Answer:
1. Why are earthquakes monitored worldwide instead of in earthquake-prone areas only?
Earthquakes are monitored worldwide instead of just earthquake-prone areas since earthquakes can happen all over the world, even far away from plate boundaries.
2. How many seismographs are needed to find the epicenter of an earthquake? Why is this number significant?
You need at least three seismographs to find the epicenter of an earthquake. The reason you need three or more seismographs is so you can see where the waves overlap to find the epicenter.