Tasmania’s Class IV Landslip Zoning

Considerable attention directed to landslip risk in Tasmania has resulted in the mapping of two categories, described as ‘recent-active’ and ‘ancient-fossil’ (or ‘old-inactive’), often termed Classes V and IV respectively. However little attention has been directed to elucidating why an area should be inactive. Recent investigation of two such sites suggests that some, perhaps many, of these areas have resulted from old seismic events rather than from changed climatic (precipitation) conditions, which profoundly reduces the risk for their use and development, as the return period for such a landslip in this region is most probably of the order of 10,000 years.