Evening star. [volume] (Washington, D.C.) 1854-1972, 1906-05-01
EARTHQUAKE ORIGIN
A Harvard Professor of .Geol-
ogy's Statement.
FRACTURE IN EARTH'S CRUST
Caused Destruction When Tremor
Reached the Surface.
NOT OF VOLCANIC ORIGIN
Not the Slightest Indication That the
Shake Was Due to Any Such
Action.

Written by W. NJ. Davis, Professor Of Geology
Harvard University.
1t will not be easy for the biologists OF
California TO turn aside from the distress
caused by the earthquake of April Is and
undertake a calm study of the geological
causes eff the shock; nor is it easy for read
ers on this side of the country to sift out
the mere mechanical facts concerning the
shock from the abundant personal stories of
it's Indirect effects; but so far as differences
can be drawn from reports thus far re-
oeived the earthquake that shook San Fran
cisco and the neighboring cities seems to
have been one of that class of disturbances
In which the quivering of the earth's sur
face is due to the sudden formation of a
fracture In the earth's crust several miles
underground. the fracture being caused by
strains and stresses that have been slowly
accommodating as the earth grows older. In
consequence OF such a snap or fracture
tremors or wave-like agitations rapidly
travel away from the center of the disturb
ance in all directions, downward. sideways
and upward. Those which reach the sur
face cause destruction in proportion to their
strength on the one hand and on the other
hand In proportion to the instability of the
rocks and buildings that they disturb
Earthquake Not of Volcanic Origin.
There is not the slightest indication that
the San Francisco earthquake was in any
way due to volcanic action. Indeed one OF
the chief results Of selsmology-the science
of earthquakes-in the last thirty or forty
years has been to show that volcanic earth
quakes are less frequent and on the whole
less violent than fracture earthquakes. The
old definition of an earthquake IAN I'M
completed effort to form volcano" has lit
tie acceptance today; ii can hardly be ap-
plicable to more than one shock in many
thousand. 1t is true that relatively local
shocks are often caused by the eruptions
of volcanoes already made, but the asso-
citation of earthquakes only with volcanoes,
as in the single chapter of the older books
on geology and geography, is not consistent
with modern studies. Most earthquakes are
now believed to be associated with growing
mountains, and not with ascending and out
flowing lavas.
The reasons for this conclusion are simple
enough. While earthquakes are common
in the districts of active volcanoes, they
are more common In non-volcanic regions
of disturbed or mountainous structure,
where the reformation of the earths crust
seems to be still in slow progress. Even III
islands so largely volcanic as those of the
japanese archipelago there is good reason
for thinking that many of the numerous
shocks there recorded are due to massive
crystal movements and not to volcanic &C
ton.
Structure Of the Coast Range.
IN so far as California earthquakes are
concerned the case is In brief as follows:
Our Pacific coast is not volcanic district;
although many extinct volcanoes occur In
the northern Sierra Nevada. and vast floods
of lava have been poured out In a past geo.
logical age over the basin of the Columbia
river The coast range is largely made of
stratfied rocks containing marine fossils
some Of which exhibit so great a resem-
blance to shells and other organic forms
now inhabiting the neghboring ocean that
the date of the deposition of the strata
must be relatively modern. in a geological
sense. The strata, originally deposited be-
meath sea level In nearly horizontal layers,
now stand above sea level, tilted, bent and
broken into the deformed structures char
acteristic of mountain ranges the world
over. The coast range must therefore, be
regarded as a belt of earth crust In which
movements of reformation are geologicaily
modern. presumably continuing into the
human era.
Geological Time is Long.
The instability of the Pacific slope would
seem to make California a dangerous place
to live in. but such an Inference is based on
an altogether wrong conception as to the
duration of geological time and the rate of
geological processes. Time is 30 long and
processes are so slow that there Is always
great amount of waiting TO a small
amount of happening. Whatever may be
the ultimate causes that produce crystal
strain and stress. they seem to operate with
extreme elaboration. Years. scores OF
years and centuries may pass In quiet; and
even then. when the accumulated strain
and stress overcomes the resistance, IN
stead of there being vast commotion, up
lifting a whole range OF mountains at once
as was the old view-there is only small
movement usually of an inch or rwo, or a
H., ~ &c Ar1NT haS
mouse-like steps. with very long waits be-
tween them. that bring forth mountains
The idea of hurried mountain growth Cd
tanned when 1t was believed that the age
of the earth was only a few thousand
years There is practically no trace of that
idea now remaining in scientific geology.
Blocks Up the Frisco Peninsula.
To be more specific. It may be stated that
the peninsula of San Francisco, de-
scribed by Lawson. professor OF geology at
the University of California, consists essen
tally of two great blocks of earth crust,
each one somewhat tilted and the two sep
arated by a long and profound fracture
trending north-northwest and south-south-
east. the northeastern block having been
uplifted some 1900 feet with respect to the
southwestern. This displacement is not
ancient in the measures of geological time,
yet took place SO long ago humanity speak
ing that the blocks have been since then
greatly worn down and deliberately carved
by valley-cutting streams. 1t requires the
trained imagination of the geologist to re-
construct the original contours Of the blocks
SO dtlapidated are they now, thoroughly
dissected. so far fallen into ruin. Whether
the recent earthquake was in any way asso-
ciated with a renewal of movement on this
ancient block-fracture, ii is impossible at
present to say anything definite. 1t is. how
ever, important to note that the area of
greatest destruction extends through belt
which lies roughly parallel to the trend of
the coast range, and this fact makes 1t
pretty certain that the earthquake is of the
mountain-fracture class. and that 1t sprang
from some one of the structural lines along
which the mountains there have long been
in process of reformation
a Happy Future for California.
1t Is absurd to think that in a state so
highly favored as is California as to climate.
soil and general situation. a temporary
catastrophe can cause any permanent loss
of population or of prosperity. A city SO
advantageously placed as San Francisco.