LOS ANGELES (AP) – A vigorous aftershock sequence is following the strongest earthquake to hit Southern California in 20 years.

A magnitude 5.4 quake at 4:07 a.m. Friday is so far the strongest aftershock of Thursday’s magnitude 6.4 jolt, and was felt widely.

Seismologists had said there was an 80% probability of an aftershock of that strength.

Thursday’s big quake struck in Kern County, near the town of Ridgecrest, which suffered damage to buildings and roads.