READING THE NUMBERS
Magnitude, depth, shaking.
Magnitude describes the source. Intensity describes what a place experienced.
Shaking at a place
Intensity runs from I (not felt) to X and above (extreme). Distance, depth and local ground affect it.
MAGNITUDE · SOURCE SIZE
One unit ≈ 32× the energy
Each one-unit increase represents about 32 times the energy released. Magnitude alone does not tell you how strongly a particular place shook.
DEPTH · BELOW THE EPICENTER
Where the earthquake began
The epicenter is the surface point above the source. Shallow: under 70 km. Intermediate: 70–300 km. Deep: over 300 km.
Why local ground can change the shaking
SAME QUAKE. DIFFERENT GROUND.
Why nearby places
can feel it differently.
The incoming wave can be the same, yet the ground underneath two places changes what reaches the surface. Try changing one site below.
Illustrative ground motion, not measured conditions or building damage at this earthquake. Soft ground does not amplify every wave equally.