Intraplate earthquakes in Australia - Intraplate Earthquakes - page 22

et al ., 2003 ; Clark et al ., 2008 ) , (3) Dumbleyung and (4) Lort River (Estrada, 2009 ) , and
(5) Lake Edgar (Clark et al ., 2011b ) . These features range from 30 to 40 km in length (cf.
Clark, 2010 ) with maximum single-event vertical displacements in the order of 1.2-3.1 m.
Recurrence data for morphogenic earthquake events is restricted to the most recent one to
three events on each fault, and indicates inter-event intervals of

10-40 ka ( Figure 2.6 ) .
Non-cratonic (D2, D4) and extended (D5, D6) domains are characterised by compara-
tively large vertical displacements ( Figure 2.5 d , f), which scaling relationships (e.g., Wells
and Coppersmith, 1994 ; Leonard, 2010 ; Leonard and Clark, 2011 ) imply must have built as
the result of multiple seismic cycles. There is, therefore, less certainty as to whether scarp
lengths are representative of single-event ruptures, or are the product of segmented rupture.
A positively skewed fault-length data distribution ( Figure 2.5 a ) might plausibly reflect seg-
mented rupture behaviour. The longest fault scarp in non-cratonic eastern Australia (D4)
that has been subject to paleoseismological investigation is the Cadell Fault ( Figure 2.4 ) .
Evidence from abandoned fluvial and tectonic landforms (e.g., Bowler and Harford, 1966 ;
Rutherfurd and Kenyon, 2005 ) is consistent with seismic rupture of the entire 80 km scarp
length, potentially involving 2-4 m of uplift (Clark et al ., 2011a ; McPherson et al ., 2012a ) .
While the timing of individual seismic events is poorly constrained, the average recurrence
interval within the 70-20 ka active period (assuming full-length rupture) may have been
as little as 8 ka. Within D2, single-event displacement values of 1.8 m (1.5 m vertical)

have been recorded on the Alma andWilliamstown-Meadows faults (Clark and McPherson,
2011 ) . The latter fault, which has a mapped length of over 100 km, is associated with a
25 km long single-event scarp.

2.3.2 The influence of crustal type and character on seismic activity rates

Given that the compressive nature of the Australian stress field (Hillis and Reynolds, 2003 )
results in a predominance of dip-slip faulting (Leonard et al ., 2002 ) , long-term qualitative
seismic activity rates across the continent might be assessed in terms of neotectonic uplift
of the landscape. With respect to the morphogenic earthquake record, this is a function of
neotectonic fault slip rate and density.
Long-term slip rates estimated for faults in the cratonic western part of the continent
(D1, D3) are typically in the order of 1m/Ma(Clark et al ., 2008 , 2012; Hillis et al .,

2008 , ), which is equal to or less than the extant erosion rates (Bierman and Caffee, 2002 ;
Belton et al ., 2004 ; Chappell, 2006). These long-term slip rates are consistent with the
low-relief landscape, and contrast with uplift rates estimated from the last several decades
of seismicity in the SWSZ, which have been suggested to be in the order of 10 m/Ma (Braun
et al ., 2009 ) .
Long-term slip rates in non-extended, non-cratonic eastern Australia (D4) are less well
constrained. The slip rate on the Cadell Fault, averaged over the life of the current stress
field (i.e.,

10 m/Ma (Clark et al ., 2007 ) . New data from
the Lake George Fault (Pillans, 2012 ) within the Eastern Highlands ( Figure 2.4 ) indicate a

10 Ma), has been estimated at