For some geological processes, the data record upon which a probability can be based are non-existent. This means deterministic methods or physical models of process must be used to provide some insight into the likelihood of the event occurring (deterministic approach).
Governmental agencies and the public often struggle with what is acceptable risk. In some ways acceptable risk is another way of defining safety. The concept of safety is a personal perception, which varies widely among individuals. This can be elastic standard. If the public has little knowledge of the hazard or its consequences, acceptable risk may be very high for lack of concern or very low due to unfounded perceptions of possible harm. Their acceptance of a particular risk level can change with their knowledge about the hazard process and its consequences. For this reason, efforts to provide accurate hazard information in forms understandable by the public are important to the society. Acceptable risk may also reflect the degree to which people feel they can influence or control the risk. Earthquake hazard may seem beyond their control.
Vulnerability addresses the degree to which the hazard occurrence would damage the elements at risk.
From the standpoint of producing land-use decisions that serve the public interest, risk assessment must be based on good science and this places a major responsibility on the geologists. Hazard zonation maps may guide land-use decisions.
From Geol. Soc. America Short Course on Environmental Geology.