2011 Tōhoku earthquake and tsunami

Based on Wikipedia: 2011 Tōhoku earthquake and tsunami

The Day the Earth Moved Japan Eight Feet Closer to America

At 2:46 in the afternoon on March 11, 2011, the entire island of Honshu—Japan's main landmass, home to Tokyo, Osaka, and 100 million people—lurched 2.4 meters eastward toward North America. The movement happened in six minutes. It was so violent that it shifted Earth's axis, sped up the planet's rotation, and shortened every day that followed by 1.8 microseconds.

The Japanese call it 3.11, pronounced "san ten ichi-ichi"—the numerical shorthand that joins 9/11 in the grim calendar of disasters that need no further explanation.

What Magnitude 9.1 Means

The Richter scale, which most people vaguely remember from school, stopped being useful for measuring truly massive earthquakes decades ago. Scientists now use moment magnitude, abbreviated Mw, which measures the total energy released. The scale is logarithmic, meaning each whole number represents roughly 32 times more energy than the number below it.

A magnitude 5 earthquake might knock items off shelves. A magnitude 6 can damage buildings. A magnitude 7 devastates cities.

Magnitude 9.1 is something else entirely.

The 2011 Tōhoku earthquake released energy equivalent to 600 million Hiroshima bombs. If you could somehow harness the seismic waves alone—not even the total energy, just what radiated outward through the rock—you could power Los Angeles for an entire year. The earthquake released nearly twice the surface energy of the 2004 Indian Ocean earthquake and tsunami that killed 230,000 people.

It was the fourth most powerful earthquake recorded anywhere on Earth since modern seismology began in 1900, and the most powerful ever recorded in Japan—a country that experiences more earthquakes than almost anywhere else and has spent centuries learning to build for them.

The Geography of a Catastrophe

The earthquake originated 72 kilometers off the Oshika Peninsula, in the Tōhoku region of northeastern Japan. Sendai, the largest city in the area with over a million residents, sat 130 kilometers from the epicenter. Tokyo, 373 kilometers to the southwest, felt violent shaking that sent millions of people diving under desks and into doorframes.

The quake registered the maximum reading of 7 on Japan's unique seismic intensity scale in Kurihara, Miyagi Prefecture. This scale, called Shindo, differs from moment magnitude—it measures the intensity of shaking at a specific location rather than the total energy released at the source. The distinction matters: a smaller earthquake directly beneath a city can cause worse shaking than a larger one far away.

Seismic instruments recorded ground acceleration of nearly 3 g—three times the force of gravity. Buildings designed to flex and sway survived. Others didn't.

Six Minutes of Violence

Most earthquakes last seconds. This one continued for approximately six minutes.

The rupture began at a depth of 32 kilometers beneath the seafloor and then propagated outward along the fault zone, tearing through rock from offshore Iwate Prefecture in the north to offshore Ibaraki Prefecture in the south. The fault zone that failed measured 500 kilometers long and 200 kilometers wide—roughly the distance from Boston to Washington D.C., and as wide as the state of Pennsylvania.

Analysis later revealed that what felt like one continuous earthquake was actually three separate events occurring in rapid succession, their seismic waves overlapping and reinforcing each other.

The Pacific Plate, that massive slab of oceanic crust that makes up much of the Pacific Ocean floor, had been slowly diving beneath the plate carrying Japan for millions of years. It moves at 8 to 9 centimeters annually—about the speed your fingernails grow. But the plates don't slide smoothly. They lock together, building stress like a compressed spring.

On March 11, the spring released. The seabed near the epicenter lurched 24 meters horizontally and rose 7 meters vertically. Closer to the Japan Trench—the deep underwater canyon where the Pacific Plate plunges beneath Japan—the seafloor shifted an almost unbelievable 50 meters.

We Knew This Was Coming

Here is the heartbreaking part: scientists had predicted this earthquake, or one very much like it, for over a decade.

In the year 869, during Japan's Heian period, a massive earthquake struck the same region. It generated a tsunami that swept across the Sendai plain, penetrating kilometers inland. For over a millennium, this event persisted mainly in historical records and local folklore.

Then geologists started finding physical evidence. Drilling into the coastal plain, they discovered layers of sand deposited by ancient tsunamis—three distinct layers in the last 3,000 years, suggesting that catastrophic tsunamigenic earthquakes occur in this region every 800 to 1,100 years.

