Southern California earthquake swarm takes an unexpected turn, and that’s reason to worry

Southern California earthquake swarm takes an unexpected turn, and that’s reason to worry

June 11, 2019– Mary Greeley News – A swarm of earthquakes has taken the dimensions of a marathon in the area of the Southern California city. Caltech seismologist Egill Hauksson said the chance that the series of tremors will turn into a large and destructive quake isn’t particularly high.

But that doesn’t mean residents shouldn’t be on their toes. The likelihood of a larger seismic event, given so many quakes over such an extended period, is higher than normal, the scientist said.

“People ought to be concerned,” said Hauksson. “This is probably the most prolific swarm in that area of the Fontana seismic zone that we’ve seen in the past three decades.”

There have been more than 1,000 earthquakes recorded in the Fontana area since May 25, ranging from magnitude 0.7 to magnitude 3.2, recorded Wednesday at 5:20 p.m., according to Caltech staff seismologist Jen Andrews. Three of the quakes have been of magnitude 3 or greater.

The swarm initially moved northward, but something unusual began Friday when the swarm turned around and went south, back toward the middle of the swarm and the 60 Freeway.

“And this is somewhat of an unexpected evolution of the activity,” Hauksson said. Furthermore, an analysis of the earthquakes shows that it’s fading pretty slowly — slower than you’d expect for a typical sequence of aftershocks following a main shock, he said.

Southern California earthquake swarm takes an unexpected turn, and that’s reason to worry

“That would suggest it’s going to continue for — I don’t know — at least several weeks,” Hauksson said. “We’re watching what’s happening and trying to track that activity.”

Hauksson said given all the seismic activity, residents should make sure to store “plenty of water. Make sure there’s nothing that can fall on them.”

Southern California earthquake swarm takes an unexpected turn, and that’s reason to worry

Earthquake fault runs through Rodeo Drive and Beverly Hills’ shopping district, California geologists say

In any home in seismically risky areas of California, experts recommend removing heavy objects around beds, strapping bookcases and dressers to walls, anchoring flat-screen televisions to walls, installing toddler safety latches on kitchen cabinets, and ensuring frames are attached to walls with quake-friendly hooks. The last fatality in a California earthquake was from a blow to the head from an unstrapped television.

Homeowners should also make sure their water heaters are properly secured to reduce the chance of a house fire. They should also have homes that sit a few steps off the ground and built before 1979 be evaluated to see whether they need to be braced and bolted to the foundation, preventing them from sliding off when shaken. Apartment owners with carports or garages on the ground floor should also consider having their buildings evaluated by a structural engineer to determine if a retrofit is needed.

Hauksson said the timing of the earthquakes is worth noting: shaking, followed by a lull and then a spurt of new quakes.

The earthquakes have been relatively shallow — beginning just 1 to 2½ miles under the surface. As a result, the shaking has been widely felt, Andrews said.

Seismic swarms can be worrisome — especially when they occur near faults that experts know are capable of unleashing huge, catastrophic earthquakes.

That was the case almost three years ago.

Southern California earthquake swarm takes an unexpected turn, and that’s reason to worry

The magenta dots show quakes recorded from May 25 to June 6 — migrating from south to north. But quakes after midnight Friday, in black dots, changed directions and moved south, toward the 60 Freeway.Caltech seismologist Egill Hauksson

On Sept. 26, 2016, a rapid succession of small earthquakes — three measuring above magnitude 4.0 — began rupturing under the Salton Sea, close to the San Andreas fault, continuing for more than 24 hours. The swarm increased the likelihood of a major quake in Southern California, at least temporarily: experts said the chance of a 7.0 or greater quake on the mighty fault increased significantly, from 1 in 6,000 in any given week to as much as 1 in 100 during that particular week.

No large quake occurred. But the warnings did prompt some residents to prepare.

With the latest swarm, there is one silver lining: Two of the most fearsome faults in Southern California — the San Andreas and San Jacinto — are not particularly close. That means the chance of a truly large quake — the kind they make Hollywood movies about — resulting from the long-running cluster of tremors is not especially high.

www.marygreeley.com

credit: In part with https://www.sandiegouniontribune.com/news/california/la-me-ln-earthquake-swarm-fontana-glen-avon-20190608-story.html