When do rocks along a fault have the highest amount of stress and stored elastic strain?

When do rocks along a fault have the highest amount of stress and stored elastic strain?

• A. Right after an earthquake
• B. During an earthquake
• C. Long before an earthquake
• D. Right before an earthquake

Answer: (D)

Rocks on a fault store elastic energy as plate motion slowly deforms them and the fault remains locked by friction. This elastic strain builds up over time and reaches its maximum just before the fault ruptures in an earthquake. When the quake happens, the fault slips and energy is released, so the stress drops abruptly. During an earthquake the system is releasing energy and not at peak stress, and long before the quake the stress is still increasing toward that peak. So the highest stress and stored elastic strain occur just before an earthquake.

Rocks on a fault store elastic energy as plate motion slowly deforms them and the fault remains locked by friction. This elastic strain builds up over time and reaches its maximum just before the fault ruptures in an earthquake. When the quake happens, the fault slips and energy is released, so the stress drops abruptly. During an earthquake the system is releasing energy and not at peak stress, and long before the quake the stress is still increasing toward that peak. So the highest stress and stored elastic strain occur just before an earthquake.