The Western news. [volume] (Libby, Mont.) 1933-current, 1935-11-14
Earthquakes Always Terror To
Mankind, Says Butte Geo|ogist
Learned Professor Gives Intensely Interesting Informa
ton Regarding One of Natures Most Obstructive
Characteristics = Helena Quake Mild Compared to
Others-99,OOO Killed in Japan

ance with the earthquake waves an
! the trembling of the earth is magnifiet
so that an irregular line is made on ;
chart which can be analysed by til,
scientist He can determine the in
tensity, direction of notion and the
distance in miles from the earthquake
area. Every major earthquake is re-
corded by many of these sensitive in
struments. They are playing ar
exceedingly important part in the adj
vancement of our knowledge concern
ing the interior of the earth and the
nature of earthquakes.
The shock is recorded on seismo-
graphs in the different parts of the
world because the waves are propagated
laterally in all directions from the CEN
ter of the disturbance as we'll as through
the earth. The zone on the surface di-
rectly above the disturbance is called
the epicentre. There the intensity is
greatest. The intensity decreases as the
waves move out from the epicentre.
The rate of decrease may be due 20
the kind of rock strata through which
the waves pass. Lines can be drawn
marking zones of equal intensity, these
lines are known as isosesrnals The
intensity scale ranges from l to TO- For
example, zone | represents shock so
weak that only an experienced OBJ
server can detect it, zone is marked
by a shock strong enough to disturb
movable objects and is felt by several
persons in motion; zone represents
shock strong enough to cause the
swinging of chandeliers, stopping Of
clocks, agitation of trees and shrubs,
and general awaking of those asleep.
zone 8 is marked by partial or total
destruction of some buildings
The Helena Earthquakes
Careful field observations following
the shocks Of the 18th, 18th, and 31st
of October establishes beyond any
reasonable doubt that all of these
shocks have been caused by faulting
(slipping Of one rock mass on another)
in rocks far below the surface Of
Helena Valley. The fault unques-
tionably trends northwest and almost
certainly dips to the northeast. This
conclusion which was reached as soon
as the effects of the relatively mild
shock at about a. m on the 18th could
be examined and which has been
further established by the shocks of
the 18th and 31st, Is corroborated BY
the records from the instruments set
up in the Federal Building at Helena
by Messrs. Ulrich and Carder IF the
U. S. Coast and Geodeic Survey after
the shock of the 18th
Because of the deep cover of gravel
and sand in the Helena Valley it is
impossible to identify the particular
fault plane along which movement has
taken place. If the fault plane was ex-
posed at the surface then it would be
possible to measure the amount and
direction of the movement, but such
is not the case in this particular in
stance.
The actual movement which has
taken place is unquestionably small,
an amount measurable in
inches. OF course, only slight move
ments of large masses of rock are
necessary for the development of mod
crate earthquakes.
When the waves reach the surface
Of Helena Valley they cause slight
rolling Of the ground so that the sur
face is alternately under pressure and
tension. On October IS the tension
caused minor shallow surface cracks
in the vicinity of Stanchfield Lake and
the compression caused shallow sub
surface water to flow out of thees new
ly developed assures for short period
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