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SCIENCE 



[N. S. Vol. XXIX. No. 734 



Lawson mentioned breaks in the continuity 

 of recent demonstrations, between the 

 southern part of California and Central 

 America, and between the northern part of 

 California and Alaska, and suggested the 

 probability of early visitations in Mexico 

 and the Oregon- Washington region. In 

 this forecast he anticipated by a few weeks 

 the Guerrero earthquake.^" Omori went 

 farther and expressed the opinion that the 

 Valparaiso earthquake was the final term 

 of a series, and that the whole Pacific coast 

 of America would be exempt for a time 

 expect the next one at some distance, and, as it 

 happened, this occurred at San Francisco. Then 

 the Valparaiso disturbance being so far to the 

 south it was probable that the next shake would 

 be somewhere between the two. The shock at 

 Jamaica was probably connected with the Val- 

 paraiso earthquake, being in the same course with 

 it. That in Mexico is more likely to be connected 

 with the course of disturbance from Alaska down.' 



" Dr. Hayes, when asked if he would venture to 

 predict the locality in which the next earthquake 

 might occur, said that he did not wish to go on 

 record as making any prediction on a matter 

 concerning which soientiiic knowledge was so lim- 

 ited, but was of opinion that it would not be 

 unreasonable to look for one in northern South 

 America in the United States of Colombia. Asked 

 whether a disturbance there would be likely to 

 affect the region of the Panama canal, he thought 

 that Panama might feel tremors from a consid- 

 erable shock, but that it was unlikely any damage 

 would result." 



"A. C. Lawson, in a lecture read to the Na- 

 tional Geographic Society, March 29, 1907, attrib- 

 uted the California earthquake to a series of rup- 

 tures that had been traveling along the western 

 coast of America. " So far it has occurred every- 

 where along the coast except in a stretch between 

 the southern part of California and Central Am- 

 erica and an area between the northern part of 

 California and the southern part of Alaska. These 

 stretches, I believe, will be visited before long and 

 then the long line of this earthquake will be com- 

 plete from Chili to Alaska." This statement pre- 

 ceded by a few weeks the occurrence of the Guer- 

 rero earthquake in Mexico, and its prognostication 

 was thus promptly verified as to the district south 

 of California. It awaits verification for the dis- 

 trict north of California. 



from great seismic activity. He expected 

 for San Francisco a period of immunity of 

 thirty to fifty years and for coastal re- 

 gions from Alaska to Ecuador of twenty 

 to thirty years. 



It will be observed that this idea of a 

 series, breaking on the American coast in 

 the course of a few years, and followed by 

 a comparatively long interval before the 

 ai'rival of another series, an idea appar- 

 ently shared by Hayes and Lawson, com- 

 bines rhytlun with alternation in the 

 theory of forecasting. 



Prediction and verification are the test 

 of hypothesis, and this group of predic- 

 tions — albeit tentative and advanced with 

 judicious caution— embodying, as they do, 

 the diverse views of independent investi- 

 gators, who approach the subject from both 

 seismologie and geologic sides, constitute 

 a valuable contribution to seismic fore- 

 casting. The outcome in verification will 

 have bearing not only on theories of 

 alternation, rhythm and rhythmic im- 

 munity, but on the order of magnitude of 

 the seismic district within which effective 

 mechanical interaction takes place, and 

 also on the profouader earth problems 

 with which the question of the ultimate 

 cause or causes of earthquakes is involved. 

 If it shall appear as highly probable that 

 yieldings to erustal stress in remote parts 

 of North America have a direct influence 

 on the dates of similar events in South 

 America, the primary sources of the 

 stresses can. hardly be of such local nature- 

 as the shifting of load through degrada- 

 tion and aggradation or the outward flow 

 of continental excess of matter, but should 

 be sought rather in forces tending to de- 

 form the planet as a whole. 



Trigger. — The third general principle 

 applicable to prediction is that of the 

 trigger — or the principle involved in the 

 parable of the last straw, which broke the 

 camel 's back. As the growing earth stress 



