Predicting Earthquakes: How Japan Is Learning From The Past

Summary

The video script covers the devastating 2011 Great Tohoku Earthquake in Japan, one of the largest recorded in history. It details the earthquake's unexpected magnitude, the massive tsunami it triggered, and the subsequent geological research aiming to understand the potential for future seismic events. Scientists are examining ancient tsunami records and drilling deep into fault lines to assess the recurrence of such disasters. The findings reveal the complexity of subduction zones, increasing concerns for Tokyo and other regions, where seismic hazards have intensified since the earthquake.

Takeaways

• 🌏 Japan, despite having one of the best earthquake research programs, was unprepared for the magnitude of the 2011 earthquake.
• 🔍 The earthquake's epicenter was in the Japan Trench, where one tectonic plate buckles under another, causing a 500 km long rupture.
• 🏙️ Tokyo's skyscrapers swayed due to the earthquake, highlighting the far-reaching effects of such a massive seismic event.
• 📉 The Great Tohoku Earthquake was the largest in Japan's history, causing the coastline to drop by a meter and shifting the main island.
• 🌊 The earthquake generated a massive tsunami, which, despite extensive sea walls, caused significant damage and loss of life.
• 🔬 Geologists are studying historical sediments to better understand past tsunamis and improve future disaster prevention plans.
• 🏞️ The discovery of mud deposits inland suggests that past tsunamis may have been more extensive than previously thought.
• 🌊 The 2011 tsunami's inundation limits were underestimated, which has implications for the planning and construction of critical infrastructure like airports.
• 🔍 The tsunami's behavior in different coastal environments, such as enclosed bays and valleys, can significantly amplify its height and impact.
• 🔬 International research is uncovering the role of low friction in the fault due to slippery clay, which can lead to sudden and large earthquakes.
• ⚠️ The increased strain on the Kanto seismic corridor post-2011 earthquake has heightened the risk of a major seismic event in the Tokyo area.

Q & A

What was the magnitude of the earthquake that hit Japan in March 2011?

The earthquake in March 2011 had a magnitude of 9, making it one of the largest ever recorded in Japan's history.

Why were seismologists surprised by the 2011 earthquake in Japan?

Even though Japan has one of the best earthquake research programs in the world, seismologists were surprised by the size and scale of the 2011 earthquake, as it exceeded previous predictions.

How did the 2011 earthquake affect Japan's coastline and main island?

The earthquake dropped the level of Japan's northeastern coastline by about a meter and shifted the entire main island of Japan to the east by up to 4 meters.

How did the earthquake affect the Earth's axis and Antarctica?

The shock from the earthquake was so great that it knocked the Earth off its axis and caused giant icebergs to break off from Antarctica.

What was the role of the sea walls and tsunami barriers during the 2011 tsunami?

Many people believed they were protected by Japan's sea walls and tsunami barriers, but the 8-meter tsunami wave exceeded the barriers, causing widespread devastation and loss of life.

What discovery has changed the way scientists interpret the geological record of past tsunamis?

Scientists discovered that mud, finer than sand, can be carried further inland by tsunami waves. This finding revealed that the true inundation limits of past tsunamis were underestimated.

How did the 2011 tsunami influence the design of new infrastructure, like the Sendai Airport?

The discovery that previous tsunami limits were underestimated suggests that infrastructure like the Sendai Airport may have been built in safer locations had the true extent of past tsunamis been known.

What is the significance of smectite clay in understanding the 2011 earthquake?

Smectite clay, a deep-sea sediment with very low friction, played a key role in the sudden and large slip of the fault during the earthquake, contributing to the massive magnitude of the event.

How has the 2011 earthquake increased the seismic risk for Tokyo?

The 2011 earthquake increased strain on the Kanto seismic corridor, which surrounds Tokyo, raising the probability of a large earthquake (magnitude 7 or greater) occurring in the city from 7% to 17%.

What are the ongoing challenges in predicting future earthquakes and tsunamis?

Despite advances in understanding seismic activity, predicting the timing and magnitude of future earthquakes and tsunamis remains difficult due to factors like unpredictable friction levels and the complexity of subduction zones.

Outlines

00:00

🌏 The Unpredictability of Earthquakes in Japan

Japan, known for its seismic and hotspot activity, was caught off guard by the massive earthquake in March 2011, despite having one of the best earthquake research programs globally. The earthquake, a 9 magnitude mega thrust, occurred along a 500 km fault line in the Japan Trench. The unexpected scale of the fault movement, estimated at 50 to 60 meters, led to significant geographical changes, including the eastward shift of Japan's main island by up to 4 meters. The quake also had global effects, such as knocking the Earth off its axis and causing icebergs to crack off Antarctica. The tsunami that followed, despite the presence of sea walls and barriers, resulted in significant loss of life and damage, highlighting the challenges of predicting and preparing for such natural disasters.

