A magnitude 6.0 earthquake was recorded nearly 800 miles off the southern California coast on Tuesday evening, a ‘bizarre’ event that had little impact but sparked the intrigue of scientists in because of its location.
“It’s a decent size, but it’s just not a common place,” said Susan Hough, a seismologist with the US Geological Survey in Pasadena. “I’ve been watching earthquakes for 40 years and I can’t remember anything so significant there.” The quake occurred roughly in line with San Diego.
Since 1900, there have only been 10 other earthquakes recorded in the northern Pacific Ocean off the southern California coast – and tremors more than 500 miles from shore, all measured under a magnitude of 5.0, according to the USGS.
Tuesday’s earthquake happened just before 10 p.m. and as of Wednesday morning no aftershock had been recorded, Hough said. She said that due to its location, it is unlikely the seismic activity caused damage or had any other effects, although she said nearby boats could have sensed the movement.
The location of the earthquake is considered odd because it did not fall near or along the boundaries of tectonic plates, but in the middle of a large plate – a phenomenon known as an “intraplate earthquake”, a Hough said. The vast majority of earthquakes occur along plate boundaries, such as along the San Andreas Fault in California, although intraplate earthquakes do occasionally occur.
“It’s a weird earthquake,” Hough said. “There really is no global explanation for intraplate earthquakes except that they happen.”
She called Earth’s plates “pretty stable” because they don’t have major fault lines that shift or shift, but added that stresses can occur in the middle of the plates, such as the cooling of oceanic crust as it ages.
“There are stresses in the crust for all kinds of reasons, so you can have these weird events popping up,” Hough said. “It’s not unprecedented to have an intra-plate ocean earthquake in a weird place.”
While some earthquakes at sea can become cause for concern, depending on their proximity to communities or their ability to form a tsunami, Hough said this one was too far away and did not move the seabed this way.
“Being a large undersea earthquake is not enough to generate a tsunami,” according to a tweet from the USGS Earthquake Count Wednesday morning. “The earthquake must also move the seabed vertically, which is not what this earthquake did.”
Hough said a handful of people in California reported to the USGS that they felt a “weak jolt” at the time of the quake, but she said it was difficult to confirm whether this was a direct result. ocean earthquake. She said she expects this quake may trigger more research into intraplate seismic activity and any lingering effects, but otherwise she called it “not so bad.”
“It’s expected to be just a bizarre event, a kind of black swan happening in the middle of the Pacific,” Hough said. “But people will keep an eye on it.”
She said in 2018 ocean seismic activity off the east coast of East Africa led scientists to find an undersea volcano, but Hough said that was after detecting earthquakes. earth and repeated movements, of which she saw no sign in this case.
But she said it underscores how difficult some seismic activity remains to predict or explain, noting that a 6.0 earthquake near Chicago or on the East Coast could cause real damage.
“These weird, intraplate earthquakes can show up where we haven’t seen them in human lifetimes,” Hough said. “An unlikely place is not a problem if it is in the middle of the North Pacific or far offshore – an unlikely earthquake near people is a problem.”
Los Angeles Times