a, Science & Technology

Christie Rowe: earthquake hunter

Christie Rowe is an earthquake hunter. The Wares Faculty Scholar and assistant professor of earth and planetary science at McGill travels the world studying fossilized earthquakes— earthquakes that occur deep in the earth’s crust, but eventually leave a visible record in rock that has risen to the surface because of uplift and erosion. 

Last April, Rowe was part of a team of 28 researchers investigating the fault that caused the massive Tohoku earthquake and tsunami of March 2011. The project, called the Japan Trench Fast Drilling Project, brought together scientists from ten countries to drill cores of the fault.

Mud core from the Japanese trench
Earthquake glass from the Sierra Nevada range in California. (Christie Rowe)

The Tribune sat down with Rowe to discuss her work studying earthquakes from Africa to Japan, and how to ride out tremours like the 4.5 magnitude quake that shook Montreal last week.

McGill Tribune: What was the deal with the earthquake last week—what happened?

Christie Rowe: Honestly, the western Quebec seismic zone is not very well understood. The theories are that we have very old fault structures in the crust that date back to the Cretaceous, but when we have earthquakes like this, we can’t really be sure that those structures are responsible.

MT: So, should we be worried?

CR: No. Most earthquakes are not dangerous, but [historically] large earthquakes have happened, that are damaging.* An earthquake like the size four that we had is absolutely the fun size of earthquake. Everybody gets to really experience it, and know that it’s happening. It’s not dangerous—not scary.

One thing that’s working in our favour is that the crust in this region is very strong because it’s old. That means that when the seismic waves move through the crust, they move quickly and you get less ground shaking [as opposed to] somewhere on the west coast, where the crust is younger and more damaged because of the seismic history. [There], the shaking lasts longer.

*Rowe is refering to the 1732 Montreal earthquake that measured 5.8 on the Richter scale.

MT: Were you awake during the earthquake?

CR: Yeah. Well, I heard the earthquake before I felt it, and that’s because the P-waves—the primary waves, the fastest travelling waves—they don’t necessarily create the type of ground motions you would feel, but they’re very effective at vibrating windows.

You hear the rumbling and you hear the shaking and that’s the P-waves. Then, the next wave arrival that comes through—that’s the S-waves [secondary waves]—and that’s the one that’s going to give you a jolt probably, a vertical acceleration … followed by the surface waves that have a rolling and lateral shaking motion.

Ben Melosh, a graduate student working with Rowe, walks along the Pofadder Shear Zone in southern Namibia home to 1.1 billion-year-old afossilized earthquakes. (Louis Smit)
Ben Melosh, a graduate student working with Rowe, walks along the Pofadder Shear Zone in southern Namibia home to 1.1 billion-year-old afossilized earthquakes. (Louis Smit)

MT: Tell us about what you do.

CR: I am a fault geologist, so I’m interested in earthquake processes, but instead of studying earthquakes that happen now, I go to where earthquake source areas have been uplifted and the rocks have been eroded so they’re exposed. These are rocks that have been uplifted 10, 20, [or] 30 kilometres, and the real guts of the earthquake system are now on the surface. I collect those and put them in my office.

… As you walk along [a fault] surface you’ll see areas that have melted rock, areas that have broken rock—there’re lots of ways that energy is used in rock destruction.

MT: How do you date earthquakes?

CR: When the rock is melted during the earthquake. Only some earthquakes produce frictional melt, but when it does happen, the glass that forms traps potassium, [which] decays over time to argon. So if you have a potassium-trapping event, and the formation of earthquake glass, then you can measure the argon isotope ratios and it gives you a little clock.

MT: Tell us about the Japan Trench Fast Drilling Project.

CR: The Japanese government, about ten years ago, built the world’s largest science ship. It’s called Chikyu, which means ‘earth,’ and it’s 600 feet long. It was basically built for this event; it can drill in deeper water, and drill deeper in deeper water than any other ship.

We went out to the very limit of what Chikyu can do, the deepest part of the Japan Trench, and drilled a few holes 850 meters deep in the sea floor, and found a lot of mud—but really weird mud, mud unlike anything I’ve ever seen … it’s made of the purest clay … it’s shiny and black because there are titanium oxides and iron oxides that are deposited on the sea floor because of black smoker activity at mid-ocean ridges.

MT: What did the expedition discover about the Tohoku earthquake? 

CR: What this earthquake did was completely run away. It started at depth as a pretty big earthquake, and as it got shallower toward the trench it got bigger, and this is something that we have not really seen before—this is a really unusual event.

One thing that might have happened is that friction heated up the water in the [mud] and effectively pressurized the fault zone, opening it like an air hockey table. There was no frictional contact, and no strength in the fault—that helped it run away.

Think of [the runaway earthquake] like a propagating crack: as the crack opens, it puts more stress on the crack tip, which causes it to open more.

MT: Is there any way to know if earthquakes like this have occurred before?

CR: Japan has the longest historical [earthquake] records. For a thousand years—at least—they have had instruments that quantify things like ground shaking—intensity and magnitude, and other things like tide gauges that show long-term changes in sea level that are actually caused by the motion of Japan, not by the sea level. We have those records going back 1,200 [or] 1,500 years almost, which is fantastic. That is about the length of time between large earthquakes, so now we have two recorded events—it’s not enough to establish a trend.

Earthquake glass from the Sierra Nevada range in California. (Christie Rowe)
Mud core from the Japan Trench

MT: Does measuring a small event help us understand a large one?

CR: The short answer is [that] we don’t know enough about large events yet to even know if there’s some kind of predictive power in a small event … I think one of the big open questions in earthquake science right now is [this]: is a large earthquake just a bigger version of a smaller earthquake, or is it a fundamentally different thing?

MT: What should everybody know about earthquakes?

CR: Don’t be afraid—ride it out, enjoy it … I know a seismologist, who, when an earthquake occurs, will just drop to the floor and lie spread-eagle on the ground and try to determine which way the waves are coming from—I didn’t react fast enough to do that the other night.

This planet is very much alive. It’s such a cool moment when the human experience intersects with the geologic time scale, and we get to experience an earthquake.

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