Mono County and Long Valley residents felt more shaking during the early morning hours on Thursday, due to a magnitude-3.8 earthquake that sent an early wake up call to numerous locals and visitors. The U.S. Geological Survey said Thursday morning that the quake, the second relatively substantial one within the past week, struck at 4:40 a.m. local time and was located along the Hilton Creek fault, about 10 miles east-southeast of Mammoth not far from the Green Church road area.
A similar quake last Saturday night at 11:16:26 p.m. local time, a magnitude-3.5 earthquake, woke up some area residents who had just turned in. The weekend event’s shaking only lasted 5-10 seconds, as opposed to Thursday morning’s quake, which lasted considerably longer. According the U.S.G.S., the epicenter was located approximately 10 miles east-southeast of Mammoth Lakes along the same Hilton Creek fault.
The U.S. Geological Survey classified both quakes as Type II-III, or “Weak.” No reports of injuries or damage accompanied any of the U.S.G.S. reports.
It’s unclear whether several lesser shakers (most of which went unnoticed) are entirely related to both the Saturday night and Thursday morning quakes, as numerous such small quakes are typical in this region of California. Volcanic activity accounts for minor Type I day-to-day quakes that can number in the dozens each week. U.S.G.S. technicians, however, said the two major events on Saturday and Thursday appear to be tectonic in nature, also not unusual.
“We’re not unduly concerned, but we’re keeping an eye on the activity,” said a U.S.G.S. spokesperson.