Evening Star Newspaper, July 14, 1935, Page 83

Magazine Section THIS WEEK o Farthquakes from the Moon’ Does the moon cause earthguakes, such as the recent Indian catastrophe which cost 40,000 lives? Science has found that major quahes often “let go” when the moon is exerting its greatest force by HARLAN T. STETSON ORTY thousand dead, thousands of others homeless, devastation and ruin — this is the report that recently came to us from Quetta, India. All thns. of course, incidental to a slight readjust- ment of the surface features of Mother Earth In attempting an adjustment to a new figure of equilibrium as the result of some sub- terranean shrinkage. The story of earthquakes is as old as history and then some, for in p.ehistoric times the shimmering and shaking of the earth'’s surface was doubtless much more in vogue than twentieth century styles allow. When geol- ogists, from a study of radioactive deposits in the earth's crust, assure us that the planet is at least two or three billion years old, one might think that the earth was indeed old enough to outgrow these tantrums of her childhood. Every such occurrence, however, assures us that the earth is still very much alive, and that “‘terra firma’ continues to instill terror in victims of her shakings and to make even scientists skeptical as to how firm the earth's crust really is. With modern seismographs, such as are exhibited in the new Harvard Seismographic Station, it becomes possible to learn a great deal about what happens when an earthquake takes place. But.seismologists, who are ex- perts at deciphering the hieroglyphics which the mysterious pen of the seismograph writes every time there is a major disturbance, are still at a loss to predict when and just where v do - Once a busy thoroughfare; devastating earthquakes will occur. So violent was the shaking in the Himalayan region on May 31, that there was no difficulty in clock- ing to the minute and secor: * the arrival of the earthquake wave as it reached the seismo- graphs on the opposite side of the world in our own United States. Just how deep-seated was the source of the disturbance is not yet known. But when the records from a large number of advantageously situated places have been compared, we shall be able to locate the very depth at which the wave originated. It may, of course, be a mere coincidence that at the time the Indian catastrophe occurred the moon was near the ‘‘new,’” that it was in the region of its closest approach to the earth, and that the earth was within a few degrees of its nearest approach to the sun. It is, too, mere coincidence that at the time of the quake we were just completing at the Institute of Geographical Exploration an intensive investigation of some 2,000 earth- quakes during the last twenty years. Investigations reported by Dr. Davidson, of England, during the last year seem to give evidence that certain types of earthquakes occur at regular intervals, dependent upon the cycle of the moon. More recently Father Rodés has presented evidence that earth- quakes are more numerous when the moon is nearest the earth than when it is more remote from us. Others have made extensive investi- gations with conflicting results. now a street of twisted ruins Author of “Man and the Stars,” Etc. - — ~ 4 A Rt o Perhaps the most striking result of our own researches thus far has been that the deep-seated earth- quakes follow in a most surprising fashion the strength of the tidal forces exerted by the moon on the earth’s crust. The same moon which causes the rise and fall of the tidal waters in the oceans produces a small tide in the crust of the earth itself, and theoretically the earth’s crust rises and falls a few inches each day as a result of the compressing and ex- panding action of the forces of the moon as it journeys about the earth. At times these forces pull directly up, at other times down, and then again sidewise or horizontally along the surface of the earth itself. The interesting thing about these latest findings is that apparently it is when the lunar forces are pulling at right angles to the well- known ‘‘faults,” or fissures, in the earth's crust where earthquakes happen that we find the largest number of these deep-seated earthquakes. By deep-seated earthquakes we mean those where the major disturbance seems to originate three, four or five hundred miles down from the earth’s surface. These tidal forces are so feeble as compared with the force of gravity that it is difficult to believe that the moon itself can cause earth- This machine records quakes in all parts of the world T Acme Photos quakes. Yet the pull of the moon on the surface of the earth as it goes overhead totals so many thousands of tons that it staggers the imagination. Then there is something per- fectly uncanny about the disastrous results that can come from a periodic push and pull, like the periodic bending of a piece of steel. It is perhaps possible that these rhythmic oscil- lating stresses may provide the occasion when the earth’s surface, trying to adjust itself toa shrinking interior, lets go — thus precipi- tating the earthquake shock. Dr. Leet, in charge of the Harvard Seismo- graphic Station, has shown me records of countless tremors which appear to be taking place continually, and are of course quite imperceptible without a delicate recording mechanism. Hundreds of superficial earth- quakes come and go apparently without con- sulting the moon. and for a long time this has baftled our scientific studies as to the reality of any definite connection between them. When, however, we restrict our data to the deep-focus earthquakes, three or four hundred miles down, we apparently find the lunar effect increasingly significant. One might say. therefore, that by and large major earthquakes which are bound to happen will more frequently let go when the position of the moon bears a certain relation to the center of the disturbance than at other times. One, too. must not forget the part which the sun plays in tidal phenomena. Everyone who visits the seashore knows that we have exceptionally high tides at new and full moon, for it is then that the pull of the sun on the earth is added to that of the moon. The sun is an enormously heavier body than the moon, but it is millions of miles farther away, so that the resultant effect of the sun’s tidal pull on the earth is a little less than half that of the moon. In the case of the Quetta catas- trophe, the sun and moon were in line, and we had nearly the maximum tidal forces that the combined bodies could produce. Perhaps it does not help greatly in pre- dicting earthquakes to discover a possible trigger action exerted by the sun and moon. At best it could only lead us to say that if conditions are getting right for another earth- quake at a given point on the earth’s surface, then the chances are a little greater that the catastrophe will take place when these tidal forces of the sun and moon are at a maximum. And this can be calculated astronomically. Earthquake studies show us that there are very definite regions on the globe where major earthquakes happen. Curiously enough, a huge circle may be passed around the globe, passing through a zone covering substantially the major earthquake regions. Such a circle may be made to encompass the Dutch East W Photograph by Ewing Galloway A quake almost completely demolished this Sicilian town Indies, Japan, the Aleutian Islands, the coast of California, Mexico and the northwestern coast of South America —all of which are highly susceptible to earthquake disturbances. Another circle passes through the West Indies, the Mediterranean, the region in northern India —the seat of our latest catastrophe —and again the general region of the Dutch East Indies. It would appear that definite fault lines, or perhaps huge cracks in the earth, lie deep-seated in these major directions. (Continued on page 12)