Precarious Balanced Rocks Suggest the Risk to LA from Earthquakes May Be Smaller Than Previously Believed.

[NNadir]

When my wife and I lived in the LA area early in our marriage, she kept an Earthquake kit, batteries, flashlight, wrenches (to shut of the gas), food, etc. The "Natives" made fun of her.

When we left California, we had to throw it all away. Shortly after we left the Northridge Earthquake produced long lines for these items. We did not need them after the Landers Quake, which was scary but not tremendously destructive in San Diego.

Northridge was not "The Big One" about which people worried in my time there.

Now there's evidence that "The Big One," at least in the LA area of the San Andreas fault may be relatively rare, if it ever occurs:

Precarious rock formations near Los Angeles hold clues to giant earthquake hazards

Subtitle:

San Andreas fault may shake less than once feared, surprisingly balanced boulders reveal.

I'm not logged into my account; the article is probably available for public reading.

Brief excerpts:

SAN FRANCISCO—Someday, a great earthquake will erupt from the San Andreas fault, which cuts through Southern California from Los Angeles to San Francisco. Geologic records make it clear. It has happened, and it will happen again.

But when the Big One does hit, it may be less devastating than once thought, at least near Los Angeles. According to new work presented this week at a meeting of the American Geophysical Union, the ground there will shake up to 65% less violently than official hazard models suggest.

The good news for Angelenos stems from five rocks balanced precariously on top of other rocks in Lovejoy Buttes, a place in northern Los Angeles County that sits just 15 kilometers from the fault. By dating when the rocks first became fragile and analyzing their structures to assess the maximum shaking they could withstand, the researchers could test official predictions against thousands of years of earthquakes. Those predictions have been found wanting, says Anna Rood, a seismic hazard scientist at the Global Earthquake Model Foundation who led the work, which is accepted in Seismological Research Letters. “The hazard estimates are totally inconsistent with these precariously balanced rock data.”

The new study is a welcome advance for an emerging technique, says Daniel Trugman, a seismologist at the University of Nevada, Reno. “They’ve applied probably the most rigorous methodology that I’ve ever seen to try and solve this problem"...

The age of the rocks and the time they've been balanced was dated using ¹⁰Be dating, related to the formation of this radioisotope in rocks from the cosmic ray flux that strikes the Earth continuously.

Nevertheless, if I lived in Southern California, I'd still have an Earthquake kit.

[2naSalit]

1. Alwys good to have...

An emergency kit regardless of where you are. There really aren't too many things in an earthquake kit than any other that I can think of though individual preferences apply. Up here near the wilderness, we keep that shit handy all the time. If you drive around in the US National Forests, you're supposed to have a shovel and a bucket in your vehicle.

Most everyone who lives out here, the actual locals who have any sense, have a "go bag" with gear needed to survive a week or two outdoors in bad weather. Don't have to be a 'prepper' to know why if you live up here in rough country. If I lived in a city in the east, I'd still maintain my 'go bag'.

Bad stuff happens no matter where you are, it's always good to have certain things handy just in case.

[quaint]

2. California native here. No one has ever teased me about my earthquake kit.

I sleep with boots near my bed and keep a small go bag under it.

[NNadir]

3. That wasn't my wife's experience.

We lived in California for about the first 9 years of our marriage, 4 years in the LA basin (Redondo Beach) and 5 years in San Diego.

We were sometimes reminded that we weren't "natives," and yes, some people told her she was overreacting by having an Earthquake kit; Perhaps this was a result of us not being "natives."

Back East we tell amusing stories about the two relatively intense - intense enough to be scary but not intense enough to cause major damage - earthquakes we experienced. (The 1992 Landers quake happened when were in bed, nekkid.) The next year, we escaped to New Jersey, but it wasn't about the Earthquakes so much as the opportunity and the reasonable cost of living.

We do have very nasty hurricanes here from time to time.

I don't remember what the first quake we experienced was called; it wasn't that big but did break some dishes and a the glass cover of a light fixture crashed to the floor.

I was a little more concerned about Landers, particularly because I had solutions of phosgene in the lab in plastic coated glass bottles. They were OK though. We had a few cracks in the wall at home - we were renters then - but no major damage.

[quaint]

4. I don't know if most of the people I am around are California natives or not; most wouldn't know that I am.

My first large quake: San Fernando Earthquake February 9, 1971 M6.5, five miles away.
Next was Whittier Narrows Earthquake October 1, 1987 M5.9, 13 miles away but right under my parents.
Not real big, but real close Chino Hills Earthquake July 29, 2008 M5.4
Feel anything over 5.0 but usually without damage.

I consider a kit and boots by the bed a wise practice.