EARTHQUAKE WAVE OF 1868.
On the i3th of August, i868, at 5:o5 P. M. an earthquake was started off the coast of Arica, Peru, said to have had a duration of ten minutes. At 5:3a P. M. the first of a series of waves from fifty to sixty feet high rushed in upon the land, penetrating a considerable distance. J. E. Hilgard published an account of these waves in the report of the Coast Survey for 1869; and his conclusions were accepted and published by the highest authorities. The wave was reported at Coquimbo eight hundred miles in three hours, Hawaii (Hilo) in four teen hours and ten minutes, in Japan upon the following day. The same wave had been reported earlier at San Diego, San Francisco, Cal., and Kodiak, Alaska, with the times respec tively of ten hours and fifty-five minutes, twelve hours and fifty-six minutes and twenty-two hours, at the average of three hundred and sixty-nine, three hundred and forty-eight and two hundred and eighty-two miles per hour, and distances of 4,030, 4.48o and 6,200 miles. To reach Lyttleton, N. Z., and Sydney, Australia, 6,12o and 7,440 miles, the time required was nine teen hours and one minute and twenty-three hours and forty one minutes at the rates of 322 and 314 miles per hour. In 1880 I saw a placard upon a cocoanut tree in Hilo, situated as much as fif teen feet above the sea level, stating the fact that an earthquake wave was noted at that altitude upon the date mentioned.
The velocity of a sea wave depends both upon the wave-length and the depth of the water. Knowing the wave length and therefore what ought to be their free velocity, and knowing their actual velocity by observation, the difference gives the retardation by dragging; and from the retardation may be cal culated the mean depth of the ocean traversed. The results stated were a depth of 12,000 feet between Japan and San Francisco, and 18,50o between Peru and Honolulu.
By a study of the facts as they were related to Hawaii it is apparent that erroneous observations were relied upon. To reach Hilo, 5,460 miles, the waves moved at the rate of three hundred and eighty-five miles per hour ; to reach Honolulu, 5,58o miles, the rate was four hundred and fifty-four miles. Now the path of the wave from Arica was the same to both Hilo and Honolulu ; and there is a manifest incongruity in saying that the rate to Hilo was three hundred and eighty five and to Honolulu four hundred and fifty-four miles per hour. The wave reached Honolulu in twelve hours and eighteen minutes, the greater distance by the same route, and Hilo in fourteen hours and ten minutes, the less distance. I
addressed an inquiry to 0. H. Tittman, the Superintendent of the Coast and Geodetic Survey, and received the following reply: "In reply to your inquiry of the 15th instant, concerning the dis crepancy in the times of the arrival of the earthquake wave from Arica, Peru, at Hilo and Honolulu, I have to state that because the disturbance reached the Hawaiian Islands near midnight and because the time is given to whole hours only, it seems probable that no accurate observations were there made upon this phe nomenon. In Petermann's "Mittheilungen," Vol. 15, 1869, pages 222-226, Prof. Hochstetter has given the same values in his col lection of times at places where the earthquake wave was felt. He notices discrepancy of the Hawaiian Islands values and uses a mean between the two." It is, of course, impracticable at this late date to discover what the original records for Honolulu should have been, so as to be able to give correct figures. It will he observed that the rates per hour for all the localities except Honolulu fall below four hundred. Hence the table as published by Professor Hil gard may be esteemed as correct with only one exception. I think it better to eliminate the Honolulu observation alto gether, and with it the estimate of the greater depth of the ocean between Hawaii and Peru as compared with that upon the side towards Australia. From the Advertiser published shortly after the event, it is learned that between Aug. 7 and 18, 1868, this same wave arose to the height of twelve feet upon the windward side of Maui. There are better observa tions derived from the transmission of waves in later years from which to draw conclusions. One such may have been the one pasing Hilo May To, 1877, which originated in South America. The damage done by it is graphically set forth in the following letter from Mr. Severance : The account is in the form of an official report of Sheriff Sever ance, addressed to Marshal W. C. Parke: Dear Sir : We have had a great disaster at Hilo. On Thurs day morning the loth inst., at about 4 o'clock A. M., the sea in the bay was seen to rise and fall in an unusual manner, and at 5 o'clock it swept in, in a mighty wave, washing up and into nearly all the stores in the front of the town, carrying off a great deal of lumber and all the stone wall makai of the wharf. The per pendicular height of the wave (as we have since ascertained by levelling with the lamp-post on the wharf) was 12 feet 3 inches above the ordinary low water mark.