The largest of the quakes was felt throughout much of Orange County.
All four quakes rumbled in a region that's had a 'swarm' of quakes since early March. The quakes are also close to the area of the Chino Hills--the so-called Yorba Linda trend--that produced a 5.4 quake last July. The region is close to the Chino and Elsinore fault zones.
Susan Hough, head of the USGS's Pasadena office, called the earthquake swarms curious earlier this month.
one of those sequences that doesn mold, we understand what a swarm is, or why they happen! Story by Senior Meteorologist Henry Margusity