EARTHQUAKE INTENSITY IN AUSTRALASIA. 



273 



The average maximum intensity is 78 millimetres per second, or 

 a little less than IV. 



In every case where an earthquake was observed at more than 

 one place, I have taken the estimate of intensity where the shock 

 was most severe. If we were to take the lowest estimate of 

 intensity, we should get about 66 millimetres per second for the 

 average intensity of shock. The mean of these is 72 millimetres 

 per second ; * that is to say, the average intensity of shocks as 

 felt in New Zealand is between III. and IV. on the Rossi-Forel 

 scale, or sufficient to make pictures move a little, and to cause 

 some doors and windows to creak or rattle slightly. 



The total maximum intensity for three years is 15,460 units, or 

 1*576 times the acceleration due to gravity (which = 9,810 units 

 per second). If the force of the 198 shocks were concentrated 

 into one, each earth-particle would receive an impulse of a little 

 over 50ft. per second. 



Neio South Wales, Victoria, and South Australia. — As in the 

 case of New Zealand before the adoption of the present system, 

 the severer shocks were noted and nearly all those of lower inten- 

 sity were not observed, or at least not recorded. From the 

 catalogue of earthquakes published in the last report of the 

 Seismological Committee f we can construct the following table, 

 which may be taken for what it is worth : — 



New South Wales 



Victoria 



South Australia. . 



Total 

 Intensity 

 of all the 

 fhocks. 



Average 

 Intensity 

 of Shock. 

 Maximum 

 Value. 



In millimetres. 



2,270 

 5,200 

 6,525 



94-6 

 85-2 



Average 

 Intensity 

 of Shock. 



75 



73-2 



59-3 



Mean 

 Average 

 Intensity 



of 

 Shock. 



84-8 

 79-2 

 63-8 



In New South Wales and Victoria the average intensity of shock 

 is certainly one degree too high ; but in South Australia, where 

 the records seem to have been more complete, the estimate is 

 lower, and probably not very far from the truth. The average 

 maximum intensity of shock is between III. and IV., and the mean 

 average intensity of shocks as felt in South Australia about III., 

 or sufficient to be felt by several persons at rest, and for the dura- 

 tion or the direction to be appreciable. 



Tasmania. — The records for Tasmania consist chiefly of those 

 for the remarkable series of shocks felt in that colony in the years 

 1883-86. Soon after these shocks began. Captain Shortt com- 

 menced a regular system of recording the observations made at 



• i^hese figures would of coursd all be reduced if we could include the shocks below 

 J . III., which generally escape notice. t Transactions, A..\.A.S., 1892. 



