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.

1941: Seismology

The only major earthquake during the year ending Nov. 30, 1941, was under the Atlantic Ocean north of the Maderia Islands on Nov. 25, but since it was far from land and unaccompanied by a seismic seawave no damage was caused. There were 43 widely recorded earthquakes many of which were submarine and 10 of which caused destruction or loss of life on a considerable scale.

In the United States there were no highly important shocks but those causing some damage include the following: New Hampshire, Dec. 20 and 24, 1940; and California, Santa Barbara, June 30, Los Angeles region Oct. 21, 22 and Nov. 14.

The United States and the regions under its jurisdiction are fairly well supplied with seismographs except that they are not uniformly distributed. There are about 112 in all, of which the principal purposes are: 34, distant earthquakes; 23, nearby earthquakes; 55, strong earthquakes, in the region of destruction. All except the strong-motion instruments record continuously, and with few exceptions photographic registration is used.

The strong-motion instruments are automatic; that is, the earthquake starts the recording which lasts only during the shock. The record of the Santa Barbara earthquake of June 30 supplied especially useful information, and the analysis of the records of the May 18, 1940, Imperial Valley earthquake gave the first accurate knowledge of the motions near a fault on which surface slipping occurred.

A map of the area affected by the earthquake is based on information from those who felt and observed the shock. Collection of thousands of reports from such witnesses is well organized. In regions of frequent earthquakes, cooperators are kept supplied with forms listing the desired information to be filled in and mailed after each earthquake; elsewhere the forms are sent out immediately after the earthquake occurs.

Organizations taking part in these various activities include: National Government through the Coast and Geodetic Survey, Weather Bureau and other services; the Jesuit Seismological Association; the Northeastern Seismological Association; colleges and universities, especially the University of California, California Institute of Technology and University of Alaska; and Science Service, which collects information making immediate earthquake location possible. In a number of western states a special representative coordinates the collection of information for a particular state.

The purposes of these investigations are to find where and at what depths earthquakes occurred; the extent of area affected; the nature of service affected; better knowledge of the earth's crust and interior, including the relation of earthquakes to slipping along fault planes; the determination of the seismicity of different parts of the earth; the determination of actual earth motions, especially in the central region of a strong earthquake.

The measurement of strong earth motion and studies of earthquake damage aid in the safe design of buildings, bridges, dams, water towers and other structures. The periods of buildings have continued to be measured to aid in the solution of these problems. Application has been made by a number of universities and engineering organizations of the information obtained, and at Stanford University and the California Institute of Technology shaking platforms have been made to simulate earth motions in the models of structures. Attention is being given to the importance of building codes.

Increase of stress in the earth's crust, possibly associated with earthquake occurrence, may be detectable by geodetic measurements and such measurements have been made during the year in the Lake Mead region of Nevada and Arizona. Measurements to determine tilt of the crust have continued at Berkeley, Calif., but without cooperative results in the absence of nearby earthquakes.

New and improved seismographs for the recording of the vertical component of the earth's motion have been developed during the year. In the past the cost and limited variety of such instruments have deprived many stations of this important adjunct.

Seismological investigation of which so much has been done in Europe has been handicapped to an unknown degree by the war, but the full effect will not be known for some years. The International Seismological Association has functioned partially in England and unoccupied France under great difficulties. Immediate exchange of earthquake information between the United States and Canada, Mexico, Guatemala and El Salvador has facilitated the location of earthquakes. See also GEOLOGY.

1940: Seismology

There were two major earthquakes, or rather series of great shocks during the year. The first was in Turkey on Dec. 27, 1939, with aftershocks for several months; the second was in Rumania on Nov. 9, 1940, apparently originating about 100 miles beneath the surface and widely destructive. The other most noteworthy earthquakes of the year occurred May 24, Callao, Peru; July 15, Tibet; and Oct. 4, Iquique, Chile.

In the United States there was only one important earthquake, in Imperial Valley, California, on May 18, with considerable property loss. Other shocks in the East as well as the West were of moderate intensity.

