Seismologists don’t bat an eye at CA’s 400 small earthquakes

Posted at 8:04 PM, Jun 03, 2019
and last updated 2019-06-03 20:04:07-04

(CNN) — Southern California’s Jurupa Valley has recently been rattled by a “swarm” of small earthquakes.

Since May 25, 432 quakes have hit the area that only spans a few square miles, the US Geological Survey (USGS) reported Monday.

The quakes, as a whole, have measured 0.8 to 3.2 in magnitude and only a few have been significant enough to be felt, USGS seismologist Robert Graves said.

There’s no need to panic, according to seismologists and geophysicists.

Andrew Newman, a geophysicist at the Georgia Institute of Technology, said that while this swarm of earthquakes is attention-getting, these kinds of events usually do not precede a larger, stronger or more widespread earthquake.

Since there are no major faults nearby, Graves said he believes this swarm is likely due to small cracks or a weak area in the Earth’s crust.

“That zone is a place of weakness and that’s what’s causing these small earthquakes to occur,” he said.

“Large earthquakes occur on large faults,” he said.

For example, Graves said a magnitude 7 earthquake would have a fault length of about 30 miles and a magnitude 8 earthquake would have a fault length of 250 to 300 miles. The area where the swarm hit is only a few square miles.

There have been a couple of other swarms in the Jurupa Valley area. One took place in February and March of this year, and another in July and August 2018. Graves said swarms in these areas go as far back as the 1980s.

“In all of those previous episodes, the largest earthquake was a magnitude magnitude 4,” he said.

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Originally Published: 03 JUN 19 19:23 ET
Updated: 03 JUN 19 19:56 ET