Seismic Intensity
Definition
A measure of the strength of shaking at a particular location, determined by observed effects on people, structures, and the natural environment. Decreases with distance from the epicenter.
Example
Intensity was VIII near the fault but only IV at 100 km away.
Related Terms
Related Guides
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Learn what causes earthquakes, how they occur along fault lines, and why some regions experience more seismic activity than others.
How Earthquakes Are Measured: Magnitude vs Intensity
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Modified Mercalli Intensity: Measuring What You Feel
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Epicenter vs Hypocenter: What's the Difference?
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Related Case Studies
The 1976 Tangshan Earthquake: The Deadliest Earthquake of the 20th Century
The deadliest earthquake of the 20th century, which destroyed 93% of an industrial city in seconds and exposed the limitations of earthquake prediction despite China's success at Haicheng one year earlier.
The 1948 Ashgabat Earthquake: The Soviet Catastrophe That Was Hidden for Decades
The most concealed earthquake disaster in history, where the Soviet government classified the true death toll of 110,000 as a state secret for 40 years.
The 1923 Great Kanto Earthquake: When Fire Destroyed Tokyo
The earthquake that proved fire -- not shaking -- is the primary killer in dense urban areas, with 38,000 people perishing in a single fire tornado.
The 1755 Lisbon Earthquake: The Disaster That Shook the Enlightenment
The earthquake that launched both seismology as a science and modern emergency management, while simultaneously triggering a philosophical revolution.
The 1556 Shaanxi Earthquake: The Deadliest Earthquake in Human History (830,000 Dead)
The deadliest earthquake in human history, killing 830,000 people -- primarily because the population lived in cave dwellings carved into loess cliffs that collapsed en masse during the shaking.
Related Tools
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.