1942: Seismology

In spite of some reduction in the number of seismological stations and the curtailment or stopping of some reports, the situation is sufficiently well known to assure that there were no major earthquakes during the twelve months ending Nov. 30, 1942. There were 42 widely recorded earthquakes, a number of which were submarine. About 10 caused serious loss of life, injury, or destruction of property.

There were no serious earthquakes in the United States. The two most important were that of Mar. 11, in the Black Hills of South Dakota, and that of Oct. 21, centering near the Mexican border west of the Imperial Valley where there was damage to a railroad.

There were no important changes in the list of seismograph stations in the United States and the regions under its jurisdiction. Two new stations were established, one in northern California and the other in central Washington. New instruments replaced the old at Spring Hill, Ala. So far as is known, though unreported changes have probably occurred, there are 114 seismograph stations, divided according to principal purpose as follows: 36 distant; 23 near earthquakes with continuous photographic recording; and 55 strong-motion instruments which record only during the shocks. Of 5 earthquakes recorded during the year only those of the shock of Oct. 21 were of great value, but this is less important than the fact that the instruments are ready to record a great shock when it comes.

The earthquake location by means of seismographs, though essential, is only part of the needed information. Reports of visible and felt effects must be furnished by observers. Through long-established methods, part of the information can be placed on a map and part requires verbal description. The cooperative system is organized on a large scale, especially in the western part of the United States where cooperators are supplied in advance with forms on which the desired information may be readily placed.

Organizations which have taken part in these activities include: the National Government, primarily through the Coast and Geodetic Survey but also through the Weather Bureau, Bureau of Reclamation and others; the Jesuit Seismological Association; the Northeastern Seismological Association; various other colleges and universities, especially the University of California, Stanford University, and the California Institute of Technology; and Science Service, which collects information that makes immediate earthquake location possible.

The main purposes of earthquake investigation have been: to locate all earthquakes in position and depth in order to associate them with geological formation; to determine the extent of area affected and the effects, for insurance and other purposes; to measure the earth movements associated with destruction, and apply this knowledge to better design of structures; and to learn more about the cause of earthquakes. Much of the information has military use, especially in connection with wartime construction.

Information regarding building codes of earthquake-resistant construction has been assembled and published. In the matter of vibration studies of buildings, the seismologist has been the only scientist possessing suitable instruments, and thereby fills a gap in such studies. It has been proved during the year that the type of skill demanded of the seismologist makes him well-suited to meet wartime needs in other fields. This has meant that special investigations in seismology have had to be deferred.

Geodetic measurements, which make it possible to detect crustal movements by determining the positions and elevations of permanent monuments at regular intervals, have been temporarily suspended, but many new monuments have been located which can be later used for the same purpose. Continuous measurement of tilt has been accomplished and extended. The value of this method has not yet been fully established, partly because of lack of earthquakes in their region and difficulty of eliminating nonseismic tilts.

International work has been curtailed, though certain activities of the International Seismological Association have continued at a reduced rate in Great Britain. There has been evidence of increased interest in seismology in Central and South America. The detrimental effect of the war on seismology throughout the year is unknown, but it is certain to increase. However, in partial compensation there are sure to be scientific developments which may be applied to seismology and which will aid with the solution of many problems.