Alma record. (Alma, Mich.) 1878-1928, 1886-10-22

| is the breaking of the earth 5 crust I'M
der the same surface contraction that
squeezcs out lava from volcanoes and
folds the regions of weakness into
mountain ranges. The earth continues
to day to give out into space the heat
which was locked in it's interior during
the early stages of its planetary history.
The rate is now slow. but even though
almost minutes NAL. it involves contrac-
ton. The settling of the crust upon a
diminishing interior necessltatcs bend
| ing of the strata, and the rock Is put
/ into n condition of gradually increasing
strain. until ut some point it suddenly
! yields with n violent conclusion. a
/ assure is produced, one wall of which
may slide past the other, producing Il
fault and z = IA - st'lug impulse to
the adjacent rock. All rock IS more or
less elastic, and the impulse is propa-
gated in all directions as an earth wave.
The violence of an observed earthquake
shock may therefore depend upon the
following conditions:
l. The degree OF strain preceding
the conclusion.
2. The extent of rock that yields.
3. 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 one 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 1t is not
unlikely that some relation paay be
traced between the recent earthquake
and the Appalachian line of weakness.
Although the production of an I'M
foreground fissure may be sudden it is
never instantaneous. \ slight tremor
is at first felt; this quickly rises to n
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 bv 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. Ncwcomb as
occurring at Oh. 53m. 2Os.; the second
/ about Oh 54m. Sos. and quiet was not
restored until Oh. 59m. The timing in
/ various parts of the country presents
! variations that arc more apparent than
real, because there is not yet uniformi-
ty in the adopt on of standard time
throughout the United States. 1t
/ should be remembered also that by stand.
ard time when it is 10 o'clock in New
York or Washington it is only o clock
at St. Louis or Chicago.
Earthquakes. especially when oc-
curing in volcanic regions, are often
not limited 10 two or three shocks in
quick succession, but come in periods
or groups.
During the twenty-four hours follow
ing the destruct on of Lima in l746 A.,
many as 200 shocks were counted. and
within the next four months 250 more
were felt At San Salvador, in Central
America, in the ncighborhood of Lake
Iopango, more than COO 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 1913. the shocks con-
tinucd for nearly five months, and dur
inc 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 b,cs sod,
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 n single point rs
focus Of disturbance. From this q
wave proceeds out specifically as a shell
OF compression. each particle traycrsed
by it receiving forward and then n
backward motion. If body be mme.
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 hor zon-
tai distance is increased. If the focus
b. long assure, as is generally the
case, the motion becomes rather more
compile. In some cases n whrling eff
feet : produced. rs in the Calabrian
earthquake of 1888, in which blocks of
stone forming square columns were
twisted at various angles.
In 1897 an earthquake occurred in