The sun., 1907-03-28
ORIGIN or E4RTHOU AXES.
Three Great shocks OF Past Year Caused
hN Mountains SnpplnE.

Almost 100 600 earthquakes had been
recorded up to the year 1903. or this mum
ber "a per cent occurred within the range
of two narrow bands forming great circles
| on the earth's 3 surface.
According TO a writer in the North Ameri-
can Rerieu, San Francisco, Valparaiso and
Kingston need aOt have felt surprised at
their shaking up. They have always
| had earthquakes and there is no reason to
think that they won't keep on having them.
They are located in the most frequently
visited portions N the two earthquake
belts
One Of these belts, in which has occurred
So per cent. Of all recorded shocks, is called
the Mediterranean. Il swings roughly
| east and west about the earth, and includes
the Mediterranean region, Asia Minor
the Caucasus, the Himalayas, the East
Indies, Central America and the West
Indies. Where the oelt crosses the oceans
little is known akout its condition.
The second be- g. called the circumpacific,
almost encircl ~ the Pacific Ocean. Passing
along the ..ndes it crosses the other belt
in the central American region, thence
eXt-7uos up the western coast OF North
America, passes across to Asia along the
Aleutian chain, thence down through
Kamchatka, the Japanese Islands. and the
Philippines, and, crossing the eMediterranean
belt in the East Indies, extends on to New
Zealand. Forty-one per cent. Of all re-
corded shocks occur in this belt
All the rest of the world, that is, surface
scores of times greater than the combined
area OF these two belts, ia the seat Of only
9 per cent. of all recorded shock Even
outside the belts. Of course, some vigorous
shocks occur, but il may be stated that the
United States EAST Of the Rocky Mountains
stands in as little danger az any portion of
the earth's surface. Only in one locality.
or possibly two. does there seem good
ground for considering an eartLuuake OF
first rank among more than the remotest
of possibilities.
the earths crust will cause an earthquake.
An explosion Of dynamite starts vibrations
which pass through the rocks as the waves
Of an earthquake DO.
For example, when the passage OF Hell
Gate was cleared away some years ago by
great explosion the shock was measured
on the sesmographs at Washington in one
direction and Boston in the other. A land
slide causes an earthquake; the falling Of
the roof Of a cavern is another cause; and
the swapping Of rocks under slight strains
another.
These are all minor causes for earth
auakes but they account for many OF the
small tremblings which are felt in limited
area. A much more important cause IL
volcanic action.
n is a popular belief that all earthquakes
are somehow caused by volcanic activity,
but as a matter OF fact, while volcanic
earthquakes are common and locally OF
great violence they are not usually world
shakinR In cases where the seismOgraphs
Of the world record a shock. as in the case
of San Francisco and of Kingston. the in
ference is unavoidable that it is due to come
other cause than volcanic action.
The cause of the san Francisco shock
Was understood by all geologists. The
coast ranges are a growing mountain chain;
| the rocks there are in a state Of strain; this
strain is being steadily increased; during
| the past history Of the mountain growth
| the strata have been broken and forced 10
move along the planes Of breakage or fault
| planes; and when great masses OF rock
| suddenly slide over one another, even
| though the movement he hut a few feet.
| the grinding OF the strata together must of
necessity set the earth trembling.
| Since the earthquake State commission
| has been carefully studying the facts and
| il reports that for at least 1856 miles there
| has been a slip. on one side Of which the
| mountains have been moved bodily in reIa-
! ton To the other side. In this instance the
movement was mainly horizontal instead
of vertical as ia normally the case,
| In places the shifting amounted to only
| two or three feet. in others 90 az much as
| twenty feet. BY IL roads we're disloCated,
fences broken and moved apart. water
pipes separated and long burrows opened
| in the ground.
The movement Of a great block of the
| earth's crust from two 10 twenty feet, along
| a plane nearly 200 miles in length and ex-
tending to an unknown depth. but probably
thousands Of feet, furnishes ample eXplana-
tion Of a shock whose vibrations reached the
seismographs in all parts Of the earth. and
whose area of destruction extended 100
miles in one direction and fifty miles in the
other.
There has not yet been a report upon the
conditions accompanying the earthquakes
of Valparaiso and Kingston, but il IL a safe
prediction TO make that when the necessary
studies have been made they too will he
found to he the result Of a slipping OF the
rocks along fault planes.