Understanding the difference between magnitude scales and intensity scales
Magnitude and intensity are two distinct concepts describing earthquakes, often confused by the public: 📊 Magnitude — measures the ENERGY of an earthquake • An intrinsic property of the earthquake, independent of distance or location • Each earthquake has a single magnitude • Common scales: Richter (ML), Body-wave (mb), Surface-wave (MS), Moment magnitude (Mw) • Modern seismology primarily uses Moment Magnitude (Mw), based on seismic moment — fault area × slip amount × rock rigidity • Each magnitude increase of 1 represents ~31.6× more energy. M8 releases ~31.6× more than M7, ~1,000× more than M6 • Largest recorded: 1960 Valdivia, Chile M9.5 📍 Intensity — measures the EFFECT at a location • Describes shaking severity and damage at a specific location • Varies by location for the same earthquake (attenuates with distance) • Uses the Modified Mercalli Intensity (MMI) scale: I: Not felt III: Weak shaking, like a passing truck V: Felt by most, hanging objects swing VII: Difficult to stand, chimneys and ornaments fall IX: Major building damage, foundations shift XII: Total destruction, landscape altered Simple analogy: Magnitude is the bulb's wattage; Intensity is the brightness on your desk (depends on distance).