SEISMIC ACTIVITY IN THE SNOWY MOUNTAINS REGION AND ITS RELATIONSHIP TO GEOLOGICAL STRUCTURES
Fig. 4. Fault plane solution for Berridale earthquake.
Fig. 5. Fault plane solution for Flat Rock earthquake.
The plane south of the epicentre must strike close to both Wambrook and Jindabyne, otherwise the orthogonality criterion would place the other plane beyond Cabramurra. The trace of this plane is thus represented by US. For reasons advanced in the preceding section, it then appears probable that US represents the trace of the fault plane. In Section V this choice will be supported by geological evidence. PQ and XW are then the azimuths of the intersection of the assumed fault plane with the cone of intersection of the Pn rays.
The azimuth of the auxiliary plane may lie between the directions of Cabramurra-Canberra and an approximately E-W direction (the latter on account of geometrical limitations), and if the simplest solution of non-oblique slip is taken, will be RV. In this position the auxiliary plane does not intersect the Pn cone and consequently no zones separated along azimuths exist to the south-east of the fault plane.
On the assumption that US rather than RV is the trace of the fault plane, the solution is that of a high-angle reverse fault with a strike of about 50 deg. and dipping about 55 deg. to the north-west.
In the above case the assumed fault plane is very closely determined by the data; for the case of Rock Flat, on the other hand, the situation is quite imprecise. First-motion data are available only from the four Snowy Mountains stations, Canberra, and Melbourne. All recorded dilatations. This is not sufficient information for the formal derivation of a solution, but, nevertheless, various faulting hypothesis can be tested.
