SEISMIC ACTIVITY IN THE SNOWY MOUNTAINS REGION AND ITS RELATIONSHIP TO GEOLOGICAL STRUCTURES
SEISMIC ACTIVITY IN THE SNOWY MOUNTAINS REGION AND ITS RELATIONSHIP TO GEOLOGICAL STRUCTURES
(With 1 PLATE, 9 Text-Figures and 3 Tables)
(Received 19th November, 1963. Read at Canberra, 25th September, 1962.)
ABSTRACT
Forty-four tremors which occurred in the Snowy Mountains of New South Wales during the years 1958–1962 have been accurately located, using a network of seismic stations operating in that area. The largest of these were a tremor of magnitude 5 north of Berridale in May, 1959, and one of magnitude 4 near Rock Flat in September, 1958. Fault plane analysis suggests that the former was caused by a high-angle thrust movement along the plane of the Crackenback Fault, while the latter may be associated with the Murrumbidgee Fault. These conclusions are supported by macroseismic data.
Twenty-one minor shocks occurred in the vicinity of the Berridale tremor, and their strain release pattern is that of an after-shock sequence. It is believed that they were produced as a result of secondary strains imposed by the original motion along an edge of the faulted block. The first motion data for these shocks is consistent with the hypothesis that the associated movements were transcurrent.
With the decrease of activity in the Berridale region, tremors became more or less random in the Snowy Mountains. The strain release curve obtained for these movements suggests a gradual rebuilding of the stress field following the Berridale shock.
I. INTRODUCTION
In the design of major engineering structures such as dams, consideration has to be given to the question of what allowance, if any, should be made to resist earthquake forces. At the time that the Snowy Mountains Scheme was initiated, information about the seismicity of the Snowy Mountains was very scanty and quite inadequate for engineering purposes, but there were indications that the region experienced minor tremors from time to time.
Griffith Taylor (1910) published a map of south-east New South Wales. by the Commonwealth Meteorologist showing a large number of localities in which earth tremors had been experienced during the previous 50 years or so. Fourteen such localities are shown in the Snowy Mountains region and vicinity, a density comparable with that in the active Dalton-Gunning area.
