Earthquakes and other earth movements

by John Milne

Assuming the origin of the wave to have been at Arica, his results are as follows:

	Distance from Africa	Time of transmission		Nautical miles per hour	Mean depth of ocean
	miles	h.	m.		feet
San Diego	4,030	10	55	369	12,100
Fort Point	4,480	12	56	348	10,800
Astoria	5,000	18	51	265	6,200
Kodiak	6,200	22	00	282	7,000
Rapa	4,057	10	54	372	12,200
Chatham Islands	5,520	15	01	368	12,100
Hawaii	5,460	14	10	385	13,200
Honolulu	5,580	12	18	454	18,500
Samoa	5,760	15	38	368	12,100
Lyttelton	6,120	19	01	322	9,200
Newcastle	9,380	22	10	332	9,800
Sydney	7,440	23	41	314	8,800

The wave of 1877.—Two sets of calculations have been made upon the wave of 1877 by Dr. E. Geinitz of Rostock.[84]

The following table is taken from Dr. Geinitz’s second paper, in which there are several modifications of his first results. The origin of the disturbance is assumed to have been near Iquique.

Observation stations	Distance from Iquique geol. miles	Arrival of wave			Time taken by wave		Velocity in feet per second	Mean depth of ocean in fathoms
		h.	m.		h.	m.
Taiohāc (Marquesa Islands)	4,086	8	40	a.m.	12	15	563·8	1,647
Apia (Samoa)	5,740	12	0	„	15	30	610·4	1,930
Hilo (Sandwich Islands)	5,526	10	24	„	14	0	667·9	2,310
Kahuliu „	5,628	10	30	„	14	5	675·2	2,361
Honolulu „	5,712	10	50	„	14	25	669·7	2,319
Wellington (New Zealand)	5,657	2	40	p.m.	18	15	524·2	1,430
Lyttelton „	5,641	2	48	„	18	23	519·8	1,400
Newcastle (Australia)	6,800	2	32	„	18	7	633·0	2,075
Sydney „	6,782	2	35	„	18	10	631·4	2,065
Kamieshi (Japan)	8,790	7	20	„	22	55	649·0	2,182
Hakodate „	8,760	9	25	„	25	0	592·5	1,818
Kadsusa „	8,939	9	50	„	25	15	604·9	1,895

The mean depths represent a mean of two sets of calculations, one made with the aid of Airy’s formula, and the other by Scott-Russell’s formula. The result of my own investigation about this disturbance, the origin of which, by several methods of calculation, is shown to have been beneath the ocean, near 71° 5′ west long., and 21° 22′ south lat., are given on next page.

Dr. Geinitz considers that his calculated depths of the ocean and those obtained by actual soundings are in accordance, a result which is diametrically opposed to that which I have obtained.

This difference between my calculations and those of Dr. Geinitz, Hochstetter, and others, chiefly rests on the origin we have assigned for the sea waves. Dr. Geinitz, for instance, although he says that the origin of the 1877 earthquake was not on the continent but to the west in the ocean, bases all his calculations on the assumption that the centrum was at or near to Iquique, and the time at which that city was disturbed was the time at which the waves commenced to spread across the ocean. This time is 8.25 p.m. At this time, however, it appears that the waves must have been more than double the distance between the true origin and Iquique, from Iquique on their way towards the opposite side of the Pacific. Introducing this element into the various calculations which have been made respecting the depth of the Pacific Ocean as derived from observations on earthquake waves—which element, insomuch as the waves appear to have come in to inundate the land some time after the shock, needs to be introduced—we reduce the velocity of transit of the earthquake wave and, consequently, the resultant depths of the ocean.

	Longitude			Arrival of wave in Greenwich mean time			Time taken by wave		Distance from the origin in miles (calculated in great circles)	Velocity in feet per second	Depth of the ocean in feet	Height of waves	Interval between waves in minutes
	°	′		day	h.	m.	h.	m.
Origin of wave	71	5	W.	9	12	59
San Francisco	122	32		10	2	28	13	29	4,578	498	7,721	9 in.
Callao	77	15		9	17	9	4	10	658	231	1,657
Iquique	70	14½		9	13	21	0	22	87	348	3,770	20 ft.	22
Cobija	70	21		9	13	19	0	20	80	352	3,857	30 „
Mejillones	70	35		9	13	27	0	28	108	339	3,587	35 „	15 or 45
Chanaral	71	34		9	15	26	2	27	455	272	2,309		10
Coquimbo	71	24		9	15	15	2	16	508	328	3,363		30
Valparaiso	71	38		9	16	16	3	17	695	310	3,000
Concepcion	73	5		9	16	52	3	53	928	350	3,824		12 to 15
Honolulu	157	55		10	3	52	14	53	5,694	561	9,807	34 to 54 ft.	25
Hilo	155	3		10	3	5	14	6	5,506	563	10,217	30 or 8 „	{ 3 or 15 18 or 27
Kahuliu	156	43		10	3	12	14	13	5,611	579	10,437
Samoa	171	41	W.	10	3	57	14	58	5,773	566	9,972	12 ft.	10
Taurauga	176	11	E.	10	8	15	19	16	5,615	427	5,697
Wellington	174	30		10	7	22	18	23	5,574	445	6,168	11 „	10
Akaroa	172	59		10	7	28	18	29	5,542	440	6,031
Lyttelton	172	45		10	7	29	18	30	5,558	441	6,055
Kameishi	140	50		10	12	37	23	38	8,844	549	9,378	6 „	15
Hakodate	140	50		10	14	7	25	8	8,778	512	8,169	7 „	20

In Dr. Geinitz’s paper there are also some slight differences in the times at which the earthquake phenomena were observed at various localities. These, however, are but of minor importance. At the end of the paper by Dr. Geinitz two interesting tide gauge records are introduced, one from Sydney and the other from Newcastle. These appear to show a marked difference in the periods of the sea waves at these two places.[85]