In 2011, when Japan was rocked by 9.0 Tohoku earthquake, something strange happened 15 minutes later; scientists missed this deep-Earth process for more than a decade
Accordingly Japan National Police AgencyMore than 15,000 people were killed and thousands more were injured or missing. For years, scientists believed they had a detailed understanding of what happened during and after the disaster.
But a new study suggests that the earthquake may have triggered an extraordinary chain of events deep within the Earth that went unnoticed for more than a decade.
Mysterious movement detected after main earthquake
Shortly after the devastating earthquake off the northeastern coast of Japan, scientists monitoring GPS stations noticed something unusual.
About 16 minutes after the main shock, instruments in Japan recorded a sudden shift eastward. The movement occurred almost simultaneously across the country and was not matched by any known aftershocks.
The researchers were baffled. No major earthquake occurred at that time that could explain the movement.
For years, this event remained a secret buried within the enormous amount of data collected after the disaster.
New study reveals a journey to the Earth’s core
A team of scientists led by geophysicist Sunyoung Park University of Chicago He believes he has finally uncovered the answer.
Their findings, published in the journal Science, suggest that energy from the original earthquake traveled deep into the Earth, reached the boundary of the liquid outer core, and was then reflected back to the surface.
The returning wave appears to have triggered movement along major tectonic plate boundaries beneath Japan.
This discovery is remarkable because it shows that the earthquake’s impact may extend much deeper and farther than previously thought.
What is ScS wave?
The responsible wave is known as the ScS wave. ScS waves are a special type of seismic shear wave. They travel through the Earth’s mantle, bounce across the boundary separating the mantle from the liquid outer core, and return toward the surface.
In the 2011 earthquake, the wave traveled approximately 3,600 miles during its round trip across the planet.
The trip took about 15 minutes, matching the timing of the mysterious ground motion recorded in Japan.
Scientists believe that the returning wave provides enough energy to reactivate movement across already tense tectonic boundaries.
The secret seismic event that changed Japan
The returning wave triggered a large-scale shift along two major tectonic plate boundaries near Japan, according to the study.
These included the boundary between the Pacific and Okhotsk plates and the boundary between the Philippine Sea and Eurasian plates.
The combined impact permanently shifted parts of Japan eastward by up to six millimeters.
This may sound very small, but even a movement of a few millimeters for an entire country is an extraordinary geological event.
The researchers estimate that the triggered slide released energy comparable to a magnitude 7.5 earthquake, although it occurred without the sharp jolts usually associated with a large earthquake.
Why did scientists miss this for so long?
One reason is that earthquake monitoring systems are designed to detect fast, high-frequency tremors.
The newly identified event was different. Instead of creating a sudden jolt, it created a broad, slow movement that spread over a wide area. As a result, the signal was entangled with the massive amounts of data produced by the 2011 disaster.
Scientists also had to deal with the immediate aftermath of the earthquake and tsunami, which naturally became the focus of research efforts.
Only after years of careful analysis and comparison of GPS and seismic records were researchers able to isolate the unusual signal and determine its possible cause.
Largest seismic event ever recorded
One of the most striking results of the research is the size of the incident. Researchers estimate that the triggered slide extended about 1,800 miles.
This makes it the most extensive seismic event ever documented. Unlike traditional earthquakes, which are usually concentrated along a specific fault, this event involved simultaneous movement across multiple tectonic boundaries over a huge region.
Scientists say this is the first known example of a deep reflected seismic wave triggering large-scale sliding at separate plate boundaries.
What does the study mean for earthquake science?
The findings could reshape how scientists think about earthquake dangers. Traditionally, earthquake risk assessments focus on aftershocks, fault stress, and local geological conditions.
New research suggests that energy reflected from deep within the Earth may also play a role in triggering fault movement after a large earthquake.
In other words, the effects of a strong earthquake can continue long after the initial shaking has ended and can involve processes occurring thousands of kilometers underground.
The study highlights how Earth’s internal systems may be interconnected.
Could similar events occur elsewhere?
Scientists believe this event is likely to occur following extremely powerful earthquakes, especially in areas where tectonic plates are already under significant stress.
Countries along active plate boundaries, including Japan, Indonesia, Chile, and parts of the United States, could potentially experience similar processes.
However, the researchers emphasize that more studies are needed before scientists can determine how common these events may be.
The discovery opens a new area of research on how seismic energy interacts with the Earth’s deep interior.
A reminder that the world still holds surprises
Although more than 15 years have passed since the Tohoku disaster, scientists are still trying to uncover new details about what happened that day.
Sunyoung Park and colleagues’ work shows that even one of the most closely watched earthquakes in history can still reveal unexpected secrets.
What appeared to be a mysterious movement in GPS data has now become evidence of a remarkable journey that took seismic energy to the Earth’s core and back.
We would like to remind you that despite modern technology and decades of research, our planet still has many mysteries waiting to be discovered.
Inputs from TOI
