Complete Story of the San Francisco Horror

by Richard Linthicum; Samuel Fallows; Trumbull White

“From the actions of the earth in April of 1892, when such a severe shock was felt in San Francisco, I have no doubt but that a second earthquake will follow closely upon the one of yesterday, as the second followed the first in 1892. In that year the first came upon the 19th of April and the second upon the 21st.”

Of 948 earthquake shocks that have been recorded in California previous to 1887, 417 were most active in San Francisco. The seismographs which record the merest tremors and determine the place of the shock show that 344 have occurred since 1888. Half of the sum total have occurred in the vicinity of the gate city and for this reason it is believed that the severe shock of April 18 was the final fall of a crust of the earth which has been gradually slipping for centuries, causing from time to time the slight shocks.

The seismic physics of San Francisco and its immediate neighborhood have engaged the careful study of physical geographers. The commonly accepted opinion is one which was formulated by Prof. John Le Conte, professor of geology in the University of California, and one of the world’s geological authorities. His explanation is based upon the mountain contours of the coast of California from the Santa Barbara channel northward to the Golden Gate. In this region are represented two peninsulas, one visible, the other to be discovered through examination of the altitudes upon the map corresponding to existing geological features. This second and greater peninsula comprises the Monte Diablo and Coast ranges, separated from the Sierra elevation by the alluvial soil of the low-lying valley of the San Joaquin. This valley is contoured by the level of 100 feet and lower for a considerable portion of its length, and practically all of it lies below the level of 500 feet. The partition thereby accomplished 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 well borings which have been abundantly prosecuted in the counties of Merced, Fresno, Kings and Kern afford evidence looking toward such a determination of bedrock depth. On the ocean side the continental shelf is extremely narrow. The great peninsula presents a most precipitous aspect toward the ocean basin. It is interrupted at intervals by deep submarine gorges extending close to the shore.

The oceanic basin of the Pacific is throughout a region of volcanic upheaval and seismic 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 of San Francisco in particular has 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 seismographic observatories have been maintained at several points about San Francisco bay, and the records have been sufficiently studied to afford data for comprehension of the varied earth waves which have 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 Davidson, 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 beginning in one of the easterly quadrants and more commonly in the southeastern. This series of light shocks is attributed to the slip along the line of the San Joaquin fault. While they may occur at any season of the year, they are more frequently observed when the San Joaquin river is running bank high under the influence of the melting snows in the foothills of the Sierra. That such a condition has recently existed is made clear by the report within less than a month of floods in the interior valleys of the State. Assuming, as the geologists 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, flat plain bounded on the west by a line of weakness 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 produce a jar in the mountain mass which will be rapidly communicated to its farthest extremity.

The earthquakes which have their origin in the disturbances to which the oceanic basin is subject always approach San Francisco from the direction of the southwest quadrant. These have 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 hitherto 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 action of the two known seismic factors of the greater peninsula had been foreseen by Prof. Le Conte. He stated that if at any time an earthquake wave of only moderate violence should come in from the oceanic basin in sufficient strength to jar the coastal mountain masses at a period when the San Joaquin Valley was bearing its maximum weight of water the conditions would be ripe for simultaneous shocks from the southwest and from the southeast. In such a condition, while neither of the shocks by itself would be capable of doing any great amount of damage to buildings in San Francisco, the combination of two distinct sets of waves might prove too much for any work of man to withstand.

In spite of the declarations of some scientists that there can be no possible connection between the eruption of Mount Vesuvius and the earthquake of San Francisco, others are inclined to view certain facts in regard to recent seismic and volcanic activity as, to say the least, suggestive.