Earthquake Early Warning (EEW)
Definition
A system that detects an earthquake and sends alerts to people and systems before strong shaking arrives. Can provide seconds to tens of seconds of warning, enough to take protective action.
Example
Japan's EEW system sent alerts 8 seconds before the 2011 Tohoku earthquake's shaking reached Tokyo.
Related Terms
Related Guides
What Is an Earthquake? A Complete Introduction
Learn what causes earthquakes, how they occur along fault lines, and why some regions experience more seismic activity than others.
P-Waves and S-Waves: How Seismic Waves Travel
Learn how P-waves and S-waves travel through Earth, why P-waves arrive first, and how scientists use them to locate earthquakes.
The 2011 Tohoku Earthquake and Tsunami: A Complete Analysis
The 2011 M9.1 Tohoku earthquake triggered a devastating tsunami and nuclear disaster. A comprehensive analysis of one of history's worst earthquakes.
The 2004 Indian Ocean Tsunami: The Deadliest Wave
The 2004 M9.1 Sumatra earthquake generated a tsunami that killed 230,000 people across 14 countries. The disaster that changed warning systems.
The 2010 Chile Earthquake: Megathrust Lessons
The 2010 M8.8 Chile earthquake showed how strong building codes save lives. Lessons from one of the largest earthquakes ever recorded.
Can Animals Predict Earthquakes? What Science Says
Reports of animals acting strangely before earthquakes go back centuries. Learn what science actually says about animal earthquake prediction.
Can We Predict Earthquakes with Apps?
No app can predict earthquakes. Learn the difference between prediction and early warning, and which apps actually provide useful alerts.
Is It True That Earthquakes Are Getting Stronger?
Earthquakes are not getting stronger. Learn why it might seem that way and what the historical record reveals about earthquake magnitude trends.
What to Do During an Earthquake: Indoor Safety
Know exactly what to do during earthquake shaking when you're indoors. Covers homes, offices, stores, elevators, and other indoor scenarios.
Earthquake Preparedness for Seniors and People with Disabilities
Earthquake preparedness for seniors and people with disabilities requires special planning for mobility, medications, and communication needs.
Related Case Studies
The 2018 Sulawesi Earthquake: Strike-Slip Tsunami and Catastrophic Liquefaction in Palu
The earthquake that defied three textbook rules: strike-slip faults generated a destructive tsunami, the rupture propagated at supershear speed, and liquefaction flows traveled 700 meters on nearly flat ground.
The 2017 Mexico City Earthquake: M7.1 on the Anniversary of the 1985 Disaster
Striking on the exact 32nd anniversary of the 1985 disaster during a national earthquake drill, the 2017 earthquake served as a live audit of Mexico City's three decades of seismic improvements.
The 2011 Tohoku Earthquake: How a M9.1 Megathrust Triggered Japan's Triple Disaster
The only earthquake in recorded history to trigger a simultaneous earthquake, tsunami, and nuclear disaster, fundamentally changing how nations assess cascading risk.
The 2010 Maule Earthquake: Chile's M8.8 Megathrust and the Power of Preparedness
The clearest modern comparison showing that building codes save lives -- a M8.8 earthquake in Chile killed 525 people while a M7.0 in Haiti (35 days earlier) killed 316,000.
The 2004 Indian Ocean Tsunami: The Deadliest Earthquake Disaster of the 21st Century
The deadliest tsunami in modern history, killing 227,898 people across 14 countries, whose aftermath created the Indian Ocean Tsunami Warning System and transformed global disaster preparedness.
Frequently Asked Questions
The epicenter is the point on the Earth's surface directly above the hypocenter (focus) where the earthquake rupture begins. It is typically reported as latitude and longitude coordinates. The strongest shaking usually occurs near the epicenter, though local soil conditions and fault geometry can shift the zone of maximum damage.
A seismograph (or seismometer) is an instrument that detects and records ground motion caused by seismic waves. Modern broadband seismometers can detect movements smaller than the width of an atom. Networks of seismographs around the world enable scientists to locate earthquakes and determine their magnitude within minutes.
P-waves (primary waves) are compressional waves that travel fastest through rock, arriving first at seismic stations. S-waves (secondary waves) are shear waves that arrive later but cause more ground shaking. P-waves travel through solids, liquids, and gases; S-waves only travel through solids. The time difference between them helps determine earthquake distance.
The hypocenter (or focus) is the point within the Earth where an earthquake rupture initiates. It is described by latitude, longitude, and depth. The vertical distance between the hypocenter and the surface directly above is the earthquake's depth, which strongly influences how the earthquake is felt at the surface.
Seismology is the scientific study of earthquakes and the propagation of seismic waves through the Earth. It encompasses earthquake detection, location, and characterization; Earth's internal structure; seismic hazard assessment; and earthquake engineering. Seismologists use data from global seismograph networks to study these phenomena.