Evening star., 1933-03-11
SHoKS RECORDED
ON >S|SMOGRAPH
OF GEoGETOwNU. U.
Southern CaIernia's Most
Serious Earthuake Had
Been Antic'eted.
PECULIAR FoRMA\oN
OF REGION DEsRIBED
Geological Condition HeldNy Sci
entists to Be Favorabh
to Temblors. \

The earthquake which rocked 10
coast of Southern California last riA
was recorded on the smoked pape
seismograph records at Georgetovd
University as a main shock starting
sharply at approximately 9:o2 pm.
followed at irregular intervals during
the night by five aftershocks.
The first shock was not severe, a.
major earthquakes go, and was in.
terpreted by Rev. F. A. Sohon, director
OF the seimolcgical laboratory, as an
ether of the long series of earthquakes
to which the California coast is Sub.
ject due to its peculiar geographical
complex.
Record Complicated.
The record received last night was
complicated because of the tangled
Garth waves set up by the succeeding
shccks and the different types of mo-
ton, so it was impossible this morning
TO calculate the center of the earth
quake. First came the waves set up
by the shaking motion, followed after
intervals by those due to the back and
forth motion and those travelling over
the earth's surface.
After the sharp beginning, Father
Sohon found indications of distinct
shocks at 10:45, 11:45, 1890, 2:30 and
4:30. Only the first could have caused
excessive damage.
The California earthquakes, it was
explained, generally are explained by
American seismologists on the principle
of isostasy, or disturbed balance far
under the surface of the earth. A few
miles below the surface, Father Sohon
explained. the rock is under such an
fn
whenever the balance is disturbed. If
the surface OF the earth was cut up
into blocks a few miles square each
block should weigh the same as every
other, and this is generally the case.
There is very good balance. Noun
tains are made of light material, while
the valleys and sea bottoms are of
heavy material.
TreInOr Anticipated.
But along the California coast there
Is a sharp change from very high noun
tains to very deep sea valleys. Soil is
continually being washed from the
mountain tops into the sea by erosion.
This makes the mountains lighter and
the floors of the ocean depressions
heavier. Consequently the balance is
upset and the extra weight of the sea
COlOOAl tSilOo W push Qp llle 1lSuI
mountain ranges.
The inhibiting force of friction tends
to prevent this change in the balance of
the earth'S crust taking place gradually
and imperceptibly. Forces are piled up
until the underlying, mobile rock gives
way and there is sudden, severe
shock.
While this is the most serious earth
quake yet recorded for the Southern
California coast it has been anticipated
Long Beach is the site Of the so-called
FONT Kismin Fault, deep and widen
ing crack in the earth which a few
years ago was shown to tourists as one
of the wonders Of nature until the
municipal authorities realized its
significance.
Recently the Coast and Geodetic
Survey set up special recording ma
chimes through the California area
which will measure the movements of
the earthquake on the spot. One of
these measures the vio1ence of the
shocks and the other the distance and
speed Of the earth's sway from side 10
side. Accurate knowledge of such
movements may be a value in con-
structing earthquake-proof buildings.