(CNN) — More than 1,000 aftershocks of magnitude 1.5 or greater have shaken Alaska since Friday’s big quake knocked out power, ripped open roads and splintered buildings in Anchorage, US Geological Survey geophysicist Randy Baldwin said Sunday.

The majority were of a magnitude of 2.5 or weaker, meaning they weren’t likely felt. But more than 350 of the aftershocks were higher than 2.5, according to USGS data.

Why do so many quakes strike Alaska?