Principal tremor occurred 6 to 8 miles under the San Jacinto Mountains (Creative Commons).

The earthquake in Riverside County occurred at 9:56 a.m. PST and caused aftershocks that radiated northeast, the Los Angeles Times reported, reaching as far as 100 miles away in Los Angeles. 

From the L.A. Times: 

The vast majority of the aftershocks were largely imperceptible, with magnitudes smaller than 2.5. Valleys and other low elevation areas feel the effects most strongly, said Susan Hough, a USGS seismologist. 

"Deeper earthquakes tend to have wimpy aftershocks," Hough said. 

Lucy Jones, a seismologist with the U.S. Geological Survey in Pasadena, told the Associated Press that the temblor was a strike-slip earthquake on the San Jacinto Fault, the most active fault in Southern California.

Reach Executive Producer Agnus Dei Farrant here.