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C~ r 1 LJ J7.2.1 Probability Based UpoB Factor of Safety ABalyses. For a detailed discussion of probabilities assigned to landslide outcomes based upon the factor of safety against sliding determined by slope stability analysis, refer to the 1999 Addendum. The limit equilibrium factor of safety from 2000 to 2001 only changed by 1%. Hence for 2001, the landslide probabilities based on slope stability analysis aze essentially the same as those computed in 1999 and 2000. J7.2.2 Probability Based UpoB Observed Landslide MovemeBts. For additional discussion oD probabilities assigned to landslide outcomes based upon observed rates of movement in the slide and landslide velocity classification, refer to the 1999 Addendum and the procedures discussed in that Addendum. Velocity of Landslide. The average velocity of the landslide through the head, body and toe in the Spring of 2001 was 0.01 feeVyeaz. Landslide Velocity Class (LVC) and Landslide Outcomes. The IandsGde movement and coaesponding LVC for the spring of 2001 is LVC=1.5 based on Figure I5-12 of Appendix J5. Coefficient of Variation of Velocity Class. The mean LVC was assumed to have a coefficient of variation of 30 percent. 2001 Probabilities. Probabilities were revised based upon 2001 movement data with a movement of 0.01 feet/yeaz and a mean LVC of 1.5. The revised LVC outcomes were normalized against this new mean and the azeas these values occupied under the normal distribution curves were computed. These azeas correspond with the probabilities assigned to each outcome. Probabilities of outcomes using 2001 conditions are summarized in Table J3, column 6. In general based on 2000-2001 movements, the probability of future extremely slow movement has again increased and the probability of rapid or slow movement has again decreased. Barr Engineering Company PCDOCS1230503/CAK December 75, 2000 15 Appendix J 4001 Addendum to 1997/98 Lendsllde Correetlva Meaeurae Report