The Pacific commercial advertiser. [volume] (Honolulu, Hawaiian Islands) 1885-1921, 1906-04-22
METHODS OF INVESTIGATION
PURSUED AT CHARLESTON.

a Charleston were those which have
teen developed by workers elsewhere
together with some modifica tons. An
earthquake would seem at first thought
d most elusive phenomenon, but yet
by careful observation and record con-
siderable definiteness can be estab-
lIshed.
One of the first things to be deter
mined is the exact time of the shock
OF shocks. in order that the rate Il
transmission to other points may be
deduced. We need to know it within a
| NIT of error of a few seconds. be-
cause, as We shall see, the shock travels
With great speed. Several standardized
clocks having second-hands were stop
ped by the shocks, and though their
c fferent records covered an interval
of over forty seconds, yet when the
C.irec1 ions whence the successive waves
I came were compared with the planes
in which the pendulums of the clocks
Sibrated, it was seen that successive
! fluctuations had brought them to rest.
After a careful analysis Captain Dutton
concluded that from Charleston the
! shock spread at a rate of about three
and one fourth miles per second. 1t
took less than four minutes to reach
! New York.
| Another important point is to plot
upon map the concentric curves
which indicate the places where the
! shock was felt at the same instants.
These are called coseismic lines, and
! they close in around the place where
the shock was first felt Since, how
ever, the time-intervals amount to but
a few seconds, and since ordinary
ali
minutes, great care is necessary in
arriving at reliable results.
The observers also note at once and
before repairs are begun the zones of
different damage. To a certain degree
their determination is a matter of
judgment; but it soon results from
careful study that a central area of
total or very great ruin is established,
which is surrounded by one somewhat
less shattering, and so on to the outer
limits of severe effects. These curves
are called isoseismic curves, and they
close in around the point, called the cpl
centrum, where the earthquake waves
reached the upper world with great
est energy. Now, if the waves origin
ated far down in the depths, as indeed
they must, they would travel outward
il we consider the earth homogeneous,
in concentric, spheroidaI surfaces and
would first reach the exterior along the
shortest path, which is the radius of
the earth itself. It therefore follows
that the place of origin technically
called the centrum or focus, is vertical
ly below the epicentrum. 1t remains
to discover how far down the centrum
is
This problem is more difficult Mr..
Robert Mallet, a distinguished English
investigator, first sought to determine
the angle at which the fluctuations
emerged from the ground along the
various isoseismic curves. He examin-
ed the cracks in those walls which stood
across the advance of the waves, and
which often showed a concentric ar
rangement, suggestive of the radiating
spherical surface. If the angle of
emergence could be determined, the
wave path might be followed down to
its intersection with the vertical be-
low the epicentrum and this would be
the centrum itself. But the undula-
tons were found to be so complex that
no good angles could be determined.
Mr.. Mallet then tried another plan. He
reasoned that theswave emerging at the
epicentrum would cause loose object
around the centrum, as it's angle of
emergence becomes ffatter and fiatter,
it would cast things more and more
horizontally. The farther it moves,
however, the less power it has so that
there is an isoseismic curve along
which the waves emerge at an angle
little less than So, where they are able
to cast things farthest. If, then by
a study of the effects, we can locate
this curve, a wave path, if followed
back into the ground at 550, would
conduct to the centrum. This method,
however, failed from the impossibiIity
of deciding on the right isoseismic
line.
Captain Dutton and Mr.. Everett Hay
den. by the mathematical treatment
of the energy of the radiations, devised
another method based on the relations
of particular isoseismic curve, where
there is sudden and necessary change
from greater to less destruction, to the
depth of the centrum below the ep-
centrum. The isoseismic curves indi-
Gated two epicentrums in the Charles
ton case, one at Woodstock, a town
northwest of the city. and one at Ran
towles. a station nearly due west. The
calculations gave for the Woodstock
centrum a depth of twelve miles, and
for the Rantowles one of eight miles
DEVICES FOR AUTOMATIC
RECORD.
Earthquakes come suddenly, and peo-
pie are apt TO be so agitated as to be
poor observers. They are also unable
to determine the directions and inten-
sites of the motions. Various instru-
mentS have therefore been invented 10
accomplish this. The simpler ones
consist of a series of cylinders or blocks
in rows at right angles to each other,
which, having bases of different sizes, +
viii be upset by shocks of different in
tensity, and by the direction of their
fall in a bed of soft sand give a clue
to the motion. Liquids especially
quicksilver i'll basins with holes at
various heights viii wash up and down
in particular directions. will spill
through particular holes, and thus give
indications. Pendulums may be set ,
swinging in different planes, and so on: