A 6.4-magnitude earthquake struck off the coast of northern California early Tuesday but there was no tsunami threat, seismologists said. The relatively shallow quake hit 25 miles (40 kilometers) southwest of the port city of Eureka, in Humboldt county, the US Geological Survey said. In a preliminary assessment, the USGS said there was a low … Continue reading 6.4-magnitude quake strikes off northern California: USGS