Intraplate earthquakes in Australia - Intraplate Earthquakes - page 32

Holdgate et al ., 2003 ; Sandiford, 2003a ) ( Figure 2.1 ) , which are manifestly amongst the
fastest deforming regions on the Australian continent (Sandiford, 2003a , b;Clark et al .,
2011a , 2012). Actively inverting basins of the Northwest Shelf (NWSSZ, Figure 2.1 ) are
also not associated with significant heat flow anomalies (cf. He and Middleton, 2002 ) .
Furthermore, the heat flow anomaly is most pronounced in the Cooper/Eromanga Basin, a
region sparse in seismicity ( Figure 2.1 ) and devoid of any known neotectonic features or
tectonic uplift.
At the sub-regional scale, a range of factors have been proposed to explain localisation
of historic seismicity. However, it seems clear that, on timescales of thousands to tens of
thousands of years, seismic potential is determined by factors at a scale much larger than a
single fault or region, and might instead relate more strongly to continetal-scale lithospheric
and crustal architecture, and the age of that architecture, as first proposed by Johnston et al .
( 1994 ) .
2.6.2 Structural architectural influences
In the context of structural architecture, intraplate seismicity worldwide is considered to
be concentrated at rifted margins (Stein et al ., 1989 ; Wheeler, 1995 , 1996; Sandiford
and Egholm, 2008 ; Cloetingh et al ., 2008 ; Etheridge et al ., 1991 ; Talwani and Schaeffer,
2001 ) , interior rifts [aulacogens] (Johnston, 1994 ; Wheeler, 1995 ; Gangopadhyay and
Talwani, 2003 ; Schulte and Mooney, 2005 ; Sinha and Mohanty, 2012 ) and at the margins
of cratons (e.g., Lenardic et al ., 2000 ; Mazzotti, 2007 ; Sloan et al ., 2011 ; Craig et al .,
2011 ; Mooney et al ., 2012 ) . A consequence of the relatively cold geotherm characterising
cratonic areas is that there is no decoupling between crustal and mantle deformation (Braun
et al ., 2009 ) . This implies that, over geological timescales, deformation of the upper crust
must be spatially uniform (e.g., Clark, 2010 ) , resulting in little strain localisation, and hence
minimal topography. Predictably, the historic record of seismicity in Australia is a poor
guide as to where localisation of seismic activity occurs over geological timescales, with
significant concentrations of seismicity occurring within cratons (e.g., SWSZ, Figure 2.1 ) ,
and far from extended crust or craton boundaries (e.g., parts of the SESZ; see also Adams
et al . [1992] and Rajendran et al . [1996]).
The major tenet of the Johnston et al .( 1994 ) SCR model - that extended crust is more
seismically active than non-extended crust, and that within the non-extended class non-
cratonic crust is more active than cratonic crust - appears to hold true for the Australian
neotectonic record if the uplift rate implied by vertical neotectonic fault displacement is
taken as a proxy for seismic activity ( Figure 2.4 d , f). Australian neotectonic data (Clark
et al ., 2011a , 2012) permit further sub-division of the extended and non-extended crustal
classes proposed by Johnston et al .( 1994 ) . In extended crust domains (e.g., D5, D6),
the age of major rifting appears to be important in terms of the record of neotectonic
activity. Paleozoic intracratonic rifts (e.g., the Fitzroy Trough [Drummond et al ., 1991 ] ;
cf. Figure 2.1 ) and passive margin components (e.g., Perth Basin [Crostella and Backhouse,