Scientists Observe Rare Slow Slip Earthquake Off Japan’s Coast

Tokyo, Japan — Scientists have recorded a slow slip earthquake unfolding along the Nankai Fault off Japan’s coast. This remarkable discovery, mentioned in a study published in the journal Science, captures the fault acting like a natural shock absorber, easing tectonic pressure over time.

Researchers from The University of Texas at Austin identified the slow earthquake as a process that resembles the gradual unzipping of the fault line between two of the Earth’s tectonic plates. Lead researcher Josh Edgington described the phenomenon as a ripple moving through the plate interface.

Unlike traditional earthquakes that release energy suddenly, slow slip earthquakes can take days or weeks to develop. This specific event detected in fall 2015 spread along the shallow section of the Nankai Fault, an area known for its potential to generate tsunamis.

The team utilized advanced borehole sensors positioned in the ocean trench, where the fault lies closest to the seafloor. These sensors, capable of detecting movements as small as a few millimeters, provided crucial data that land-based monitoring systems could miss.

The 2015 slow slip earthquake was followed by another similar event in 2020. This discovery indicates that the Nankai Fault may not release significant energy during large tsunami-generating events, acting more like a pressure release valve. The knowledge aids researchers in understanding subduction zone faults throughout the Pacific Ring of Fire.

Notably, the research shows that fluids play a significant role in slow earthquakes. Elevated fluid pressures observed during the events strengthen the connection between fluids and slow seismic activity.

Historically, the Nankai Fault produced a major earthquake in 1946, resulting in significant devastation. While another significant earthquake is anticipated, the slow slip events suggest that the fault disposes of some stress harmlessly through these minor occurrences.

This study emphasizes the need for further exploration of similar regions, particularly in areas like the Cascadia Fault in the Pacific Northwest, which may exhibit different behaviors. UTIG Director Demian Saffer highlighted the importance of high-precision monitoring methods to understand such faults better.

The borehole observatories involved in this research were implanted by the Integrated Ocean Drilling Program. The study underscores ongoing efforts to monitor and understand deep-sea seismic activities.