In 2001, researchers calculated that since more than 1,100 years had passed since the 869 event, another major tsunami striking the Sendai plain had become highly likely. In 2007, scientists estimated a 99 percent probability of a magnitude 8.1 to 8.3 earthquake in this zone within the following 30 years.

They underestimated the magnitude. But they were right about the danger.

The Wave

When the seafloor rose 7 meters in an instant, it displaced an almost incomprehensible volume of water. That water had to go somewhere.

Tsunami waves in deep ocean are barely noticeable—perhaps half a meter high but hundreds of kilometers long, racing across the Pacific at jet airplane speeds. Ships at sea might not even feel them pass. But as these waves approach shore and the water grows shallow, they slow down and pile up. All that energy compresses into an ever-smaller space.

The tsunami that struck Japan's northeast coast reached heights of 40.5 meters—a 13-story building of water—in some locations near Miyako. In the Sendai area, waves traveling at 700 kilometers per hour reached 10 kilometers inland.

Residents of Sendai had eight to ten minutes of warning. That sounds like time to escape. But consider what escaping means: getting from wherever you are to ground higher than 30 or 40 meters. More than a hundred designated evacuation sites were themselves washed away.

The temperature was freezing. Snow fell. The city of Ishinomaki, which would suffer more deaths than any other location, was at 0 degrees Celsius when the wave arrived. Survivors who made it to high ground faced hypothermia. Rescue workers struggled through ice and snow to reach victims trapped in debris.

The Nuclear Nightmare

Forty kilometers south of Sendai, the Fukushima Daiichi Nuclear Power Plant sat on the coast. It had operated since 1971, generating electricity from six boiling water reactors.

Nuclear reactors require constant cooling, even after they've been shut down. The fission reaction can stop in seconds, but the radioactive decay of fission products continues generating heat for days, weeks, months. Without cooling, the nuclear fuel heats up. If it gets hot enough, it melts.

The earthquake triggered automatic shutdowns. The reactors stopped their chain reactions. So far, so good.

Then the tsunami arrived.

Fukushima Daiichi's seawall was designed for a 5.7-meter wave. The tsunami that struck measured over 14 meters. It swept over the wall and flooded the plant's lower grounds, destroying the emergency diesel generators that were supposed to power the cooling systems.

Batteries provided some cooling capability, but they were designed to last only eight hours—long enough, engineers had assumed, for either external power to be restored or new generators to arrive. Neither happened in time.

Over the following days, three of the plant's six reactors experienced full meltdowns. As the nuclear fuel overheated, it reacted with water to produce hydrogen gas. Without ventilation, this hydrogen accumulated in the upper levels of the reactor buildings. On March 12, 14, and 15, hydrogen explosions blew apart the containment buildings of reactors 1, 3, and 4.

The explosions weren't nuclear—they were chemical, hydrogen combusting with oxygen—but they scattered radioactive material and released it into the atmosphere. The Japanese government evacuated everyone within 20 kilometers of Fukushima Daiichi and 10 kilometers of the nearby Fukushima Daini plant. Hundreds of thousands of people fled their homes, many never to return.

The Human Cost

The official death toll, finalized in 2021, stands at 19,759 confirmed dead with 2,553 still missing. Another 6,242 people were injured. These numbers are almost certainly undercounts—bodies carried out to sea were never recovered, entire families vanished with no one left to report them missing.

Most victims drowned. Unlike earthquakes that kill through collapsing buildings, the Tōhoku disaster killed primarily through water.

The destruction displaced 228,863 people from their homes, according to a 2015 report. Some moved to temporary housing, others relocated permanently. The evacuation zones around Fukushima remained uninhabitable for years; some areas are still restricted today.

And there is another category of death that statistics struggle to capture: the disaster-related deaths from suicide, stress, illness, and disruption of medical care. The earthquake didn't just kill people directly—it set in motion cascades of tragedy that continued for years.

The Economic Reckoning

Initial estimates placed insured losses from the earthquake alone at 14.5 to 34.6 billion dollars. The true economic damage exceeded 300 billion dollars, making it the costliest natural disaster in recorded history.

On March 14, the Bank of Japan pumped 15 trillion yen—183 billion dollars—into the banking system to prevent a financial crisis on top of the humanitarian one. Economic studies later calculated that the disaster reduced Japan's real GDP growth by 0.47 percentage points in the following year.

