Research to Help Prepare for the Next ‘Big One’

A California native, Grasshopper Anderson-Merritt has always been intrigued by earthquakes. Today as a doctoral student in the UMass Amherst Department of Earth, Geographic, and Climate Sciences, Anderson-Merritt is conducting research with real-world implications by simulating the stress levels and mechanical interactions of California’s San Andreas Fault.

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Anderson-Merritt works with advisor Michele Cooke, professor and associate department head for professional development in the Department of Earth, Geographic, and Climate Sciences, on research funded by the Southern California Earthquake Center. This spring, Anderson-Merritt’s research presentation won the UMass Amherst Graduate School’s Three Minute Thesis (3MT) competition. This annual competition challenges graduate students to explain the significance of their research to a general audience in three minutes or less, helping them hone their presentation and communication skills.

“In their Three Minute Thesis presentation, Grasshopper did a fantastic job of clearly describing some very complex models that simulate evolution of stresses along the San Andreas fault. I've been very impressed with Grasshopper's careful attention to the myriad of factors and uncertainties that need to be considered in these complex models,” said Cooke.

Anderson-Merritt came to UMass after earning undergraduate and master’s degrees in geology from the University of California, Davis, and working in environmental consulting. In their PhD research at UMass, Anderson-Merritt writes code for complex 3D geometric computer models, which they use to produce and analyze videos and graphs showing stress levels before and after earthquakes.

“In between earthquakes, friction on the fault plane prevents the plates from sliding past each other, causing stress to build up. When enough stress builds up to overcome this friction, an earthquake happens: the fault becomes un-stuck and the two sides slide past each other, relieving some or all of the accumulated stress,” Anderson-Merritt explained. The amount of relieved stress is known as the stress drop.

“My models are helping to inform whether the accumulated stress and the stress drop are always consistent, or whether they vary,” Anderson-Merritt said. “The stress drop is also closely related to the amount of slip in an earthquake —important to know about if you're building infrastructure that crosses a fault line—and how bad the shaking is.”

According to Anderson-Merritt, developing these models has opened up many more questions to explore. One question of interest is the size of the stress drop at the time of an earthquake. Does the stress level of the fault fall to zero after the earthquake, or is only some stress released? How does that affect the appearance of simulated stress histories over time?

“One clear outcome we’ve seen so far is that the size of the stress drop, and whether it’s complete or not, matters a lot in predicting future earthquakes,” said Anderson-Merritt. “This research reaffirms the need for more information about stress drop.”

Ultimately, Anderson-Merritt hopes to improve understanding of earthquake cycles relative to the buildup and release of stress. This work may help forecasters understand how concerning it is to see long gaps between earthquakes in a particular location. It also may help dynamic rupture modelers estimate the intensity of shaking when earthquakes do occur.

Reflecting on their research, Anderson-Merritt said, “Geology is fun because you’re looking at an integrated view of many different kinds of information and trying to fill in all the pieces. There is an inductive game to it.”

Anderson-Merritt has not yet settled on a path for their future, though becoming a professor is one possibility. No matter what they end up doing, they are eager to share their passion and enthusiasm for earthquake research with others.

This story was originally published in May 2023.