Nav: Home

Seismic biomarkers in Japan Trench fault zone reveal history of large earthquakes

January 27, 2020

In the aftermath of the devastating Tohoku-Oki earthquake that struck off the coast of Japan in March 2011, seismologists were stunned by the unprecedented 50 meters of shallow displacement along the fault, which ruptured all the way to the surface of the seafloor. This extreme slip at shallow depths exacerbated the massive tsunami that, together with the magnitude 9.1 earthquake, caused extensive damage and loss of life in Japan.

In a new study, published January 27 in Nature Communications, researchers used a novel technique to study the faults in the Japan Trench, the subduction zone where the Tohoku-Oki earthquake struck. Their findings reveal a long history of large earthquakes in this fault zone, where they found multiple faults with evidence of more than 10 meters of slip during large earthquakes.

"We found evidence of many large earthquakes that have ruptured to the seafloor and could have generated tsunamis like the one that struck in 2011," said coauthor Pratigya Polissar, associate professor of ocean sciences at UC Santa Cruz.

Japanese researchers looking at onshore sediment deposits have found evidence of at least three similar tsunamis having occurred in this region at roughly 1,000-year intervals. The new study suggests there have been even more large earthquakes on this fault zone than those that left behind onshore evidence of big tsunamis, said coauthor Heather Savage, associate professor of Earth and planetary sciences at UC Santa Cruz.

Savage and Polissar have developed a technique for assessing the history of earthquake slip on a fault by analyzing organic molecules trapped in sedimentary rocks. Originally synthesized by marine algae and other organisms, these "biomarkers" are altered or destroyed by heat, including the frictional heating that occurs when a fault slips during an earthquake. Through extensive laboratory testing over the past decade, Savage and Polissar have developed methods for quantifying the thermal evolution of these biomarkers and using them to reconstruct the temperature history of a fault.

The Japan Trench Fast Drilling Project (JFAST) drilled into the fault zone in 2012, extracting cores and installing a temperature observatory. UCSC seismologist Emily Brodsky helped organize JFAST, which yielded the first direct measurement of the frictional heat produced by the fault slip during an earthquake (see earlier story). This heat dissipates after the earthquake, however, so the signal is small and transient.

"The biomarkers give us a way to detect permanent changes in the rock that preserve a record of heating on the fault," Savage said.

For the new study, the researchers examined the JFAST cores, which extended through the fault zone into the subducting plate below. "It's a complex fault zone, and there were a lot of faults throughout the core. We were able to say which faults had evidence of large earthquakes in the past," Savage said.

One of their goals was to understand whether some rock types in the fault zone were more prone to large slip in an earthquake than other rocks. The cores passed through layers of mudstones and clays with different frictional strengths. But the biomarker analysis showed evidence of large seismic slip on faults in all the different rock types. The researchers concluded that differences in frictional properties do not necessarily determine the likelihood of large shallow slip or seismic hazard.

Savage and Polissar began working on the biomarker technique as postdoctoral researchers at UC Santa Cruz, publishing their first paper on it with Brodsky in 2011. They continued developing it as researchers at the Lamont-Doherty Earth Observatory of Columbia University, before returning to UC Santa Cruz as faculty members in 2019. Hannah Rabinowitz, the first author of the new paper, worked with them as a graduate student at Columbia and is now at the U.S. Department of Energy.

"We've tested this technique in different rocks with different ages and heating histories, and we can now say yes, there was an earthquake on this fault, and we can tell if there was a large one or many small ones," Savage said. "We can now take this technique to other faults to learn more about their histories."

In addition to Rabinowitz, Savage, and Polissar, the coauthors of the paper include Christie Rowe and James Kirkpatrick at McGill University. This work was funded by the National Science Foundation. The JFAST project was sponsored by the International Ocean Drilling Program (IODP).

University of California - Santa Cruz

Related Earthquake Articles:

Earthquake symmetry
A recent study investigated around 100,000 localized seismic events to search for patterns in the data.
Crowdsourcing speeds up earthquake monitoring
Data produced by Internet users can help to speed up the detection of earthquakes.
Geophysics: A surprising, cascading earthquake
The Kaikoura earthquake in New Zealand in 2016 caused widespread damage.
How fluid viscosity affects earthquake intensity
A young researcher at EPFL has demonstrated that the viscosity of fluids present in faults has a direct effect on the intensity of earthquakes.
Earthquake in super slo-mo
A big earthquake occurred south of Istanbul in the summer of 2016, but it was so slow that nobody noticed.
A milestone for forecasting earthquake hazards
In a new study in Science Advances, researchers report that their physics-based model of California earthquake hazards replicated estimates from the state's leading statistical model.
Mw 5.4 Pohang earthquake tied to geothermal activity?
The Mw 5.4 Pohang earthquake that occurred near a geothermal site in South Korea last year was likely triggered by fluid injection at the geothermal plant, two separate reports conclude.
Seismologists introduce new measure of earthquake ruptures
A team of seismologists has developed a new measurement of seismic energy release that can be applied to large earthquakes.
Residual strain despite mega earthquake
On Christmas Day 2016, the earth trembled in southern Chile.
The losses that come after the earthquake: Devastating and costly
The study, titled, 'Losses Associated with Secondary Effects in Earthquakes,' published by Frontiers in Built Environmen, looks at the devastation resulting from secondary disasters, such as tsunamis, liquefaction of sediments, fires, landslides, and flooding that occurred during 100 key earthquakes that occurred from 1900 to the present.
More Earthquake News and Earthquake Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at