Intraplate earthquakes in Australia - Intraplate Earthquakes - page 27

Most recent active period

Long term slip rate

Penultimate active period

Second penultimate
active period

~x

(b)

t 2 t 3

<2x

>10t >10t

t 1

Pliocene? present

Time

Figure 2.7 Generalised fault-slip diagram for Australian SCR faults based upon data from the Cadell
Fault (Clark et al ., 2007 ; McPherson et al ., 2012a ) . Three active periods of fault growth (earthquake
occurrence) are denoted by t 1 ,t 2 ,andt 3 . These active periods are relatively short-lived, and each is
composed of only a few ruptures ( c . < 6 events per active period). Inter-event times between successive
ruptures within an active period may range up to several thousands to several tens of thousands of
years. We adopt a characteristic earthquake rupture model based upon paleoseismic data from the
Cadell (Clark et al ., 2007 ; McPherson et al ., 2012a ) and Lake Edgar (Clark et al ., 2011b ) faults. Long
quiescent periods separate the active periods, and the length of the quiescent periods can range from
many tens of thousands of years to greater than a million years.

1997 , 2003; Clark et al ., 2008 ; Estrada, 2009 ) . In non-cratonic eastern Australia (D4),
recently acquired data on the Cadell Fault (Clark et al ., 2007 ; McPherson et al ., 2012a )
indicatemore frequent rupture, with up to sixmorphogenic events in the interval c . 70-25 ka.
It is inferred that three uplift events of similar magnitude had occurred on the Cadell Fault
prior to the diversion of the Murray and Goulburn Rivers at c . 45 ka (Bowler and Harford,
1966 ; Bowler, 1978 ) , suggesting that these events are likely to have been spaced thousands
of years apart, similar to the Meers and Cheraw faults in the western Central United States
(Crone and Luza, 1990 ; Crone and Machette, 1995 ) . This contrasts with the New Madrid
seismic zone in the intraplate Central United States, where sequences of large earthquakes
have occurred on average every 500 years for at least the last two seismic cycles in the
current active period (Tuttle et al ., 2002 ) . While Talwani and Shaeffer (2001) propose
a similar recurrence for earthquakes large enough to produce liquefaction in the South
Carolina Coastal Plain, it has not been determined whether their data reflect rupture on a
single fault or multiple faults. Quiescent intervals can be sufficiently prolonged (hundreds
of thousands to millions of years), in the western and central parts of Australia in particular,
that most or all relief relating to an active period might be removed by erosion prior to the
next active period (Crone et al ., 2003 ; Clark et al ., 2007 , 2008, 2011a).

2.5 Maximum magnitude earthquake

Large earthquakes are so infrequent in SCRs such as Australia that the data distribu-
tions upon which recurrence and M max estimates are based are heavily skewed towards