4.24
545
--4.83
170
--3.38
350
--4.26
550
--4.84
175
--3.40
355
--4.28
555
--4.85
180
--3.43
360
--4.30
560
--4.86
185
--3.45
365
--4.32
565
--4.87
190
--3.47
370
--4.34
570
--4.88
195
--3.50
375
--4.36
575
--4.89
200
--3.53
380
--4.38
580
--4.90
385
--4.40
585
--4.91
390
--4.42
590
--4.92
395
--4.44
595
--4.93
400
--4.46
600
--4.94
AN
INSTRUMENTAL
EARTHQUAKE
MAGNITUDE
SCALE,
7
several
stations
normally
agree
within
one
unit
or
less,
especially
when
allowance
is
made
for
certain
instruments
which
regularly
register
un-
usually
large
or
small
amplitudes.
Accordingly,
in
published
reports
the
magnitude
is
stated
to
the
nearest
half-unit
of
the
logarithm.
This
means
that
the
true
energy
of
the
shock
may
be
more
than
three
times
larger
or
smaller
than
that
computed
from
the
given
magnitude
number.
The
procedure
may
be
interpreted
to
give
a
definition
of
the
magni-
tude
scale
number
being
used,
as
follows
:
The
magnitude
of
any
shock
is
taken
as
the
logarithm
of
the
maximum
trace
amplitude,
e~pressed
in
microns,
with
which
the
standard
short-period
torsion
seismometer
(To
-~-
0.8
sec.,
V
z
2800,
h
--~
0.8)
would
register
that
shock
at
an
epicentral
distance
of
100
kilometers.
This
definition
is
in
part
arbitrary;
an
absolute
scale,
in
which
the
numbers
referred
directly
to
shock
energy
or
intensity
measured
in
phys-
ical
units,
would
be
preferable.
At
present
the
data
for
correlating
the
arbitrary
scale
with
an
absolute
scale
are
so
inadequate
that
it
appears
better
to
preserve
the
arbitrary
scale
for
its
practical
convenience.
Since
the
scale
is
logarithmic,
any
future
reduction
to
an
absolute
scale
can
be
accomplished
by
adding
a
constant
to
the
scale
numbers.
Table
I
presents,
unaltered,
the
result
of
studying
a
comparatively
small
group
of
shocks--those
of
January,
1932.
This
was
immediately
applied
to
the
shocks
of
subsequent
months.
The
magnitude
numbers
computed
from
the
several
stations
should
agree
within
reasonable
limits;
and
this
is
the
case.
A
representative
example
is
the
shock
of
February
15,
1932,
recorded
at
stations
distant
39,
100,
107,
255,
260,
and
345
kilometers
with
amplitudes
of
6,
3,
1.2,
0.3,
0.3,
and
0.2
mil-
limeters.
The
magnitudes
derived
from
Table
I
are
then
3.20,
3.48,
3.13,
3.29,
3.31,
and
3.54.
Considering
the
large
range
in
distance
and
amplitude,
neither
of
which
is
determined
with
precision,
the
range
of
0.41
in
the
computed
magnitude
is
surprisingly
small.
Instances
of
this
kind
could
easily
be
multiplied;
but
a
very
much
better
test
of
the
method
is
available.
For
his
study
of
the
propagation
of
seismic
waves
in
Southern
California
2
Professor
Gutenberg
employed
the
records
of
twenty-one
well-registered
earthquakes.
The
epicenters
o5
these
shocks
are
thus
determined
with
unusual
accuracy;
although,
as
may
be
seen
from
Table
I,
slight
errors
in
distance
will
not
much
affect
computed
magnitudes,
these
shocks
afford
the
most
reliable
test
of
the
2
B.
Gutenberg,
"Travel
Time
Curves
at
Small
Distances,
and
Wave
Velocities
in
Southern
California,"
Gerlands
Beitriige
zur
Geophysik,
35,
6,
1932.
