Imagine you’re at home or at the office, when the walls of the room you’re in start shaking
violently. Books fall off the shelves, cabinets threaten to topple over. You
quickly realise this is an earthquake. And then you look up, and it occurs to you that
there is another entire storey of building above you. As the walls continue to wobble,
you know that should they fall, that roof above you is coming down, and you stand a good chance
of dying. So you look up as the quake goes on and on, and you wonder… will it hold? Will it hold?
When you see the footage from the Japan 2024 Noto peninsula earthquake that struck in the
afternoon on New Year’s day, when families were gathered in their homes, it’s easy to envision
the fear that must have been felt by those who experienced it. This was a deadly tragedy,
with 241 people killed and 1296 injured. In spite of its relatively small size, Japan is the country
with the 4th largest number of major earthquakes in the world over the last few decades.
Our planet Earth is frequently shaken by earthquakes. But there are things
about Noto that make it different from any other earthquake that we’ve seen before.
I’m Alex McColgan, and you’re watching Astrum. And today we’ll be entering a world
of earthquake swarms and changes to the Earth’s rotation. Of earthquake shake tables carrying
buildings 10 storeys high, and a geological mystery that remains unsolved to this day.
It’s no wonder that Japan is regularly impacted by earthquakes. Japan sits on the Western edge of the
ring of fire, one of the most tectonically active places on Earth. These vast plates
of rock and soil constantly and inexorably shift over the course of millions of years,
sometimes pulling apart and sometimes moving together. To further complicate matters,
Japan sits along the edge of multiple smaller plates at once. The Pacific Plate pushes west,
and subducts (or slides underneath) the Philippine Sea Plate and the Okhotsk Plate.
But the Amurian Plate also pushes up against the Okhotsk Plate, while the Philippine Sea Plate
subducts underneath the Amurian Plate and the smaller Okaniwa Plate at the same time.
It’s a complex geological wrestling match, one which led to the formation of the islands
of Japan in the first place, but one that also causes a lot of friction and tension
beneath the surface. And what happens when the forces at play become too much for the
friction that holds it back, and things slip? That’s when you get earthquakes.
However, in the case of the Japan January 2024 earthquake that struck in the Noto peninsula,
it caught locals by surprise. Why? Because Noto was not actually on one of the major fault lines,
and scientists are not yet quite sure why earthquakes are even happening there. If
you map out the location of earthquakes by depth and location over the last 25 years,
you can see they congregate mostly on the eastern side of Japan, where the Pacific plate subducts
under the Okhotsk plate. You can even see how earthquakes that are further west are
also triggered deeper beneath the ground, representing the fact that the subducting
plate has moved further underground with the additional distance. But rather than
striking on the eastern side of the island, the January 2024 earthquake hit Noto to the west.
There are other peculiarities. Strange things have been happening beneath Noto over the last 3 years.
Since 2020, Noto has been experiencing tens of thousands of small earthquakes,
in a geological event known as an earthquake swarm. But counterintuitively, this consistent
rumbling is normally not something to worry about, as several small shakes are better than
one big one, and earthquake swarms generally die out quietly, rather than producing large
earthquakes. Noto’s earthquake swarm bucked the scientific models, lasting too long and
producing the exceptionally powerful January 2024 earthquake, and scientists do not really know why.
The consequences were serious. The January 2024 earthquake was a magnitude 7.5 and
struck at 4:10pm Japanese time on New Year’s Day, when people were gathered in their homes.
It was not just one event, but hit with a number of foreshocks and aftershocks – 1200
of them – that ranged across an area over 150km across. At least 7 were magnitude 5
or higher. 40,000 homes immediately lost power. Roads cracked. Buildings
collapsed. The Japanese government quickly issued a tsunami warning across the west coast of Japan,
the first waves of which arrived just 1 minute later in Suzu. A wave as high as 5 metres was
expected, although most of the footage captured is of a wave only 1-2m high. Certainly, the force was
enough that buildings along the coast were swept away. All told, there were hundreds of deaths and
over a thousand injuries across 6 prefectures, and over 18 billion USD in property damage.
