On March 11, 2011, Japan faced the most devastating natural disaster in its history. The 9.0 magnitude earthquake shattered the coastline and unleashed a tsunami that left more than 27,000 dead or missing and destroyed over 125,000 homes within hours. This overview explains how such disasters unfold, from the planet’s inner workings to the enormous waves that reach shore.
WHAT IS AN EARTHQUAKE? Earthquakes happen when the earth’s crust moves. The crust is broken into huge slabs called tectonic plates that ride on the partially molten mantle beneath them. When plates collide, slide against one another, or pull apart along faults, the stress builds until rocks rupture and energy is released as seismic waves. The point where the quake begins beneath the surface is the hypocenter; the surface directly above it is the epicenter. When the shaking is strong, earthquakes can trigger avalanches, landslides, and tsunamis.
HOW ARE THEY MEASURED? Seismologists measure the strength by the energy released using the modern moment magnitude scale, which replaces the older term commonly known as the Richter scale for accuracy. The numeric value indicates the quake’s energy; higher numbers mean more powerful shaking. The March 11, 2011 quake in Japan registered about 9.0 on the moment magnitude scale, placing it among the most powerful earthquakes on record. Source: United States Geological Survey.
AFTERSHOCKS After the initial rupture, smaller quakes called aftershocks almost always follow, continuing as the crust settles. Their strength tends to decline over time, though larger aftershocks can occur days, weeks, or even months later. If a later quake is stronger than the initial one, it becomes the main event and the first quake is treated as a foreshock.
DID YOU KNOW? Canada experiences relatively fewer earthquakes, though global seismic activity remains high. Scientists estimate about 500,000 earthquakes occur worldwide each year, with roughly 100,000 of them felt by people. Source: United States Geological Survey.
TSUNAMIS Tsunamis are colossal waves generated when large volumes of seawater are displaced by underwater earthquakes. The energy released travels through the ocean, pushing water forward and upward. The most destructive tsunamis are typically linked to earthquakes of magnitude 7.5 or higher on the moment magnitude scale. If powerful enough, one tsunami wave can travel thousands of kilometers in a matter of hours. In Japan’s 2011 event, the tsunami swept away cars and destroyed entire towns. Source: United States Geological Survey.
LANDSLIDES Like tsunamis, landslides can follow earthquakes. They often occur when the ground on slopes is shaken hard enough to crack, or when liquefaction causes saturated soils to lose strength and flow downhill. Debris from quakes can destabilize slopes, triggering deadly slides. Source: United States Geological Survey.
FOR THE RECORDS Before Japan’s 9.0 quake on March 11, the world’s most powerful earthquakes were:
5. Arica, Peru (now a part of Chile) – Magnitude: 9 August 13, 1868
4. Kamchatka – Magnitude: 9 November 4, 1952
3. Off the west coast of northern Sumatra – Magnitude: 9.1 December 26, 2004
2. Prince William Sound, Alaska – Magnitude: 9.2 March 28, 1964
1. Chile – Magnitude: 9.5 May 22, 1960