Loma Prieta Quake Introduced Public To Liquefaction

Holly Quan
October 16, 2019 - 5:00 am
General view of rescue attempts in the Marina District disaster zone after the earthquake, measuring 7.1 on the richter scale, rocks game three of the World Series between the Oakland A's and San Francisco Giants at Candlestick Park on October 17, 1989.

Otto Greule Jr /Getty Images

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The 1989 Loma Prieta quake introduced many Bay Area residents to the phenomenon of liquefaction.

The damage to buildings in the South of Market and Marina districts made it clear where some liquefaction zones existed. 

Since then, scientists have created maps indicating where unstable soil could give way in a quake and essentially liquefy. Those areas are mostly along the Bayshore line, including the Oakland airport and East Palo Alto. 

"Most of those areas were filled a long time ago before we knew about liquefaction. so they just pumped the sand in there, let it dry out and then started building on it and now that’s particularly vulnerable," said Keith Knudsen is deputy director of the Earthquake Science Center at the U.S. Geological Survey. 

Related: 'We Were Made Of The Right Stuff,' Ex-Mayor Recalls How City Handled '89 Quake

“So in order to have liquefaction, you need  three ingredients: you need water, groundwater. you need loose soils and then you need intense shaking," said Knudsen. "So anything that addresses any of the three of those...so if you can drain the ground water, that makes it so it won’t liquefy. If you can make it so it’s more dense, not so loose, or if you can put grout or cement in so it’s not a loose sandy mix.”

The problem is it’s expensive and not easy to remedy when there's already a building standing on the land. An alternative is to beef up the foundation so if soil does give way, you might be able to right the house by righting the foundation.