The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1922-12-14
CAUSE OF EARTHQUAKES
SCIENCE LEARNED MUCH
FAULTlNe AND sHEARlNe Ex-
PLAlNED-MAY IN TIME BE
ABLE FORECAST THEM.
(New York Herald)


The rock envelope or outer layer O
the earth. often called the crust, seem.
rigid and brittle but is really elastic
Any force which jars the earth pro-
duces vibrations or tremors: and wher
these become acutely perceptible to
humanity they are classed as earth
quakes. These shocks originate al
a considerable distance below the sur
face of the earth and when they reach
the surface they spread out much like
the circular waves seen when a stone
is thrown into still water.
Near the center of the shock they
seem almost like hard blows; at a
distance they become tremblings
which gradually disappear. The ex-
plosion of heavy blasts produce the
shocks which differ from natures
earthquakes in energy only. The
blowing up of He'll Gate rock was felt
40 miles away. The munitions explo-
sions which shattered the windows of
lower Manhattan during the war
stopped the chronograph clocks in the
weather bureau laboratory at Mount
Vernon. AS a matter of fact artif
cial earthquakes resulting from mine
explosions have been used in Europe
for the study of earthquake phenom-
ena; in the future it is likely that they
will be extensively employed for that
purpose.
Earthquake vibrations travel very
rapidly. AS they traverse the rock
layer they progress with a velocity
estimated at from 100 to $50 miles
minute. The earth waves created in
the ocean move more slowly. Their
velocity varies from six to ten miles !
a minute
Causes of Quakes.
OF the various causes of earth |
quakes two have been pretty thor |
oughly investigated In volcanic re-
gions explosive displacements of sub
terranean steam or other gases cause
violent and destructive shocks. As a
rule shocks of this kind are almost l.
momentary, each lasting from a few
seconds to a minute. Sometimes they
precede a volcanic eruption; some
times volcanic outburst produces all I
the phenomena of an earthquake. The
eruption of Krakatoa, a volcano near
Java, was coincident with a severe
earthquake; the volcanic explosion it.
self caused the earth tremors
But a fundamental cause of earth !
luakes is the gradual adjustment of
The rock envelope around a shrinking
interior. The great mountains systems ,
wrinkles, folds and block -,
'anges are the result of such adjust
nent The rock layer folds itself
lbout the shrinking interior not by
pending but by innumerable fractures
u breaks. The breaks and shearings =
If the various strata which form the r
rust are the faults of the geologist. =
some of the faults thus produced are il,
hundreds of miles in length; others ,,
re almost insignificant in extent. One !,
nay see many of the minor faults >
long the rock cuts of the New York, b
Westchester & Boston railway The y
parallel seams in the granite rocks are Il
aults; and where the shearing oc- q
urs the rock has been thrust upward =
r downward or sidewise. These dis q
placements are slight and the shock +
ne to the breaking may have been q
Il
But when the shearing and the dis =,
lacement are sudden, aggregating
0, 20 or even so feet, thrusting bill -
ons of tons of rock out of place ii
here occur the jars and tremors that a
make the earth tremble over an area Il
f many thousands of square miles. If ~
he displacement occurs little by lit .,
lie at intervals the shocks may last q,
Or days and even months. Not very h,
iuch adjustment is going on along ii
ne Appalachian mountains; for these -.
anges are old as mountain making p,
oes. But the great Cordillera which
ncircles the Pacific ocean is compar-
lively young and the folding and O.
sGltinS are manifest IN the great III
lumber of disastrous shocks, espe is
ally in the Andean ranges and in re
lie Japan chain of islands. III
San Francisco Earthquake. Il,
The earthquake which wrought dis h,
ster to San Francisco in 1906 was due pe
iii uSlS anu uloBletNNiiAtHNo e"ACA5 a I'm
iult several hundred miles in length. dc
he character of the displacements he
lried-an upthrust here, a slip down ca
ard there but always a rift with its
iges pulled apart. DR.. Omori, the aft
lpanese seismographer, who is prob TT
by the foremost authority on the ia
Inject, laid especial emphasis on the w,
ct that the strain was diagonal. ne
Dads. fences and walls lying across ca
lie fault were not merely broken ed
ross they were pulled out of align wi
ent as well-in some instances six be
eight feet M
The rift of the Charleston earth ex
lake was probably quite as severe
that of California; but the build ca
gs were substantial and less dam
-, ,.o-,,1t,4 The W