There are 115 seismograph stations of various kinds in the United States and the regions under its jurisdiction. The number and the principal purpose are about as follows: 37, recording of distant earthquakes; 18, nearby light and moderate earthquakes; 55, strong earth motions; and 5, volcanic earthquakes of all types (Hawaii).

The teleseismic (distant earthquake) stations are fairly well distributed; the others, except as mentioned, are chiefly in the Pacific Coast and western mountain regions. The strong-motion instruments are automatic, that is, the earthquake starts the recording which lasts only during the shock. Several valuable records were obtained for the Imperial Valley earthquake. All other instruments are continuously recording and, with few exceptions, photographic recording is used in all types in the United States.

The complete description of an earthquake requires both an instrumental epicenter and information from thousands of observers and eyewitnesses. In regions of frequent earthquake, forms listing the desired information are placed in the hands of individuals in advance; elsewhere they are sent out immediately after the earthquake. Organizations taking part in these varying activities include: the Coast and Geodetic Survey and the Weather Bureau, with collaborating state representatives in the western mountain states; Jesuit Seismological Association; Northeastern Seismological Association; University of California and associated institutions; California Institute of Technology; and the University of Alaska.

The purpose of these investigations is to find where and at what depth earthquakes occurred; the extent of area affected and nature of surface effects; better knowledge of the earth's interior and crust, including the relation of earthquakes to faults, or slips at the surface; and the character of the earth motion in the central region of an earthquake.

The last-named information, together with studies by engineers of earthquake destruction, aids in the design of buildings, bridges, dams and other structures to resist earthquake. The periods of buildings and ground vibrations are measured to aid in the solution of the problems. The application of this information which is collected by the Coast and Geodetic Survey and collaborators has been made chiefly at the Massachusetts Institute of Technology, California Institute of Technology, and Stanford University, which also operate shaking platforms of various types on which models of structures are subjected to actual reproductions of the earthquake motion. A number of organizations are working on improved building codes.

Increase of stress in the earth's crust, possibly associated with earthquake occurrence, may be detected by geodetic measurements, and such work has been done in the Lake Mead region of Nevada and Arizona and in southern California. Tilt measurements have continued at Berkeley, California, but without conclusive results in the absence of nearby earthquakes. Studies of microseisms made at St. Louis University have resulted in better knowledge of their form and method of propagation.

1939: Seismology

The year had one major earthquake causing great destruction, that of Central Chile on January 24. The other most noteworthy earthquakes of the year were March 20 and May 1 in Japan; June 18 at Accra, Gold Coast, Africa; and Sept. 22 at Izmir (Smyrna), Turkey.

In the United States there was a destructive earthquake in western Washington on November 13; others occurred on May 4 near Boulder Dam, in northeastern Alabama May 5, and southern New Jersey November 14. On Oct. 18 a shock originating at the confluence of the St. Lawrence and Saguenay Rivers in Canada was felt over a large part of New England.

There are more than one hundred seismograph stations of various kinds in the United States and the regions under its jurisdiction. The number and the principal purpose are about as follows: 39, recording of distant earthquakes; 16, nearby light and moderate earthquake; 51, strong earth motions; and 5, volcanic earthquakes of all types (Hawaii).

The teleseismic (distant earthquake) stations are well distributed; the others, except as mentioned, are chiefly in the Pacific Coast and western mountain regions. The strong-motion instruments are automatic, that is, the earthquake starts the recording which lasts only during the shock. All other instruments are continuously recording and, with few exceptions, photographic recording is used in all types in the United States.

The complete description of an earthquake requires both an instrumental epicenter and information from observers and eyewitnesses. The collection of the latter information from thousands of individuals is well organized. In regions of frequent earthquake, the forms listing the desired information are placed in the hands of individuals in advance; elsewhere they are sent out immediately after the earthquake. Organizations taking part in these varying activities include: the Coast and Geodetic Survey and the Weather Bureau, with collaborating state representatives in the western mountain states; Jesuit Seismological Association; Northeastern Seismological Association; University of California and associated institutions; California Institute of Technology; and the University of Alaska. There are also many scattered activities of universities and scientific institutions.

