LACK OF DATA

Press, Volume LXXIII, Issue 22083, 4 May 1937, Page 8

LACK OF DATA

. —♦—■ — ■■ FINDING DIRECTION OF EARTHQUAKES TRACING OF SHOCKS NEAR CITY . For full data to be obtained of earthquakes felt in Christchurch, the centre of the shocks must be more than 700 miles from the city. The exact direction of those occurring closer to the city cannot be determined. This was ascertained yesterday when inquiries were made at the Magnetic Observatory of the direction of three slight shocks, two of which occurred on Sunday night, and the third yesterday morning. The shocks themselves (described as slight) were recorded at the observatory; but there is not the equipment there to give their direction. One instrument can record these shocks nearer the city than most earthquakes are; but to find the direction, three are needed—two to record the horizontal movements and one the vertical. The observatory is equipped with seismographic equipment enabling the direction and centre of the shocks more than 700 miles (approximately) distant from the city, and many valuable details have been ascertained of previous shocks felt by residents. It is only when the centres are so close to the city as to be outside the compass of the observatory's instruments that recourse has to be made to guesswork to fix a shock's origin. The shocks recorded in the last two days happened at 10.57 and 11 p.m. on Sunday, and 7.7 a.m. yesterday. -Although slight, they are described as being of such a rapid period, and so short, that they could be heard, and actually were heard. It is thought that their centre was nearer Christchurch than was that of the shock a few days before, which was considered to be near Akaroa. It is understood that the provision of additional equipment for the observatory is under consideration by the Department of Scientific and Industrial Research, which controls the work.