BULLETIN
OF
THE
SEISMOLOGICAL
SOCIETY
OF
A1VIERICA
magnitude
scale.
Gutenberg's
results
are
given
in
Table
II;
the
letters
in
the
first
column
were
assigned
by
him
for
purposes
of
identification.
TABLE
II
E0icenter
Shock
Date
North
West
Latitude
Longitude
Location
A
......
Aug.
17,
1930
35
°
13'
116
°
51'
Mojave
Desert
B
......
Sept.
26,
1929
34
50
116
31
Near
Newberry,
Mojave
Desert
C
......
May
28,
1930
35
30
117
14
Garlock
fault
near
Searles
Lake
D
......
April
20,
1930
34
39
117
04
Northeast
of
Victorville
E
......
Feb.
24,
1930
34
57
117
02
Near
Barstow
F
......
Jan.
8,
1931
34
56
117
03
Near
Barstow
G
......
Jan.
15,
1930
34
11
116
55
San
Bernardino
Mountains
H
.......
Jan.
15,
1930
34
11
116
55
San
Bernardino
Mountains
Y
.......
April
23,
1931
35
25
117
36
Near
Trona
K
......
April
27,
1931
34
21
116
17
Southern
Mojave
Desert
a
.......
Oct.
31,
1929
33
38
118
12
San
Pedro
Channel
b
.......
Sept.
13,
1929
33
38
118
12
San
Pedro
Channel
c
.......
Nov.
8,
1929
35
46
120
28
West
of
Coalinga
d
.......
Aug.
30,
1930
33
56
118
37
Santa
Monica
Bay
e
.......
May
12,
1930
33
12
116
43
SanDiegoCounty(Elsinore
fault)
f
.......
Jan.
17,
1931
37
35
118
03
Southeastern
Mono
County
g
.......
Aug.
18,
1930
34
26
120
11
Off
Point
Concepcion
h
.......
Feb.
23,
1931
35
46
120
40
Northeast
of
Paso
Robles
i
.......
April
24,
1931
33
46
118
29
Off
Point
Vicente
k
.......
April
21,
1931
35
19
118
55
Bakersfield
district
l
.......
April
29,
1931
34
°
15'
118
°
39'
Near
Chatsworth
In
the
following
tabulations
the
letters
P,
MW,
R,
SB,
LJ,
T,
H,
are
used
as
abbreviations
for
the
names
of
the
stations
at
Pasadena,
Mount
Wilson,
Riverside,
Santa
Barbara,
La
Jolla,
Tinemaha,
and
Haiwee,
respectively.
Table
III
gives
the
epicentral
distances
for
the
several
shocks
at
the
recording
stations;
the
distances
are
either
as
given
by
Gutenberg,
or
as
measured
from
a
map
with
an
error
not
over
two
kilometers.
Table
IV
gives
the
maximum
seismographic
trace
amplitudes
in
each
case.
Where
possible,
the
amplitudes
for
both
horizontal
components
are
gi,~en,
that
for
the
N
component
being
entered
above
that
for
the
E
component.
The
readings
in
parentheses
for
the
N
component
at
Pasadena
are
to
be
doubled
in
computing
magnitudes,
since
they
refer
to
a
period
when
the
optical
system
on
this
particular
instrument
was
so
arranged
as
to
give
only
half
the
usual
magnification.
Where
the
reading
is
followed
by
a
q-
it
may
be
considerably
less
than
the
true
maximum,
owing
to
photo-
graphic
underexposure.
AN
INSTRUMENTAL
EARTHQUAKE
MAGNITUDE
SCALE
9
TABLE
III
Epicentral
Distances
(kilometers)
Shock
P
MW
R
SB
LJ
T
H
A
......
173
160
146
278
263
235
140
B
......
171
157
122
295
226
291
192
C
......
176
163
170
257
292
194
95
D
......
117
103
75
245
197
295
181
E
......
139
124
111
261
155
F
......
137
109
253
262
155
G
......
118
106
48
265
142
345
230
H
......
