The sun. [volume] (New York [N.Y.]) 1833-1916, 1915-01-31

tude of Rome. The pen' NJ als,f,
stresses were probably gr,yit.r IN .r.
italian district than iu the Spanish -ec.
ton. which, by the way. is a mountain.
Gus one.
Prof Reid sums up his conclusion,
thus:
The observations ~ tho Calfor,,
earthquake and the deductions drawn
from them. based as thoy are uupf
elastic properties Of r,ck and t',Jn tie
we'll known relative movemA ,or us
ferent parts Of the earth's Nus' lly.
led TO certain general conceptions o,
the mass movements which take p.l,.
before and at The timo Of '.cto7lr
earthquakes, which may be expressed
as follows:
al. The fracture OF the rock which
causes a tectonic earthquake. {. fr,
result Of elastic strains. greater Than
the strength OF the rock can withstand
produced by the relative displacement,
of neighboring portions OF the .ur;hs
crust.
80. These relative displacemonts A..
not produced suddenly az the time or
the fracture, but attain their maytmmo
amounts gradually during a moro or
Tess long period or time.
"3. The only mass movements that
occur AT the time OF the earthauaka
are the sudden elastic rebounds Of tho
sides OF the fracture toward positions
OF no elastic strain; and these move.
ments extend 10 distances of only a few
miles from the fracture.
-. The earthquake vibrations oriri-
nate in the surface of fracture. the
surface from which they start has az
first a very small area. which may
quickly become very large, but AT
rate not greater than tho velocity %
congressional elastic waves IN the rock
20. The energy liberated at the time
OF an earthquake was, Immediately be-
fore the rupture. in the form Of energy
o. elastic strain OF the rock
These statements. which may ~
called the elastic rebound theory Of ter.
tonic earthquakes, do not breach tho
original cause of earthquakes. whicN
lies in the source OF the slow move.
ments accommodating the elastic energy.
hut merely give the mOdus operandi Of
the accumulation and the liberation Of
this energy"
What Is plain, however, is the rela.
lively small part played by volcanic aPi-
tations in earthquakes generally. and
the scientific world is gradually reach
ing a broad agreement in regard 10 tbs
causes giving birth 10 volcanoes them
selves. In brief. this is that tho fric-
ton set up by moving surfaces Of great
rock masses held in contact by enor-
nous pressures and shifting under the
slow but Irresistible impulses OF crustal
waves 10 sufficient 10 generate hes;
enough to melt the sliding faces Of ths
rock and thus to provide the charac-
teristic lava.
This molten stone coming IN contact
with subterranean springs or infitra-
lions from large bodies of water, gener-
stes steam which may reach degrees Of
explosive pressure with resulting vio-
lence. Thus tho volcano is substantially
another expression Of the game energies
that induce tectonic earthquakes, an
energy whose primary source science
has not yet been able to trace.
In the case OF the California earth
quake OF 1906 II was the horizontal dts
placement of the fault region. Prot
Stephen Taber in recent issue NJ IN.
Bulletin OF the Seismological Society
disastrous earthquake of August II.
1856. which occurred in and about tho
neighborhood OF Charleston, s. G., and
has tabulated the $50 seismic disturb
ances which have shaken that part OF
tho Atlantic coastal plain more or less
severely since. The thing that vii
probably be most surprising is his pro
nouncement that the energy developed
af AtK,,o 90 IA, IL. -
in South Carolina was good dcs
greater than that eXerted IN tho slip
ping of tho San Andreas fault in Cali
fornis in 1906.
In the case of the coastal plain d.
trict near Charleston, the fault in tie
crystalline rock base underlying that
area probably resembles something Ike
two vast gravestones leaning against
each other, and thus held in a partly
standing position. Lying upon this
fault Is the earth and sedlmentary ma
terfal deposited there in the ages gone.
and the country is low, even swlmpy
with moderate elevations probably no.
exceeding 60 or 20 feet. Nevertheless
the subterranean ridge Of the fault
divides the region between Charleston
and Summervillein such fashion that We
may liken the physical condition 10 tho
balance maintained between the sloplrg
sides OF n house of cards. where un-
even pressure on either side, II su''i-
Client, might destroy the equilibrium,
According to Professor Taber earth
quakes in this region have generally
been colncident with greater baromet-
rio pressure on the western region
everything the fault--the general line or
the fault runnig from northeast 10
southwest. Thus a state OF the atmo'-
phere. when the stresses in the faux
are at a proper stage. may suffice 20
produce n readjustment Of this under
lying rock.
Again, long continued periods - ran-
fall, especially when there Is q greater
precipitation on one side Of this deeply
buried ridge, may likewise stimulate
seismic tremor. This is not hard tn
understand. because "as a result ~
heavy local showers It Is easily pos
sible TO have a difference OF onN inch
In the amount of rainfall At the two
places-east and west sides % the fault
IN tho course OF a few hours ana
this would mean n difference Ia tho
actual pressure applied 10 the earths
surface OF over 1900 tons per square
mile"