The Journal of San Diego History
SAN DIEGO HISTORICAL SOCIETY QUARTERLY
October 1964, Volume 10, Number 4
Ray Brandes, Editor

Tidal Marigrams

By Helen Gohres

On April 17, 1889, an instrument in Potsdam, Germany, recorded the first distant earthquake, a shock in Japan.1 Yet on December 23, 1854, in San Diego Bay, a United States Coast Survey self-registering tide gauge successfully recorded a tsunami. This "earthquake wave", as it was then called, was eventually traced to a disastrous earthquake in Japan.

The San Diego gauge not only recorded a documented tsunami, but also apparently recorded an undocumented local earthquake on July 23-24, 1854. On this tidal sheet, or marigram, are two hand-written notes:

It is possible ... that the sudden rise and fall here noticed is due to submarine earthquake. Earthquake phenomena are frequent in this vicinity.2

So noted Second Lieutenant William P. Trowbridge, U.S. Engineers. His observer, Andrew Cassidy,3 added:

This very great vibration is caused by the motion of the tide ... by observing the staff for the last 2 hours I find the water to rise or fall suddenly. There is no heavy swell ... the water around the gauge is calm.

The self-registering tide-guage invented by Joseph Saxton.

The gauge is now believed to have been the earliest instrument to successfully record an earthquake. The instrument was invented in Washington, D.C., by Joseph Saxton for use by the Coast Survey. (See Fig. 1) It is described in minute detail by Lieutenant E. B. Hunt, U.S. Corps of Engineers, assistant in the Coast Survey.

The principle ... is simple ... A float, rising and falling with the tides, is so connected with the recording pencil as to cause it to traverse across the record sheet whenever the float moves vertically. A clockwork moves the record sheet lengthwise under the pencil and pricks into it the hours and half-hours. From these motions of the pencil and the paper, the record-curve results ...

It is the observer's business, at first, to visit the gauge daily until fully assured that all is proceeding correctly, when a visit every other day will suffice....

 

To give a uniform motion to the sheet of paper, a clock work is used. The moving parts of the old-fashioned eight-day clocks, with the striking parts taken out, are employed for this purpose.... The float (F) is in an air-tight, cylindrical or canister-shaped copper boil, which is first roughly painted for protection....

The duty of the supervision involves a careful watch on all the details ... the clock must, of course, be punctually wound, and should never be stopped except from an absolute necessity.... The clock should keep mean solar time ...

This tide-gauge has been tested by about eighteen months experience ... Fourteen gauges have already been put in operation ... Six ... to the Western coast...4

The San Diego observer, Andrew Cassidy, visited the gauge regularly to see that all was proceeding correctly. The building shown here was constructed in 1853 to house the tide guage. This is found in the notebood kept by Andrew Cassidy while recording information at the house. The book is in the Serra Museum library.

During these years Alexander Dallas Bache was the Superintendent of the Coast Survey. A great-grandson of Benjamin Franklin, he inherited some of his great-grandfather's shrewd power of observation and scientific curiosity. He was astonished by the reports and tidal sheets sent from San Diego. In his Annual Report to the Secretary of the Treasury, he described at great length the notice of earthquake waves on the west coast of America, on December 23 and 25, 1854. Later he read a paper on the subject to a meeting of the American Association for the Advancement of Science:

I would respectfully call your attention to the singular curve traced by the self-registermig tide-gauge at San Diego, from December 23rd to December 25th. The irregularities of the curve cannot be traced to a disturbance of the ocean surface by storms, as the meteorological records for the whole coast show the continuance at that time of the ordinary state of the weather; and, moreover, the length of the wave traced is too great for an ordinary surf ace-wave. There is every reason to presume that the effect produced was caused by a submarine earthquake....

In his official report, Bache included the letter he received from Lieutenant Trowbridge calling attention to the singular curves traced by the self-registering tide-gauge at San Diego. To the Association for the Advancement of Science he presented a copy of the curves traced by the gauges located at the Coast Survey tidal stati ons at San Diego, San Francisco, and Astoria, on De- cember 23 and 25, 1854.6

On the 20th of June, 1855, Bache received accounts from Japan of a violent earthquake which had occurred on December 23, 1854. Commodore Matthew Calbraith Perry had sent these accounts to him, including a letter written to Perry by Captain H. A. Adams, who wrote:

Simoda has suffered dreadfully since your visit here. On the 23d of December there were several shocks of earthquakes. The sea rose in a wave five fathoms above its usual height.... It rose and sank this way five or six times.... The entire coast of Japan seems to have suffered by this calamity...

Bache reported that there seemed little doubt that the extraordinary rises and falls of the water at short intervals recorded on the San Diego and San Francisco tidal sheets were produced by the same cause which determined the extraordinary rise and fall in the harbor of Simoda, Japan. The distance from San Diego to Simoda is 4,917 nautical miles!

Although a tidal marigram is not a seismogram, it would seem that San Diegans may credit a gauge (or gage, modem spelling) in San Diego Bay as an instrument that successfully recorded not only a tsunami, but also a local tremor thirty-five years before the registration in Germany.



Helen Gohres, always a welcome contributor to this Quarterly, received her B.S. from the University of Minnesota and an M.A. from Northwestern University. As a teacher at Chula Vista High School, with an avocation in history research, Helen has an uncanny knack for coming up with subjects which have not previously been touched upon.