A UCLA geophysicist warned last week that an earthquake measuring at least 6.4 on the Richter scale could shake Southern California by Sept. 5. Scientists have never been able to accurately predict earthquakes, but professor Vladimir Keilis-Borok said he had discovered the Holy Grail of earthquake science. By tracking seismic patterns along fault lines, Keilis-Borok and several colleagues last year forecast earthquakes in California and Japan months in advance. The patterns now point to a big quakes striking soon within a 12,000-square-mile patch of the Southern California desert. State geologist Michael Reichle said the latest prediction was a reminder that earthquakes were inevitable in California, but it doesnt mean the Big One is imminent.