The terrain itself bucked and rose. One strange feature of Noto is that there
has been an unexplained upswell that has been taking place there, beneath the crust, since
the earthquake swarm started in 2020. The edge of the peninsula had risen by about 3 cm since then,
indicating something was gathering down there. Perhaps water? Perhaps magma? Scientists aren’t
really sure. When the earthquake itself hit, however, that’s when the peninsula really
started to rise. Some sections of the land rose as much as 4 metres, and you can see the effects in
these satellite images. The change in the land’s elevation altered where the sea met the shore,
pushing the coastline back 250m, leaving some ports completely cut off from the water.
And when this much land moves, it can even influence the rotation of the planet itself.
Changing the distribution of mass on the planet’s surface changes how quickly it spins, in the
same way a ballerina pulling her arms in will rotate faster. In 2011, the magnitude 9 Tōhoku
earthquake in Japan shortened Earth’s days by 1.8 microseconds, or 1,8 millionths of a second. It’s
not much, and other effects such as differing sea levels also change the earth’s rotation speed,
but it’s amazing to see how interconnected the planet is. An earthquake in Japan can affect the
entire world. No matter where you are, your life was imperceptibly altered by the Noto earthquake.
With all of this, it is no wonder that scientists across the globe are working
hard to understand the causes of earthquakes. But for those who live under their constant threat,
such as for the people of Japan, (or other countries like Indonesia, China,
or Iran) it’s also important to defend against their consequences. So in an effort to improve
their architectural design to make them more earthquake resistant, Japan’s National Research
Institute for Earth Science and Disaster Resilience (or NIED) has taken steps such
as developing the world’s largest earthquake simulator; E-defense. This 20-15m shake table
supports buildings as tall as 10 storeys, and can use real-life data to simulate the
most devastating earthquakes Japan has ever experienced. By testing different designs
in different types of earthquake scenarios, architects have been able to design braces,
beams and metal joints that reinforce traditional Japanese houses, making them more Earthquake
resistant. It can be the difference between a building staying upright, or collapsing entirely.
Interestingly, NASA’s space program indirectly helped with creating earthquake-resistant
buildings in Japan. Consider the Tokyo skytree, the world’s tallest tower at 634 m, a place I
saw with my own eyes once when I was visiting Japan. Given the risk of earthquakes in Tokyo,
it was vital that engineers designed a building that could withstand large shakes. They did so
using a central 360m tall concrete column that sits on 6 massive rubber bearings,
which attaches to the building around it using fluid dampeners developed during the
NASA apollo program. When an earthquake strikes, these fluid dampeners cause the
central column to sway at a different rate to the exoskeleton of the building around it. The
different rhythms of motion counteract each other, reducing the motion in the
building overall. Incredibly, these effects can reduce the force of earthquakes by up to 50%.
Earthquakes can carry a terrible cost, in lives and destroyed homes and livelihoods. For the Noto
peninsula, the people there have slowly begun the task of rebuilding their lives. Although
the broken roads initially made it difficult for emergency services and repair workers
to get around, power has been restored to the majority of the 40,000 homes that were affected,
although as of March 2024, 790 still were without electricity. 18,880
were without water, and 11,400 people were still in evacuation shelters in Ishikawa prefecture.
Earthquakes are overwhelming examples of the natural forces that exist beneath us at all
times. They can shatter cities, and recovering from them is a slow task. But it speaks to the
hardiness and the determination of the people who make places like Japan their home. They seek to
find solutions to powerful earthquakes to predict them, and to mitigate their damage with clever
engineering .
This can help us all. Through studying the processes that take place beneath our feet,
we can better navigate this world that we live on in a way that helps us thrive. This
world is dangerous, but also beautiful, and like life, its face is ever-changing.
It’s up to us to face that change, until we can overcome any disaster that befalls us.
Science continues to make discoveries at an awesome pace. It may have taken tens of thousands
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