The sun. [volume] (Morris, Stevens County, Minn.) 1882-1895, 1886-10-07


5. The nature Of the rock transmit
ting the impulse.
4. The distance of the observer from
the starting point Of the earth wave.
Faults have been frequently found
where ono wall was slipped past the
other, not merely several feet. but many
thousands of feet. One or more such
are found in the Appalachian mountain
chain, near the Atlantic coast. It is not
unlikely that some relation may be
traced between the recent earthquake
and the Appalachian line Of weakness.
Although the production of an un-
derground assure may be sudden it is
never inst antaneous. A slight tremor
is at first felt; this quickly rises to a
maximum, and then dies out more
slowly, the entire shock lasting from
ten seconds to two minutes or more.
Usually this is followed by several
more shocks. At first they may be sep
arated by few minutes or few hours,
the first being nearly always the most
violent. The intervals become greater
with the diminishing intensity until
quiet is res tored.
Many persons in New York and
Brooklyn felt two or three shocks on
Tuesday night. At Washington the
first was timed by Prof. Newcomb as
occurring at Oh. 53m. 2Os.; the second
about Oh. sam. Sos, and quiet was not
restored until 9h. 59m. The timing in
various parts of the country presents
variations that are more apparent than
real, because there is not yet uniformi
ty in the adoption of standard time
throughout the United States. 1t
should be remembered also that by stand
ard time when it is 10 clock in New
York or Washington it is only 9 o'clock
at St. Louis or Chicago.
Earthquakes, especially when &C.
curing in volcanic regions, are often
not limited to two or three shocks in
quick succession, but come in periods
or groups.
During the twenty-four hours follow
ing the destruction of Lima in l746 as
many as 200 shocks were counted, and
within the next four months $50 more
were felt. At San Salvador, in Central
America, in the neighborhood of Lake
uopango, more than 600 earthquake
shocks were felt within the last ten
days of 1879. The water of the lake
was thrown into commotion, the ground
was broken into network OF cracks.
and in January, 1880, new volcano
rose in the center of the lake. These
earthquakes were obviously products of
volcanic energy. After the New Zeal
and earthquake of 1S48, the shocks con-
tinued for nearly five months, and dur
ing much of the time at the rate of at
least 1000 shocks per day. By COM
parison with this, the afflicted people of
Charleston may call themselves blessed,
even though the earth shocks did not
cease there until twelve hours after the
first one had passed.
The nature of earth waves is best un-
derstood by assuming single point as
a focus of disturbance. From this a
wave proceeds out specifically as shell
of compression, each particle trayersed
by it receiving forward and then a
backward motion. If a body be imme-
diately over the focus it is thrown YER
tically upward. Elsewhere the motion
is both upward and sideward, the up
ward component becoming less in COM
parison with the other as the horizon
tai distance is increased. If the focus
be long assure, as is generally the
case, the motion becomes rather more
complex. In some cases whirling eff
feet is produced, as in the Calabrian
earthquake of 1888, in which blocks Of
stone forming square columns were
twisted at various angles.
In 1897 all earthquake occurred in
the Andes, its focus being almost under
the village of Riobamba, The grounc
was shattered in many places; the
bodies of men were thrown upward full
ly one hundred feet into the air ant
found afterward on hill across :
small river. Graves were said to bt
rent open and corpses hurled out o
them.
In 1912 Caracas. the capital of Yen
ezuela, was destroyed by an earthquake
and ten thousand of it's inhabitants per
ished within two minutes.
Despite such violence the extent o
swing imposed upon the ground by ar
earth wave is seldom more than n few
inches. BY the use OF seismometers il
Japan the verticomponent has beer
found rarely to exceed one-tiftieth of al
INCH, and when the horizontal compo
neat exceeds one-fourth Of an incl
buildings begin to be shattered. Thi
limit must have been considerably ex
ceeded at Charleston. In New Yorl
chandeliers and doors were made t.
swing throug considerable arcs, but tn
extent of swing depends more on tn
violence than the amplitude of the in
itial impulse.
After the Neapolitan earthquake O
1857 Mr.. Mallet. by careful examina
ton of the cracks produced in building
and the direction in which bodies wer
thrown, estimated the focus to be fis
sure nine miles long, the point of great
est commotion being near one end of
and NOT more than ten miles below tn
surface. BY the use of seismometer
the direction of motion and angle Q
emergence may be registered at man
different places around the same focus
| By comparing these and notinr tn