The sun., 1883-08-19
Concerning Enrthaunke..

The recent calamity in the island OF Ischia
has naturally given impetus to the study OF earth
quake phenomena. Considering that there 10 hardly
moment when the earth is not Qunking somewhere.
though not always cognzant of it. because it
occurs at the bottom of the in unin ed dis
ircts and that according to Prof Alexis Perrey's caa
logue OF earthquakes they average SIS per annum
astonishing that their phenomena have not been
fuiy studied until within comparatively recent years
The advance in this study has been slow. During
earthquake the scientific mind is hardly In
condition TO make minute observations. Scientific
generally prefer to investigate earthquakes after they
They wait until they hear that earthquake
has occurred somewhere. and then pack up their seis
mometers and 60 TO work with enthusiasm to ind the
focus and the epicentrum
In studying earthquake phenomena investigators
have arrived at various conclusions 1t has been shown
that earthquakes are more frequent whom the 10
on the horizon than when It Is the meridian. They
are also frequent when the Ia nearest tho
earth than when 1t il furthest of. These positions
respond to the nes Of ordinary flood tide and Of high
eat Hood tide Some have concluded from these facts
that the interior Of the earth is in fluid condition be-
meath thin crust and that this fluid matter Is affected
by the tide generating forces Of the mud But
Prof lac Conte has said Of this theory II were true
the effect ought to be far than hnd it." and
he concludes that 1t is better to regard the position Of
the moon incidental phenomenon.
1t may be regarded. however. us almost established
that the forces which produce earthquakes and volcanic
posve are often preceded or accompanied by earth
Quakes Earthquakes also cease after eruptons from
neighboring volcanoes and vice versa For instance,
s,rombo ceased erupting during the famous Calabran
earthquake and the earthquake in which Riobamba
destroyed and 5000 people pershed took place under
similar circumstances. An earthquake map prepared
by Prof Maet shows that the distribution Of earth.
quake centres is much the same as that of volcanoes
Elevation and depression OF great of the earths
crust connected with earthquakes After the South
American earthquake in 1885 the coasts Of Chill and
Patagonia were elevated from two TO feet and old
beach marks found there from 100 feet 800 feet
above the level indicating that the whole southern
end Of south America has at time been elevated
TO this extent In the Mississippi valley earthquake
there was fssure one side Of which dropped lower
than the other. thus forming what IL called the
sunk Country" around the mouth of the Ohio.
From the phenomena of volcanic eruption and Of the
movements of great two separate theories have
been formed Earthquakes is said originate by the
sudden subterraneous formation or escape OF vapor.
This will account for local earthquakes but for the
movements of large areus. Both phenomena seem to
be covered by the following theory: There is greater
contraction In the interior OF the earth than the
crust consequently the crust is forced upon itself by
horizontal pressure and where the yields
suddenly by the formation OF assures. Tile yielding
produces jar in the interior OF the earth the jar
produces an earthquakes the earth wave reaches the
surface at what is called the opicentrum and spreads
from that point.
This wave theory explains many phenomena. For in
stance in great earthquakes the velocity with which
the shock travels rarely exceeds twenty miles a minute
in small earthquakes 1t runs to 40 miles In great
earthquakes the trough Of tho is deep and
quenty II is continually striking nelustic strata. where
in slight earthquakes the trough Is shallow and
meets few nterfer.nces. The nerferences gradually
break the force Of the wave Again. in all earthquake
regions there districts called bridges which
affected In these districts the original wave strikes
| inelastio stratum before emerging and Ia detected