An earthquake that occurred October 17, 1989 is motivating San Francisco to retrofit the Golden Gate Bridge. The bridge will be retrofitted to withstand a 8.0 or greater magnitude earthquake, should the epicenter be near the bridge. Without retrofitting the bridge, an earthquake 7.0 or greater magnitude with an epicenter near the bridge could possibly close the bridge for an extended period of time. Without the Golden Gate Bridge, many people would be unable to travel from San Francisco to the rest of Marin County without use of a ferry, as it is an important transportation link.
Just how likely is such a massive earthquake in the San Francisco area? According to a study conducted by the US geological survey, there is a 62% probability of at least one magnitude 6.7 or greater earthquake in the San Francisco Bay area to occur before 2031. Since 1992 engineers have been working to develop methods of retrofitting the bridge to withstand such magnitudes.
Interested in teaching your students more about Engineering? Check out SSR's Vol 41 DVD, episode Engineering – Bridges by Design. If your school would like to receive this free resource, visit http://www.ssrvideo.com/nhcmsp.html.
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