Landslides in the Sydney Basin - Geoscience Australia

Seismic Hazard in SydneyProceedings of the one day workshopMountain Lagoon, Burralow Swamp, Blue Gum Swamp, Shaws Creek Swamp and WarrimooSwamp). Other smaller unnamed swamps are also juxtaposed with the Kurrajong Fault System.Figure 4: Valley cross sections across selected easterly flowing streams passing through thenorthern Lapstone Structural Complex. a) Burralow Creek, b) Morgans Creek.Smaller BasinsMost of the smaller basins investigated were found to have a marked paucity of sedimentaccumulation at the fault, the exceptions being Burralow Swamp, Blue Gum Swamp, and possiblyShaw's Creek Swamp. Morgan Creek Swamp was found to contain no more than 3 metres ofsediment at the fault, Winmalee Creek only 5 metres, and Warrimoo Creek only about 3.5 metres.Sediments are generally organic fine to medium sands, with minimal clay or silt fraction. In eachcase the maximum sediment depths were found in localised regions adjacent to a very narrowswamp. Away from the swamp axes, bedrock depth decreases sharply and sandy surface sedimentsare considered to be primarily slope wash deposits. Wide, flat floored basins first identified from airphotos as large accumulations of sediment are in fact largely bedrock controlled.These reaches of low gradient are considered to be caused by the imposition of a local base level atthe fault, and it seems that the only effect of fault displacement is to maintain this perched base leveland thus hinder incision upstream. Sedimentation could only have taken place immediatelyfollowing major uplift events, whereas incision into the uplifted zone would act against theaccumulation of sediments. The lack of sediments in the fault angle depressions, combined with the"neotectonic" features of the basin morphology suggests a long term average condition whereincision largely matches uplift. This is an indication of slow and persistent uplift along theKurrajong Fault System.24