The Region : Earthquake Shakes Parts of 3 Counties

A moderate earthquake shook parts of Los Angeles, Riverside and San Bernardino counties but there were no reports of damage or injuries. Robert Finn, a spokesman for the Caltech Seismological Laboratory in Pasadena, said the temblor occurred at 3:15 p.m. and was centered about two miles north-northwest of Fontana, in the San Gabriel foothills not far from where Summit Avenue crosses Interstate 15. Finn said the quake registered 4.2 on the Richter scale. The Richter scale is a measure of ground motion as recorded on seismographs. Every increase of one whole number means a tenfold increase in magnitude--a reading of 7.5 reflects an earthquake 10 times stronger than one of 6.5.