Manchester Democrat. [volume] (Manchester, Iowa) 1875-1930, 1906-05-23
quake at San Francisco and at Charles.
ton. these have been OF slight i'm

Authentic Dat. Needed.

Il s
Authentic Data Needed.
Before the student of earthquakes
can say certain district is likely to
be free from seismic tremors great
deal more authentic data must be ac-
CURED. As it is. all that can be said
Of any section Of the country is that
1t has or has not been frequently
shaken. The cause of the Charleston
earthquake, for Instance, has not yet
been determined. but 1t is true that in
recent years the origin of many earth
Quakes has been discovered. Many
others. however. cannot be accounted
for with certainty.
Seismology, like meteorology. is not
yet far enough advanced to announce
any invariable laws. 1t had been the
opinion that serious earthquakes never
occurred on low lands which had a
gentle gradient into the sen. The de-
struction OF Charleston, while not null
llfying this principle. at least showed
that 1t was not to be considered, rs In
variable. On the other hand. there are
mountainous districts in which earth
qunkes are of great rarity and In which
devastating shocks are unknown In
historic times.
Scientific study Recent.
While earthquakes have been noted
for the last 5000 years. they have been
made the subject of scientific study for
only comparatively recent time. Many
circumstances are responsible for this
delay In attempting to collect and col
late data In a systematic manner. One
Of the chief causes was the absence
Of an instrument to record the move
ments and duration of the seismic ire
mors. The invention of the seislno-
graph has made possible the important
progress Of late years. 1t records every
earthquake, no matter IN what part of
the world 1t is central, for every earth
quake lie felt nll over the surface of
the earth. but when 1t Is thousands of
miles distant the waves are not per-
ceptible excepting to the delicately bal
anced instrument designed to respond
to the most feeble pulsation.
Another valuable contribution to the
science has been the tables of the dis
tribution of seismicity prepared by De
Montessus de Ballore. In these tables
the observations have been brought
down to the year 1897 In those districts
In which seismic occurrences have been
most frequent and best observed. They
include all earthquakes recorded in his
torlc times, and list total Of 181, 202
quakes and 10,4a9 epicentrcs. or points
OF origin. The records, naturally, are
incomplete, but sufficient data are given
to show that earthquakes are Of great
frequency, and that practically they
occur In every part Of the world The
tables also show markedly that GER
tain parts of the world are especially
liable to be shaken, while In others
seismicity is rare or at least infrequent.
Great Circle of Fire.
The so-called great circle of fire"
around the Pacific Ocean Is found to
produce the largest number Of record
ed earthquakes. In Central California
alone there We're observed between 1860
and 1897 no fewer than 1896 earth
Quakes at 113 epicenters. Dwarf, Japan,
Is much more frequently shaken, 1856
shocks being recorded at 4s epicentres,
or an average frequency of 24.74. The
mean average of frequency at Toxic,
however, Is 92.25. the highest average
in the world. It should be remember
ed that these are sefsmologic observa.
lions, made'of those shocks which were
perceptible to the human senses with
out the aid Of Instruments.
The study of the geographical dis
trlbution Of earthquake centers brings
out some significant facts, but ut the
same time 1t falls to account satisfac-
torily for some phenomena observed.
As has been remarked. earthquakes are
divislble Into two classes, volcanic and
tectonic. according to their causes. 1t
Ia not always possible. however. to de-
clare With confidence to which of these
classes particular quake should be
assigned.
One of the significant facts when
ever the question Of class arises Is the
situation Of the eplcenter with respect
to All active or recently extinct vol
cano. Close proximity to volcano
raises presumption that the quake
IL Of volcanic origin. Tectonic quakes
also have certain characteristics which,
though not always exclusively exhibited
by them. nre much more common with
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