A magnitude 4.2 earthquake struck offshore near the Northern California region, which experienced a strong magnitude 7.0 earthquake on Thursday. According to the United States Geological Survey, the earthquake occurred at 6:36 a.m. and was centered near Petrolia, California. This is the strongest aftershock since a magnitude 4.7 quake at 10:46 a.m. Thursday, one of many aftershocks the region has experienced following the powerful quake. According to the USGS, the area off the coast of Petrolia experienced eight aftershocks ranging in magnitude from 2.5 to 4.2 at the time of publication Friday morning. Most of the aftershocks from Thursday’s quake were concentrated within 10 to 40 miles of Petrolia.