Landslides in the Sydney Basin - Geoscience Australia

More documents

Recommendations

Info

Seismic Hazard in SydneyProceedings of the one day workshopFigure 2 Coastal, West Head and Berowra Waters Lineaments (after Mauger et al, 1984; andNorman, 1986).The strike-slip faults and related structures, (including strongly developed shear zones, and possiblythe breccia features) have attracted some attention in recent years as they have been encounteredduring various large engineering projects in the region and have required special treatment.Slickensides patterning on the Mooney strike slips, and a similar fault at Normanhurst appearssurprisingly fresh (Branagan & Packham 2000), but no evidence is known of any movements onthese features, although such cannot be discounted. Norman (1986) and Whitehouse and Branagan(1998) discussed aspects of the “Coastal Lineament’ of Mauger et al (1984), the West HeadLineament and related structures (Figure 2), and more recently Ochs et al (2004) have produced acoloured map of the Sydney CBD showing mapping by Branagan, 1985; Norman, op. cit., withadditional more recent mapping. For further discussion on Sydney faulting see Branagan, 1977;2000a, and 2000b; Branagan and Norman, 1984; Branagan et al., 1987; Branagan and Mills, 1990).THE LAPSTONE STRUCTURAL COMPLEXAs mentioned earlier this structure marking the eastern edge of the Blue Mountains has been thefocus of attention by geophysicists as the most likely site for a reasonably large earthquake toaffect the Sydney region. Cotton (1921) presented information on the last reasonably largeearthquake here, in 1919, and there are some additional notes on this earthquake in his personalpapers (University of Sydney Archives).It is not proposed to discuss the geology of this region here. It has been covered to aconsiderable extent in Pedram, 1983; Rawson 1989; Branagan & Pedram, 1990, 2000), whichalso list many of the earlier papers.My only concern is to comment on the suggestion put forward by a number of speakers at therecent symposium on Sydney Earthquakes, and also in some papers in this volume (e.g.Fergusson, 2005) that the major movement on the Lapstone structure has been a thrust(variously suggested as high angle, and low angle) from the west. This has been based to some9
Seismic Hazard in SydneyProceedings of the one day workshopdegree on the suggested pattern of reverse faulting in the north-south striking faults in theLachlan Foldbelt to the west, and on the not too detailed seismic records obtained during coaland oil exploration in the region, (Herbert, 1989)..Figure 3. The Lapstone Structural Complex and its associated faults to the north and Southseem more consistent with normal down warping to the east, rather than thrust deformationfrom the west [after Bembrick et al, 1973].While the classical explanation of the formation of the originally named Lapstone Monoclinerequired an uplift of the Blue Mountains in the Late Pliocene (The Kosciusko Uplift) (Andrews,1910), Branagan (1975) suggested an alternative – down dragging of the Cumberland Basin duringthe period of sea-floor spreading at the beginning of the Tertiary. Herbert (op. cit.) attributed theorigin of the faulting to a late Triassic movement, during reactivation of underlying LachlanFoldbelt deformation, including some wrench faulting (see also Harrington, 1982).Although the author has recognised overturning of the steep Mt. Riverview Fault (east of theHawkesbury Lookout) and also of the Nepean Fault at Bents Basin (Branagan & Pedram, 1990) hebelieves these are very localised events. One problem with the west-dipping thrust suggestion is thatit seems only to be looking at the north-south fault forming the main scarp of the edge of the BlueMountains. I believe we also have to take into consideration the associated faults and flexures which10
Page 5 and 6: Seismic Hazard in SydneyProceedings
Page 13: Seismic Hazard in SydneyProceedings
Page 65:
Seismic Hazard in SydneyProceedings
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120:
show all

Landslides in the Sydney Basin - Geoscience Australia

Create successful ePaper yourself

Delete template?

Save as template?