A powerful earthquake struck last night off the northern California coast .
It registered at a magnitude 6.9
The U.S. Geological Survey says it struck at 10:18 p.m.
Its epicenter was about 4 miles beneath the ocean floor.
It was about 50 miles west of Eureka.
Hundreds reported feeling the quake.
But there were no reports of damage in northern California.
There were several aftershocks, the strongest of which measured 4.6 on the Richter scale.
No tsunami warnings were issued.