The average recurrence interval for these large earthquakes is approximately 500 years, but it can vary widely. The shortest known interval between such earthquakes is about 200 years, and the longest is about 1,000 years. Part 2: Annual Probability Now that we have a recurrence interval (RI) for major earthquakes, we can now calculate the probability that one of these earthquakes will occur within any given year! Again- this is referred to as the "Annual Probability", or AP for short. QUESTION 4: Using Using your RI from Question 3, calculate the AP for the Magnitude 9 (M9 ) Cascadia earthquakes. Give your answer in 2 forms: A. Decimal probability: B. Percent probability