The Republican. [volume] (Oakland, Md.) 1877-current, 1885-06-27
EARTHQUAKES.
A Distinguished Scientists Opinion of the
Cause of Subterranean Activities.


hurricanes which followed the Spanish
earthquakes were not followed by those
| Subterranean disturbances, and alex
planning electricity has been called upon
/ to explain how earth-throes might have
caused atmospheric disturbances. l
know of no way in which such conse-
quences could have followed from dis
| placement of the earth's crust To me
it seems far more natural to conclude
| that the hurricanes and earthquakes
were alike produced (the hurricanes
chiefly, the earthquakes partially by
the atmospheric compression which pre-
coded the subterranean disturbances.
| This compression indicated heaping of
air over the disturbed region; the earth s
crust yielded under this increase of
| pressure, combined with the action of
other forces, and earthquakes followed;
the compressed air swept away to re-
| giOns of less pressure, and the rarefac-
ton following led in the usual way to
the indraught which precedeS cyclonic
| disturbance in the air.
But while the action of atmospheric
| pressure in helping to excite subterran-
| can activities must not be overlooked,
the varying pressure eXerted by seas and
oceans is more potent disturbing fac
| tor. Atmospheric pressure is distribu-
ted in such way that though the weight
of air on any given area is continually
changing, there are no sharply defined
lines, at any time, which separate re-
! gions of less pressure from regions of
/ frVn fn1. -, ,th
| the sea along Il shore line. Here we
have the sea acting with constantly
varying intensity, as its level changes,
on the seward side of the shore line,
while on the landward side there are no
such variations of pressure. Let us con-
slider what this means. Take a tolera-
| bly, straight shore line SOC miles in
length, and suppose that along this
shore line a region of ocean 100 miles
broad rises through height of three
feet under the combined action of sun
and moon raising tidal wave, and
fayorlng strong winds urging the water
shOreward. Then we have 80, 600 square
miles of sea-Water, three feet deep, adj
ded as so much lightweight to that part
of the earth S crust which underlies
the seas along that shore. Each
! sqnare mile contains in round num-
,berS 5000, 900 square yards, or 81
100000 square feet. The addition
al weight corresponds, then Gas the
added layer is three feet deep,) to So
600 times $1,000, 600 cubic feet of water,
each weighing 644 pounds, or to 49,
co., 900, 600 tons. 1t is clear that the
addition of so enormous a weight as
this to the submerged part of the earth
crust, outside the shore line, may well
! produce strains too great to be resisted.
! 1t must be remembered that the very
existence of a PERCEPTIONS shore line Gas
i distinguished from one where the land
above water and the parts submerged
form one great slope) indicates the com
| parative weakness of the crust along
that coast. 1t has yielded on one side
to pressure thrusting it upward above
! the Sea-level, and on the other side to
! the pressure of the water forcing it
down. 1t is true, the actual line of
/ yielding may not coincide with the
! existent shore line. For the action of
the sea waves may (and generally musD
have altered the position of the coast
from that which it occupied when first
! AOIliANNA buI II may w ltthth lOI dilJCll
that not far from every PERCEPTIONS
shore line lies a line of weakness. where
the crust has given way in the past, and
may give way again. In this considera-
ton undoubtedly we find part OF the
explanation of the observed fact that
almost all the great regions of subter-
ranean activity on the earth lie near the
sea-ShOrc.
But while the changes of atmospheric
and oceanic pressure are potent factors
in the production of earthquakes, and
are probably in the great number of
cases their direct occasion, it is. of
! course, to the subterranean regions
| themselves that we must look for the
forces at work in upheaying the crust
of the earth. The forces acting from
the outside are, as the pull on the
trigger; the imprisoned gases and
vapors generated by internal heat are as
the powder by whose explosion the
missile is elected.
Yet even in considering the earth's
| subterranean activities we still have to
look outside for a part at least of the
causes Of disturbance. The air perhaps
may in this respect be neglected, but
+ the water is all-important. 1t has been
said. indeed, and probably with a nearer
approach to truth than usual in the
case OF. congratulations of the sort,
'WithOHt water there can be no vol
cano," and a similar rule (not quite so
-generaD applies to earthquakes. Few
probably occur possibly none, save
through the action of water in some
way or other. All active volcanoes ex-
cept one Gin mid-Asia) are by the sea
shore. Nearly all the great earthquakes
recorded by history have taken place.
and have apparently had their center of
disturbance, near the sea.
There can be very little doubt, in
deed that the direct cause of every
great subterranean disturbance is water
in the form of steam-steam super
heated, under great pressure, and there
fore possessing much greater expansive
| power than steam at ordinary tempera-
lures. -RicharG A. Proctor. IN Harper'S
Magazine. 4.
Great Improvement.
|
Captain Jasman, who owed a bill in
| a neiUhbOrinp town was drawn on