Are earthquake magnitude and intensity always correlated?

• A. Yes
• B. No
• C. Sometimes
• D. Always

Answer: (B)

Shaking at a location and energy release are different things, so they don’t always move in step. Magnitude measures the total energy that an earthquake releases, and it’s a single number on a logarithmic scale. Intensity describes how strongly the ground shakes at a specific spot, which is observed effects on people, buildings, and surfaces. Because intensity depends on distance from the rupture, depth, how seismic waves travel through the Earth, and local ground conditions (like soft soils that amplify shaking), the same earthquake can cause very different shaking in different places. A huge, distant, or deep quake might release a lot of energy but produce only moderate shaking at a far-off city, while a smaller quake that is shallow and near soft sediments can produce severe, damaging shaking locally. So they are related concepts but not perfectly correlated.