12 MR. R. D. OLDHAM ON THE INTERPRETATION [Feb. 1909, 



§ 4. This conclusion, so much at variance with ideas prevalent 

 at the present time, necessitates a brief examination of the history 

 of our knowledge of the connexion between faults and earthquakes. 



The earliest published description of the appearance of faulting 

 at the surface of the earth at the time of an earthquake, contem- 

 poraneously recognized as such, appears to be in the account, 

 ■compiled by Sir Charles Lyell from the narratives of eye-witnesses, 

 of the New Zealand earthquake of January 23rd, 1855 x ; but in 

 this, and for some time subsequently, the fault-movement was 

 regarded as a consequence, not the cause, of the earthquake. The 

 nature of an earthquake was inaccurately appreciated — it might 

 almost be said, was wholly misunderstood — before the publication 

 of that remarkable series of researches by which Robert Mallet 

 established seismology as a science; to him, an earthquake was a 

 wave or series of waves of elastic compression, propagated outwards 

 from a focus or origin of small size relative to the area over which 

 the shock was felt. A disturbance of this character could not 

 produce fissures in solid rock, but the connexion of earthquakes with 

 faults and fractures was recognized and regarded as that of effect to 

 cause ; and when the Mino-Owari earthquake of October 28th, 1891, 

 was found to have been accompanied by the production at the 

 surface of a fault more than 60 miles ioug, with a throw of 

 20 feet in places, it seemed obvious that here was a sufficient cause 

 for the XDhenomena which accompanied it. Moreover, the know- 

 ledge that regions where earthquakes are most frequent are also 

 regions of great and recent tectonic changes, gave rise to a habit of 

 connecting earthquakes with the production of the great structural 

 features, more especially with the great faults or flexures which can 

 be recognized by surface-observations. The Assam earthquake of 

 1897 was associated by Mr. La Touche 2 with the great monoclinal 

 flexure along the southern edge of the Assam range ; and in 1906 

 the San Francisco earthquake was immediately ascribed, by more 

 than one authority, to fresh movement along the San Andreas fault. 5 

 In the former case, the prophecy was not borne out by subsequent 

 investigation; in the latter case, it received an apparent fulfilment, 

 which loses value with a fuller consideration of the facts known in 

 regard to this and other earthquakes. 



used for tho second. Exception has been taken to this proposal ; and, on con- 

 sideration, I admit the inconvenience which might arise from an attempt to 

 limit the meaning of the word earthquake, which I use in its ordinary sense 

 and take to include all the phenomena concerned. There seems to be, however, 

 a real need for special terms to be used when it is necessary to distinguish 

 between these two forms of earthquake-disturbance : for the molar displace- 

 ments I propose to adapt the verb fiox^evw, I heave or displace, which, being 

 only used for the displacement of heavy weights or masses, appears appropriate 

 in this connexion, and from it we obtain mochleusis for the result, and, less 

 legitimately but conveniently, mochleuseism for the disturbance by which it 

 is produced. Similarly, for the vibratory movement I suggest orchesis and 

 orcheseism, from the verb opxeopai, I dance or tremble.] 



1 Bull. Soc. Geol. France, ser. 2, vol. xiii (1856) p. 661, and ' Principles ' 

 10th ed. vol. ii (1868) Chap, xxviii. 



2 ' Nature,' vol. lvi (1897) p. 444. 



3 ' Popular Science Monthly ' August 1906, p. 104. 



