Risk Frontiers’ new earthquake model shows reduced losses for Australia

Valentina Koschatzky and Paul Somerville

We are excited to announce we have released our new probabilistic earthquake loss model for Australia, QuakeAUS 6.0. The updated model, developed by Dr Valentina Koschatzky with input from Risk Frontiers’ Chief Geoscientist, Dr Paul Somerville, incorporates Geoscience Australia’s recent revision of the Australian Earthquake Catalogue (Allen et al., 2017), which has more than halved the rate of earthquakes exceeding 4.5 in magnitude.  The main features of the new model are:

  • New Distributed Earthquake Source Model (based on RF analysis of the new GA catalogue – 2018)
  • Inclusion of an Active Fault Model
  • Updated Soil Classification (McPherson 2017)
  • Updated Soil Amplification Model (Campbell & Bozorgnia 2014)
  • Updated Variable Resolution GRid (VRG), Exposure & Market Portfolio (Gnaf 2018 + Nexis 9)
Distributed Earthquake Source Model

A new distributed earthquake source model was implemented using the revised Geoscience Australia earthquake catalogue from the National Seismic Hazard Assessment (NSHA18) project (Allen et al., 2017), which will be released by GA in September 2018.

Active Fault Model

The active fault model incorporates earthquakes on potentially active faults based on GA’s Neotectonic Feature Database (Clark, 2012).  These geologically identified rare and large prehistorical events are not represented in the short historical record of earthquakes in Australia.

Updated Soil Class and Soil Amplification Models

We implement the Australian Seismic Site Conditions MAP (ASSCM) released by GA in June 2017 in the calculation of site amplification. This is a significant revision and upgrade of the previous map published in 2007. The site amplification model has also been updated (Campbell & Bozorgnia, 2014).

Variable Resolution Grid

We implemented the latest GNAF (2018) and Nexis (2018 V.9) data in the design of an updated variable resolution grid (VRG) and market portfolio to best reflect the current property exposure across all lines of business.

Effects on Losses

Compared with the previous version of Risk Frontiers’ QuakeAUS model, losses have generally decreased across the country (average annual loss is 80% and the 200-year return period loss is 63% of former values on a testing national portfolio) due to the update of the historical earthquake catalogue. This effect is partly mitigated at longer return periods in regions where active faults have now been modelled. The changes in losses are not uniform spatially or temporally. Sydney, for example, shows a drastic reduction in losses at every return period, while the losses for Melbourne show a slight increment. In other areas such as Adelaide the losses are lower than in the previous model for short return periods, but that trend is reversed for return periods greater than 1,000 years

Reference

Allen, T., J. Griffin, M. Leonard, D. Clark and H. Ghasemi (2017). An updated National Seismic Hazard Assessment for Australia: Are we designing for the right earthquakes? Proceedings of the Annual Conference of the Australian Earthquake Engineering Society in Canberra, November 24-26, 2017.

Campbell, Kenneth & Bozorgnia, Yousef. (2014). NGA-West2 Ground Motion Model for the Average Horizontal Components of PGA, PGV, and 5% Damped Linear Acceleration Response Spectra. Earthquake Spectra. 30. 1087-1115.

McPherson, A. A. (2017). A Revised Seismic Site Conditions Map for Australia. Record 2017/XX. Geoscience Australia, Canberra. DOI

Clark, D. (2012). Neotectonic Features Database. Commonwealth of Australia (Geoscience Australia).