The purpose of these investigations is to find where and at what depth earthquakes occurred; the extent of area affected and nature of surface effects; better knowledge of the earth's interior and crust, including the relation of earthquakes to faults, or slips at the surface; and the character of the earth motion in the central region of an earthquake.

The last named information together with studies by engineers of earthquake destruction aids in the design of buildings, bridges, dams and other structures to resist earthquake. The periods of buildings and ground vibrations are measured to aid in the solution of the problems. The application of this information which is collected by the Coast and Geodetic Survey and collaborators has been made chiefly at the Massachusetts Institute of Technology, California Institute of Technology, and Stanford University, which also operate shaking platforms of various types on which models of structures are subjected to actual reproductions of the earthquake motion. A number of organizations are working on building codes.

Complete earthquake prediction is impossible, but determination whether stress in the earth's crust is growing probably is not. For this reason crustal movements are measured by geodetic means. Tilt is being measured on the Hayward fault at the University of California. On the same fault near Oakland the noise at the fault is recorded in a deep well, in the expectation that minute slipping preceding an earthquake would cause slight noises. No earthquake has occurred along the fault since observations were started. See also GEOLOGY.

1938: Seismology

During the past few years there have been no major destructive earthquakes, and the year 1938 has been no exception. Few earthquakes have occurred outside the recognized earthquake belts. The most noteworthy earthquakes of the year were in Europe and the Near East: April 19 in Anatolia, Turkey; June 11 in Belgium; July 20 in Greece.

In the United States several minor earthquakes had some interest; those of February 12, July 29, and August 22 (near Trenton, N.J.) were felt respectively in Chicago, New York, and Philadelphia; the Blair County, Pennsylvania, earthquake of July 15 was in a region without previously known earthquakes.

There are more than one hundred seismograph stations of various kinds in the United States and the regions under its jurisdiction. The number and principal purpose are about as follows: 35, recording of distant earthquakes; 15, nearby light and moderate earthquakes; 51, strong earth motions; 5, volcanic earthquakes of all types (Hawaii).

The teleseismic stations are well distributed; the others, except as mentioned, are chiefly in the Pacific Coast and western mountain regions. The strong-motion instruments are automatic; that is, the earthquake starts the recording which lasts only during the shock. All other instruments are continuously recording; and, with few exceptions, photographic recording is used in all types in the United States.

The instrumental determinations of the earthquake epicenters do not tell the whole story, and reliance must be placed on reports of observers and eye witnesses. The collection of information from thousands of individuals is well organized. In regions of frequent earthquake the cards listing the desired information are placed in the hands of individuals in advance; elsewhere they are sent out immediately after the earthquake. Organizations taking part in these varying activities include: The Coast and Geodetic Survey and Weather Bureau; Jesuit Seismological Association (northeastern seismological association); University of California and associated institutions; California Institute of Technology; University of Alaska. There are also many scattered activities of universities and scientific institutions.

The purpose of these investigations is to find where and at what depth earthquakes occurred; the extent of area affected and the nature of surface effects; to get a better knowledge of the earth's interior and crust, including the relation of earthquakes to faults (slips at the surface); and to learn the character of the earth motion in the central region of a destructive earthquake.

The last named information is needed in designing buildings, bridges, dams, and other structures, to resist earthquake. For the same reason the periods of building and ground vibrations are measured. The question is whether earthquake damage is due to large measure to resonance; that is, whether agreement of the natural period of vibration and the principle periods in an earthquake results in excessive movement of the structure and consequent damage. Work is being done on the application of this information which is chiefly collected by the Coast and Geodesic Survey, at Massachusetts Institute of Technology, California Institute of Technology, and Stanford University. Several of these institutions operate shaking platforms which can be put into the same motion as an actual earthquake, so that models can be tested.

Complete earthquake prediction is impossible; but it may be possible to determine whether stress in the earth's crust is growing, and for this reason crustal movements are measured by geodetic means. Tilt is being measured on the Hayward fault at the University of California. On the same fault, near Oakland, the noise at the fault is recorded in a deep well, in the expectation that minute slipping preceding an earthquake, will cause slight noises. No earthquake has occurred along the fault since observations were started. See also GEOLOGY.