Memorial to L. Don Leet 1901-1974 FRANCIS BIRCH, MARLAND P. BILLINGS, JAMES B. THOMPSON Harvard University, Cambridge, Massachusetts 02138 Lewis Don Leet, professor emeritus of geology, died on January 2, 1974, after a notable career as seismologist, geologist, and engineering consultant. The destructive Japanese earthquake of September 1, 1923, coming shortly after his graduation from Denison College, drew his attention to seismology. From the study of natural earth motions he was led to an interest in explosion­ generated vibrations, and much of his subsequent pro­ fessional activity was devoted to observations and analysis of blasting. Leet was born July 1, 1901, at Alliance, Ohio, the son of Kline Fetterman Leet and Lela Grace Caskey Leet, both graduates of Mt. Union College. His father, a lawyer in Cleveland, traced his ancestry to William Leete, governor of the New Haven Colony (1661-1665) and of the Colony of Connecticut (1676-1683). After schooling in East Cleveland and a year at Columbia University, Leet received an S.B. degree in 1923 from Denison College, where he was attracted to geology by Kirtley F. Mather, who soon thereafter came to teach at Harvard. When the great Japanese earthquake aroused his interest, Leet was selling bonds in Cleveland. He obtained a position as secretary in the Tokyo office of the YMCA, where he spent a year with ample opportunity to study the damaged region. In 1927 he was admitted to the Harvard Graduate School for the study of seismology. Research in this branch of Earth science at Harvard had been initiated by J. B. Woodworth with the installation of two Bosch-Omori horizontal seismographs in the University Museum in 1908, but when Leet entered the Department of Geology and Geography, there was no advanced instruction in seismology. Arrangements were made with Ernest A. Hodgson, director of the Dominion Seismological Observatory at Ottawa, to accept Leet as an apprentice. Leet completed a doctoral thesis, “Empirical Investiga­ tion of Surface Waves Generated by Distant Earthquakes,” in 1930. His Ph.D. degree in seismology is said to have been the third such degree granted in this country. He was immediately appointed an instructor in geology and director of the Harvard Seismograph Station. After a wartime leave of absence, when he served in administrative positions in the Radio Research Laboratory and the Underwater Sound Laboratory, he became a professor in 1946. From 1946 to 1947 he was a member of the Board of Freshman Advisers and from 1954 to 1958, chairman of the Department of Geology and Geography. He became professor emeritus in 1968. In 1930 geophysics at Harvard was given a new impetus by Reginald A. Daly, L. C. Graton, and D. L. McLaughlin in geology, joined by Harlow Shapley in astronomy, and P. W. Bridgman in physics. An interdepartmental Committee on Experimental Geology and Geophysics succeeded in raising funds for a program of research, which included the construction and instrumentation of a new seismograph station on the grounds of the Harvard Astronomical Observatory in Harvard, Massachusetts. The 2 THE GEOLOGICAL SOCIETY OF AMERICA museum had long been unsuitable for sensitive instruments—the recordings showed principally the coming and going of classes and the traffic on Oxford Street. Leet designed and supervised the new installation in a vault excavated in bedrock. With the acquisition in 1935 of a full set of Benioff seismometers and accessory equipment, the Harvard station became a first-class unit. Leet kept the station in operation from 1933 to 1955 and published 45 bulletins of observation. The deliberate use of explosives to generate seismic waves for exploring near-surface geological structure had become a standard prospecting technique by the 1930s, and occasional accidental explosions had given seismologists opportunities for calibrating natural sources. Leet’s first published paper was entitled “Earth Vibrations from Dynamite Blasts.” In early collaboration with Maurice Ewing, he undertook seismic surveys in several quarries, where the results could be reasonably attributed to the properties of well- defined rock masses. This brought him into a mutually beneficial collaboration with quarry operators; soon all planned quarry blasts in New England were reported to Leet in advance. The travel times of the shocks from the quarries to the seismograph station were used to analyze the regional seismic structure, and Leet quickly found deficiencies in studies based on earthquakes alone. In particular, his determination of the velocity of propagation of compressional waves in the upper crust, at variance with then-accepted values, has been generally confirmed by later work. As consultant on seismic prospecting, Leet undertook widely scattered projects in the search for oil, gold, bauxite, and bed rock. An important early contribution to the technique of seismic exploration was the introduction of the “weathering correction,” an allowance for anomalous propagation in the near-surface rock. Operators of quarries and other blasting operations frequently