Last night at 11:23 p.m. a M4.5 earthquake rattled Southern California epicentered 1 mile north of Yorba Linda, CA. This morning at 9:33 a.m. another M4.5 earthquake rattled the same region epicentered 1 mile north-northwest of Yorba Linda, CA. This by definition is an earthquake doublet. Given the level of seismic activity at this location at present this qualifies as an earthquake swarm. Watch this activity unfold below on the interactive map which updates regularly.