The Indianapolis journal. [volume] (Indianapolis [Ind.]) 1867-1904, 1902-12-12
NOTWITHSTANDING EARTHQUAKES.
Prof. Milne on chronological Obser-
vatiOns and Earth Physics"
London Standard.

In the theater OF the University, Burlng-
ton Gardens. Prof John Milne read a paper
before the members of the Royal Geograph-
ical Society on Notwithstanding Earth.
quakes." or rather his paper was more ac-
curateiy styled archaeological Observations
and Earth Physics" He said the chief
Sbee or nf b Pepe 10 our
earthquake investigations, which threw
light upon the physical nature OF the In
terror of the world, and the geomorpholog-
ical changes in operation on or near the
surface. The earthquakes considered were
divided into two groups-hrst, those which
disturbed continental areas. and frequently
disturbed the world as whole; ana, Sec
ond local earthquakes, which usually only
disturb of a few miles radius and
seldom extended over an area with radius
of 100 or 200 miles The former class were
the result of sudden accelerations in the
process of rock folding accompanied by
faulting and molar displacements of con-
siderable magnitude; while the latter were.
for the most part, settlements and adjust
ments along the lines of their primary
fractures The relationship between the
two groups OF earthquakes was, therefore,
that of parents and children. The former
would be referred to macroseismic dis
turbances, or large earthquakes. and the
earthquaSes. With regard to the violent ,
movements OF large earthquake, they
gradually changed I'm character they
radiated. until at certain distance from
their origin, although they could not be
felt, evidence of their existence still re-
manned.
After the earthquake of Lisbon. in l755.
observed in England. Scandinavia and
North America, although the ground itself
was not observed to move. was attributed
to pulsations in the soil, which had radf-
ated from the coast of Portugal Another
form of evidence had. from time 10 time.
been furnished by astronomers: one M.
Nyren, May 10, 1871, observed disturbances
in the level on the axis of the transit OF
Pulkova. This was attributed to an earth
quake which had occurred at Iquiqve. M.
Nyren also referred to other oscillations
of level observed at Pulkova to distant
earthquakes. 1t was not unlikely that
every large earthquake might, with proper
appliances. be recorded at any point on the
land surface of the globe. When a large
earthquake took place II seemed TO propa-
gate a series Of waves all through the
world. and in all directions over it's surface.
ameter of the earth in about twenty-five
minutes, which implied an average velocity
of about SO Kilometers per second Tnese
movements were congressional In char
acter. The second phase of motion. and
forming the principal or seismogram.
were the larger waves. Their average
period varied between fifteen and thirty
seconds, but periods exceeding sixty sec
onds had been observed He inclined 10
the opinion that the movement was OF an
undulatory character-like an ocean swell.
Contrary observations supported a surface
undulation. He declared that IL was easy
to measure the difference I'm time between
the arrival OF preliminary tremors ana
large waves of motion.
There is no doubt that there was re-
lationship between the distribution Of the
origins of large earthquakes and the pro-
nounced Irregularities on the surface or
the earth. Where steep slopes existed on
the shores of all quarters of the world the
larger earthquakes originated. When a
world shaking earthquake took place. and
the origin was suboceanic. they occasion
ally got evidence that IL had been accom-
panied by the bodily displacement OF very
large masses of material; and a long series
OF such cases were quoted between 1892 and
1899. Illustrations of the relationship be-
tween sudden movements I'm rock-fords and
displays of volcanic activity were 10 be
found in the eruptions I'm the West Indies.
and the large earthquakes which had oc-
Cured in that region. The Antillean ridge
was one of unusual instability. and. In
consequence of this CHARACTERISTIC, IL was
responsive to adjustments in neighboring
fords. There were about $1,000 small earth
quakes every year throughout the world.
but these did not give rise 10 serious dis
turbances, though they affected an area
varying from ten miles to several hum
dreds OF square miles He urged In con-
clusion. the utility and Importance OF max
ing observations all over the world.