The 31-item survey was conducted this spring by Matthew S. Davis, Ph.D., professor of psychology at Dominican, with the help of a team of students from his "Human Response to Disaster" course. They distributed 300 questionnaires to residents of coastal towns in Del Norte, Humboldt, Mendocino, Sonoma, and Marin counties. Eighty-five surveys were returned by business reply mail, for a 28 percent response rate. This is the first social science study to focus on tsunami awareness/preparedness in California.
California coastal residents are vulnerable to tsunami caused by both distant events such as an earthquake in Alaska or Japan, as well as local-source earthquakes. Of particular concern would be an earthquake along the Juan de Fuca Subduction Zone, which runs along the coast from northern California up into Canada. However, 38 percent of the survey respondents said they had not received any information on how to prepare for tsunami hazards. In a breakdown by county, the percentage of people saying they have not received such information is as follows: Del Norte (21 percent); Humboldt (36 percent); Mendocino (54 percent); Sonoma (60 percent); and Marin (47 percent). Of the 62 percent who said they had received information, most listed as common sources of information television or newspapers (72 percent and 64 percent, respectively). In comparison, only 40 percent of respondents said they received information from either city or county government.
"The survey shows that many people living in towns along the northern California coast have not received enough information about their exposure to tsunami and how to prepare for tsunami hazards," notes Dr. Davis, a social psychologist who studies people's responses to living in areas prone to natural disasters. "Residents of these coastal communities are vulnerable to tsunami, and with education we can help to prevent loss of life." Davis also notes that one of the most important reasons respondents give for failing to prepare for disaster is lack of information.
Davis found that residents' fear of tsunami is greatest in Del Norte and Humboldt counties, which have experienced 17 measurable tsunami since 1940. Emergency services officials in these counties have worked together to produce pamphlets to increase tsunami awareness, and Crescent City in Del Norte County has a warning siren system in place.
But while Mendocino, Sonoma, and Marin also have been visited by tsunami in the past, lack of development on the coast has resulted in little damage, notes Davis. Only 8 percent of respondents from Mendocino County and 16 percent of respondents from Sonoma and Marin counties knew of any past tsunami.
"Mendocino County has been making some progress toward public education, but Sonoma and Marin are just now beginning to develop an educational campaign for tsunami hazards. And as a result, a large proportion of people don't know how much time they have to evacuate in the event of either a local-source earthquake or a tsunami warning."
If a major earthquake occurred on the Juan de Fuca Subduction Zone, coastal residents of Del Norte, Humboldt, and Mendocino counties would probably have between 15 minutes and at most 30 minutes before a tsunami hit, says Davis. Because of the contours of the coastline and their greater distance from the Juan de Fuca Subduction Zone, Sonoma and Marin are less at risk from a local-source event than the northern counties, though they are just as vulnerable to the effects of a distant-source tsunami.
A relatively high percentage of survey respondents in Humboldt and Del Norte counties accurately stated that if they felt an earthquake in their area, they would have less than 30 minutes to respond (68% and 52%, respectively). Among respondents from Sonoma/Marin 48 percent answered this item correctly and in Mendocino only 25 percent of respondents were correct. Furthermore, while only 22 percent of Del Norte respondents stated that they did not know how quickly a tsunami could reach the coast, 32 percent in Humboldt, 42 percent in Sonoma & Marin, and 50 percent of those in Mendocino stated that they did not know the answer to this question.
In the event of a distant-source event, several hours warning time is likely as the Pacific Tsunami Warning System is in place to alert at-risk populations. When asked how much time they would have to respond to an approaching tsunami if a warning was issued for their community, only 4 percent of respondents from Del Norte answered that they did not know how much time they had to respond. In contrast, 32 percent in Sonoma & Marin, 36 percent in Humboldt, and 50 percent of those in Mendocino stated that they did not know the correct answer to this survey item.
Of particular concern to Davis were the answers he received to a question that asked what actions respondents would take if a tsunami warning were issued. In all of the counties studied, large percentages of respondents knew correct actions to take, such as going inland or uphill, and checking their radio for information. In Del Norte, Humboldt and Mendocino counties many people also mentioned the importance of avoiding the coast for at least three hours after a warning has been issued. However, in Mendocino 17 percent stated that they would watch for the sea waves to come ashore and another 17 percent said they did not know what action they might take. In Marin and Sonoma counties, 21 percent said they would watch the waves.
"Many people do not seem to realize how big a threat a tsunami could be," says Davis. "What worries me is that if a warning were issued, while many respondents from Del Norte and Humboldt counties said they would go inland, large numbers of people in Mendocino, Sonoma and Marin said they would stay put and watch the waves. Even if their homes are fairly high above sea level, they may not be high enough to be safe."
Davis plans to compare the results of his study with a similar study done in Washington State in 2002 by David Johnston, a geologist from New Zealand. Davis also plans to share the information collected in this study with emergency preparedness officials in Marin as they work to develop educational programs about tsunami risk for county residents. In the future Davis - whose e-mail moniker is disasterman- will work on studies of the public's perceptions of volcanic risk at Vesuvius in Italy and at Mt. Rainier in Washington State.
The tsunami survey was funded in part by a Disciplinary Research Grant from Dominican University of California.