Imperial Valley press., 1919-03-08


warm and humid day, some people
will remark:
"This feels like earthquake wealth
err"
There is no such thing as "earth-
quake weather." unless it be among
few whose knowledge on the sub
iect, or, | should say, lack Of llnowl- /
edge, is on a par with the old fash
oned idea that piece of raw meat |
wrapped in a dishrag would cure a ,
wart on the back Of their neck Earth |
quakes are of two kinds-volcanic and |
tectonic. Many indications are that |
some of them are produced by causes
vet to be learned A volcanic quake |
is, of course, as the name implies, in |
The vicinity of active volcanoes. Vol |
canic quakes are seldom felt at great |
distances from their epicentres. An |
example Of this is that quakes are
common around Vesuvius and the
Island of Stromboli. These tremors
are seldom felt in Sicily or Italy. |
This is explained by the shallow
depth Of their origin. Many quakes
Of doubtful origin we have reason
to believe are volcanic, as there is
evidence of volcanic action in the
depths of the earth that is not visible
on the surface, but which left per-
manent results in ancient rock ex-
posure. Since we are not in the vol
canic regions, tectonic quakes are all
that we will have to contend with.
The point of origin is known as the
centrum. 1t cannot be a literal
point. 1t must be locus occupying
space of three finite dimensions
It's shape may be anything. There
are many quakes which we have rea-
sen to think are caused by shearing
movements of rocks that produce
what are called faults. A sudden
| dropping of a large area of the earth's
surface causes the earth to tremble
many hundreds of miles away. A
ooint on the surface vertically over
the centrum is called the epicentrum
This is an ideal point and can never
the located with exactitude. The in
,ensity of quake is greatest at the
epicentrum and diminishes unequally
n all different directions. In the
depths Of the earth there occurs a
sudden movement or displacement of
matter in some locus, as a result of
which strain is quickly generated
or relaxed This change of stress
causes wave, in fact many waves,
5ropogated indefinitely through the
earth. These waves reach the sur
face and cause the soil and superfi-
cial rocks to vibrate, constituting the
sensible earthquake. AS the wave
expands, its intensity diminishes.
The motions which are felt and seen
at the surface are not the original
! waves rushing through the solid
earth, but are secondary movements
resulting from them. Great quakes
come without any ineligible warn
ing. Some have been preceded by
minor shocks and ,quires and by ON
nous sounds. A great quake comes
| quickly and quickly gone. Its dura-
tion is usually a matter of seconds
rather than minutes. The down
! throws in the crust do not signify
| that there are large subterranean
| ,avities into which large masses OF
;he earth may fall. Thew are regard
ed as results of unequal stresses
| which have become so great that the
rocks must yield to them along the
line of least resistance. Said masses
seek new readjustment or equilib-
! rum of stress and the motion may
| be upward in one locality, down in
| another. or be compounded with
horizontal shifting in either case.
! The California quakes as a class sug-
gest teconic origin. The lighter
intensities are felt over considerable
areas, which shows great depth Of
focus. The seismographic traces
show considerable length of period
and we'll marked separation between
the short preliminary tremors and
the longer waves, which is indicative
OF considerable distance travelled by
the vibrations between the centrum
and the recording station. / have
consulted freely a volume by c. f.
Dutton on this subject, to whom ac-
acknowledgement is due. But enough
IF this quake stuff. Let US sum up
the situation:
The Valley is not going to sink.
We have yet to find some portion Of
this globe that is earthuuake- proof
When siXteen-cylindered, 700
horsepower would-be rain or hay
maker, charged to the brim with hot