TRACKING EARTHQUAKES

Hokitika Guardian, 23 July 1925, Page 1

TRACKING EARTHQUAKES

- "■ (Charles Davison, D.Sc,, FdLS. in i lie* “Daily Mail.”) One of the most striking atlvauces lately made in the study of earthquakes. is that, from the records of a sirnde complete seismograph, it is possible as a. rule to tell the position ol the spot below which a great earthquake occurred. It is no longer of any avail for the President of a Central American Bopublic to sup,press the news of a great and destructive shock, the waves o which have already spread outwards at ■i sp„ed oi several miles a second, and revealed the secret to a seismologist sitting in Ids .'ludv thousands oi nd'S

away. . , \W measuring tlio duration ol tne small tremors with which the earthquakes record begins the seismologist knows at once the distance ol the » - pin. which must lie upon a circle ’Atm that, distance as radius. A similar observation at another station gives a second circle on orii'in also lies, the position of "'!<■• must be one of the two points in which Z Circles meet. Which i, is can he decided by a third ol»ser\ation else ' 'fVtl'O first station should he provided with one of the most complete nm^i seismogra T .lis the direction ol h. movement recorded gives the . .reel.on of the origin, which, with tne distance, determines the position usually with « close approach to accuracy . The mysterious feature of the eaith(|llake felt recently in New A l), 'k ami ' her places is that the se,sinographs have so far failed to tell m "here the earthquake occurred. The record .. an instrument in New A ork -egesis . place 3T5 miles to the »o.tli. oi »<. iween Quebec and Montreal. sL'vkr' : ”V',i“l »! miles Horn - . near AVashingtom places'the origin hi the neighhourh° An laHhquake' felt oyer so extensive a tract must, one would have ought i . K.,„ n „f destructive violence at maces near its centre, which may be not sr«*. point on tin. suna destructive strength r