Question

Why are earthquakes monitored worldwide instead of in earthquake-prone areas only?

How many seismographs are needed to find the epicenter of an earthquake? Why is this number significant?

What is the relationship between P- and S-waves?

How did the study of earthquake waves lead to a greater understanding of the interior structure of Earth?

Not all earthquakes are felt by people; however, such earthquakes are often detected on seismographs. Why?