5 Plenary Session
A Time-dependent Update of the National Seismic Hazard Model for the Canterbury Earthquake Sequence
M.C. Gerstenberger, K. Berryman, A. Christophersen, B. Fry, G.H. McVerry, A. Nicol, J. Pettinga, M. Reyners, D. Rhoades, S. Steacy, M.W. Stirling, T. Webb & C. Williams
In November 2011, a three day expert panel workshop was held to consider a time-dependent update of the National Seismic Hazard Model (NSHM) for the Canterbury earthquake sequence. The ongoing sequence is in what is a moderate hazard area in the NSHM. With significant rebuilding effort required, a re-investigation of the NSHM was requested in terms of the NZ building code and other needs. Initially a time frame on the order of weeks was given for the update. On this schedule, modifications were made to both the ground motion prediction equation and to the source models. To re-investigate some of these decisions, a later expert panel workshop was convened.
The panel, made up of international and NZ-based scientists, was presented with 50 questions for which they were expected to provide weights. The questions were divided into five categories: 1) Time-dependent seismicity models, 1 and 50 year forecast; 2) Long-term seismicity models, 50 year forecasts; 3) Min and max magnitude of forecast models; 4) Depth distribution of forecast models; and 5) Variability in predicted ground motions. The experts were presented existing work done in response to the Canterbury sequence; the goal of the workshop was not to develop new ideas for immediate consideration in the NSHM. Understanding the uncertainty in the hazard was a primary goal of the workshop. To this end, the expert panel followed the methodology of Cooke where the responses of each expert were weighted based on answers to questions which targeted how well experts estimate the uncertainties in their own knowledge. Here we will present the model and forecasts that resulted from the workshop.
Presentation 136
A review of post-earthquake building control policies with respect to the recovery of the Christchurch CBD
B.D. Galloway & H.J. Hare
The Canterbury earthquake sequence was particularly disruptive for building owners and businesses located within the CBD. The initial damage to buildings in the relatively moderate September 2010 earthquake was surpassed by the significantly more damaging February 2011 event, challenging the way in which engineers have traditionally considered earthquake recovery.
Internationally, re-occupation of buildings following an earthquake has been based on the need to get businesses operating from buildings that are rapidly identified as having suffered minor structural damage. However, following the February 2011 earthquake, the shift in risk profile was reflected by limiting re-occupation unless it could be shown that the building also had a minimum capacity to resist earthquakes. This challenges the balance between continuing function and safety in the traditional post-earthquake evaluation process.
The timeframe for commencement of repairs has a significant impact on the speed of recovery. The importance of well defined regulations was highlighted in the well insured Christchurch building market, where legal arguments halted repairs in many instances. There is also a clear need for a modified, streamlined building consent process for the repair of earthquake damaged buildings.
This paper looks at the various building control policies enacted during the Canterbury earthquakes, and their effectiveness in aiding the recovery of the Christchurch CBD.
"Low risk does not equal no risk": understanding barriers to earthquake risk reduction in low seismic hazard areas
D.M. Johnston, C. Orchiston, C. Weaver, J. Becker, S. McBride, D. Paton, J. McClure & T.M. Wilson
Over the past few decades considerable effort has been devoted to improving our knowledge of seismic risk. Much of this work has resulted in improved seismic risk models and hazard maps, delineating variations in relative risk. However, disparities still are common between these expert assessments and the manner in which the public and authorities interpret and act on seismic risk information. Public understanding of and response to earthquake risk is determined by a range of factors, including scientific information, direct past experience of earthquakes, as well as the interaction of social, cultural, institutional and political processes. Many people in lower seismic hazard regions falsely interpret their relatively low seismic risk as a reason not to prepare. This phenomenon is common in many parts of the world, and it is a theme that will be explored in this paper within the context of Canterbury, New Zealand and eastern Washington, USA.