Map showing the location of the July 21, 2020 magnitude-7.8 Simeonof earthquake on the Alaska Peninsula. The star shows the epicenter, and the reddish ovals delineate areas that ruptured in past earthquakes, shown with the magnitude and date. In the top left is a cross section, or 3D view, representing a rupture patch between the two plates (not this earthquake specfically). As the Pacific plate descends beneath the North American plate, earthquakes occur when strong friction built up between the plates ultimately ruptures, but the entire interface does not usually slip. Around the rupture patch, the fault plane remains locked, or unmoving, building stress toward the next earthquake. Credit: Alaska Earthquake Center