USING THE RECURRENCE INTERVAL AND ANNUAL PROBABILITY TO TEACH ABOUT PAST, PRESENT, AND FUTURE GEOLOGIC HAZARDS IN CASCADIA

Recurrence interval and annual probability calculations are useful to geoscientists interested in forecasting geologic events that may pose hazards. These types of statistical analyses are often taught in introductory geoscience courses in the context of flooding, but can also be applied to earthquakes and volcanic eruptions. A general understanding of the recurrence interval and annual probability allows non-scientists to better understand media reports on past and present geologic events and plan and prepare for future geologic hazards. This is especially important for Pacific Northwest residents because Cascadia poses significant seismic and volcanic hazards due to the subduction of the Juan de Fuca Plate beneath the North American Plate.

Students enrolled in Linn Benton Community College's Geology 101 perform statistical analyses on seismic events and volcanic eruptions to calculate recurrence intervals and annual probabilities. This helps students understand the frequency of past geologic hazards in the Pacific Northwest and the likelihood of future occurrence. In this course, students first study geologic and geophysical data on how and why geologic hazards pose a threat to Pacific Northwest residents. Students then perform statistical analyses using actual scientific data posted on the web by the Pacific Northwest Seismic Network, US Geological Survey, and the Smithsonian’s Global Volcanism Program. These calculations provide excellent examples of geologic context in which to place mathematical concepts that are often lacking in introductory geoscience courses. Finally, students are given a project in which they must develop a rubric for determining risk in a hypothetical geologic setting similar to Cascadia that requires them to apply an understanding of recurrence interval, annual probability, and hazards related to an active margin.