The Coolidge examiner., 1931-04-10

epicenter the pulsing waves strike
the surface at a slant and so ac-
centuate the effects of the side
wise" waves and create new sur
face undulatiOnS. The shaking at
the epicenter, too, throws the
earth's surface there into undula-
tory waves like ripples on a pond,
and these also travel outward in
widening circles. These surface
waves are those of greatest motion
but least speed. They register the
heaviest vibrations on the siesmo-
graphs of the world.
The second important question
in regard to an earthquake is: What
starts the waves?
No one has ever seen an earth
quake wave start outward from its
center, and it is safe enough to say
that no one ever will. But science
has built certain hypotheses about
the matter that seem to account
satisfactorily for the happenings,
and which are accepted pretty gen.
orally.
Hold a dry stick as big as your
thumb in your hands and bend it
until it breaks. AT the snap, waves
will travel to your hands and usu-
ally give you quite a painful sensa-
ton.
Hold an iron bar by one end and
strike the other sharply with
hammer Again the vibrations car
ried to your hand may be violent
enough to produce a stinging pain.
Breaks Start Most of Them.
1t is generally believed that
earthquake waves flow from point
where one of the three forces illus
trated is suddenly released-a
break, blow or an explosion.
Breaks are credited with the re-
Sponsibillty for most earthquakes.
1t is believed that because of slow
contraction or shrinking which may
result from the cooling of the out
cause of pressure from deposited
silt, strains are set up below the
surface like those in the bending
stick. Eventually the strain
reaches the breaking point and
there is a swapping of the rocks
which send violent waves to the sur
face causing earthquakes.
The blow type of earthquake is
probably less important. Such
blow might result from the falling
in of great cavern, but probably
would cause only local shiver. A
might be slipping of one mass of
rock over another with a collision
at the end of the slide. Such a
blow often follows break, the
two acting together.
Earthquakes in active volcanic
regions may often result from ex-
plosions of gases far beneath the
surface; though many times there
seems to be an intimate connection
between earthquakes and vol
canoes, the law regarding them has
not been established. Some re-
markable condolences have been
observed in late years. however.
The terrible cataclysm of Mount
Pelee, which, on May s, 1902, al
most instantly killed 10000 inhab-
itants, was preceded by the earth
quake which in January and April
of the same year wrecked num-
Der of cities in Mexico and Guate-
mala. The distance between these
points is at least 1000 miles, show
ing how deep-seated must have
been the disturbances, If, as has
been suggested, there was COM
munication between them. The
great San Francisco earthquake
was preceded only two days by one
of the most violent eruptions of
Vesuvius recorded in many years.
Phenomena in Alaska.
1t is also a significant fact that
the fuming island off the coast of
Alaska, called Bogoslof No. 3, ap-
peared at almost the same time. A
revenue cutter, visiting this island.
was astonished to see that the
mountain. or hill, some 400 feet
high, on the island, had disap-
peared, and in its place a bay had
been formed. Soundings showed
depth of from s to 25 fathoms of
water.
The greatest of recent volcanic
disturbances which blew the top
off of Mount Katmai in Alaska and
gave birth to the wonderful Valley
of Ten Thousand Smokes was pre-
ceded and accompanied by a series
of severe earthquakes.
That the earth's "crust" is sub
jected to squeezing, pinching and
elevation is evident from mountain
ranges, which are the portion of
the crust that is pinched or thrust
up. If mountains were ever thrust
up at all rapidly the earthquakes
at the time must have been terri
BILE. Even now there are certain
mountains that, though millions of
years old, are still geolOgically
young" and are slowly rising.