SFU researchers make breakthrough discovery on earthquakes and tsunamis in Greater Tokyo region

Jessica Pilarczyk talks about her discovery of potential new earthquake source

Two people, one kneeling down on the left (Dr. Pilarczyk) and one standing on the right. Both holding sand samples in their hands. They are standing on a blue tarp, and there are more sand samples on the tarp

By: Tamanna T., Staff Writer

SFU earth sciences assistant professor Jessica Pilarczyk leads her team in making a new discovery related to a plate boundary that affects the risk of earthquakes in the Greater Tokyo region. The present and historic earthquakes taking place in Tokyo can now be traced to the Philippine Sea-Pacific plate boundary, making it a place of interest for detecting seismic risk.

The plate boundary, which lies in the southern part of the Japan Trench, received stress from the Tohoku earthquake and tsunami in 2011, generating questions about its seismic risks, as this plate didn’t rupture. The impact of the event was felt across the ocean, including in BC. Pilarczyk and her team have been working on this research for a decade and recently published their findings on Nature in early September.

As tsunamis come onto shores, they bring sand and marine sediments, creating a tsunami deposit, Pilarczyk explained. “We went looking and trenching [digging], which would tell us whether a tsunami had happened here or not. 

“We went to a lot of rice paddies [ . . . ] We wanted something very close to the coastline, we want it to be low-energy, we don’t want it to be too manipulated by anthropogenic or human-induced changes,” said Pilarczyk. The team also used paleoecological (sifting through sand for small fossils), geological (looking at the sand and measuring mountains), and radiocarbon dating methods for their research. Microfossils and micro-organisms in sand samples were analyzed and dated using radiocarbon analysis, which utilizes the predictable way radioactive carbon atoms break down to date organic material. 

Pilarczyk and her team found three sand layers, of which the second layer could be traced for 50 km “along the shoreline.” According to Pilarczyk, this was extremely “unusual” and was a key discovery in this research. Collaborating with a modeler from Japan, the team was successful in understanding the type of earthquake that could create a tsunami with deposits as far as 50 km. 

“The lowest magnitude [earthquakes], we call those our preferred model because it’s the smallest earthquake possible [ . . . ] basically came from a subduction zone between the pacific plate boundary and the Philippine sea plate boundary.” Subduction zones occur when two tectonic plates are next to each other and one slides beneath the other. These boundaries were not previously recognized as an earthquake source. 

Pilarczyk explains “there is a high probability that this major [Tohoku] earthquake and tsunami actually came from that boundary.” Pilarzyck’s finding will help inform the Japanese seismic hazard maps used to build hospitals and apartment buildings. 

By understanding other subduction zones and plate boundary processes, Pilarczyk hopes to help Canada mitigate hazards, such as an earthquake in the Cascadia subduction zone located from California to BC. This zone has been predicted to pose a big risk of earthquakes in the future. 

Pilarczyk, a Tier II Canada Research Chair in Natural Hazards, will go to Vancouver Island with her team in search for more geological evidence related to plate boundaries and subduction zones.