A lifelong outdoor enthusiast, geophysics professor Paul Segall Ph.D. ’81 ascended the peak of Snowmass Mountain in the Colorado Rockies as a high school senior. Sitting near the mountain’s lake at an altitude of 10,000 feet, with temperatures dipping below 10 degrees Fahrenheit, Segall discovered his calling: studying the Earth and its natural hazards. 

Segall explored his passion for the outdoors in the classroom as an undergraduate in Earth sciences at Case Western Reserve University. In 1975 — during Segall’s junior year — Chinese scientists predicted an earthquake in Taichung, saving an estimated 100,000 lives. 

“I thought, ‘How cool is it that you can take physics and geology and apply it to natural hazards and save lives?’” he said. “I knew that’s what I wanted to do.”

This breakthrough in earthquake monitoring served as inspiration for Segall’s graduate studies at Stanford focusing on earthquake and volcanic processes and his later work as a research scientist in the earthquake program at the United States Geological Survey (USGS). There, he realized he could “combine things that [he] found intellectually stimulating and that had a social impact.”

Nowadays, in his research, Segall uses precise Global Positioning System (GPS) positioning, Interferometric Synthetic Aperture Radar and other methods to measure the deformation of volcanic environments to millimeter-level accuracy. Prior to an eruption, the ground of a volcanic site commonly bulges upwards, enabling scientists to forecast eruptions using ground and space-based sensors.

“Paul’s approach to research consistently reflects a willingness to question basic assumptions, the vision to see new possibilities in theory and observations and the clarity of thought required to synthesize that into a deeper understanding of the Earth,” said Earth sciences professor Greg Beroza, who has collaborated with Segall on past research projects.

Segall said that although it is not yet possible to issue short-term forecasts for earthquakes, his team can measure strain building on active faults, including the Bay Area’s San Andreas and Hayward Faults. “From repeated GPS measurements, we know something about the rate at which strain is building up,” he said. “That can be used as some of the information that goes into issuing long-term forecasts.” 

Over the past five years, Segall’s research group has focused on seismicity induced by human activities. Beginning in 2018, the development of horizontal drilling and fracking projects in the midwestern U.S. caused local earthquakes due to the injection of large amounts of wastewater into the Earth’s subsurface, according to Segall.  

Segall said he finds himself drawn to induced seismicity due to the controlled environment it represents relative to natural earthquakes. Since the causes of induced earthquakes are better defined, Segall said, scientists can study them to provide guidance on how to mitigate natural earthquakes. 

More recently, Segall has focused on the 2018 eruption of Hawaii’s Mount Kilauea, which he says is his favorite volcano. The volcano gained global attention when it rapidly released massive amounts of magma in a phenomenon known as a caldera collapse. The historic eruption locally dropped the Earth’s surface nearly 500 meters, changing the geography of Hawaii permanently. 

“I don’t think I’ve ever been to a place where the ground had moved 500 meters,” Segall said. “It was just hard to wrap my head around.” 

Segall noted that the eruption produced a series of daily magnitude five earthquakes, providing insight into the statistical frequency of seismic activity. “We’ve been really drilling in trying to understand the earthquakes every day, but there’s some variability to that,” he said. “What’s controlling [the seismicity]? Can we see increases in the rate of small earthquakes leading up to the big ones? It turns out we can.” 

What drives Segall now is what lies ahead: “If we understand these fundamental physical problems, we can do better at mitigating the hazards.” 

While Segall enjoyed issuing forecasts and warnings for earthquakes and volcanic eruptions at USGS, he was ultimately drawn back to academia by the “smart young people” that “come in and challenge me,” he said. “It keeps me on my toes.” 

In his teaching of STEM and non-STEM focused students alike, Segall seeks to blend admiration for the marvels of Earth’s natural processes with quantitative approaches to understanding the planet’s hazards. 

Laura Blackstone, fourth-year Ph.D. student in geophysics and one of Segall’s students, appreciates that he crafts course content to be “more relevant to what students want to learn about” and “most useful for students beyond the classroom,” she said. “As a research mentor, his number one priority is that his students are able to be curious and ask questions.” 

Rebeca Ursu, first-year Ph.D. student in geophysics who has also studied under Segall, echoed Blackstone. “Professor Segall is not only a visionary scientist, but also an exceptional mentor and teacher,” she said, praising Segall’s dedication to his students and his capacity to foster an encouraging group environment. 

Segall emphasizes the societal dimensions of predicting seismic and volcanic activity in his teaching and research. One of the classes he teaches is an introductory seminar titled GEOPHYS 20N: How to Predict a Super Eruption. The class focuses on the interface between science and society by illuminating the challenges facing scientists and policymakers seeking to issue warnings for natural hazards.

Outside of his academic pursuits, Segall enjoys exploring the wilderness of the Bay Area through hiking, sailing and bike riding. “We live in this incredible area [where you can] be in the Redwood forests in 20 minutes,” he said. “It’s just such a gift.” 

Of all the spots on campus, Segall said that the Papua New Guinea Sculpture Garden is his favorite. When he first joined the faculty in 1993, Segall said he would take his lunch and talk with the carvers as they worked on creating it. He came to know one of the sculptors, Teddy Balangu, so well that Balangu made two sculptures for him. Segall still proudly displays those in his living room. 

“It was so neat to converse with people from such a different culture,” Segall said. Nearly 10 years ago, he said he read in The Daily that Balangu would be at the sculpture garden.

“I walked up to him, and he said, ‘Hi Paul.’ I had not seen him in 20 years,” Segall said. “There’s something magical about that connection, and to look at those huge sculptures… the garden is a very, very special place for me.” 

As the field of geophysics adopts new technologies, ranging from fiber sensing to machine learning, Segall looks forward to future advances in earthquake and volcanic forecasting. 

“The better the computing resources become, the more potential we have to explore things that we couldn’t before,” Segall said. “It’s a great time to be in the business.”