Evening star., 1923-09-16

was probably less than five miles.
| From the focus many secondary
| faults and fractures proceeded, some
reaching the surface of the ground
Enormous landslips accompanied
the earthquake. and as an indirect
| effect of these slides the form of
water courses became in certain
cases modified. Permanent changes of
level were also observed. Eight years
after the Assam quake there was
another, known as the Kangra.
While this was not as severe as the
Assam, nevertheless about 10000 lives
were lost.
s0NE Of the peculiar incidents OBJ
~ served in the Jamaica quake of
1907 was the turning of the statue of
Queen Victoria one-eight of a revolution
On its pedestal, In August of the pre-
ceding year a disastrous shake took
place at Valparaiso. In fact, the entire
year 1906 was marked with exceptional
seismic activity.
There are many who remember the
terrible earthquake that occurred in
CaIabria and Sicily on December 2S,
1908. practically destroying Messina and
Reggie. The total loss of life at that
time was more than 1900. The prin-
cipal center of the disturbance was in
the Strait of Massina, although there
were independent centers in the
Calabrian peninsula, region that had
been visited by severe earthquakes in
1906 and 1907. That these could not be
traced to any volcanic source is shown
by the fact that neither during nor be-
fore the catastrophe was there any spe-
ciaI volcanic disturbance at Etna
or Stromboli. The only deduction
that may be made with any degree of
certainty is that there must have been a
movement along a great plane of weak
ness in the vicinity of the Strait of
Messina. The sea floor of the strait
no doubt, suffered great disturbance,
resulting in the remarkable movement
of water observed on the coast.
According to the record, at first the
sea retired and then great wave rolled
in. followed by others of lesser size, al
to have been larger than the first At
Messina the height of the wave was 2.7o
meters, while the peak was reached at
San Alessio, where it was III meters.
Great Britain has not been immune to
earthquakes, but most of those that
have been felt from time to time in
that section of the world may generally
be traced to the formation of faults,
or, rather, to incidents in the growth of
old faults.
The East Anglican earthquake in 1884
was the most disastrous of many CEN
turtles. DIR. c. Dawson, who has given
much study to the matter, is respons-
ible for the theory that several of the
quakes in Great Britain were twins"
A twin earthquake has two maxima
of intensity proceeding from two foci.
whereas a double earthquake has its
successive impulses from what is
practically a single focus.
While the great majority of earth
quakes are of the tectonic type, there
are some which are evidently connected,
directly or indirectly, with volcanic ac-
tivity-for example. the quakes that
disturbed the Isle of Ischia in 1881 and
1888. These, according to the belief of
scientists, were due to volcanic ac-
tivities.
In addition to the two types just
mentioned there are occasional
quakes of minor Importance which
may be referred to as the collapse of
the roof of caverns or other falls of
rock in underground cavities at no
great depth. Prof. T. j. ]. See holds
that most earthquakes are due, di-
rectly or indirectly. to the explosive
action of steam, formed chiefly by the
leakage of sea water through the
ocean floor.
y X y
THO measure the surface speed at
i which earthquake waves travel
1t is necessary to have accurate time
measures. Observations during the
Charleston earthquake were at that
time of exceptional value. since they
were made over a large area where
standard time was kept. Unfelt move
ments of the ground are registered in
the earthquake records. or seis-
mograms. obtained by the delicate in
strumenss used by modern seismolog-
lists.
From the study of records of q
great earthquake from a distant
source. sometimes termed a taleseis-