But GDP figures obscure the texture of economic devastation. Fishing fleets destroyed. Rice paddies contaminated with salt water or radiation. Factories shuttered. Supply chains broken. The Japanese automobile industry—the most sophisticated and tightly optimized in the world—ground to a halt as missing components from Tōhoku factories idled plants across the country and around the globe.

The Physics of Planetary Change

The earthquake's effects extended far beyond Japan.

When the fault slipped, it redistributed mass on Earth's surface. Think of a figure skater pulling her arms in during a spin—she speeds up because her moment of inertia decreases. Earth experienced something similar. The redistribution of mass changed the planet's moment of inertia, and conservation of angular momentum required the rotation rate to adjust.

Every day since March 11, 2011 has been 1.8 microseconds shorter than it would otherwise have been.

The earthquake also shifted Earth's axis by somewhere between 10 and 25 centimeters—estimates vary based on different calculation methods. This affected the Chandler wobble, a small, slow oscillation in Earth's rotation that scientists have tracked since 1891.

In Norway's Sognefjord, the longest and deepest fjord in the country, standing waves called seiches began forming about thirty minutes after the earthquake struck Japan. These waves, reaching 1.5 meters high, continued for three hours—caused by seismic waves that had traveled through Earth's interior and were now gently rocking the Norwegian coastline, 8,000 kilometers away.

In Antarctica, the Whillans Ice Stream—a river of ice flowing toward the Ross Sea—slipped forward by half a meter.

The GOCE satellite (Gravity Field and Steady-State Ocean Circulation Explorer), orbiting 260 kilometers overhead, detected infrasound waves from the earthquake passing through the upper atmosphere. It became, accidentally, the first seismograph in orbit.

The Land That Sank, Then Rose

Immediately after the earthquake, a 400-kilometer stretch of Japan's Pacific coastline dropped by about 60 centimeters. This subsidence allowed the tsunami to travel faster and penetrate further inland—the water found a landscape that had suddenly become lower than its seawalls were designed to protect.

But then something remarkable happened. Over the following three years, the coastline began rising. It didn't just recover its pre-earthquake height—it exceeded it. The same tectonic forces that had caused the devastating sudden drop now worked more gradually in the opposite direction.

The land remembers.

The Aftershocks That Wouldn't Stop

In the first month after March 11, Japan recorded over 900 aftershocks of magnitude 4.5 or greater. Eighty exceeded magnitude 6.0. Several topped magnitude 7.0—events that would be considered major earthquakes anywhere else but were overshadowed by the main event.

Three significant aftershocks struck within an hour of the initial earthquake: magnitude 7.4 at 3:08 PM, magnitude 7.9 at 3:15 PM, and magnitude 7.7 at 3:26 PM. Imagine surviving a magnitude 9.1 earthquake and then, while still in shock, experiencing three more events that would each have been newsworthy disasters on their own.

A month later, on April 7, a magnitude 7.1 aftershock struck offshore Sendai, killing four people and cutting electricity across northern Japan—including to nuclear facilities still recovering from the initial disaster.

Four days after that, another magnitude 7.1 hit Fukushima directly, killing three more.

The aftershocks followed a mathematical pattern discovered by Fusakichi Omori in 1894: the rate declines with the reciprocal of time since the main shock. The formula predicts that aftershocks taper off but never entirely cease. Years later, significant events continued. On December 7, 2012, a magnitude 7.3 aftershock generated a minor tsunami. On October 26, 2013, a magnitude 7.1 caused another small tsunami.

By March 2016—five years after the main event—there had been 869 aftershocks of magnitude 5.0 or greater, 118 of magnitude 6.0 or greater, and 9 exceeding magnitude 7.0.

The Fire Mountain

Three days after the earthquake, Shinmoedake—a volcano on the southern island of Kyushu, roughly 1,000 kilometers from the earthquake's epicenter—erupted. The volcano had already erupted in January 2011, two months before, so scientists couldn't definitively link the March eruption to the earthquake.

But they noticed something else. Inspection of Mount Fuji, Japan's iconic volcano looming over Tokyo, revealed that the earthquake had cracked the roof of its magma chamber.

Mount Fuji last erupted in 1707, triggered by a magnitude 8.6 earthquake. The 2011 event raised the specter of history repeating, though no eruption has occurred.

