Evening Star Newspaper, September 13, 1931, Page 84

FHE SUNDAY STAR, Synthetic Farthquake While You Wait! BY JAMES NEVIN MILLER. N an obscure field, not far from Boston, a young Harvard scientist, Dr. L. Don Leet, is conducting experiments which are ex- pected to revolutionize the study of earth- quakes. Already he has succeeded, for the first time in history, in making synthetic, or artificial, quakes, simulating in a fashion estonishingly close to nature all the terrific strains and stresses of the terrible cataclysm that spreads so much terror and destruction throughout the world. The dreaded earthquake is one of the last ominous threats of nature. Men have pene- trated most of the vast jungle mysteries. They have flown into the remote recesses of the Arctic. They are devising new means of con- quering strange and terrible diseases. Yet ever since the white man first set foot on the Amer- ican continent he has been forced to confess himself well-nigh helpless before the earth- quake. It may appear in any month, at almost any hour of the day or night, carrying away the very house he lives in as well as the loved ones whose lives he strives to protect. Small wonder, then, that the learned men of science are watching with the keenest interest the important experiments of the youthful Dr. Leet. His studies brirg renewed hope of solv- ing the many mysteries that have been bound up with the problem of earth shocks ever since e dawn of history. urely no one is better qualified to explain the revolutionary earthquake tests being con- ducted at Harvard than Dr. Leet himself, $nternationally known as director of the Har- vard Seismograph Station. He points out: “Our experiments, with a scientific staff including C. J. Roy and Allen Waldo, have been described as the manufacturing of artificial earthquakes. Made by a small charge of dynamite, the shocks used in these tests move the ground so little that instruments which magnify a disturbance 12,000 times have to be used to get a reccrd of UST what 1s an earthquake? A striking illustration iz offered by Dr. Reginald Daly, elso a distirguished scientist at Harvard: “When with your hands you bend a stick until it breaks, the sudden snap sends vibra- tions, often painful, along muscle, bone and nerve of the arm. The ‘strain’ of the stick is relieved by fracture and the elastic energy accumulated in the stick during the bending is largely converted into the energy of wave motion, “In a somewhst similar way the rocks of the earth's crust have been and are now being strained. Every day, somewhere in the world, they are snapping and sending out elastic waves from one or more centers. The passage of these waves in the earth we call an earthquake, or seismic disturbance. " %A major quake has enormous energy. At and near the center of shock it shatters the works of man and may rupture into the very hills and mountainsides. As each wave spreads into the earth, the intensity of the vibration falls very rapidly, so that not many hundreds of miles from the center the heaviest shock cannot be felt by a human being. Much less can he, at the ‘other side of the globe,’ feel the impact of a wave which has plunged to a slepth of a thousand miles or more and emerges under his feet. a~In order to watch and time accurately each *le as it makes its long journeys around and through the earth, highly sensitive instruments are used. Those wonderful devices, called seis- W hat effect has heavy traffic on the immedi- ate surrounding terri- tory? 4 seismograph is here shown making recordings of tremors in Philadelphia. WASHINGTON, D. C, SEPTEMBER 13, I'93h For First Time in History Science Succeeds in Making Artificial Quakes, Simulating Terrific Strains and Stresses of Destructive Cataclysm, and Revolutionizes Modern Study of Earth Shocks. mographs, magnify the motion of the vibrating rock and give a written record or graph' of that meotion.” UT to return to Dr. Leet's own description of his tests: “Geologists have long believed that the continents were underlaid by granite. They have been trying for many years to de- termine how thick this layer is. The only means of study has been, and still is, the velocities with which earthquake waves travel through this layer. “Little knowledge now exists about these velocities. If such speeds are determined, they will indirectly contribute to the aim of scientists to learn the exact thickness of this foundation layer, or, on the other hand, the study may reveal that this foundation is not granite at all. “Our experiments will take two forms. One will be the measurement of the speed through which vibrations travel through the supposed granite. The other will be the measuring of the thickness of drifts left by glaciers some 10,- 000 years ago, revealing the original formation of the land. “In recnt years earthquake waves recorded by seismograph stations less than 700 miles from the centers of disturbance have given some necesgary data. Such records have led to the conclusion that certain earthquake waves travel through the continental foundations at