The Oskaloosa herald. (Oskaloosa, Mahaska County, Iowa) 1885-1919, 1914-03-05
THE NEW YORK EARTHQUAKE.

| The recent earthquake in New
York, SO far as can be decided from
Information now at hand, was strong.
est in the northeastern part of the
state and less intense in all direct
ions fIGm that section, according to
a statement by Arthur Keith, of the
| United States Geological Survey,
who has made a special study of the
geologic history and structure of the
Appalachian Mountain region. AS
earthquake shocks are regularly
weaker outward from center, the
area of greatest intensity at the sur
face is nearest the point of origin, al.
though this point probably is not at
the surface. The earthquake center,
therefore, appears to be in or north
iof northeastern New York
| Earthquake shocks are caused by
the breaking and moving past each
other of great masses of rock in the
earth's crust. Rocks are more or
less elastic, particularly crystalline
and igneous rocks like granite, and
they transmit shocks for very long
distances. Rocks in the earth's crust
are always in a state of strain, and
release from this strain by tract.
|
bound that may b. violent. Even Vt
the surface of the earth this move
ment is continually noted in quarries
when new layers of stone are set
free, and it is still stronger in the
depths of the earth. When the
strain finally exceeds the strength
Iof some of the rocks they break and
snap, and there is an elastic rebound
from each movement. This causes
the lesser trembling after the first
shock.
Earthquakes are commonly associa-
tied with faults or riffs which are
breaks or fractures in the rock crust
along which the rocks move, past one
another. Some faults are character.
liZed by repeated motion alongNa Civ.
Ell plane or narrow zone, like that
which caused the San Francisco
earthquake. The vast majority Of
faults, however are practically dead
land no motion takes place on them
because the strain has been satisfied
ior diverted into other directions. Oh
this kind are most of the old faults
in the Appalachian area, from Ala
bama to Canada, including the noun
famous country of the East. Young
er faults are also found in the East
but most of these are dead and their
strains have long ago been satisfied
The latest set of faults displaceS the
youngest geologic formations, al
though their source is in the underly
ing hard rocks.
1t is usual to associate earthquake
shocks with the greatest OF the faults
on which the motion is measured in
miles. These, however, are the old
est and the most certainly dead OF
the faults, and later and different
strains have acted on their areas and
produced different faults. Neither
length nor great motion on fault is
needed TO make a disastrous shock
as was plain at San Francisco, where
few feet of motion caused the ruin
The factor which makes shocks dan
garous or not IS their intensity, and
this Is directly due to the rapidity
OF growth and yigor of the strain
Quick and violent strains accompany
the growth and rise OF new parts OF
the earth's crust where il is being
compressed until it moves. In the
old Appalachian country OF the east
ern part OF the United States such
rise Is so exceedingly slow as 10
make its existence in historic times
a matter of dispute. In any case, II
is now OF the cOmpressive char
acter that causes lateral or violent
movements and dangerous shocks
Therefore while earthquakes are not
unknown in the East, it is exceeding
ly probable that they will be dis
astIOuS.
The destructive Charleston earth.
quake of 1886 was east of the Appal'
achians, in tract which in recent
geologic time has risen unevenly
| from the sea as result OF earth
strains. Its effects were especially
severe. as is usual in loose forma'
tons like the sand and clay which
prevail in that district.