SEISMIC ACTIVITY IN THE SNOWY MOUNTAINS REGION AND ITS RELATIONSHIP TO GEOLOGICAL STRUCTURES
The blocks between the north-east trending lineaments are intersected also by two sets of secondary lineaments trending north-north-west and north-west respectively, without any noticeable difference in elevation between them. Many of the lineaments south of the Crackenback have a strikingly fresh appearance on air photos when compared with those on the Kosciusko block which appear to have been much more modified by erosion.
In interpreting the earthquake data the assumption was made that the movements occurred along existing faults rather than on fresh fractures. In view of the highly faulted nature of the region, this assumption appears reasonable. The problem is then to determine which of the many existing faults best fits the analytical data.
- The fault-plan analysis of the Berridale earthquake provides two alternative solutions.
- (1) A high angle reverse fault with a strike of about 50 deg., dipping about 55 deg. to the north-west. The strike is parallel to the Crackenback fault and the trace of the plane on the surface is along the north-eastern extension of the fault line.
- (2) A low angle reverse fault with a possible range of strikes between 40 deg. and east-west dipping about 35 deg. south~east or south.
The plane with strike 40 deg. meets the surface near Cabramurra and is parallel to a system of overthrust faults in the Tumut 1 power station locality, dipping at 30 deg. to 45 deg. south-east (Moye, 1959, Fig. 2). These faults may be part of the Khancoban-Yellow Bog fault system which forms the western margin of the zone of faulting along the western side of the Kosciusko block. Exploratory drilling near Khancoban has proved several faults, the largest a probable overthrust dipping 25 deg. to 30 deg. east with more than 80 feet of intensely crushed granite in the fault zone. The Khancoban-Yellow Bog system appears similar to the Tawonga fault of Beavis (1960), which has thrust granite over Pleistocene river gravels.
The overthrust faults in the Tumut 1 area appear to terminate against the powerful Tumut Pond fault (Moye, 1955) which dips steeply east, and it appears probable that the Khancoban-Yellow Bog fault system may also terminate against the Bogong Creek fault which is the southern extension of the Tumut Pond fault.
