A seismic reflection traverse was surveyed across the Perth Basin, Uestern Australia, between the townships of Rockingham and Mundijong. It was planned in order to give information regarding the depth of the Basin and its structure adjacent to the Darling Scarp. Seismic refraction traverses were surveyed to give the longitudinal velocities in the near surface granitic gneisses on the Precambrian Shield, and in the Cardup Series (Proterozoic) abutting the Darling Scarp. At least 14,000 ft of sediments are indicated in the deepest part of the Basin but there is no clear seismic evidence of what a maximum thickness might be.
Seismic reflection results indicate that the sediments on the west of the Darling Scarp abut the older rocks on a plane that dips at about 60 degrees to the west and that cuts the surface some distance in front of the present position of the scarp. This suggests that the Darling Scarp at Eundijong is the surface expression of a normal fault. However, the presence of reflection alignments east of this postulated fault plane, and thus apparently arising within the granitic gneisses, is contrary to the fault hypothesis. The true nature of the tectonic features is thus unresolved. Seismic results indicate that faulting occurred within the Basin and such faulting may have completed closure of possible oil traps. Further seismic investigation of the faults and associated structures is recommended.
