[joxel]

Earthquakes can be sensed from basically anywhere, only the time it takes the P/S waves to travel to you are different, especially if the quake is M>5.

More sensors don’t really add more detections, but are useful for pinpointing an origin.

[citrin_ru]

If you don’t have enough sensors how do you distinguish between M<5 far away and M<5 in proximity?

[joxel]

The timing it takes for the P/S waves to reach you. One travels through the center, and the other travels along the surface of the earth.

Here's a quick rundown: https://slcc.pressbooks.pub/physicalgeography/chapter/4-3/