Fellow Works to Predict Which Levees may Collapse in Event of Earthquake

The “next big one” (earthquake) is one of the greatest threats to the Sacramento-San Joaquin Delta’s aging 1,100-mile collection of levees. These earthen levees hold back and channel one of the state’s most important sources of water for drinking and irrigation-water that is used by about two-thirds of all Californians; more than 25 million people.

To help guide levee reinforcement projects, Delta Stewardship Council/Delta Science Fellow Emma Gatti, a postdoctoral researcher at Stanford University, is working with the U.S. Geological Survey and California Department of Water Resources to figure out which levees are most vulnerable to damage from an earthquake. Her work ties in directly with the Delta Plan directive to prioritize state investments in Delta levees and is a prime example of research directly relevant to forthcoming decisions that benefit the state as a whole.

Gatti is in the process of developing a hazard map for predicting “hot spots” of potential earthquake-induced ground failure in the Delta, caused by liquefaction (conversion of soil into a fluidlike mass during an earthquake or other seismic event) of sands or deformation (alteration of form or shape) of soft clays. She will map the locations of underlying sediments-young river channel sands, soft clays and flood basin deposits-that are most likely to liquefy, fail or deform in response to seismic activity.

The U.S. Geological Survey (USGS) group Gatti collaborates with-Thomas Holzer, Dan Ponti, John Tinsley, and Keith Knudsen-has been working on Delta geology for many years. They used maps made by Brian Atwater, a USGS geologist and current member of the Delta Independent Science Board who mapped the entire Delta in the beginning of the ’80s, to start to decipher the failure risks associated with the underlying sediments.

“This group knows well the earthquake-related risks to which the Delta is exposed, but more work is required in order to assess such risks properly,” Gatti said. The available mapping needs to be updated and the problem of liquefaction properly addressed with a more quantitative modeling approach.

Her personal interest in the research comes from the fact that she worked with rivers and unconsolidated sediments (sands, silts, mud) for her Ph.D.

In her research project, Gatti will use state-of-the-art modeling software to translate existing 2-D data combined with real cores extracted from the Delta into a 3-D model, which will allow her to selectively analyze specific sediment characteristics (liquefaction capabilities). (Two-dimensional (2-D) models include measurements across a surface area-usually length and width--while three-dimensional (3-D) models show length, width and depth).

The advantage of such an approach is that it promotes a deep understanding of the geology of the Delta with a simulation of the spatial distribution of the geological units most likely to fail, thus allowing a much more accurate assessment of local hazard.

Gatti is from Milan, Italy and received her bachelor’s degree in geology from the University of Milano, Bicocca. At 24, she moved to the United Kingdom for a master’s in Geographic Information System (GIS) and Remote Sensing at the University of Cambridge. After her master’s she won a scholarship for a Ph.D. at Cambridge, so stayed four more years. She did her Ph.D. on the environmental impact of a super-eruption (the Toba super-eruption on the island of Sumatra 74,000 years ago-one of the biggest volcanic eruptions of the past two million years).

 


“Science for the society is how I see myself doing science.”

--Emma Gatti


 

She moved to California in January 2013 and would like to stay for a while. “There is a lot to learn from the American way-of-thinking and working approach,” Gatti said. “Also, this project has a strong social-community component. It is highly rewarding and motivating, thinking that my study will be useful to someone, will be taken into consideration in future decision planning. Science for the society is how I see myself doing science.”

“I am interested and inspired by my mentor (Thomas Holzer) to learn more about hazard prediction techniques and liquefaction,” she said. The topic is extremely important for any urbanized area exposed to liquefaction-areas that include some of the most populated areas in the world.

When she is not busy thinking about the Delta, Gatti goes to the theater and builds bicycles in her backyard.