Final answer:
The shaking duration in Mexico City in 1985 was decreased due to seismic energy being trapped in soft sediments.
Step-by-step explanation:
The correct answer to the question is B) Seismic energy trapped in soft sediments. The shaking duration in Mexico City in 1985 was decreased due to seismic energy being trapped within the soft sediments. When an earthquake occurs, the seismic waves travel through different layers of the Earth, and when they encounter soft sediments, they can be trapped and attenuated, causing a decrease in the intensity and duration of shaking in the area.