Intraplate earthquakes in Australia - Intraplate Earthquakes - page 29

Table 2.2 Ninetieth (90th) percentile fault scarp length
values for each neotectonic domain of Clark et al.
( 2012 ) and corresponding characteristic earthquake
magnitude (M W ) values determined using the scaling
relation of Leonard ( 2010 ) assuming a 45

dipping
fault and a seismogenic depth of 15 km.

°

Domain Length [90%] (km) Magnitude ( M W )

1 51 7.3

2 78 7.4

3 104 7.6

4 124 7.6

5 57 7.3

6 124 7.6

Population 101 7.6

In most regions of Australia the neotectonic catalogue is far from complete, the preser-
vation time of seismogenic features in the landscape is uncertain, and single-event scarp
length and slip data are largely absent. Without these data, key assumptions of the curve-
fitting approach to M max estimation described above are not satisfied. However, scarp length
variation across the continent ( Figure 2.5 ) does imply variation in characteristic earthquake
magnitude (and M max ).
Across Australia there is a strong positive skew in the length data distribution, with 90%
of scarps less than 101 km in length ( Figure 2.5 a ; Table 2.2 ) . Assuming a generic fault
dip of 45

and a seismogenic depth of 15 km (Collins et al ., 2003 ) , the 90th percentile
value for length corresponds to a value of M W 7.6 (cf. Leonard, 2010 ) ( Table 2.2 ) . Without
paleoseismic data on the longest scarps it is difficult to assess the validity of this estimate
as a value for M max . The longest scarp with paleoseismological evidence consistent with
entire length rupture is the 80 km long (

°

M W 7.4) Cadell Fault scarp in eastern Australia
(D4) (Clark et al ., 2007 , 2011a; McPherson et al ., 2012a ) ; however, rupture segmentation
is plausible for intraplate faults of several tens of kilometres in length or greater (e.g.,
Machette et al ., 1991 ) . The modal scarp length value of 53 km for all neotectonic features
( Figure 2.5 a ) corresponds to an earthquake of magnitude

M W 7.3.
Fault scarp length data for all individual domains ( Figure 2.5 e ) show a similar positive
skew to the aggregated population data distribution ( Figure 2.5 a ), which highlights the
same uncertainties with respect to possible fault segmentation. The 90% values for fault
length provide magnitude estimates in the range of M W 7.3-7.6 ( Table 2.2 ) . The values for
D1 and D3 are within error of the M max estimated by Leonard and Clark ( 2011 ) . Within
D2 the only known single-event scarp is 28 km long ( M W 6.8-6.9) and relates to the