“If you don’t move the water vertically, you don’t make a wave,” Minson said. “Most of these earthquakes are happening offshore,” Minson said, “so the amount of shaking onshore is less.”Īnd the way the faults tend to move - side to side rather than up and down - lessens the potential for an earthquake related hazard, such as tsunamis or seismic sea waves that can produce devastating flooding. Ghilarducci said Tuesday’s temblor was about eight miles from shore. Magnitude-5.6 quake reported off the coast of Humboldt Countyĭespite the high potential for earthquakes, Minson said that unlike the Bay Area, the fault lines and earthquake epicenters along the Humboldt County coast tend to be far out to sea, lessening their severity. “So people do need to be prepared especially if they’re in weakened structures,” Pridmore said. She said strong aftershocks are a concern - by Tuesday afternoon there already had been about 80 aftershocks, the strongest magnitudes 4.6, 4 and 3.9 - and there’s a 13% chance of a magnitude 5 or greater striking in the near future. “The area over the last century has had about 40 earthquakes that are magnitude 6 to 7, so it’s not unusual for us to have earthquakes this size in this region,” said Cynthia Pridmore, senior engineering geologist for earthquake hazard communication at the California Geological Survey, at Tuesday’s news conference. The USGS noted moderate earthquakes, including a magnitude 5.2 south of Eureka on June 7, 1975, that produced more damage than the 1980 quake because its epicenter was onshore and closer to populated areas. It was felt from San Francisco to Salem, Oregon, though only six people were injured, and damage was relatively minor, given the magnitude, the USGS reported. 8, 1980, a magnitude 7 quake struck northwest of Eureka, with strong shaking for half a minute. The strong shaking damaged buildings, roads and bridges and triggered landslides in many of the same small towns affected Tuesday - Ferndale, Fortuna, Petrolia, Rio Del and Scotia, the California Department of Conservation said. One of the most powerful recent earthquakes in the area struck April 25, 1992, a magnitude 7.2, followed the next day by powerful 6.5 and 6.6 magnitude aftershocks. The main actors, the North American plate and the Pacific Plate, meet along the notorious San Andreas fault, which runs from Mexico east of Los Angeles and along the coast from San Francisco to Cape Mendocino, Minson said. Geological Survey’s Earthquake Science Center at Moffett Field in Mountain View, said the seismic activity is due to a mashup of tectonic plates in the earth’s crust. Sarah Minson, a research geophysicist at the U.S. “They’ve had pretty good sizeable earthquakes up in this area in the past, and we’re happy that this one wasn’t as large as it could have been and as we’ve seen in the past.” “It’s not an area where they’re strangers to earthquakes,” Mark Ghilarducci, director of the California Office of Emergency Services, said at a news conference Tuesday. In fact, a year to the day before Tuesday’s earthquake, a magnitude 6.2 struck in the same area. It’s been home to more than three dozen magnitude 6 or 7 quakes in the last century. The Monterey County town of Parkfield, dubbed the Earthquake Capital of the World.īut the Humboldt County coast where a magnitude 6.4 earthquake struck offshore early Tuesday might be among the state’s most regular if unheralded quake customers. Many places in California are linked to a history of powerful earthquakes - San Francisco, struck in 1906 and again in 1989 with the rest of the Bay Area and Santa Cruz.
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