SEISMIC ACTIVITY IN THE SNOWY MOUNTAINS REGION AND ITS RELATIONSHIP TO GEOLOGICAL STRUCTURES
On both the eastern and western sides the Kosciusko block is bounded by a zone of nearly parallel faults and warps trending northerly on the eastern side, and north-north-easterly on the western side. These result in a series of relatively long narrow fault blocks stepping down from the Kosciusko plateau to an altitude of about 3,000 feet on the east and 1,000 feet on the west. Relatively depressed blocks form grabens along the Jindabyne valley to the east, and along the Geehi-Tom Groggin depression to the west.
The southern part of the Kosciusko block is broken into a mosaic of minor fault blocks by two intersecting sets of faults expressed on the surface by strong lineaments, but without much vertical or lateral displacement between blocks. One set has a north-north-west trend, examples being the valleys of the Guthega River, Munyang River, Finns River, Tolbar Creek, and Burrungubugge River. The other set has a general north-east trend parallel to the Crackenback, as for example the upper Snowy-lower Gungarlin valleys.
The Crackenback valley forms a gorge 2,000 feet deep which runs north-east in a straight line for 22 miles from the Great Divide as far as the escarpment forming the western edge of the Jindabyne valley. On aerial photographs it is the strongest lineament in the whole of the Snowy Mountains region (Fig. 10). The lineament continues south-west through Dead Horse Gap on the Divide down Dead Horse Creek a further six miles into the upper Murray. There is a fall in plateau summit levels of about 1,000 feet across the Crackenback valley presumably due to faulting.
Powerful lineaments occur further to the south-east parallel to the Crackenback along Wollondibby Creek-Little Thredbo and along the Mowamba River dividing the country into blocks stepping dowm to the south-east. Like the Crackenback, these lineaments also die out along the western side of Jindabyne valley, but continue less strongly to the south-west across the headwaters of the Murray River into Victoria.
Crohn (1950) shows two inferred faults with about the same trend which appear to be the extension of this system. The first extends from the upper Murray up Limestone Creek along the Tambo River to about Mt. Baldhead stepping down 500 feet also to the south-east, and the second between Ensay and Swift’s Creek with a strong escarpment 400 to 500 feet high facing south-east.
