In the past two days, malfunctions in the network of sensors that detect earthquakes in Northern California have issued three false alarms, forcing the U.S. Geological Survey to make a series of embarrassing retractions.. Just after midnight Friday morning, a magnitude 6.7 quake struck off the coast of Alaska. When its waves reached sensors operated by the Northern California Seismic Network, they were mistakenly interpreted as a 5.1 temblor near the Oregon border in Lewiston, officials say. ... The error occurred again Saturday morning after a magnitude 7.8 quake struck off the coast of Japan and the same Northern California...