The focal mechanism shown below graphically portrays the orientation of the fault plane on which the earthquake occurred and the direction of relative motion on that plane. This information was automatically calculated from the first motion directions of the compressional (P) waves. A more detailed explanation describes how to interpret a focal mechanism. If more than one mechanism exists for this earthquake, then any of the solutions fit the first-motion data equally well.
USGS/CIT SOUTHERN CALIFORNIA SEISMIC NETWORK P FIRST-MOTION FOCAL MECHANISM (double-couple source assumed) Event Date & Time : 12/20/2012 17:54:31 GMT = Thu Dec 20 9:54:31 PST 2012 Location : 32.5228 N, 117.9785 W : (32 deg. 31.37 min. N, 117.deg. 58.71 min. W) Depth : 22.2 km. deep ( 13.9 miles) Magnitude : 2.8 Ml # P First motions : 14 Strike uncertainty : 20 deg. Dip uncertainty : 20 deg. Rake uncertainty : 10 deg.