AFTERSHOCK FORECASTS FOLLOWING THE M7.0 ANCHORAGE, ALASKA EARTHQUAKE

The 2018 M7.0 Anchorage earthquake generated several “firsts.” It was the first large urban earthquake with intense shaking to strike the United States since the M6.7 Northridge earthquake in 1994. The 2018 earthquake also saw the release of several new USGS communication products: 2PAGER, which provides quick estimates of a variety of earthquake impacts; a new ground failure product that estimates the likely extent of landslides and liquefaction; and an aftershock forecast. This paper focuses on the development of the aftershock forecast, and on how it was communicated by the media and received by users.

The aftershock forecast, part of the field of Operational Earthquake Forecasts (OEF), builds on developments in forecasting that initiated with publication of the Reasenberg and Jones model in 1988. Challenges in this field include the refinement of forecasts using various algorithms and models, and the communication of such forecasts to a variety of people with different educational backgrounds and informational needs. Our challenge was to develop a template that can be released within the first two hours of a +M5.0 earthquake in most regions of the U.S., with format and contents that make it easy to understand, useful to a variety of audiences, easy to update, and still technically robust enough for use by scientists and engineers.

Our study focuses on the development of an aftershock forecast template, which we did using results from social science research combined with experiences from scientists who have communicated such forecasts operationally overseas. We also explore early insights from media and social media about how the information was communicated and how it was used by various groups of people. Finally, we explore proposed improvements to the USGS aftershock forecast, including visualizations and tables.