118
106
48
265
142
345
230
J
......
178
166
179
250
302
179
78
K
......
180
170
110
320
186
249
a
......
54
63
86
165
123
378
274
b
......
54
63
86
165
123
378
274
c
......
276
280
347
168
440
248
235
d
......
46
59
117
113
176
351
247
e
......
178
175
108
308
57
454
345
f
......
381
403
381
530
59
162
g
......
188
199
267
45
324
343
279
h
......
288
362
175
265
244
i
......
49
63
108
132
153
366
260
k
......
145
144
204
124
205
120
l
......
44
54
123
100
200
315
216
Table
V
gives
the
magnitudes
of
the
shocks
as
calculated
from
Table
I
and
the
data
of
Tables
III
and
IV.
The
arrangement
of
the
data
for
the
two
components
is
the
same
as
for
Table
IV.
At
the
right
of
the
table
is
entered
the
mean
of
all
the
magnitudes
calculated
for
each
shock.
It
is
e-eident
that
the
deviations
of
the
individual
determinations
of
magnitude
from
the
mean
for
each
shock
are
numerically
small.
Since
the
distances
range
from
44
to
530
kilometers,
this
is
good
evidence
for
the
validity
of
Table
I.
It
will
be
observed
that
the
mean
magnitudes
of
the
several
shocks
do
not
differ
greatly.
This
is
a
reasonable
result,
as
the
shocks
used
in
Gutenberg's
study
were
necessarily
moderately
strong,
and
no
very
strong
shock
occurred
in
the
region
during
the
interval
for
which
records
were
then
available.
Still
closer
agreement
can
be
obtained
if
attention
is
given
to
the
be-
havior
of
each
individual
instrument.
Thus,
the
E
component
at
Tine-
maha
regularly
registers
larger
amplitudes
than
the
mean.
If
the
excess
of
the
magnitudes
calculated
from
this
instrument
over
the
mean
magni-
tude
is
determined
for
each
shock,
and
the
average
taken
for
all
shocks,
the
result
is
0.40.
This
is
a
quantity
to
be
subtracted
from
the
magnitude
calculated
from
this
instrument,
as
a
correction
for
the
ground
conditions
and
instrumental
constants.
i0
BULLETIN
OF
TI-IE
SEISMOLOGICAL
SOCIETY
OF
AMERICA
TABLE
IV
MAXIMUM
SEISMOGRAPHIC
TRACE
AMPLITUDES
(MILLIMETERS)
UpperFiguresRefertoN-SComponent,
Lowerto
~W
Shock
~
MW
R
SB
LJ
T
A
(0.5)
2.3
1.9
0.9
1.1
1.1
0.8
1.9
2.8
1.1
1.2
1.1
B
27
24
14
56+
23
17.5
C
(1.4)
4.4
2.3
4.2
2.5
4.5
2.5
3.9
3.1
3.8
2.3
3.9
D
(0.9)
2.9
1.8
1.4
1.9
0.6
1.4
2.9
1.9
0.8
2.3
0.7
E
(1.8)
3.1
1.1
4.6
3.1
3.5
2.4
F
3
1.9
1.8
3.3
2.8
