When a fault starts shaking .. it can sometimes continue for days or months.
They have sensors all over the place and can usually tell which fault line has been affected. As other quakes continue on that same fault line, they are considered “aftershocks” of the same quake. The original quake is usually much larger than the aftershocks.
You’d have to check with the USGS for info as to the fear of one quake causing a larger one - I believe it’s very unusual, but I don’t have any stats.
Thank you for your answer, that makes sense.....GG