The sun. [volume] (New York [N.Y.]) 1833-1916, 1906-04-19
LANDSLIP AND SEAQUAKE.
TWAS FORESEEN THAT ONE DAY
THEY MIGHT CONE TOGETHER.

q Volcanic VpneaNnl IN the RACINE w
curing With q Simultaneous slip Along
the Mile DeepSan joaquin Valley Fault.
The seismic physics OF San Francisco
and its immediate neighborhood has en-
gagged the careful study of physical geog-
raphers. The commonly accepted opin-
ion is one which was formulated by Prof.
John lie Conte, professor of geology In
the University OF California, and one OF
the worlds geological authorities His
explanation is based upon the
contours OF the coast Of California from
the Santa Barbara Channel ~northward to
the Golden Gate. In this region are repre-
scented two p%eninsulas, one visible, the other
to be- discovered through exa mination
Of the attitudes upon the map correspond
ing to existing geological features. This
second and greater peninsula comprises
the Monte Diable and Coast ranges, sepa-
rated from the Sierra elevation by the allu-
vial soil Of the low lying valley OF the San
joaquin. This valley is oontoured by
the level OF q hundred feet and lower for a
considerable portion Of Its length, and
practically all Of 1t lies below the level OF
500 feet. The partition thereby accom-
plished between the Sierra mountain mass
and the coastal mountains is sufficiently
pronounced to indicate what was at no
remote period an extensive peninsula.
This valley OF the San Joaquin lies above
the line of a geological fault, at a depth
which can only be estimated as somewhere
about a mile. The artesian we'll borings
which have been a~bundantly prosecuted in
the counties OF MERGED, Fresno, Kings and
Kern affor evidence looking toward such a
determination Of bedrock depth. On the
ocean side the continental shelfis extremely
narrow. The great peninsula presents q
most preoipitous aspect toward the ocean
basin. It Is Interrupted at intervals by
deep submarine gorges extending close to
the shore.
The oceanic basin otthe Pacific is through
out a region of volcanic upheaval and seis-
mic disturbance.
Conditioned on the one side by the known
fault Of the San Joaquin Valley and on the
other by the volcanic activity Of the Pacific
basin, the greater peninsula in general and
the, visible peninsula Of San Francisco in
particular have always been subject, so far
as the memory of white settlers can go,
to frequent, shocks Of earthquake. In the
last score or more of years ~seismographio
observatories have been maintained at
several points about San Francisco Bay,
and the records nave been sufficiently
studied to afford data for comprehension
OF the varied earth waves which nave made
themselves felt either TO the perception Of
the citizens of the Golden Gate or to the
sensitive Instruments. Such observations
have been conducted by Prof. George David
son, for many years in charge OF the Coast
and Geodetic Survey upon the Pacific
Coast: by Prof. Charles Burckhalter Of the
Chabot Observatory in Oakland, and by the
staff Of the Lick Observatory on Mount
Hamilton.
Careful inspection Of these records shows
that two systems Of earthquake disturbances
act upon San Francisco. Those OF the
lighter series show a wave movement be-
ginning In one Of the easterly quadrants
and more commonly in the southeastern
This series of light shocks Is attributed to
the ship along the line Of the San Joaquin
fault. While they may OCCUR at any season
OF the year they are more frequently OBJ
served when the San Joaquin River is run-
ming bank high under the influence OF the
melting SHOWS in the foothills Of the Sierra
That such a condition has recently existed
IL made clear by the report within less than
a month OF floods in the interior valleys
Of the State. Assuming, as the biologists
do, that the fault in the valley lies near the
roots of the Monte Diablo range on the
western edge Of the alluvial plain, it will be
seen that the physical factors involving the
slip are very simple. There is a wide fiat
plain bounded on the west by a line of weak
ness in the rock supports. When this plain
is carrying an abnormal weight Of water
the tendency is to break downward at the
line Of the fault, This tendency will pro-
duce a jar in the mountain mass which
will be rapidly communicated to its furthest
extremity.
The earthquakes which have their origin
in the disturbances to which the oceanic
basin is subject always approach San Fran
cisco from the direction of the southwest
quadrant. These nave been uniformly
more violent than those whose origin is
attributed to the San Joaquin fault. While
the records OF San Francisco earthquakes
up to the present have exhibited a mild
type, the damage to property having hith-
erto been slight, it would appear from the
! extent and violence Of the present temblor
that both causes had for once united,
The possibility of such simultaneous ac-