part 1] ANNIVERSARY ADDRESS OF THE PRESIDENT. IxV 



which is the really important one in its bearing on geology, of how 

 the strain is produced. It can hardly be the result of those 

 tectonic processes which result in folding, for these must necessarily 

 be slow in their action ; the change of form involved in the 

 bending of solid rock from its original shape into complicated 

 folds, without breach of continuity, can onlj have been a slow one, 

 and, as we have seen, the deformation which produces earthquakes 

 must be a rapid one. With favilts the case is different ; many 

 earthquakes are known to have been accompanied by movement 

 along pre-existing fault-planes, in others the origin evidently agrees 

 in position with known faults, and in all of these the distribution of 

 the intensit}^ of disturbance is closely correlated with the faults, 

 being greatest in proximity to them and decreasing as the distance 

 becomes greater. So much is indisputable, yet, despite a general 

 acceptance of the explanation, that the earthquake was a result 

 of the same process as that which gave rise to the formation of 

 the fault, it must be recognized that the proof is not logically 

 complete, for it might be that the cause and processes which gave 

 rise to the earthquake Avere wholly different from, and independent 

 of, that which produced the fault, the on\j connexion being that 

 the weakness, resulting from the fault-fracture, served to localize 

 the yielding, and so controlled the distribution and intensit}^ of the 

 earthquake. In a study of the Californian earthquake of 1906, 

 where the greatest intensity of disturbance ranged along the line 

 of the San Andreas fault, and Avas accompanied by considerable 

 displacement and distortion of the surface along the fault-line, I 

 was able to show^ that the ultimate cause of the earthquake was 

 quite distinct from that which produced the fault, and tliat the 

 fault was not tlie cause of the earthquake, nor the earthquake an 

 incident in the formation of the fault. 



In support of the supposition that earthquakes are not j^roduced 

 hy, or at any rate are not necessarily the product of, the tectonic 

 processes which have given rise to the displacements in faults, may 

 be instanced the fact that in some cases of minor earthquakes, 

 where it has been possible to fix the position of the epicentre with 

 s, close approach to definiteness, it has been found that surface 

 -examination gives no indication of the presence of a fault. This, 

 however, is not conclusive, for there might have been a deep- 

 seated, incipient, fault which had not yet extended to the surface, 

 and so could not be recognized by geological surve}^ 



Much more w^eighty and suggestive evidence is to be derived 



VOI. LXXAHII. C 