05:01

🔍 Reevaluating Tsunami Risks from Geological Evidence

The script discusses the importance of looking beyond recent history to understand the risk of tsunamis. Geologist Kisa Goto and his team study sediment cores to uncover evidence of past tsunamis. They found that the 2011 tsunami's inundation was significantly greater than previous estimates, with mud deposits indicating that the water reached further inland than sand deposits suggested. This discovery has implications for disaster prevention planning and infrastructure development, such as the Sendai airport, which was rebuilt post-tsunami. The team also uses computer models and video evidence to understand the flow speed and direction of the tsunami, which is crucial for predicting future events. The investigation also extends to the Sanriku Coast, where the tsunami's behavior was influenced by the geography, and to the discovery of boulders that provide clues about past tsunamis, including the potential for larger and more frequent earthquakes than previously thought.

10:03

🌊 The Role of Friction in Earthquake Frequency and Impact

This section delves into the role of friction in the frequency and intensity of earthquakes. Seismologist Jim Mori leads a project that investigates the fault's frictional properties, discovering that the presence of slippery deep-sea sediments, specifically a clay called smti, can cause sudden and large slips. This understanding challenges the predictability of earthquake intervals and highlights the potential for more frequent and impactful quakes. The increased strain on the Kanto seismic corridor post-Tohoku quake has doubled the likelihood of a magnitude 7+ earthquake hitting Tokyo in the coming years. The narrative emphasizes the need for engineers and planners to consider geological history to mitigate the risks associated with future earthquakes and tsunamis, as the geological evidence suggests that the threat of such events is more unpredictable than previously believed.

Keywords

💡Seismic

Seismic refers to the shaking or trembling of the Earth's surface caused by the release of energy in the Earth's crust, often due to tectonic activity. In the context of the video, Japan's location on a seismic zone makes it prone to earthquakes, which is a central theme as the video discusses the country's preparedness and the impact of the 2011 earthquake.

💡Tectonic Plate

A tectonic plate is a massive slab of solid rock that makes up the Earth's lithosphere. The video mentions how one tectonic plate buckles under another at the Japan Trench, which is a key geological process leading to the massive 2011 earthquake. This concept is crucial for understanding the forces behind such natural disasters.

💡Mega Thrust Earthquake

A mega thrust earthquake is a type of seismic event where one tectonic plate is forced under another, causing a massive release of energy. The video describes the 2011 Tohoku earthquake as a mega thrust earthquake of magnitude 9, highlighting the scale and severity of the event.

💡Inundation Limits

Inundation limits refer to the farthest extent of floodwaters, in this case, tsunami waves. The video discusses how the 2011 tsunami exceeded previous inundation limits, indicating that the event was more severe than historical records had suggested. This concept is important for understanding the scope of the disaster and the need to reassess safety measures.

💡Sediment Cores

Sediment cores are cylindrical samples of sediment extracted from the ground, which can provide a historical record of geological events. The video describes how geologists use sediment cores to study past tsunamis, providing a deeper historical context to the 2011 event and informing future disaster prevention plans.

💡Geological Evidence

Geological evidence is the physical record of past geological events preserved in rocks, sediments, and landforms. The video emphasizes the importance of incorporating geological evidence into disaster prevention plans, as it can reveal patterns and histories of events like tsunamis that are not captured in recent historical records.

💡Tsunami

A tsunami is a series of ocean waves caused by a large-scale disturbance in the ocean, such as an earthquake. The video details the tsunami that followed the 2011 earthquake, causing significant damage and loss of life, and how understanding the geological history of such events can help in disaster planning.

💡Subduction Zone

A subduction zone is an area where one tectonic plate moves under another, descending into the Earth's mantle. The video discusses how the Japan Trench is a subduction zone, which is a critical factor in the occurrence of large earthquakes and tsunamis.

💡Friction

Friction in the context of the video refers to the resistance that one surface or object encounters when moving over another. The video explains that low friction in the fault due to slippery clay allowed for the sudden and large slip during the 2011 earthquake, which has implications for understanding the behavior of such geological events.

💡Seawalls

Seawalls are coastal defense structures designed to protect against tsunamis and storm surges. The video mentions that despite the presence of seawalls, the 2011 tsunami caused significant damage, indicating the need to reassess the height and design of these structures in light of historical geological data.

💡Disaster Prevention Plan

A disaster prevention plan is a strategy developed to reduce the risk and impact of disasters. The video discusses the importance of creating disaster prevention plans that take into account geological history and the potential for large-scale events like the 2011 earthquake and tsunami.

Highlights

Japan's earthquake preparedness was challenged by the unprecedented size of the 2011 earthquake.

The 2011 Tohoku earthquake was a magnitude 9 mega thrust event, the largest ever recorded in Japan.

The earthquake moved the coastline by about a meter and shifted Japan's main island to the east.

The tsunami caused by the earthquake was unexpected in its scale, despite extensive sea walls.

Geological evidence suggests that past tsunamis were larger than previously thought, indicating underestimation in historical data.

Mud deposits found inland are a key indicator of past tsunamis' reach, suggesting they traveled further than sand deposits alone would indicate.

The 2011 tsunami's impact was so severe it influenced the design of new sea walls and disaster prevention plans.

The discovery of a longer inundation limit for past tsunamis challenges current understanding of historical earthquake magnitudes.

International research expeditions are drilling into the Japan Trench to understand the cause of large earthquakes.

Low friction in the fault, caused by slippery clay, explains the sudden and large slip during the 2011 earthquake.

The increased strain on the Kanto seismic corridor post-Tohoku quake raises the risk of a major earthquake in Tokyo.

The probability of a large earthquake in Tokyo has more than doubled since the 2011 quake.

Reconstruction efforts are informed by geological history to better prepare for future disasters.

The new 40 km seawall along the Sendai Coast is designed with the lessons from the 2011 tsunami in mind.

Subduction zones with slippery clay pose an unpredictable threat for giant earthquakes and tsunamis worldwide.

Understanding the geology of subduction zones is crucial for predicting and preparing for large-scale seismic events.

Transcripts

for a country straddling a seismic

hotspot Japan is better prepared for

earthquakes than

most but the sheer size of the one in

March 2011 took even seismologists by

surprise Japan is probably one of the

best earthquake research programs in the

world but we were not able to anticipate

this kind of event and I think a lot of

Si olist lot scientists F felt very

badly about

that 30 km below the Pacific Ocean where

one tectonic plate buckles under another

in the Japan trench the seaf Flor ripped

apart the Fulton zipped along a length

of 500 km in a mega thrust earthquake of

magnitude

9 several hundred kmers away in Tokyo

skyscrapers started to sway

the fault moved a lot more than we've

ever seen before it moved like 50 or 60

M which is just a huge

amount the Great tohoku Earthquake was

the largest ever recorded in Japan's

history it dropped the level of this

Coastline by about a meter and shoved

the entire main island of Japan to the

east by up to 4

M so great was the shock it knocked the

Earth off its axis and as the whole

planet shuttered giant icebergs cracked

off

[Music]

Antarctica and of course when you have

that much fault movement on the ocean

floor then you get a very large

tsunami less than an hour after the

Quake a massive tsunami slammed into the

northeastern

Coast

tragically many of the 18 A2 thousand

people killed or still missing must have

believed they were protected by the

world's biggest network of sea walls and

tsunami

[Applause]

barriers this is the highest hill in

Yuri AGA District so it was a natural

place for people to evacuate to when the

tsunami hit but even on top of this hill

the wave was over my head

[Music]

hundreds died here when the 8m tsunami

raced up the nearby River and swept away

the town and fishing

[Music]

port so how do we know if this

catastrophe was a rare event or one that

could happen again

soon to find out needs a much deeper

view of History Way Beyond the last

century or so our geological evidence is

not well Incorporated in uh disaster

prevention plan so now uh we are

thinking uh to go back further to

several thousand years and then making a

disaster prevention plan for future

tsunam risk

[Music]

assessment geologist Kisa goo reads the

prehistoric record of tsunami from what

they've written into the

landscape like time capsules old

sediments hold evidence about the reach

of tsunamis in the distant

[Music]

