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Southern California Hit By Swarm of 400+ Earthquakes Over Past Week: USGS

By Eva Fu

A swarm of over 400 small earthquakes has jolted the Inland Empire of Southern California over the course of last week, U.S. Geological Survey officials said on June 3.

Beginning on May 25, the stretch of only several square miles around Riverside County has seen at least 432 quakes. The largest one, which took place in Gen Avon on Monday around 4:30 a.m., had a magnitude of 3.2, while the smallest was around 0.8, according to USGS.

Dozens of smaller quakes also hit the area on Monday.

Experts said that they have yet to identify the cause of the earthquake swarm, but noted that the frequency of the quakes was not uncommon in the area due to the active fault lines.

“We live in an earthquake country, so these earthquakes in and of themselves are not going to cause any damage, but it’s certainly a chance for people to take a look at their emergency supplies,” Robert Graves, a researcher at the USGS, said in a press conference.

earthquakes California
A map showing the earthquakes that occurred in California from May 25 to June 3. (USGS)

Southern California has experienced over 1.8 million small earthquakes in the past decade—about one earthquake every three minutes, according to a new study published in April. About 90 percent of the quakes were so small that they have slipped through the detection system’s computing algorithms.

“You don’t feel them happening all the time,” but “they’re happening all the time,” Daniel Trugman, a seismologist at Los Alamos National Laboratory who co-wrote the study, told National Public Radio.

Despite the volume of the quakes, the experts said there is no reason to panic, as these small tremors that are common to the region don’t result in damage—it’s the 4 or 5 magnitude quakes and higher that need attention.

“This is the Fontana trend—a perennial hotspot of small quakes,” USGS seismologist Lucy Jones wrote on Twitter, referring to the city north of Glen Avon.

“When it has quakes, they are usually in clusters like this. In other words, ordinary, common California quakes,” she continued.

Most of the small quakes only hit as deep as 1 or 2 miles below the earth, which makes them much easier to be felt than those that take place 5 miles deep, according to Jones.

“This is just a place where the earth sputters along instead of letting go all at once,” she wrote in another tweet.

Small Earthquake Hits New Jersey

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Screenshot showing the small earthquake that took place in New Jersey on June 1, 2019. (USGS)

A minor earthquake occurred off the New Jersey coast on Saturday morning, although no reports of shaking were registered.

According to USGS, the 2.0-magnitude earthquake happened around 10:00 a.m. about 40 miles off the Atlantic County from a depth of around 4 miles under the Atlantic Ocean.

Earthquakes with a magnitude of 2 or less are classified as low-intensity microearthquakes and not easily felt, according to USGS.

According to the state website, earthquakes are rare in New Jersey despite there being numerous fault lines in the region. The damages experienced by historic quakes have also been minor: “items knocked off shelves, cracked plaster, and masonry, and fallen chimneys.” No deaths from earthquakes in New Jersey have ever been reported.