Interpretations of aftershock advice and probabilities after the 2013 Cook Strait earthquakes, Aotearoa New Zealand

Abstract

Probabilistic statements can be a valuable tool for natural hazard risk communication, including forecasts. However, individuals can have a poor understanding of such forecasts. Their interpretations of event likelihoods are often distorted. This causes them to think the event is more likely towards the end of the time window and discount the risk today. We investigated the use of an ‘anchoring’ time statement to reduce this bias. We did this via a survey after the 2013 Cook Strait earthquakes, near Wellington, Aotearoa New Zealand. Participants rated their interpretations of likelihoods for an immediate aftershock forecast, and for an earthquake in the future. The anchoring time window statement lessened the skew in interpretations for the short (24 hour to within 1 week) aftershock forecast statement. However, the skew still existed for the longer future earthquake forecast (7 days to within 1 year). We found that those who felt the shaking or had emotional reactions (nervousness, fear, alertness) during the earthquakes were more likely to think that future events were likely. Gender was found to significantly influence results, with women rating higher levels of information concern and anxiety. Women also recorded higher perceived likelihoods for the immediate aftershock forecast. Our research shows the importance of ‘anchoring’ time windows within a forecast to encourage immediate preparedness actions. The findings support effective crafting of these forecasts and warnings.