|Session 8.1 - Seismic Hazard and Risk|
Probabilistic Earthquake Risk Assessment of Newcastle and Lake Macquarie, Australia: Part 1 – Seismic Hazard
Geoscience Australia is examining the risk to Australian communities from a range of geohazards which include earthquakes. As part of this project a detailed study of the risk posed by earthquakes to Newcastle and Lake Macquarie has been recently completed This paper is the first of two companion papers that detail the earthquake risk for the Newcastle and Lake Macquarie region.
Detailed analysis of local seismicity and geology was used to define a seismic source model consisting of three distinct source zones. This source model, amplification factors developed from local geotechnical data and an attenuation model developed for central and eastern North America were used in a probabilistic earthquake hazard assessment of the Newcastle and Lake Macquarie region. The results of this hazard assessment suggest that the region has a higher level of earthquake hazard than suggested by the current Australian Standard for earthquake loading.
Keywords: probabilistic earthquake hazard, Australia
Probabilistic Earthquake Risk Assessment of Newcastle and Lake Macquarie, Australia: Part 2 - Earthquake Vulnerability and Risk
This earthquake risk assessment focuses on economic losses caused by building damage from ground shaking. The hazard model is presented in a companion paper. A comprehensive field survey in the study region was conducted to document the vulnerability characteristics of a sample of more than 6,000 buildings. Australian damage models based on the capacity spectrum method were prepared and a modified HAZUS economic loss model was used. Damage and economic loss was calculated in a stratified Monte Carlo simulation of 1,200 events. The results were then aggregated to produce a loss curve for the study region. Natural variability was incorporated by allowing parameter values to vary in the simulations. Simulations of the 1989 Newcastle earthquake were compared with observed data.
Results show that the annualised loss for the study region is of the order of 0.04%, or around $11 million per year. The majority of the earthquake risk is from events with return periods in the range 50 - 1,000 years. The 1989 Newcastle earthquake had an economic impact with a return period of the order of 1,500 years. Differences in regolith distribution and thickness cause strong local variations in the risk. Timber frame buildings contribute about three-quarters of the total risk and unreinforced masonry buildings contribute a further one-sixth. The risk of casualties is low.
Keywords: risk, Newcastle, Australia, economic loss, vulnerability
In planning for a new town at Pegasus Bay, 30 km north of Christchurch, the risk of seismic liquefaction was considered and evaluated. URS New Zealand Limited evaluated the likelihood of liquefaction within the soils beneath the areas proposed for residential development. The liquefaction assessment was developed using the results of a geological site investigation and a seismic hazard evaluation based on a Probabilistic Seismic Hazard Assessment.
This paper describes how the results of recent earthquake hazard research were incorporated into the analyses and an assessment of design criteria for liquefaction mitigation in the proposed residential subdivision.
The study demonstrates that liquefaction could occur at the site during the 50 year design life of the houses and commercial buildings, and that current New Zealand codes and standards require that countermeasures be provided during the subdivision design phase. It also demonstrates that the Alpine Fault is not the most critical earthquake source in terms of the liquefaction effects predicted for the site. An assessment of the mitigation options demonstrates that it is possible to construct the subdivision with a lower risk of liquefaction than comparable sites in eastern Canterbury.
Keywords: liquefaction, risk, New Zealand, residential, mitigation