A different way of thinking about seismic risk
A call for debate
Seismic risk has traditionally been approached using probabilistic analysis. This dilutes the potential impact of low probability, extreme events that may lead to severe consequences including excessive land damage, building damage, injuries and death. The communication of risk in probabilistic terms is also not clearly understood by most audiences. Further, it is evident that few building developers, owners and users have a good understanding the implications of this and the capacity design of buildings, which may not be repairable after a severe event.
There is also an adverse impact on planning and land use, where decisions that may affect many people are based on a limited view of adverse outcomes such as liquefaction, lateral spread and slope stability in severe earthquakes.
A different way of thinking about seismic risk is proposed. An approach of using scenarios derived from a combination of deterministic as well as probabilistic thinking would prompt consideration of impacts over a range of events. This would allow full consideration of which outcomes are clearly not acceptable and which are. This may facilitate planning for both private and public sector, with a common understanding that is relatively easily communicated to both experts and lay people.
This risk evaluation framework would also facilitate consideration of mitigation, by bringing focus on unacceptable outcomes of severe events that are currently obscured by pure probabilistic analysis. This was missing in Christchurch, which experienced the sort of event we can readily anticipate and should actively plan for in other parts of New Zealand.
This would help us avoid future red zones and excessive damage and demolition. It will inform development of building codes and standards and will help us evaluate risk and provide resilience and redundancy across the range of interconnected infrastructure networks.
Informed debate is needed with key decision makers to discuss the underlying objectives of our regulation and how these may be better met by such an approach, without engineers allowing themselves to be trapped in past thinking and assumptions.
Government of New Zealand (2006). “Building (Specified Systems, Change of Use, and Earthquake-prone Buildings) Regulations 2005, Reprint as at 12 January 2006”. New Zealand Government, Wellington, NZ.
SNZ (2016). “NZS1170.5:2004 Structural Design Actions – Part 5 Earthquake Actions – New Zealand, Incorporating Amendment No 1”. Standards New Zealand, Wellington, NZ.
SNZ (2016). “NZS1170.5 Supp 1:2004 Structural Design Actions – Part 5 Earthquake Actions – New Zealand Commentary, Incorporating Amendment No 1”. Standards New Zealand, Wellington, NZ.
Government of New Zealand (2017). “Building Act 2004, Reprint as at 1 December 2017”. New Zealand Government, Wellington, NZ. http://www.legislation.govt.nz/act/public/2004/0072/141.0/DLM306036.html (Accessed August 2019).
NZBC (2018). “New Zealand Building Code, Clause B1 Structure, Amendment 16, April 2018”. New Zealand Government, Wellington, NZ.
NZSEE (2017). “The Seismic Assessment of Existing Buildings, Parts A, B and C”. Prepared by Jury R et al. for MBIE/NZSEE/SESOC/NZGS.EQC. New Zealand Society for Earthquake Engineering, Wellington, NZ.
SNZ (1984). “NZS4203:1984 Code of Practice for General Structural Design and Design Loadings for Buildings”. Standards Association of New Zealand, Wellington, NZ (Withdrawn).
SNZ (1992). “NZS4203:1992 Code of Practice for General Structural Design and Design Loadings for Buildings”. Standards Association of New Zealand, Wellington, NZ (Withdrawn).
GNS Science (2019). “GeoNet Geological Hazard Information for New Zealand, Historical Events”. https://quakesearch.geonet.org.nz/ (Accessed August 2019).
GNS Science (2019). “New Zealand Active Faults Database”. https://data.gns.cri.nz/af/ (Accessed August 2019).
Auckland Regional Council (1997). “Auckland Engineering Lifelines Project Stage One Report”. Auckland Regional Council Technical Publication No 116, Auckland, NZ.
Sarrafzadeh M, Elwood KJ, Dhakal RP, Ferner H, Pettinga JD, Stannard M, Maeda M, Nakano Y, Mukai T and Koike T (2017). “Performance of Reinforced Concrete Buildings in the 2016 Kumamoto Earthquakes and Seismic Design in Japan”. Bulletin of the New Zealand Society for Earthquake Engineering, 50(3): 394-435. DOI: https://doi.org/10.5459/bnzsee.50.3.394-435
Chiaro G, Alexander G, Brabhaharan P, Massey C, Koseki J, Yamada S and Aoyagi Y (2017). “Reconnaissance Report on Geotechnical and Geological Aspects of the 14-16 April 2016 Kumamoto Earthquakes, Japan”. Bulletin of the New Zealand Society for Earthquake Engineering, 50(3): 365-393. DOI: https://doi.org/10.5459/bnzsee.50.3.365-393
Bradley BA (2015). “Benefits of Site-Specific Hazard Analyses for Seismic Design in New Zealand”. Bulletin of the New Zealand Society for Earthquake Engineering, 48(2): 92-99. DOI: https://doi.org/10.5459/bnzsee.48.2.92-99
NZSOLD (2017). “New Zealand Dam Safety Guidelines”. New Zealand Society on Large Dams, https://nzsold.org.nz/2017/08/31/the-new-zealand-dam-safety-guidelines/2015 (Accessed August 2019).
Copyright (c) 2019 John Hare
This work is licensed under a Creative Commons Attribution 4.0 International License.