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Precarious Balanced Rocks Suggest the Risk to LA from Earthquakes May Be Smaller Than Previously Believed. [View all]
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"...
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.
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