Intraplate earthquakes in Australia - Intraplate Earthquakes - page 30

greater than 100 km long Williamstown-Meadows Fault (Clark and McPherson, 2011 ) .
However, paleoseismological evidence exists elsewhere in D2 for very large single-event
displacements ( > 7m-Quigley et al ., 2006 ; Reid, 2007 ; Clark et al ., 2011a , 2012),
consistent with modeled event magnitudes of M W 7.3-7.5 (Somerville et al ., 2008 ) . Very
long 90th percentile values for D3 and D4 require validation in terms of equivalence to
M max as these scarps also tend to have accumulated significant neotectonic throw (tens of
metres), implying multiple morphogenic events. The dominance of folding as opposed to
discrete faulting in D5 has thus far prevented estimation of single-event rupture lengths and
displacements (Clark et al ., 2011a ) .
As expected, overall indications are that the historic catalogue of seismicity significantly
underestimates the large earthquake potential (and, by proxy, M max ) in most regions of
Australia. To a first order at least, the sub-division of the continent into domains on the
basis of geology and tectonic history (Johnston, 1994 ; Clark et al., 2011a , 2012) provides
useful insights into variations in faulting character that can facilitate the interpretation of
the neotectonic and historic catalogues. The use of fault-length data from the neotectonic
catalogue provides reasonable preliminary estimates of M max when applied in conjunction
with appropriate scaling relations (e.g., Leonard, 2010 ) . Analysis of the current neotectonic
catalogue for Australia suggests that a range of M max values of M W 7.0-7.6 could

reasonably encompass all geological and tectonic settings continent-wide (Clark et al .,
2011a , 2012; Leonard, 2012 ; Burbidge, 2012 ) .

2.6 Implications for SCR analogue studies: factors important
in earthquake localisation

Analogues between the Australian neotectonic domains (Clark et al ., 2011a , 2012) and
SCR crust elsewhere in the world (cf. Johnston, 1994 ) are readily apparent. For example,
poly-phase deformation of a compressional nature is a common feature in the post-rift
evolution of many extended passive margins and rifts (D5/D6 analogues) (van Arsdale,
2000 ; Balasubrahmanyan, 2006 ; Cloetingh et al ., 2008 ) . Archean cratonic nuclei fringed
by Paleoproterozoic mobile belts (D1 analogues) make up a large portion of the geology of
Peninsular India (Kroner and Cordani, 2003 ) and North America (Hoffman, 1989 ) . Meso-
andNeoproterozoicmobile belts involved in the accretion of the supercontinent Rodinia (D3
analogues) are found worldwide (e.g., Collins and Pisarevsky, 2005 ; Cawood and Buchan,
2007 ) , as are Phanerozoic accretionary terranes associated with the amalgamation of the
supercontinent Gondwana (D4 analogues) (e.g., Hoffman, 1989 ) . The temporal clustering
of morphogenic earthquake events seen in studies on Australian faults (Quigley et al ., 2010 ;
Clark et al ., 2011a , 2012) also appears to be mirrored in the Central and Eastern United
States (Crone and Luza, 1990 ; Crone et al ., 1997 ; Cox et al ., 2006 ) . Inferences made
regarding mechanisms responsible for localising intraplate seismicity in Australia might
then be assessed in terms of their crustal and lithospheric setting, and tested on analogous
crust elsewhere in the world.