a speed of about 18,000 feet per second, or more than three miles a second! Since these waves travel through different materials with diffe ent speeds, the next step is Lo determine the rock which transmits waves of the same char- acter at a similar velocity. “*More specifically, the research in the glacial phase of our study will attempt to determine the thickness of the vast coverings of rock and earth debris left by the gigantic ice sheets in the last ice age. Beneath these deposits lie the solid rock formations that were at the surface before the ice advanced in its relent- less march. “A charting of the old land surfaces would reveal a general picture of the land before it was changed by the glaciers, demonstrating, possibly, that hills occurred in places now oc- cupied by valleys, and that rivers some 10,000 vears ago ran in different directions from those of today. “The principal means for studying these problems is a portable seismograph, first de- veloped commercially for discovering important oil deposits. The Harvard Seismograph Station, in the course of its present tests, is using two of these instruments, one a commercial type, the other an instrument unique in its field. VI"THE ordinary type records vibrations travel- ing in only one direction. The other, especially constructed for this kind of research by H. Gordon Taylor of Washington, D. T, Getting ready to produce a man-made earthquake. Several assistants of Dr. L. Don Leet, Harvard scientist, are preparing to set off a blast of dynamite and make recordings of the effects. records waves in three dimensions at right angles to one another. “The principle of our procedur: is simple. Small charges of dynamite are fired at some convenient point and recorded at warious dis- tances frcm there by our portable seismcgraphs, Vibrations of the ground are record:d by one of these instruments on fast-moving photo- graphic film. A reccrd is made of the vibra- tions from each of thz series of explosions. “On each record a vibrating tuning fork, by interrupting a beam of light, places a line every hundredth of a second. By an electric circuit connected to the dynamite charge, a mark is placed on the record at the very instant of ex- plosion. By counting the timing lines from that point, then, it is a relatively simple matter to determine to within a couple thcusandths of a second the exact time which elapsed between the explosion of the dynamite and the arrival of the first waves at the seismograph. “If all the waves followed the same path, say, a2long the surface cf the ground. a com- paratively small number of shots might suffics for determining their velocity accurately. This, however, is not the case. The first-arriving waves at successively greater distances often penetrate into the ground more and mors deeply befcre reaching the recording instru- ment. As a result, it is necessary to make a large number of observations in such cases and subject them to mathematical analysis in order to determine the true velocity at various depths.” R. LEET goes on to explain that the vibrations travel through locse earth at the surface, such as glacial till, at a far slower speed than through the solid formations below. By discharging the dynamite at successively greater distances, the first waves to reach the instrument will, for a short distance, travel only through the low-speed material. Beyond a certain point, however, depending upon the thickness of the surface material, the waves will be able to make better time by traveling part of the distance in the underlying, high- speed solid rock. Thus they would arrive ahead of the schedule they would follcw on the surface. For exam- ple, the vibrations may travel through ordi- nary earth at 2,000 to 6,000 feet per second, while they will travel in rock formations at speeds of 15,000 feet or more a second. There- fore. in taking a set of observations along a straight line, a profile of the rock below the surface will be revealed. One important question which the Harvard experiments should open up is: How hot is it in the very center of the earth? We are told by Dr. Daly of Harvard: “The pressure in the region of the earth's core ranges from 15,000,- 000 to 50.000,000 pounds to the square inch. Under such colossal pressure the earth's core, which is probably made of iron, can be in a fluid condition only if the temperature of the earth is enormously high—at tens of thousands of degrees Centigrade. Both pressute and tem- perature down there are far beyond the range of the experic:emea? laboratory. “The pnysical state of the iron core cannot as yet be described. Is it a liquid, a gas or iron in a ‘state’ unknown to physics? The con- ditions of the earth’s core are starlike. From their study can physicists of the future tell us something more of the true nature of the stars? If they can they will be pretty sure, incidentally, to shed new light on the structure and life story of the atoms, for the secret of the star and the secret of the atom are proving to be a part of a single problem, the ultimate nature of matter.”