The seismicity of the Gunning and surrounding areas, 1958–1961

Abstract

Between October 1958 and August 1961, 98 tremors were located within 100 km. of Yass, New South Wales, of which 52 were in the vicinity of Gunning. Many of the epicentres appear to be closely associated with granite boundaries and with known faults in the area. The Gunning epicentres form two arms of a wedge, and activity oscillates between these arms. Temporary cessation of activity at Gunning is often accompanied by an increase in the frequency of events in the surrounding areas, which suggests that the wedge acts as a “safety valve” for the region. Only one tremor was observed in the vicinity of Lake George. Fault plane analysis of the tremor gave a solution consistent with movement on a meridional high angle fault. It is inferred that recent movement on the Lake George Fault has been largely eliminated by the formation of the Gunning wedge.