Mag 5.2 earthquake, Southern California, San Jacinto fault

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Discussion Overview

The thread discusses the recent 5.2-magnitude earthquake that occurred near Borrego Springs, California, along the San Jacinto fault. Participants share personal experiences, speculate on the implications of the earthquake, and reference related seismic activity in other regions.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants describe their personal experiences during the earthquake, noting the intensity of ground motion and sound.
  • There is a suggestion that earthquakes below a magnitude of 6.5 may reduce stress in the region and decrease the likelihood of larger quakes, though this is contested.
  • A participant mentions the occurrence of a 6.3-magnitude earthquake in the Solomon Islands shortly before the California event.
  • A geophysicist's insights are shared regarding the typicality of magnitude 5 earthquakes in the area and the unusual distribution of aftershocks, with at least 600 recorded.
  • Some participants challenge the notion that smaller earthquakes significantly relieve stress in the region, arguing that the energy released is minimal compared to larger events.

Areas of Agreement / Disagreement

Participants express differing views on the implications of smaller earthquakes for regional stress and the likelihood of larger quakes. There is no consensus on whether the recent earthquake is a positive sign or a precursor to more significant seismic activity.

Contextual Notes

Participants reference various seismic events and their implications without resolving the complexities of stress distribution and aftershock behavior. The discussion includes assumptions about the relationship between earthquake magnitudes and regional tectonic stress.

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5.2-Magnitude Earthquake Rattles Southern California, Felt in Los Angeles, San Diego

https://gma.yahoo.com/5-2-magnitude-earthquake-rattles-southern-california-felt-112449426--abc-news-topstories.html

M5.2 - 20km NNW of Borrego Springs, CA
http://earthquake.usgs.gov/earthquakes/eventpage/ci37374687#general

I was in San Diego, actually in Lakewood to the east of SD, many years ago, when I experienced waves from a Mag 6.3 in that same area as the Mag 5.2. The ground motion was pretty impressive. The couch on which I was sitting was bounced and shaken. I sounded like a jet engine roaring, like when a plane lands and uses thrust reverse.
 
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Shouldn't anything below 6.5 be seen as good news for it reduces tensions and therewith the likelihood of the big one?
 
Ahhh! I felt this one. I shouldn't have been up that late, but never mind that. The largest earthquake I've felt in a long time!
 
I just read the Solomons had a 6.3
 
fresh_42 said:
Shouldn't anything below 6.5 be seen as good news for it reduces tensions and therewith the likelihood of the big one?
It releases tension/compression at the location of the quake, but that means tension/compression builds elsewhere. It could be a precursor, or not.Geophysicist Explains the Aftershocks
https://www.yahoo.com/movies/southe...physicist-explains-aftershocks-202406590.html
Friday's 5.2 earthquake along the San Jacinto fault network, part of the San Andreas system, rippled across southern California communities in the early morning hours, causing no casualties, but raising questions about what the quake could portend.

Ross Stein is an earthquake geophysicist who spent 34 years with the U.S Geological Survey. He left in 2014 to start Temblor.net, a startup that aims to help people assess their own risk from earthquakes, and take steps to mitigate that risk. He is also a consulting professor at Stanford, with an upcoming course this fall. He helps scientists and P.h.D students learn how to better convey the results of their work to the public.
Is this unusual, the rate of the aftershocks?
The rate may be typical, but they're very widespread, and that's interesting. Magnitude 5s are typical in this area. There have been four others since 1980 of same size and in the same general location. That's not unusual. It makes sense. It's an active area. What's unusual is that the bookshelf faults that connect the strands create opportunities. And there's a lot of run-out to the northwest, with a significant portion that hasn't erupted in 150 years. If that were to happen it's not unexpected and it wouldn't be a surprise.

But the aftershocks were surprising here?
There were an awful lot of them -- at least 600 aftershocks spread over an area of about 10 miles wide. The rupture area for a magnitude 5 should be 2x2 miles. So that's odd. They were widely distributed and some or most of them are on these weird, secondary bookshelf faults.
 
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fresh_42 said:
Shouldn't anything below 6.5 be seen as good news for it reduces tensions and therewith the likelihood of the big one?

that's a pretty common misconception ...
compared to the energy released in a M 7 to M8 event, it's just a small percentage and doesn't really change the overall stress in the region very much

fresh_42 said:
I just read the Solomons had a 6.3

yup around 4 hrs before the California event... recorded that one and several other M 6+ events in the SW Pacific / Indonesia region
over the last few days. Didn't record the Calif. event a bit small for my distance from it. Need to be around M6 and higher

upload_2016-6-11_18-35-59.png
the upper event is the M 6.2 from the Solomons
the lower event is a M 5.7 from the Fiji regionDave
 
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