The Dominion Observatory, Wellington

Abstract

THE report for the year ended December 31, 1942, of the Dominion Observatory, Wellington (Bull. No. R28) deals chiefly with time service and seismology. During most of the year the control of the time service was greatly facilitated, enabling additional check time signals to be received from Greenwich and Washington. The clocks were seriously affected by local earthquakes on June 24, August 2 and December 2, but they suffered no permanent damage. The free pendulum was frequently disturbed by local earthquakes, and investigations showed that marked changes of rate are not due to defects in the clock mechanism but are associated with one or other of the following causes: (1) violent fluctuations in barometric pressure; (2) changes in the direction of local ground tilt; (3) local earthquakes. The severe outbreak of seismic activity in the Wairarapa district on June 24, 1942, followed by severe aftershocks on August 2 and December 2, has been already referred to, and a considerable number of subsidiary shocks also occurred, six hundred being recorded at Wellington. On June 27 a shock took place the epicentre of which was near White Island. The focal depth, 230 miles, was the deepest origin so far recorded in the New Zealand region. Another notable occurrence was a shock on November 1, centred in the south-east Tasman Sea, about 150 miles off the Milford Sound coast. Information is given in the bulletin on various other matters connected with the different seismographic stations and their instruments, on the research carried out on the distribution of earthquake activity in New Zealand, and on matters of general interest.