Hogben. — Earthquake-origins in the South-west Pacific. 141 



The most interesting of all these earthquakes is perhaps that of the 9th 

 November, 1910, the origin of which appears to have been below the ocean, 

 a little to the south-west of Espiritu Santo, in the New Hebrides Group. 



The ascertained elements of the preliminary tremors of this earthquake 

 with reference to eleven stations are given in the table below. 



Earthquake of 9th November, 1910. 



(Bpicentrum, 17 L 8. Lat.. 167° E. Long. Time at Origin. 6h. 03-7 min. 



G.M.C.T.) 



Place of Observation, 



and 

 Instrument. 



Apia (Wiechert) 



S y d n e y (Wiechert 



and Milne) 

 Wellington (Milne) 

 Perth (Milne) 

 Honolulu (Milne) . . 

 Batavia (Wiechert) 

 Zikawei (Wiechert) 

 Victoria, B.C. (Milne) 

 Madras (Milne) 

 Edinburgh (Milne). . 

 San Fernando, Cadiz 



(Milne) 



Latitude. 



13° 48' S. 

 33° 56' S. 



41° 17' S. 

 31° 57' S. 

 21° 19' N. 

 6° 08' S. 

 31° 15' X. 

 48 24' X. 

 10° 14' X. 

 55 57' N. 

 36 c 28' X. 



Longitude 



v. 



(Chord) 

 Kilom. 

 per min. 



171° 46' \Y. 

 151 c 12' E. 



174° 



115° 



158° 



109° 



121° 



123° 



77" 



3° 



6° 



47' E. 

 50' E. 

 03' W. 

 50' E. 

 26' E. 

 22' W. 

 28' E. 

 11' W. 

 12' W. 



2,296 

 2,452 



2,800 

 5,365 

 5,711 

 (,,317 



7,235 

 10,056 

 10,285 

 15,667 



17,889 



761 

 761 



761 



755 

 778 

 758 

 781 

 830 

 807 

 652 

 665 



Note. — P 1; preliminary tremors ; V, , velocity of P x waves. 



It will be seen that in this case there is a closer agreement between the 

 velocities (values of V x ) for paths calculated along the chord than for those 

 calculated along the arc ; in other 

 words, that the chords represent a 

 closer approximation to the actual 

 paths than the arcs. (It will be 

 understood that the chord cannot be 

 the actual path of a wave passing 

 through layers of varying density, 

 and subject, therefore, to refraction 

 at the bounding surfaces.) 



It will be seen that the velocity 

 (P x ) of waves, calculated along the 

 chord, for places not more than 60° 

 from the origin is about 760 kilo- 

 metres, per minute ; that for places 

 between about 60° and 90° from the 

 origin the chordal velocity is 

 greater ; that for distances over 90° 

 it is considerably less. 



This enables us to formulate a p ossible Paths of Pj Waves, 9th November, 

 i, 4-V ■ -n 4.- ± J l ^ j- 191 °. t0 Wellington, OW ; Perth, OP: 



hypothesis illustrated by the dia- Zikawei, OZ; Victoria (B.C.), OV; Sari 

 gram (fig. 2). Disregarding the sur- Fernando, 111, or 222, or 3 r 3. O, origin, 

 face rocks, which I have elsewhere 



shown to be not more than twenty-five to thirty miles in thickness, we 

 may assume a shell of much greater density about 500 miles in depth (AAA,) 



Fig. 2. 