1.9
1.8
G
(39)
88+
66+
24
39+
60+
54
H
(38)
82
8~
10
30+
26
56+
19.5
f
12.2
2.9
4.6
2.2
5.1
7(2
13.4
4
4.4
3.6
7.2
K
3.6
2.5
0.7
3.9
2.5
3.3
1.0
5.2
a
1.5
3.4
12.1
2.0
5.7
0.4
1.9
6.3
4.8
2.1
4.5
0.6
b
5.4
6.5
3.8
0.8
11.6
11
3.8
9
1.2
c
1.9
0.7
14.3
0.3
8.2
0.8
12.2
0.3
15.9
d
65
52+
33
135+
61+
6~
39
e
(1.8)
2.9
9.0
2.1
20,2
1.2
3.8
5.0
11.1
1.6
15.6
2.0
f
(0.2)
0.2
1.3
0.2
29
0.4
0.3
1.8
0.2
36
9
(0.5)
1.4
0.4
22.7
0.4
0.7
1.4
1.7
0.3
~.1
0.5
1.0
h
(0.4)
0.6
6.1
5.7
1.1
0.3
5.7
i
30
28
20
1.6
19.3
25
~
20.4
4.8
k
1.7
4.3
0.3
2.9
2.6
1.7
2.3
0.3
3.1
3.0
l
8+
5.0
8.9
2.1
0.6
13.1
12.1
4.1
6.6
3.8
1.6
H
̧
2.6
2.2
25
6.7
0.8
1.2
1.4
2.2
3.0
39+
58
23
31
22.5
1.6
1.7
0.3
0.6
1.1
1.3
7.7
5.2
37
31
1.3
1.6
1.9
2.2
0.9
0.7
4.2
2.6
1.0
1.7
1.6
AN
INSTRUMENTAL
EARTHQUAKE
MAGNITUDE
SCALE
11
Shock
A
B
C
D
E
F
G
H
J
K
b
c
d
e
f
g
h
i
k
1
P
3.39
3.29
5.12+
3.86
3.81
3.37
3.26
3.79
3.89
3.74
5.00
4.70+
4.99
4.59+
4.28
3.99
3.83
2.88
2.98
3.42
4.67+
3.98
4.00
3.98
3.98
3.46
3.61
3.88
4.02
4.09
3.90
3.51
3.51
3.64
TABLE
V
CALCULATED
Upper
figures
refer
to
)/[W
R
3.68
3.56
3.60
3.73
4.74
3.98
3.74
3.93
3.87
3.48
3.13
3.48
3.15
3.57
3.63
3.62
3.55
3.52
4.98
4.95
4.45
3.88
4.49
4.02
3.78
3.90
3.31
4.02
3.58
3.62
3.75
3.84
3.98
4.22
4.10
4.15
3.86
4.01
4.10
4.11
3.77
3.95
3.68
3.46
3.76
3.34
4.09
3.79
4.18
3.90
3.03
3.64
3.03
3.59+
3.84
3.79
3.75
S
ttO,CK
MAGNITUDES
N-S
component,
lower
to
E-W
SB
LJ
T
H
Mean
3.88
3.88
3.76
3.64
3.69
3.97
3.92
3.76
3.57
5238
5.13
4.88
5.12
5.36
5.22
4.44
4.39
4.14
4.06
4.40
4.35
4.08
3.81
3.92
3.79
3.78
3.33
3.54
3.67
3.87
3.85
3.87
3.38
3.71
4.21
3.45
4.08
4.10
3.64
3.84
4.08
4.10
3.78
5.07+
5.62
5.29+
5.24
5.04+
5.97
5.46
5.15+
5.24
5.06
5.10
5.26
5.00+
5.53
5.19
4.45
4.37
4.13
4.24
4.30
4.43
4.59
4.28
3.97
4.04
3.99
3.98
4.12
4.17
4.02
3.65
3.90
3.97
3.39
3.61
3.67
3.79
4.15
3.69
3.93
4.27
3.95
3.97
3.93
4.09
4.45
4.02
4.53
4.07
4.69
4.61
4.39
4.46
4.07
4.98
4.44
4.90
5.12+
5.78
5.35
5.22
4.88+
5.18+
5.85
5.27
4.38
4.03
4.71
4.35
4.22
4.26
3.92
4.93
4.44
4.49
4.10
4.23
3.61
4.07
4.64
4.10
4.32
3.67
3.90
3.74
4.08
3.89
3.76
3.88
3.84
4.23
3.79
4.19
4.61
4.38
4.14
4.16
4.51
4.50
4.52
4.24
4.40
4.52
4.51
5.00
3.60
3.97
3.12
3.54
3.62
4.04
3.95
3.85
3.88
3.86
3.86
3.82
4.11
4.31
3.83