Earthquake intensity: human-based seismology

As long as I keep posting on geology and human affairs, let me continue with one about a scientific tool based on the perceptions of people rather than machines. That's seismic intensity. Whereas earthquake magnitudes measure the total energy of a quake, intensity describes the quake's effects at a particular place. Magnitude is how big the quake is, but intensity is how bad it is.

Earthquake researchers began their work in the 1800s with the first intensity scales. Without useful seismometers or well-developed physical theory, reports of intensity were all they had to work with. You wouldn't expect such a low-tech method to still be relevant today, but it is. In fact, with intensities cross-checked against seismograph readings now, it allows us to derive intensity data from odd things like piles of cans in groceries and balanced rocks in the desert.

_{San Francisco Cyclorama, 1906 — EERC, Univ Calif Berkeley}