H.—34.

Seismograph Stations. —The following table shows the number of earthquakes recorded at the various seismograph stations for each month of the year 1939. The stations are classified according to the type of seismograph. Class I stations possess sensitive local recorders of Wood-Anderson type ; Class 11, local strong-motion recorders, mostly of Jaggar type ; and Class 111, teleseismic instruments of varying sensitivity.

The installation of a Wood-Anderson seismograph at Tuai has proved of great value in locating and studying earthquake activity in and around the North Island. The Jaggar station at Stratford was closed on 31st March. Other stations have carried on as previously. , Records from Rotorua were interrupted at times owing to clock trouble. Towards the end of December recording was interrupted at both Tuai and New Plymouth owing to technical trouble. In August the Milne-Shaw seismograph, No. 36, was lent to the Magnetic Observatory, Christchurch, for the purpose of investigating microseisms and for testing the conditions for seismographs of high sensitivity at Greymouth and Monowai. The Imamura strong-motion seismograph at Wellington was overhauled in October, and re-erected in the Centennial Exhibition. Measurement of Tilt— The Ishimoto tiltometer has continued recording the E-W component of tilt; the N-S component being recorded by the Milne-Shaw seismograph. Tilt records are now available over a number of years, and are being subjected to an intensive study. Seismologieal Research. -The following research work has been pursued during the year by various members of the staff: — Mr. R. C. Hayes —(1) Correlation of earthquakes and rainfall in New Zealand. (2) Study of local earthquake record types. (3) The direction of the initial movements of earthquakes as recorded at Wellington. Mr. W. M. Jones—(l) Investigation of local earthquake waves and crustal structure. (2) Results of Geophysical Survey work in North Auckland. Mr. C. N. M. Watson-Munro —(1) Measurement of vibrations duo to the Printing Office machinery, using some of the Geophysical Survey apparatus. This work was undertaken at the request of the Public Works Department, which was furnished with a comprehensive report on the results. Assistance in seismologieal research has been given to the following voluntary workers : Dr. K. E ■ Bullen, of Auckland ; Dr. L. Bastings, of Wellington ; Mr. R. D. Thompson, of Stratford ; and Mr. L. A. C. Warner, of Wellington. General.—Three papers, by R. C. Hayes, on seismology in New Zealand and the Pacific, were sent to Dr. B. Gutenberg for presentation at the Sixth Pacific Science Congress, at San Francisco, in July-August, 1939. A report on seismology in New Zealand during the years 1936-1937-1938 was prepared and forwarded to the Secretary of the Seismologieal Section of the International Geodetic and Geophysical Union for the Seventh General Assembly of the Union at Washington in September, 1939. A number of original seismograms were lent to seismologists abroad, for the study of special earthquakes. Workshop. The workshop continued to carry out instrument work for this Observatory, as well as for other branches of the Department. In addition to maintenance-work, a new seismograph recorder was completed early in the year. , In September the control of the workshop was transferred to the newly formed Physical Testing Laboratory, and the staff and equipment moved to more spacious premises in Molesworth Street during November.

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Stations. Jan. Fell. Mar. J Apr. May. June. July. Aug. Sept. Oct. Nov. j Deo. j Totals. Glass I. Tuai .. 14 18 25 16 14 87 New Plymouth .. 16 13 17 13 10 8 13 8 9 14 19 9 149 Wellington .. ..31 23 19 25 17 15 22 19 24 23 28 19 265 Christchurch ..24 6 9 9 4 3 12 22 10 11 12 3 125 Class II. Rotorua .. .. 0 0 0 10 0 3 0 13 Tuai .. .. 0 1 0 0 1 0 1 3 Stratford .. .. 0 0 0 ■ . • • • • ■ • • • • • • • • • ■ ■ 0 Hastings .. ..1 6 0 I 3 0 3 3 5 2 4 1 -9 Bunnythorpe ..01000 0 100202 6 Takaka .. ..000 0 00000000 0 Greymouth .. 0 0 0 0 0 0 0 0 0 0 0 0 0 Monowai .. 22 6 3 2 0 0 3 1 3 6 1 0 47 Glass III. Arapuni .. ..4287623559 13 14 78 Wellington .. ..32 25 22 27 29 20 19 27 8 12 14 19 254 Christchurch .. 36 22 24 33 29 16 10 6 3 22 18 18 237 Chatham Islands ..1 00002000003 6