Evening star., 1952-03-17
Footsteps Will Show
On New Quake Meter
Super Sensitive Apparatus
Is Installed on Nj. P0Iomur
By Thomos r. Henry

The most sensitive earthquake record.
ing apparatus IN the world now Is being
installed on Mt Palomar, site or the
earth's most powerful telescope.
Designed on new principle. the Mt.
Palomar SeiSmOgraph win record earth
strains of less than Six-millionths Of
an inch caused by shock waves passing
through the rock. The apparatus now
being set up by the California Institute
OF Technology Is so sensitive that q
mans footsteps far above win be re-
corded because Of the minute waves
they set up in the rock.
Because Of this the apparatus Is bur-
led deep In the mountain, miles away
from the observatory and win be visited
only once week by an attendant who
comes to change the records. With this
complete lack Of man-made disturb
ances it Is expected to record waves Of
longer period than hitherto have been
obtained In the world.
For Horizontal Purposes.
The new instrument Is designed to
record horizontal displacements in the
earth's surface rocks. AL previous
seiSmographs have recorded up-and-
down vibrations.
Another piece Of apparatus now being
designed In the Cal Tech laboratories
viii actually produce q phonograph rec
ord Of the voice Of Mother Earth due to
earthquake vibrations. It Is tape re-
corder, moving continuously but at o
speed Of less than q twentieth Of an
inch q second. The vibratory move
ments Of the earth generate minute
electric pulses. which actuate the re-
corder.
'When q local earthquake occurs" :"
says q report on the new apparatus. 1T
comes through on the tape like o pistol
shot. A distant quake sounds like o
lO-strike In q mammoth bowling alley.
Varies Day to Day.
"The machine will be valuable IN
studies Of the micro-SeiSlnic movement
of the crust Of the earth. This move
ment varies from day to day, like the
sea. It is certain that this movement
is related in some way to the waves OF
the ocean and that 1t is. In fact, gen
Grated at sea. The sounds Of the earth
at rest are exactly like the steady, regu-
lar rise and fall of ocean waves"
Another new instrument being IN
stalled at the Mt. Palomar station will
enlarge these wave motions approxi-
mately 5000 times and make possible
photographs Of the earth's surface roll
ing and tossing like the surface OF the
ocean.
Another new instrument win provide
accurate information on the direction
of arrival Of earthquake waves. TINS
determination Of direction is very dim
cult with existing instruments. A seis-
nograph of the conventional type pro-
duces a very complicated record showing
two kinds of shock waves coming
through the earth at different speeds.
This is complicated by various echoes
from the surface Of the earth and from
underlying rock strata. Except for very
deem shocks, all this is followed by
long train Of waves travelling over the
surface of the earth. The whole proc
ess may take hours to record. even when
the quake itself last only few minutes.
because the shock sets up commotion
that takes SO long to die down.
Two Kinds or Waves.
Every earthquake sets up two kinds
or shock waves, called and s waves.
p waves vibrate longitudinally while
the vibratory motion Of s waves Is
at right angles to the direction Of
propagation. p waves move faster than
S waves, and the time interval between
them varies from a few seconds at short
distances up to more than IL minutes
when the shock is 1000 miles away. BY
means Of this time difference 1t Is
possible to get a rough idea Of the
distance Of the disturbance, but about
the best accuracy expected Is within
approximately so miles
The new apparatus will provide three
sets of measurements by which the focus
of q quake can be determined with far
greater accuracy. Other apparatus Is
designed to find the relation between
extremely minute waves travelling
through the earth's surface and varia-
tions in atmospheric pressure.
The entire set-up, says the Cal Tech
report, "will probe deeper into the core
Of the earth than man has ever been
before"