Three earthquakes rattled the U.S. West Coast on Wednesday, serving as another reminder that one of North America's most dangerous seismic zones lies just offshore. The strongest of the trio struck off the southern Oregon coast, where the U.S. Geological Survey reported a magnitude-5.7 earthquake approximately 100 miles west of Pistol River . The quake occurred at a depth of roughly 10 kilometers (6 miles) within the offshore Blanco Fracture Zone, a geologically active area where several tectonic plates interact. According to the USGS and the National Tsunami Warning Center, no tsunami threat was generated by the event. The Oregon quake was accompanied by two additional earthquakes elsewhere along the West Coast on the same day. While none caused significant damage or injuries, the cluster attracted attention because of its proximity to one of the most closely watched seismic regions in North America, let alone the entire world.…