have to deal with the complaints of householders who, after the shots, discover cracked plaster and broken window panes that they had not noticed before. Leet developed a portable seismometer that could be used for monitoring earth motion in the vicinity of explosions, and soon he was in demand as an expert witness in damage suits. His equipment was used by himself and by assistants for recording shocks on every scale, from small quarry shots to such gigantic explosions as the 1.3-million pound shot for the South Holston, Tennessee, dam of the Tennessee Valley Authority in 1949, and most notably, the “Trinity” nuclear explosion of July 16, 1945, in the Jornada del Muerto, New Mexico. Leet was a consultant or expert witness on blasting problems for numerous private and governmental agencies, among them the U.S. Corps of Engineers, the Isthmian Canal Commission, and manufacturers of explosives. He advised on safety regulations con­ cerning explosives for Connecticut, Massachusetts, New Hampshire, New Jersey, and New York. The pressure of consulting commitments led to the formation of a company, Leet Associates, which undertook studies of ground motion caused by blasting, traffic, and heavy machinery. In the debate on detection of underground nuclear explosions, he drew on his long experience with chemical explosions to advocate methods of discrimina­ tion, resembling in principle criteria now considered most useful. Besides papers on earth structure, microseisms, and vibrations from blasting, Leet wrote books notable for their clarity and excellent illustrations: Practical Seismology and Seismic Prospecting (1938), Earth Waves (1950), Vibrations from Blasting Rock (1960). Following Mather’s retirement, he gave the introductory course in physical geology for four years, and this led (with the collaboration of Sheldon Judson) to a highly successful introductory text, Physical Geology (1954 and later editions). There were also several popular books: Causes of Catastrophe (1948), (with his wife, Florence J. Leet) The World MEMORIAL TO LEWIS DON LEET 3 of Geology (1961), and Earthquakes—Discoveries in Seismology (1964). He gave lectures on “earth waves” at the Lowell Institute in 1946, and he was in demand for lectures on blasting effects and procedures at conventions of the crushed-stone industry. His ability to present technical matters in simple, intelligible terms, with a welcome dash of humor, made him a popular speaker and a successful witness in numerous court proceedings. Leet was married in 1925 to Frances Adeline Brokaw, by whom he had a daughter and a son; this marriage ended in divorce. In 1956 he married Florence Jane Anderson Blanchard, subsequently adopting a son and a daughter. Mrs. Leet, together with his children, survive him. He was a member or Fellow of the following: Sigma Xi, Phi Beta Kappa, the Seismological Society of America, the Geological Society of America, and the Society of Exploration Geophysicists. Denison University awarded him an honorary degree of D.Sc. in 1948. SELECTED BIBLIOGRAPHY OF L. D. LEET 1930 Earth vibrations from dynamite blasts: Am. Geophys. Union Trans., Reports and Papers 1929, p. 49-62. ------ (and Ewing, Maurice) Seismic propagation paths: Am. Inst. Mining Metall. & Petroleum Engineers Tech. Pub. 267, 18 p. 1931 Empirical investigation of surface waves generated by distant earthquakes [Ph.D. thesis]: Dominion Observatory Ottawa Pubs., v. 7, no. 6, p. 261-322. ------ Seismic prospecting: The Mil. Engineer, July-August. 1932 (and Ewing, Maurice) Velocity of elastic waves in granite: Physics, v. 2, no. 3, p. 160-173. 1933 Velocity of elastic waves in granite and norite: Physics, v. 4, p. 375-385. 1934 New recording vault of the Harvard Seismograph Station: Seismol. Soc. America Bull., v. 24, p. 47-50. ------ Some phases on explosion records in a 3-layered region: Gerlands Beitr. Geophysik, v. 42, p. 246-251. ------ Analysis of New England microseisms: Gerlands Beitr. Geophysik, v. 42, p. 232-245. 1935 The Provincetown, Massachusetts, earthquake of April 23, 1935, and data for investigating New England’s seismicity: Natl. Acad. Sci. Proc., v. 21, p. 308-313. ------ When the Earth shakes: The Telescope, v. 2, p. 102-108. 1936 Seismological data on surface layers in New England: Seismol. Soc. America Bull., v. 26, p. 129-145. 1937 A plutonic phase in seismic prospecting: Seismol. Soc. America Bull., v. 27, p. 97-98. 1938 Travel times for New England: Seismol. Soc. America Bull., v. 28, p. 45-48. ------ Longitudinal velocities in some weathered and unweathered carboniferous rocks: Seismol. Soc. America Bull., v. 28, p. 163-168. ------ Earthquakes in Northeastern America, July-December, 1937: Seismol. Soc. America Bull., v. 28, p. 169-176. ------ Practical seismology and seismic prospecting: New York, D. Appleton-Century Co., 430 p. 1939 Earthquakes, natural and artificial: Harvard Alumni Bull., June 9. ------ Ground vibrations near dynamite blasts: Seismol. Soc. America Bull., v. 29, p. 487-496. 1940 Adapting the Milne-Shaw Seismograph to registration of diurnal tilts: Seismol. Soc.