How are they different, yet related?
Magnitude and intensity are different, yet related concepts. The size of an earthquake, or magnitude, is a single value, while seismic intensity, a measure of the strength of shaking at a specific location, varies depending on location. Three learning options of different lengths (5, 15, and 45+ minutes) provide hands-on activities to understand an earthquake’s magnitude and intensity using a lightbulb analogy and comparing factors that affect shaking intensity using USGS ShakeMaps and analyzing “Did You Feel It?” personal accounts to create a shake map.
Why is it important to learn about an earthquake’s magnitude and intensity? An important tool for earthquake mitigation is the ShakeAlert® Earthquake Early Warning (EEW) system for the West Coast of the U.S. which detects significant (magnitude 4+) earthquakes quickly so that alerts can be delivered to people and automated systems often before shaking arrives (intensity). ShakeAlert delivery partners incorporate magnitude and shaking intensity thresholds to determine whether to send ShakeAlert-powered alerts.
Learners will be able to:
• Explain that magnitude is a single value that measures the energy released at the source of the earthquake’s rupture.
• Explain that the intensity of shaking describes the severity of an earthquake.
• Understand that analyzing the personal accounts of shaking following an earthquake can be used to calibrate the intensity of official USGS ShakeMaps.
