Zhongwen Zhan (PhD '14) Begins Five-year Term as Caltech Seismo Lab Director

When an earthquake happens in the Southern California region, all eyes turn toward Caltech's Seismological Laboratory, or Seismo Lab for short.

For over 100 years, the Seismo Lab has pioneered geology and geophysics research, and provided information on earthquakes to the general public—where they occur, how strong they are, and what the likelihood is for aftershocks, for example. Indeed, local news trucks are often seen parked outside of the lab, which is located in the South Mudd building, mere minutes after an earthquake in the Southern California region.

Professor of Geophysics Zhongwen Zhan (PhD '14) has begun a five-year term as the Clarence R. Allen Leadership Chair and director of the Caltech Seismo Lab. Zhan takes over the position from Mike Gurnis, the John E. and Hazel S. Smits Professor of Geophysics and director of the Schmidt Academy for Software Engineering, who led the Seismo Lab for the past 15 years.

Zhan spoke with us about his vision for the future of the Seismo Lab.

What does the Seismo Lab do?

The Seismo Lab has a very long history. We try to understand the physics of larger earthquakes or earthquakes in general around the world, and we run some of the best seismic networks in the world. We use that network's data to provide earthquake information. When, where, and how large are they? Especially after big earthquakes, sometimes we provide some of the most important information for both the general public and also emergency responders about where we think the most major damage has happened and so on.

What kind of new technologies will we see in the Seismo Lab in the next few years?

In addition to our public outreach, we study the physics of earthquakes, and we run some of the best seismic networks in the world. The Southern California Community Seismic Network (SCSN) runs throughout the region and contains over 500 seismometers. We're planning on adding to networks like these with even more precise tools to measure seismic waves. For example, my laboratory has been developing a method to repurpose telecommunications fibers as a dense array of seismic sensors. With these we can improve the resolution of measuring earthquakes.

We've also been applying AI to extract information about earthquakes more quickly to better characterize patterns. There is also a lot of work on using both better satellite observations and better computational tools to extract more information from the data. These are the directions where we'll continue to innovate how we do things.

Even though we have been running a seismic network for more than a hundred years, the network is always changing over time, so every several decades we'll innovate and reinvent what the seismic network looks like, and that's still happening today.

Tell us more about the SCSN.

The Southern California network, established originally in 1921, is one of the first seismic networks in the world. It started from less than a dozen seismometers distributed around Southern California. By today's standard, those were not particularly good seismometers. After the first few quantitative measurements of earthquakes, the network continued to expand. We keep bringing new technology, and many other places in the world started to build their own seismic networks. Many of these networks are now integrated into national or even global seismic networks. But the Southern California network continues to stay at the forefront in terms of how we build networks, what technology we use, and how to best use the information from the network.

Though it's not possible to predict earthquakes, what do we want to know about them? What can earthquakes tell us?

Earthquakes are actually happening all the time. The majority of the earthquakes are so small that we don't feel them at all. But the seismic sensors can pick up very small ones. By detecting, locating, and characterizing the size of a lot of earthquakes, we really get a much more complete picture of the forces involved and how active the faults are. We also get a lot of understanding of the subsurface geology, like where there is harder rock or soft sediment and how that affects where earthquake shaking will be more damaging. It's really important to understand earthquakes in order to be prepared.

Big earthquakes are inevitable. We know they're going to happen. Plate tectonics continue to strain the crust around Southern California, and someday that strain is going to be released in the form of a large earthquake. The best thing we can do is be prepared, and that preparation requires information from scientists and the network. Our fundamental research about earthquakes is really trying to provide that information as best as we can.

We're working on technologies like earthquake early warning. For that, you must be able to get the information about the earthquake very quickly. The network can actually transfer data within a fraction of a second after the earthquake begins to a central computer that analyzes the data and provides the early warning. And then in the couple of minutes to hours after an earthquake, we can get much more detailed information, produce products like shake maps, and see where shaking has been the worst. Some of these tools were born here in the Seismo Lab in 1980s and '90s, and they're now used around the world.

How does the Seismo Lab fit in with other research happening on campus?

Seismology has traditionally been centered around earthquakes, but in the last couple of years we are starting to see how it can also help with environmental problems. Seismology allows us to study geophysical processes just below the surface, such as how groundwater is stored. We can even use it to study climate change in the ocean because different ocean properties will affect seismic wave propagations.

Caltech is pushing forward in the direction of studying climate, especially the cryosphere [the planet's ice]. We can bring new observational and modeling capabilities so that we can understand all those processes better. This is a new direction for the Seismo Lab. I believe we'll continue to thrive focusing on earthquakes, but we're also getting into the business of studying climate-related processes, ice-related processes, and water-related processes.

So, seismic waves can act like X-rays in enabling us to see below the surface?

Yes! We can use satellites to measure processes on or above the Earth's surface, but it's much harder to observe or continuously monitor processes happening under the ground, even just a few centimeters below the surface. The seismic wave is like an X-ray to look inside the Earth, enabling us to see thousands of kilometers to the core, or just a few meters down to groundwater reservoirs. There's a lot of potential for using seismic waves to look underground, often with implications for environmental studies.

What does the future of the Seismo Lab look like?

We'll be continuing our core strengths of combining fundamental geophysics research and communicating public information. Especially after the LA wildfires, we see how much people are hungry for information after natural disasters.

I spoke already about environmental geophysics, and there are several faculty members here very interested in that direction. We're also adding a glaciologist to our faculty this summer.

There are also new opportunities in planetary geophysics. We have a long history here—Don Anderson, a previous director of the Seismo Lab from 1967–1989, was part of the deployment of the first seismometer to Mars. Many of the questions we're interested in on other planets involve what's happening underneath the surface, and geophysical studies are the best way at that information. For example, we apply seismology tools to study vibrations on other planets and geodesy tools to measure deformation on other planets. Saturn's icy moon Enceladus is a great example. Enceladus is squeezed regularly by Saturn's gravity as it orbits, and we need geophysical expertise to study what's going on under the surface as it deforms and heats up. In another example, we can send seismometers to Venus to measure acoustic waves from Venusquakes or volcanic eruptions. There are so many ways for us to bring the best new technologies from Earth to do better science on other planets.