DATA. Some countries have made a definite effort to organize a reporting system for earthquake information. This type of data is collected by sending out to volunteer cooperative observers printed questionnaire cards. The observers complete these forms and return them to the official seismological service, which is then able to evaluate the earthquake intensity at any given place. Data can be obtained by this means at relatively little expense and can yield an amazing amount of information with regard to the location and intensities of felt shocks. Even when some seismographs are available, non-instrumental information is still extremely useful, because such a system, if adequately organized, can provide far more detailed coverage than would ever be possible with instruments alone.

2. COLLECTION OF INSTRUMENTAL DATA. The data so far acquired on ground motions during destructive earthquakes are only a beginning and far more information is required before engineers can determine adequately the forces against which they must provide in an engineering design. These data are difficult to obtain.

If a strong motion instrument is to record really destructive ground motion, it must be near the epicenter. Since the epicentral locations vary greatly for different shocks in any general seismic region, it is very necessary for the recording instruments to be thoroughly distributed over the zone; otherwise, there may not be an instrument near enough to an epicenter to yield a record of engineering value. Closer spacing of instruments will be possible if less expensive types of strong motion seismographs are devised. At present the Coast and Geodetic Survey is working on the development of such equipment, which will make possible the acquisition of data much more rapidly than has been possible with a relatively few costly instruments.

New sensitive seismograph stations are urgently needed so that all shocks, including very light disturbances, can be located accurately, for the purposes of evaluating regional seismicity and extending our knowledge of earthquake causes.

3. IMPROVEMENT OF CONSTRUCTION PRACTICES AND FORMULATION OF BUILDING

CODES.- -Construction practices in the various countries must be carefully examined in order to determine just how existing methods can be modified to give reasonable assurance against serious damage, with a minimum increase in cost of construction. Model studies can be used to great advantage in this work. The findings should be embodied in building codes and strictly

enforced. Provision should be made for checking engineering design as well as for inspection of structures while under construction. Such regulations are necessary to prevent the erection of additional buildings which are nothing more than death traps. The formulation and enforcement of adequate earthquake code provisions is admittedly a large undertaking, but the hazard cannot be removed to any extent without making the seismic provisions mandatory. There is no such thing as an ideal code. It is consequently far preferable to complete a code and place it in operation with the understanding that revisions can take place as required to make it more workable and more equitable. One of the difficult problems in evolving a satisfactory earthquake code is the zoning of a country, because danger is usually greater in some districts than in others. However, unless the earthquake history of a country is fully known, it is almost impossible to assign a probability value to any given region. Clearly, countries with no complete earthquake history should compile such data as soon as possible. Data from the sensitive type of seismograph can be very helpful in determining the boundaries of these seismically active zones.

4. GEOLOGICAL INVESTIGATIONS.-Elaborate geological studies are vital to a constructive earthquake program. Specialists in tectonic geology, that is, on the phenomena involved in deformations of the earth's crust, should undertake the correlation of existing geological information for the Western Hemisphere in relation to the distribution of the seismic belts. This work should be supplemented as necessary by original geological investigations in areas for which the available data are insufficient. Publication of results for the Western Hemisphere could not fail to be of great scientific and practical value.

5. GEOPHYSICAL INVESTIGATIONS.-Care

ful surveys, involving triangulation and leveling, along a known fault before and after an earthquake have shown the detailed characteristics of the permanent horizontal and vertical displacements resulting from an earthquake. Of course, in cases where a fault fracture extends to the surface with a definite offset, as in figure 5, such permanent changes are apparent without the aid of surveying instruments. Since the accumulation of stress in the earth's crust preceding a major shock must produce some distortion at the surface before actual fracturing occurs, it has been thought that frequently repeated surveys in the vicinity of active faults may succeed in disclosing just what portions of the faults are being stressed, thus indicating where the next earthquake may occur. In order to test the efficacy of the method, data must be collected over long periods in many different regions. The method has sufficient promise to justify a great deal of trouble and expense.

Measurements of the intensity of gravity are needed to understand more fully the cause of earthquakes. Abnormal values of gravity intensity are encountered in regions of extreme crustal deformation. This has been demonstrated in the Caribbean and in the Netherlands East Indies. Gravitational anomalies in these regions are theoretically due to the forcing of the lighter upper rocks to greater depths during the process of crustal folding. It is consequently highly desirable to carry out elaborate gravity studies in seismic zones in order to clarify further the relation of gravity anomalies to seismic activity. There is every reason to believe that results would be of great value in more accurately determining the boundaries of known seismic zones, either land or sea; also, potentially active regions not yet recognized might be detected.

Summary

In the foregoing paragraphs the following points have been touched upon:

1. The geographical distribution of severe earthquakes in North, Central, and South America has been emphasized. This distribution is such that few of the American Republics can afford to neglect the earthquake problem. Brief mention. has also been made of the relation of earthquakes to volcanic activity and to mountain building.