past his team samples hundreds of

settlement cores in lines across the

Sendai plain of Northern

Japan our Transit is coming from the the

shore and then passing through here

to um let's say three km farther Inland

from here more than a thousand years ago

a mega tsunami called called Jan tore

through here amid the dust and Rubble of

reconstruction work Gotto shows me Jan's

geological fingerprint in one of his

sediment cores this sun layer is

deposited by the 2011 toi tsunami band

you can see a yellow sun here so it's

probably uh 161 K tsunami deposit so

that was the samurai AG on here and then

this is a 869 Jan uh

deposit so that's

1,145 years ago that's right

yeah before 2011 the inundation limits

for ancient tsunami were defined by the

end of the sand

layer but the recent tsunami has changed

how scientists interpret the geological

record we found that the sun sickness is

30 cm in the coastal area then it's

sinning and sinning for the inland

while the sand here stopped 2.8 km in

land the water continued much further to

4.5 km so then there is a big gap

between the sand uh limit and also the

the water limit so we need to think how

to fill this Gap you looking for the

missing set that's right yeah and that

Missing Link is mud finer than sand it's

carried further Inland by the wave so

the height of the tsunamis are likely to

be bigger than previously thought yeah

that's right yeah it could

be so uh in in case of the 2011 deposit

sand distribution is just uh

60% of the tsunami inundation um

limit discovering mud in land nearly

half as far again as the sand is a

crucial clue it means the inundation

limits of previous meat tsunami have

been underes estimated and if their true

size had been known maybe the

International Airport would have been

built somewhere else the Sendai airport

has been rebuilt since the tsunami sent

cars and trees hurtling through here but

a graphic reminder remains of the horror

of that day a water level more than 3 m

High informed by their siment CES and

measurements of flow depth daa sugara

recreates the 2011 tsunami in a computer

model now H this is the primary part of

the main wave and this SC shows the

sediment concentration within the water

for the first time the videos provide

information he can use to validate his

simulation it's very important video

provides us the good estimate of flow

speed and also the temporal change of

flow Direction and so many

things further north on the San Ru Coast

the jagged Coast line even looks like

giant

waves the enclosed Bays made the tsunami

behave much differently than on the flat

Coastal

plane we at sea level this seaw wall is

10 m

High here was a gate and it's removed by

Itami so it's just smashed the gate it

was coming over the wall and this narrow

Valley it must have been like water

pouring too quickly into a funnel yeah

so water concentrated and and getting

higher and higher how high did it go uh

it said around 28 M 28 M so that's 10 m

28 M around the edge of this Valley

that's right can you see traces of that

along the mhm there you can see the

fence and it is partly broken so that

means that the tsunami reached uh

somewhere on the top of the of the

fence the current was so strong it

rolled massive Boulders far in land have

you been able to estimate the velocity

of the water flow here yeah so we use

the border to estimate how fast camic

current is required and it should be uh

faster than 9 m/ second 9 m a second so

roughly 30 km an hour that's right yeah

that's faster than most people can run

to almost uh 1 kilm from the coast

line further up the valley is one of the

boulders from the 2011 tsunami the team

estimates its mass and calculates the

flow speed needed to wash it

here and just nearby is an even larger

Boulder that locals say has always been

here A Relic from a tsunami in

prehistoric times possibly

Jan okay if we can identify the Jan

tsunami idence in the farther north then

we need to extend the

for so that means that the the magnitude

must be much larger and

larger add to that the discovery of a

longer inundation limit for Jun and

there's evidence of a much stronger

earthquake back in 869

ad the model say that the J magnitudes

should be larger than

8.6 so is that fault in the Japan trench

generating magnitude 9 earthquakes Once

In A Thousand Years or in a more random

patternn

the surprising answer lies deep

offshore an international Expedition has

been drilling into the fault in water 7

km deep to investigate the cause of its

massive

slip seismologist Jim Mori is one of the

Project's

leaders one of the most important things

that is not at all well understood in

seismology is friction how easily or how

hard does it it take or how much force

does it take to move the fault they

found friction in The Fault to be very

low because of a layer of deep sea

sediments that's very

slippery these very soft muds one thing

we've identified is something that's

called smti smti is a well-known clay

and it's well known for its very low

frictional property a lubricated fault

explains why the slip was so sudden and

large and how intervals between

magnitude n Quakes may not be constant

this complication is also driven by this

frictional level these low low slip

environments which sort of sort of can

go at almost any time once you get an

earthquake

started and the KnockOn effects are

major Tokyo is surrounded by a belt of

fols called the Kanto seismic Corridor

now under greater strain since the

tohoku quake the 32 million residents of

Greater Tokyo have long been bracing for

the next big one and the 2011 earthquake

added to that fear because it increased

the seismic hazards here the chance that

a large shock of more than magnitude 7

will hit Tokyo in the next few years has

now more than

doubled since the main Quake the

probability has risen from 7 to 177% a 1

in six chance these are very low

probability events that probably won't

happen in your lifetime but could and if

they do happen then the consequences are

very

high 3 years on as shattered defenses

are rebuilt the tsunami detectives want

the engineers to take geological history

into

[Music]

account this new seaw wall stretches for

40 km along the Sendai Coast given the

he of the 2011 tsunami MH is this seaw

wall big enough um this seaw wall is

designed for much more smaller one it's

7.2 M high but the tsunami wave here was

10

[Music]

m throughout the Pacific Rim wherever

subduction zones have slippery clay

giant earthquakes and mega Army remain

an unpredictable threat this is really

just the beginning uh in terms terms of

understanding the geology and using that

to understand these big slips of um

subduction zones all over the

[Music]

[Applause]

[Music]

world