Author Topic: California earthquakes du jour.  (Read 339 times)

rcjordan

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California earthquakes du jour.
« on: July 06, 2019, 01:13:56 PM »
California earthquake: A 7.1-magnitude quake rocks Ridgecrest just one day after a 6.4 earthquake. Experts predicted it
https://www.deseretnews.com/article/900078437/california-earthquake-ridgecrest-nba-summer-league-los-angeles.html

For comparison, the 2010 earthquake that devastated Haiti was 7.0 magnitude.  Why is CA suffering less reported catastrophic damage?  Population density? Better earthquake-aware construction?  Both?

rcjordan

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Re: California earthquakes du jour.
« Reply #1 on: July 06, 2019, 01:19:37 PM »
Looks like the answer is A: Population density.

"The United States Geological Survey reported that the latest earthquake’s epicenter was in the Mojave Desert"

nffc

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Re: California earthquakes du jour.
« Reply #2 on: July 06, 2019, 03:11:12 PM »
Felt the last one down here in Laguna Beach.

Mackin USA

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Re: California earthquakes du jour.
« Reply #3 on: July 06, 2019, 05:29:57 PM »
Laguna Beach

My #1 son did also.

Did you feel it MAP
https://earthquake.usgs.gov/earthquakes/eventpage/ci38457511/dyfi/intensity
Mr. Mackin

littleman

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Re: California earthquakes du jour.
« Reply #4 on: July 06, 2019, 06:29:53 PM »
I was going to hike Devil's Slide tomorrow, but holding off because of the remote chance that those quakes trigger one up here.  I don't want to be on a narrow cliff, known for rock slides during a quake.

rcjordan

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Re: California earthquakes du jour.
« Reply #5 on: July 13, 2019, 02:09:28 PM »
This oblique photograph shows the surface faulting from the M7.1 earthquake happened on July 5, 2019 in Searles Valley, California . The dirt track is right-laterally offset approximately 2.5 m (~8 ft)

https://old.reddit.com/r/Damnthatsinteresting/comments/ccmmeo/this_oblique_photograph_shows_the_surface/

ergophobe

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Re: California earthquakes du jour.
« Reply #6 on: July 13, 2019, 04:35:58 PM »
I was going to hike Devil's Slide tomorrow, but holding off because of the remote chance that those quakes trigger one up here.  I don't want to be on a narrow cliff, known for rock slides during a quake.

You might find this interesting from the Yosemite park geologist

Quote
Recent Earthquakes And (Lack Of) Rockfalls
Recent earthquakes centered near Ridgecrest, CA, were strongly felt in and around Yosemite Valley. The largest of these, a magnitude 7.1 earthquake at 8:19 pm on July 5, caused shaking of the floor of Yosemite Valley that lasted tens of seconds. Despite this shaking, it seems that there were not any rockfalls triggered by these earthquakes (please let Greg Stock know if you know otherwise!).

Earthquakes are one of the most reliable rockfall triggers in Yosemite.  At 2:30 am on March 26th, 1872, John Muir awoke to strong ground shaking, and, stepping outside of his cabin, observed a large rockfall sweeping down the cliff behind the Chapel (he could see it in the dark because of the sparking produced by pulverizing quartz). The Lone Pine earthquake, centered in the southern Owens Valley, was estimated to have been at least magnitude 7.4, and possibly as high as magnitude 7.9. Nine other large rockfalls were triggered by that earthquake, including one from Liberty Cap that generated an airblast that knocked Snow's Hotel (formerly near the base of Nevada Falls) off of its foundation.

More recently, a series of earthquakes May 25-27, 1980, centered near Mammoth Lakes, CA, triggered many rockfalls in Yosemite Valley.  The largest of these, a magnitude 6.3, triggered rockfalls from above the Sierra Point Trail, causing injuries and leading to the permanent closure of that trail.

Given this history of earthquake-triggered rockfalls, why is it that the strong ground shaking last week didn't trigger rockfalls? The answer likely has to do with the sensitive relationship between earthquake magnitude and epicenter distance. The recent earthquakes were relatively large magnitude, but they were centered 175 miles away from Yosemite Valley, so their energy was greatly attenuated by the time it reached Yosemite. In contrast, the smaller Mammoth Lakes earthquakes were centered just 35 miles from Yosemite Valley, generating strong ground shaking and rockfalls. So although the recent earthquakes were widely felt in Yosemite Valley, the long distance to the epicenter translated into shaking was apparently not strong enough to trigger rockfalls.

Fortunately Yosemite Valley is is a relatively low seismic hazard zone for California, but there are infrequent, large earthquakes along the eastern front of the range that could (will) trigger future rockfalls. If you experience strong ground shaking in Yosemite Valley, move away from the cliffs as quickly as you can.  (G Stock)

>>oblique photograph

Wow! Imagine if that had been in the middle of a city.