The fourth earthquake this week to rattle Californian nerves occurred off the state's northern coast late on Thursday, with a strong magnitude of 6.6, the U.S. Geological Survey said. There were no reports of injuries or damage. Seismologists were investigating whether it was an aftershock from a major magnitude 7.2 earthquake late on Tuesday which prompted a brief tsunami warning for the entire U.S. west coast and part of Canada. The latest quake did not prompt such a warning. It struck at 10:21 p.m. (11:21 PDT/0621 GMT on Friday) local time at its epicenter, which was 120 miles (193 km) west of Ferndale, California, and about 300 miles (482 km) northwest of San Francisco, California. "It's south of and farther out to sea than the 7.2 quake," Bruce Presgrave, a geophysicist at the USGS National Earthquake Information Center in Golden, Colorado, told Reuters. He said there was a good chance it was an aftershock. Seismologists do not consider it particularly noteworthy that four significant seismic events occurred within a few days in California and off its coast. --More 1242 Local Time 0942 GMT
