EARTHQUAKE AREAS OF THE EARTH 449 



of April 18, of the same year (1906). The last and the southernmost 

 of the series occurred on August 12, 1906, and devastated southern 

 Peru and Chile. These various shocks occurred, as stated, along the 

 same line of crustal weakness and parallel to geologically young and 

 lofty mountains, which appear to be still in process of growth. In the 

 same way the Messina, Calabrian, and now this, the most recent of the 

 Italian earthquakes, have all occurred along a line of movement which, 

 starting in southwestern Italy, has experienced movement both further 

 to the southwest and to the north — the last developing along this line 

 of dislocation in the extension of the uplift marked by the Appenines 

 into the division of Abruzzi. Along the same line other shocks will 

 probably be felt from time to time, though there is no telling even ap- 

 proximately as to what the length of this time interval may be. An- 

 other series of shocks may occur while this article is being printed, or 

 months, years, or even a century or more may pass before another pro- 

 nounced movement takes place along the Calabrian-Abruzzi line of frac- 

 ture ; but that it must occur again sooner or later is almost a certainty. 



In the regions of old rocks of the earth's crust or in regions of old 

 mountain ranges, a state of equilibrium has been so nearly approached 

 that few earthquake shocks occur. However, in those areas of the earth 

 where young mountain ranges rise or where earth movements are in 

 progress, seismic disturbances are more or less frequent. With the 

 data now available we may map with a very fair degree of accuracy 

 eleven such earthquake areas, all of which are shown on the accompany- 

 ing map. Also it is worthy of note that the areas chiefly affected by 

 earthquakes are occupied by rocks which are post-Paleozoic in age, and 

 hence, geologically speaking, are relatively young. 



The largest earthquake region of the world, which we may term the 

 Alpine-Himalayan area, extends from the Alps to the east of central 

 China. As is shown on the accompanying map, Italy, the eastern Medi- 

 terranean, and the warped-down basin of the Caspian, all fall within 

 this area, as do also the Alps, and the young and probably still growing 

 mountain chain of the Himalayas, whose rocks were laid down in the 

 sea at a time, in the geological past, when the Mediterranean formed a 

 connecting link between the Atlantic and Pacific oceans. Within the 

 limits of this region shown on our map, it is estimated that fully 20 

 per cent, of the more important and widely felt earthquakes occur. 

 The Malaysian earthquake region lies further east. It extends from 

 the Bay of Bengal, across northern Australia, to the region of the Pa- 

 cific north of New Zealand, and it also embraces all of the East Indian 

 Islands. Its axis probably follows the alignment of the various young 

 and growing mountain regions that traverse the islands of this Archi- 

 pelago, To the north of the Malaysian belt is the earthquake region 

 which includes the Archipelago of Japan and the Philippine Islands. 



VOL. LXXXVI. — 31. 



