Risk communication and individual response: Impact of 1990 revised earthquakeprobabilities for the San Francisco Bay Area

This study investigates hazard response of home owners in the San Francisco Bay area to revised, upgraded earthquake probabilities released by the United States Geological Survey in late 1990. The revised forecast, widely disseminated, warns that a major earthquake, of magnitude 7 or larger, is likely to impact a heavily populated urban area in the Bay region between the years 1990 and 2020. The purpose of this study is to assess the extent to which these home owners in the Bay area heard, comprehended, and personalized the low-key warning message, and then acted to adopt protective measures.; Existing data from two previous studies sponsored by NSF regarding the purchase of earthquake insurance combines with data collected in a survey from this study that results in: (1) identifying relationships among communication factors that provide the most explanation of behavior response; (2) examining the effects of intensity of experience on the communication process; (3) analyzing the shifts in perception and response that occurred over the time periods of before, after and one-year later from Loma Prieta; (4) combining risk communication factors to provide most explanation of behavior response; and, (5) illustrating the process of communicating risk.; The study finds that clear and specific written information from official sources sent directly to the individual captures the greatest attention and thus educates the public most effectively of its potential risk to the earthquake hazard. Supplementing the warning message using multiple information sources, such as the broadcast and newspaper media reinforces the effectiveness of the message. In addition, intensity of experience from the 1989 Loma Prieta earthquake produces measurable changes in perceptions and response. This study concludes that previously held, perceptions of personal vulnerability to future occurrences, past experience with an earthquake and prior response are factors that motivate those with intensity of experience to mitigate in more recent periods. However, the factors that motivate those with less intensity of experience include hearing non-emergency warning messages and confirming the information from official sources--the message substitutes for direct experience. This implies that it is important to understand the context of a particular situation in order to effectively forewarn the at-risk public. For individuals with intensity of experience, the dissemination of a warning message proves redundant and ineffective, while for others with less intensity of experience, the message is essential.