Aftershock Forecast Communication for Risk Reduction

Science Center Objects

Studies of the communication of aftershock information during the Canterbury, New Zealand earthquake sequence conducted by Hazards Societal Consequences and Risk Communication team members and collaborators in New Zealand are examining the use of risk communication products, risk communication strategies, and risk-based decision-making. Focus groups and interviews were conducted with a range of roles (fig. 1) and members of the pubic in 2013 and public health professionals and emergency managers in 2016, six years after the sequence began.

Graph of Christ Church focus group participants

Figure 1. How much participants said they knew about aftershocks prior to the initiation of the sequence. (Credit: Anne Wein, USGS. Public domain.)

The Canterbury earthquake sequence was initiated by a moment-magnitude (Mw) 7.1 earthquake on September 4, 2010 in a rural area (fig. 2). By the end of 2012, 3,500 earthquakes over Mw 3.0 were designated as aftershocks. A Mw 6.3 earthquake on February 2011 in an urban area caused 185 fatalities in Christchurch and resulted in the closure of the central business district. This earthquake sequence included significant earthquakes on June 13 and December 23 in 2011 that triggered more earthquakes. Throughout the sequence, damages accumulated from recurrent shaking, liquefaction, and rock falls. Importantly, throughout the sequence GNS Science communicated aftershock forecasts providing an opportunity to study earthquake forecast communication needs.

Communicating aftershock risk: roles for reassuring the public 

Map of Christ Church, NZ aftershocks

Figure 2. Map of seismic activity near Christchurch, New Zealand, from 9/4/2010 to 4/11/2014 (Credit: GNS Science. Public domain.)