Magnitude measures the energy released at the source. It is a single number for an event, and it does not change with where you are.
Intensity measures the strength of shaking at a specific place, expressed on the Modified Mercalli scale from I to XII. A magnitude 6.0 at 100 km depth may produce intensity III at the surface; the same magnitude at 10 km depth may produce intensity VII.
Depth, distance, and local soil conditions all change intensity. Soft sediment amplifies shaking; bedrock reduces it.
When you read an alert, ask both questions: how large was the source, and how far was it from me?
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