10 March 2025—“Moment tensors are a model to describe earthquake sources based on forces acting at the seismic source,” explains Boris Rösler. “In the 1960s, it was shown that these forces generate a seismic wavefield equivalent to slip on a fault. We can thus describe the geologic process of an earthquake source using moment tensors.”
Sounds straightforward enough, right? But Rösler, an assistant professor of seismology at the Center for Scientific Research and Higher Education at Ensenada (CICESE), is taking a closer look at quantifying uncertainties that arise from the complex inversion procedure that uses seismic wave data to model earthquake source processes as described by moment tensors.
In particular, Rösler is looking at uncertainties in moment tensor components called non-double-couple (NDC) components, which describe processes beyond the traditional description of slip on a planar fault by the strike, dip and slip angles.
There are hints that the main source of uncertainty in moment tensors lies in these NDC components, and that the “uncertainties are much larger than assumed due to the assumptions made in the inversion, in particular about the Earth structure,” he says. “Thus my current research aims at a more accurate description of seismic sources, in particular of the possible geologic processes described by non-double-couple components.”
Rösler takes a statistical approach to this task, comparing a global catalog of more than 62,000 moment tensors of earthquakes since 1976—“coincidentally, the same year I was born,” he jokes—to other catalogs containing the same earthquakes to address uncertainties in quantities derived from moment tensors.
There are few statistical seismologists out there, and most of them deal with seismicity and seismic hazard rather than seismic sources, Rösler says. “But over the last half decade, interest has noticeably grown in uncertainties in moment tensors.”
An increase in available data and significant increases in computing power now make it possible to carry out this work, he says. “Two decades ago, numerical simulations for large numbers of earthquakes and data would’ve taken weeks, but now we can do them in a matter of days.”
It may be a small community of researchers, but Rösler says it is a very active one. He is a co-convener of a session at the 2025 SSA Annual Meeting on advances in reliable earthquake source parameter estimation. “I find it useful to attend as many scientific conferences as possible for an overview of the research being done around the world, which reading papers cannot provide,” he says.
Rösler’s undergraduate research in math and physics prepared him for his computational research, and a crash course in statistics from Northwestern University statistics professor Bruce Spencer, who joined his advisor Seth Stein on Rösler’s Ph.D. committee at Northwestern University, was extremely helpful.
“I can’t stress enough the importance of having a good committee and people you regularly exchange information with,” Rösler says. “It’s important for your career to have information not just about research, but also on aspects related to transitioning into a faculty job.”
“For as long as I can remember, I have been interested in studying the Earth,” Rösler says, “and when I was a kid, I preferred to read maps rather than books. It just took me a while to find out that you can turn research into a profession. Ever since I noticed that the coastlines of Africa and South America looked like they had once been together, I have been fascinated that the Earth as we know it has changed so much over time. I guess this is why I like to focus on the big picture,” he adds.
In his lectures, Rösler asks students to be aware of the evidence for the facts we take as given in Earth science. “There is an unbelievable wealth of proof that the Earth is round apart from seismic waves traveling through the interior of the Earth, and yet, there are still people who ignore them,” Rösler says. “Listening to experts seems a bit out of fashion these days, and many people just accept the myths about Earth science that pop up on social media.”
Living in Baja California, for instance, he often hears the myth that one big earthquake would detach the peninsula from the North American continent.
“Communication is key, to provide the knowledge to destroy these earthquake myths,” Rösler says. “People are not used to thinking of plate motions on timescales of millions of years—or understand that faults could not store enough energy in friction to detach the peninsula in one event!”
Rösler also hopes to convey the excitement of seismology as a “very young science,” because although it has roughly 150 years of recorded data, the modern data-intensive digital era is only a few decades old.
“We are still in the beginning of discovering all of the problems that still have to be solved,” he says. “It is really interesting to work in seismology these days, because right now we have the computing power, and we have the data to answer these open questions.”
SSA At Work is a monthly column that follows the careers of SSA members. For the full list of issues, head to our At Work page.