A friend tells you he witnessed books and other objects falling off his bookcase during an earthquake. What was the magnitude of this earthquake but on the modified Mercalli scale?

V. Moderate

IV–V falls within the range of

4.0–4.9 so we put at 4.9

Explanation:

This V. Moderate earthquake is the type felt by nearly everyone, with many people awakened. Some dishes and windows are usually broken, and unstable objects are overturned such as books in a bookcase. Pendulum clocks may also stop.

answer conditional instability;