2. The direct and indirect effects of severe earthquakes have been discussed. Direct damage is due to intense ground motion. Indirect damage may result from seismic sea waves, severe landslides, and conflagrations. Attention has also been called to the fact that fault displacements extending to the surface may raise havoc with roads, railways, and canals crossing the line of dislocation.

3. Three methods of attacking the problem of designing earthquake resistant buildings were described. The first consists of observations of actual earthquake damage. The second consists in amassing sufficient records of destructive ground motion so that the engineer can judge the maximum values of acceleration and displacement ever likely to occur for any given period of ground motion. The third method makes use of dynamical models of engineering structures which are subjected to simulated earthquake motions on shaking tables.

4. Recommendations have been made for a constructive earthquake research program for the Western Hemisphere. These recommendations include facilities for the collection of non-instrumental data; increased instrumental equipment for obtaining data on strong earthquake motions; new sensitive seismograph stations for delimiting the seismic zones more accurately; thorough investigation of design

and construction procedure in the various countries, aided by model studies, with a view of determining how the existing methods of construction can be so modified as to give security against earthquakes with a minimum increase in economic burden; incorporation of these principles into mandatory building regulations; and detailed geological and geophysical studies of active seismic belts.

ACKNOWLEDGMENTS

A number of individuals within the U. S. Coast and Geodetic Survey have been of very great assistance in the preparation of this article. Especial thanks are due the following: Lt. Comdr. Elliott B. Roberts, Chief of the Division of Geomagnetism and Seismology; Mr. Frank Neumann, Chief of the Section of Seismology; Mr. Ralph R. Bodle, also of the Section of Seismology; and Mr. Franklin P. Ulrich, Chief of the Seismological Field Survey in San Francisco and American Republics Seismological Representative for the years 1944-46 inclusive.

Figure 5 is from the files of the Imperial Irrigation District. All other illustrations are from the Coast and Geodetic Survey files.

REFERENCES

1. A Catalogue of Destructive Earthquakes, A. D. 7 to A. D. 1899. Milne

2. Erdbebengeographie, Volume IV, Handbuch der Geophysik, 1932. Sieberg

3. Consideraciones sobre la Historia Sísmica de la República Dominicana. Domingo Martínez Barrio

4. Contribución a la Geología Sísmica de Chile. Bruggen

5. Earthquake Conditions in Chile. Willis 6. Historia Sísmica de los Andes Meridionales. Montessus de Ballore

7. Mapa Sísmico y Tectónico de Colombia. Ramírez and Duran

8. Estudios Sismológicos. Centeno-Grau 9. Geología del Perú. Steinman

10. Earthquake History of the United States, Parts I and II. U. S. Coast and Geodetic Survey 11. List of Seismic Sea Waves. Heck (U. S. C. & G. S.)

12. Other Coast and Geodetic Survey data. 13. Earthquakes. Heck

14. Great Earthquakes. Davison

mittee of Rotary International. They include stops in Uruguay, Argentina, Bolivia, Brazil, Chile, Guatemala, Mexico, Panama, Peru, Puerto Rico, and Trinidad.

This mass convergence upon Rio in May by Rotarians representing 80 different countries and geographical regions of the world has a serious purpose in the administrative work of the Rotary organization and in the presentation of important addresses. Heading the list of convention speakers is General Eurico Gaspar Dutra, President of Brazil. Among the other outstanding speakers will be General Angelo Mendes de Morais, Mayor of Rio de Janeiro; the Honorable W. D. Pawley, United States Ambassador to Brazil; and the Honorable Lewis R. Macgregor, Australian Minister to Brazil.

The plenary meetings will be held in Rio's impressive Municipal Theater. The general sessions of May 18 and 19, when a similar program will be conducted simultaneously in two different halls, will be an innovation in Rotary conventions. In one, the languages will be Portuguese and Spanish, and in the other, the language will be English. These two programs will be patterned after the "town hall" type of meeting, and will include open-forum discussions on matters of timely interest.

The convention will be conducted by the president of Rotary International, S. Kendrick Guernsey of Jacksonville, Florida. Two past presidents from Latin America will make important contributions to the program. They are Armando de Arruda Pereira of São Paulo, Brazil, and Fernando Carbajal of Lima, Peru.

One of the highlights of the convention will be visits by Rotarians to the offices, stores, and factories of Rio Rotarians who are engaged in businesses and professions similar to their own.

The business side of the proceedings will include action on Rotary legislation and

Rotary convention programs, however, do not consist entirely of business matters, and Rio Rotarians are planning entertainment features in keeping with the spirit of the city's world-famed carnival. A Festa Brasileira, a colorful celebration featuring Brazilian music, dancing, and pageantry, will be staged one evening and, later in the week, a Festa Regatta, a brilliant nautical display, will be held in Rio harbor.

In the Ministry of Education building, a notable example of modern architecture, will be found the traditional Rotary "House of Friendship," an attractive lounge where Rotarians and their families from the four corners of the earth will doubtless enjoy many memorable experi