USGS Finds Greater Risk Of Earthquakes In Bay Area

Tim Ryan
December 13, 2019 - 3:09 pm
General view of the Marina district disaster zone after an 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 in San Francisco.

Otto Greule Jr /Getty Images

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The U.S. Geological Survey says major parts of the Bay Area are at risk for even stronger earthquakes than previously though.

The USGS released its latest earthquake hazard map for the country at the American Geophysical Union’s annual meeting in San Francisco on Thursday. It shows most of California at an elevated risk (over 74%) of an earthquake striking in the next 100 years that could cause slight or more serious damage. 

USGS earthquake hazard map
U.S. Geological Survey

Soil conditions could make those earthquakes even more intense.

“There are some depressions in the ground that have been filled with sediment over the years – probably several miles thick of sediment – that modify the ground motion,” says USGS research geophysicist Mark Petersen, who worked on the new map.

That soft soil could exaggerate seismic activity and make an earthquake feel even more intense. The new research suggests the effect could be as strong as 5-10% more ground movement in San Jose and up to 10-25% more movement in Walnut Creek.

The impact would be especially noticeable in tall buildings and on long bridges.

Petersen said the findings are not meant to alarm the public. Instead, this data can be used to strengthen building codes and property insurance and better prepare the region for the next quake.