As usually defined, Risk is a simple product of (Probability x Consequences). However, when probability (P) tends to zero and consequences (V) tend to be high, Risk (R) tends to become a paradox kind of  (0 x Infinite) which is difficult, if not impossible to deal with.

Decision aid, Economic behaviour theory, Decision under uncertainty, Utility theory, ..., usually use the formula R=PxV to predict or indicate possible (maximum utility) courses of action (homo aeconomicus). However, as seen in the later formulation, in such a case, risk becomes something difficult to percieve. So, other approaches  seem necessary to address seismic risk. Should we, (homo sapiens), invest in reducing high consequences from  plausible but not probable threats ?.