Rates of seismogenic landscape change in intraplate Australia

Australia is one of the lowest, flattest, most arid, and most slowly eroding continents on Earth (Quigley et al. 2010). The average elevation of the continent is only c. 330 m above sea level (asl), maximum local topographic relief is everywhere <1500 m (defined by elevation ranges with 100 km radii) and two-thirds of the continent is semi-arid to arid. With the exception of localized upland areas in the Flinders and Mt Lofty Ranges (Quigley et al. 2007a, Quigley et al. 2007b) and the Eastern Highlands (Chappell 2006, Tomkins et al. 2007), bedrock erosion rates are typically 1-10 m/Ma (Wellman & McDougall 1974, Bishop 1985, Young & MacDougall 1993, Bierman & Caffee 2002, Belton et al. 2004, Chappell 2006, Heimsath et al. 2010) (Fig. 1A). Despite this apparent geomorphological longevity (e.g. Fig. 1B), Australia has had a dynamic Neogene to Recent tectonic history. In the last five decades seven locations in intraplate Australia are documented as having experienced earthquakes large enough to rupture the ground surface (Clark et al. 2013). These earthquakes produced scarps up to 2 m high and 37 km long. Several hundred features consistent in form to the historic ruptures have since been identified Australia-wide (Fig. 2), mainly through interrogation of digital elevation data (Clark et al. 2011, Clark et al. 2012). Palaeoseismic analysis of these features indicates that periods of earthquake activity comprising a finite number of large events are separated by much longer periods of seismic quiescence. While morphogenic earthquake events in an active period on a given fault may be separated by a few thousand years (-0.4 mm/a uplift rates in an active period), active periods might be separated by a million years or more (long term uplift rates -0.001mm/a). A rupture sequence of this kind has the potential to have a dramatic effect on the landscape, especially in regions of low local topographic relief, such as the Murray Basin. For example, uplift across the Cadell Fault (see Fig. 2 for location) in the interval 70 - 20 ka resulted in the formation of a 15 m high and 80 km long scarp which temporarily dammed, and ultimately diverted the Murray and Goulburn Rivers (McPherson et al. 2012). Even in upland regions, the effects can be marked, as demonstrated by the formation of Lake George over the last ca. 4 Ma as the result of uplift on the Lake George Fault (Pillans 2012). Over timescales of millions of years, such activity, in combination with mantle-related dynamic topographic effects (Sandiford 2007, Sandiford et al. 2009, Quigley et al. 2010), might be expected to have a significant influence on the distribution and thickness of regolith over large areas.