Aspects of Decision-Making for Risk Reduction during the Prolonged Earthquake Sequence in Canterbury, New Zealand

An earthquake sequence is a prolonged natural hazard event. Scientists can dynamically forecast aftershock frequency within bounds of uncertainty. We examine how this capability can be used in decision-making to reduce risk during a period of heightened seismicity. We draw from experience of the Canterbury earthquake sequence initiated by a magnitude 7.1 mainshock on September 4, 2010 near the city of Christchurch, a population of 370,000. The sequence impacted the built, economic, social and natural environments of the Canterbury region.

We study the use of aftershock forecasts in decision-making across the roles of policy makers, emergency managers and responders, critical infrastructure providers, insurers, communication officers, scientists, and the public. We held focus groups and interviews involving 53 participants using a semi-structured message centered approach in May and June of 2013. Transcripts from the focus groups and interviews were thematically coded using qualitative analysis.

Responses to a pre-questionnaire suggested that aftershock information for decision-making increases slightly in importance throughout the four phases of a disaster – mitigation, preparedness, response and recovery. We summarize our findings from this research, including

• the use and barriers to the use of aftershock forecasts in decision-making across the disaster phases by roles
• conflicts of interest that arise in the decision-making hierarchy
• challenges with providing and using forecasts during a prolonged event.

Finally, we reflect on implications for Operational Earthquake Forecasting and how our findings may be generalized to other prolonged hazards.