EARTHQUAKES.

Press, Volume LXIX, Issue 20807, 17 March 1933, Page 17

EARTHQUAKES.

NEED FOR RECORDING I INSTRUMENTS. AN AMERICAN WRITER'S VIEWS. Interesting observations on the latest developments in earthquako research, with frequent, references to the Napier disaster of .193.1, are made in the annual report of the ►Smithsonian Institute by Mr N. 11. Heck, chief of the division of Terrestrial Magnetism and Seismology, United States Coast and Geodetic Survey. The writer draws particular attention to the need for better instruments in New Zealand:— "On February 2, 19.11, we had another reminder that the problem of safeguarding- cities against damage from severe earthquakes is as yet unsolved, when the beautiful coast resort city of Napier was nearly destroyed by a great earthquake," says the writer. "This earthquake also demonstrated that in designing structures to resist earthquakes the possiblo cumulative effects of a number of severe shocks must not bo overlooked, since there were at least three aftershocks comparable with the main shock. "The earthquake is always of absorbing interest to the seismologist, but we aro rapidly approaching a condition in which the* heretofore sporadic interest of the average citizen is being converted into continuous interest in many parts of the earth, and accordingly the engineer and architect in the regions concerned are beginning to be quite as much interested as the seismologist. The two fields of activity—geophysics and engineering—although having different purposes, aro not independent, and results in either field may throw light on the problems of the other. Prominent engineers have begun to criticise the seismologist for not giving them the information they need, and the time now seems ripe for closer co-ordination of activity. Experiments with Models.

"For a number of years engineers have been gathering information regarding earthquake effects on structures, and to some extent are basing design of structures on the observed

facts. At (Stanford University they are operating a large shaking table on which types of structure and models of buildings are tested under conditions simulating earthquakes. With all this they feel the need for more exact knowledge in. regard to motions of strong earthquakes, a demand which the seismologists have not yet met. The recent New Zealand earthquake has shown, as have many other?, that certain types of earthquako damage are inevitable. Types of construction matter little if a building is directly over a fault line with, horizontal or vertical slipping, or in the path of a great landslide. . If a great tidal wave occurs, buildings in its path will be swept away. However, for most earthquakes the number of buildings exposed to these special hazards is not a large proportion, and the most common needs are ability to resist strong shocks and fire prevention. Earthquakes are no more numerous or more severe than in the past. but. the earth is 60 much more intensively occupied that the risk of important" damage is greater than ever before, and is constantly increasing. The problem, then, is prevention of disaster duo to moderately severe earthquakes and the reduction of damage due to great ones. Engineers arc beginning ; to agree that major structures should be | designed with regard to earthquake stress if the history of the region indicates that they are likely 1o be subjected to such stress. They are recognising the lack of information and are demanding that more accurate information should .be obtained. Funds for the Work. "It is of particular interest, to know that in 1931 Congress provided funds for undertaking this work. Suitable plans have been worked out in co-oper-ation with organisations on the Pacific Coast, and the first instruments for securing information regarding earthquake motions of interest to engineers will be made in this region. The purpose is to install instruments capable of recording accurately strong earthquake motions in places where history indi-» cites that there is probability of earthquake activity of some intensity. "It is regrettable that such instruments were not installed-in New Zenland when valuable information could have been collected. However, instruments of a satisfactory character were not in existence, nor are they to-day except for several types that have been developed in Japan which are adapted to frequent, strong activity. Earthquakes are in many cases related to movements of the earth's crust which may occur at the time of a severe earthquake or during the interval between great earthquakes. The only satisfactory way to determine such movements is by precise triangulation and levelling repeated at suitable intervals. Much work of this sort has been done in Japan. The Japanese havo added another type of investigation that they have found very useful. Even before the days of instrumental observation, as far back as 1793, the inhabitants of a coastal village noticed a sudden movement of the shore beneath their feet, and assuming that it meant the arrival of a tidal wave they rushed to the hills. Nothing occurred for four hours. "Then came a great earthquake and tidal wave. This phenomenon has been observed to a lesser degree in other earthquakes, and the natural assumption ifl that the surface of the earth tilts just before the earthquake. In four earthquakes the intervals have varied fiom one-half to four and one-half hours. Quoting Captain B. S. Patton, Director of the Coast and Geodetic Survey, the writer adds that in recent years there has been most gratifying progress in the attack upon problems of seismology in the United States. There is need for increased future effort, and any such increase will necessitate a more lormal means of co-ordinating the,activities of the various participating groups. There will be particular need to clarify and to dovetail together the respective fields occupied bv the two general groups consisting, on the one hand, of the geophysieists, concerned with the pure science of scismologv and. on the other hand, the engineer's, architects, and others who are concerned v-ith earthquakes because of their potential menace to life and propcrtv. "