The Liquefied Ground

When strong shaking hits loose, water-saturated soil, something disturbing happens: the ground temporarily behaves like a liquid. This phenomenon, called liquefaction, causes buildings to sink, tilt, or topple—not because they've collapsed, but because the earth beneath them has lost its ability to support weight.

Areas of reclaimed land around Tokyo experienced significant liquefaction, particularly in Urayasu and several other cities in Chiba Prefecture. Reclaimed land—created by dumping fill into coastal waters—is especially vulnerable because it consists of loose material that hasn't had time to compact naturally.

Approximately 30 buildings were destroyed by liquefaction and over 1,000 damaged to varying degrees. Remarkably, Haneda Airport, though built mostly on reclaimed land, escaped damage. So did Odaiba, Tokyo's artificial island entertainment district.

Why Weren't They Ready?

Japan is the most earthquake-prepared nation on Earth. The country experiences hundreds of earthquakes every year. Buildings are designed to sway without breaking. School children practice earthquake drills. The government operates one of the world's most sophisticated early warning systems.

The seismic preparation worked. Buildings designed to survive magnitude 9 earthquakes survived a magnitude 9.1 earthquake. The early warning system gave Sendai residents those crucial eight to ten minutes.

But the tsunami preparation didn't.

Part of the problem was historical: the seawalls protecting the Tōhoku coast were designed based on the 1960 Chilean tsunami, which had crossed the Pacific and struck Japan. That event produced waves of 5 to 6 meters. The 2011 tsunami exceeded 14 meters in many locations and topped 40 meters in some.

Part of the problem was complacency: the thousand-year recurrence interval for the truly catastrophic events made them easy to deprioritize. The 99 percent probability estimate for a major earthquake within 30 years assumed a magnitude of 8.1 to 8.3—large, but not catastrophic. The actual event exceeded even the upper estimates.

And part of the problem was the irreducible challenge of preparing for events that exceed all previous experience. The Fukushima Daiichi Nuclear Power Plant had backup systems for its backup systems. But those backup systems shared a vulnerability: they were all located in areas that the tsunami could reach.

The Surprise That Shouldn't Have Been

Some seismologists were surprised by the magnitude. The conventional understanding held that the fault zone off northeastern Japan couldn't produce an earthquake exceeding magnitude 8.5 because the plate boundary wasn't straight enough. Long, straight faults produce the largest earthquakes; curved, segmented faults tend to rupture in smaller sections.

This earthquake broke the rules—or rather, revealed that the rules were incomplete. The rupture jumped across segments that scientists thought would fail independently. The fault, which should have released stress in multiple moderate earthquakes over decades, released it all at once.

In retrospect, the pattern was there. The fault zone had a high coupling coefficient—meaning the plates were strongly locked together rather than sliding past each other gradually. The accumulated stress, unreleased since 869, had been building for over a millennium.

Earthquakes since 1926 had released only about 7 percent of the accumulated energy. The other 93 percent waited.

What We Monitor Now

The first indication that the earthquake had produced global effects came from GPS stations. The United States Geological Survey operates a worldwide network of Global Positioning System monitors, including several near the earthquake zone. The station closest to the epicenter moved almost 4 meters—an almost unimaginable displacement for solid ground.

This observation prompted NASA's Jet Propulsion Laboratory to calculate the earthquake's effect on Earth's rotation. The results confirmed what the GPS data suggested: the earthquake had fundamentally, if minutely, altered the planet.

The Ongoing Story

More than a decade after 3.11, the story continues. Decommissioning the Fukushima Daiichi Nuclear Power Plant will take 30 to 40 years and cost tens of billions of dollars. Some former residents have returned to areas where evacuation orders have been lifted; others never will. The psychological trauma persists across generations.

The earthquake also changed how scientists think about extreme events. The 2011 magnitude, the 2004 Indian Ocean magnitude, the potential for cascading failures—these exceeded what previous models predicted. We now know that the tail risks are longer than we thought.

The next major earthquake in the Tōhoku region might not come for another 800 years. Or it might come tomorrow—the recurrence interval is an average, not a schedule. What we know for certain is that the forces that produced 3.11 haven't stopped. The Pacific Plate continues sliding beneath Japan at 8 to 9 centimeters per year. The stress continues building.

Eight feet closer to America. 1.8 microseconds shorter every day. The planet still carries the memory of those six minutes in March 2011, and will for as long as it continues to spin.