West Coast Earthquakes

[bjdeming]

Nothing major, just a swarm about 270 miles due west of me, on the ever-active submarine Blanco Fracture Zone. It's reportedly not related to the Cascadia subduction zone megathrust quake threat (about 40% chance in the next 50 years for that, experts report). No tsunami threat, either.

Just thought it might be handy to have a thread for this in case the Hayward or some other fault breaks loose.

I've been out here 7-1/2 years and only felt a fleeting little quiver from an active site northwest of Eugene (I was in Eugene then). It zoomed through so quickly no one realized what had happened! May all our quakes be so harmless and minor.

 

[TH2002]

There was a small earthquake (3.6 Mw) centered about 7 S Lytle Creek which is not far from where I live. Nothing huge obviously but of note is that it happened at about 2 in the morning and I woke up a few seconds before the (most intense?) shaking started.

 

[bjdeming]

Oops:

Three loud sonic booms that shook buildings and people along the central Oregon coast Tuesday afternoon was caused by a mistake by an Oregon Air National Guard pilot during training exercises, a military spokesman said Wednesday.

Some authoritative person from the USGS, PNSN, or a university should take this opportunity for outreach and explain to the public the basic difference between a subduction zone (Cascadia):



And a transform fault (Blanco here; Mendocino and San Andreas offshore and in California, respectively):



Both are capable of intense damaging quakes, but they are two entirely different plate tectonics structures.

It would really cut down on public anxiety, if people understood this better.

The PNSN did note on their website (their emphasis):

The slip on these earthquakes are unlikely to have caused significant changes in stress along the Cascadia Subduction Zone 200 km closer to shore, which in the past has produced M9 earthquakes as recently as January 26, 1700.

Feeding off something mentioned in that second video, the Salton Sea area had a swarm earlier this year.

 

[bjdeming]

Speaking of the Mendocino fault zone...an M6.2:

The location and faulting mechanism indicate that the earthquake likely occurred on or near the east-west trending Mendocino fracture zone that demarks the plate boundary between the Pacific plate and southern Juan de Fuca plate (alternatively termed the Gorda plate).

The earthquake was located in the vicinity of the Mendocino triple junction – the region where the Pacific, North America, and Juan de Fuca plates meet.

The faulting mechanism of the December 20 earthquake is most consistent with the earthquake having occurred between the Juan de Fuca/Gorda and Pacific plates, as opposed to on the San Andreas fault (the boundary between the North America and Pacific plates) or on the Cascadia subduction zone interface (the boundary between the North America and Juan de Fuca plates)...

-- USGS

There was some damage but no deaths reported.

Aftershock forecast lists less than 1% chance of anything stronger here.

That Mendocino fault zone is really complex because it's also a triple junction. It might even shut down the Cascade volcanoes in the distant future (hopefully not before I get to see a small, pretty, nondamaging red-lava flow!).

Blanco is carrying on, too.

This is all just business as normal for transform faults, I think.

 

[bjdeming]

 

[TH2002]

Not sure why I felt like mentioning this until today, but occasionally my interest in earthquakes significantly ramps up, and this time I decided to take a little field trip - 800 feet from my front doorstep to be exact. As long as I can remember I always thought this gutter and fence looked kind of funny - but after zooming in on the interactive San Andreas Fault map, it was easy to see why it looks the way it does.


For reference:

The fault runs parallel to the street at the top of mine, crosses the road in the lefthand side of the photo and undercuts some houses - no , really, it's directly underneath them (and people live in those houses, unfortunately).

Well, at least I may be slightly better off in comparison to the poor folks in the northern end of nearby San Bernardino... maybe not really saying much in my case, though:

A few articles (including one by Dan Robinson):

We Visit The Doomed Homes On The San Andreas Fault

Some very big quakes shook Indonesia yet again, the mega-quakes of this last decade have been astonishing and the ‘aftershocks’ are still quite strong. Meanwhile, in North America, the…

emsnews.wordpress.com

San Andreas Fault, Part 6: San Bernardino

stormhighway.com

 

[bjdeming]

Just checking around after this morning's offshore (barely) M6.4 in California.

Per the USGS (see aftershock forecast link):

The
USGS estimates the chance of more aftershocks within the next week until December 27, 2022 16:40 (UTC) as follows:

• There is a more than 99% chance of magnitude 3 and above aftershocks within the next week, and it is most likely that 5 to 24 of these will occur.
• There is a 73% chance of magnitude 4 and above aftershocks within the next week, and it is most likely that 0 to 4 of these will occur.
• There is a 13% chance of magnitude 5 and above aftershocks within the next week, and it is most likely that 0 to 1 of these will occur.
• There is a 1% chance of magnitude 6 and above aftershocks within the next week, such an earthquake is possible but with a low probability.
• There is a 1 in 200 chance (0.6%) that this earthquake becomes a foreshock to a larger earthquake (magnitude 6.37 or greater) in the next week, such an earthquake is possible but with a low probability.
• There is a 1 in 700 chance (0.1%) of magnitude 7 and above aftershocks within the next week, such an earthquake is possible but with a low probability.

 

[bjdeming]

And a seismologist I follow retweeted this very helpful thread -- "Be mindful of [the] hazard":



Incidentally, migration of that triple junction northward is slowly, inexorably shutting down the Cascadia subduction zone and our volcanoes.

 

[WesL]

Sounds like there was some damage and gas leaks.
I spotted this tweet early on -



Can't imagine all the inspection work they have to do after something like this

 

[WesL]

Not sure why I felt like mentioning this until today, but occasionally my interest in earthquakes significantly ramps up, and this time I decided to take a little field trip - 800 feet from my front doorstep to be exact. As long as I can remember I always thought this gutter and fence looked kind of funny - but after zooming in on the interactive San Andreas Fault map, it was easy to see why it looks the way it does.
View attachment 15477

For reference:
View attachment 15480
The fault runs parallel to the street at the top of mine, crosses the road in the lefthand side of the photo and undercuts some houses - no , really, it's directly underneath them (and people live in those houses, unfortunately).

Well, at least I may be slightly better off in comparison to the poor folks in the northern end of nearby San Bernardino... maybe not really saying much in my case, though:

A few articles (including one by Dan Robinson):

We Visit The Doomed Homes On The San Andreas Fault

Some very big quakes shook Indonesia yet again, the mega-quakes of this last decade have been astonishing and the ‘aftershocks’ are still quite strong. Meanwhile, in North America, the…

emsnews.wordpress.com

San Andreas Fault, Part 6: San Bernardino

stormhighway.com

That is insanely crazy!! 800 feet you say.... woah!

 

[TH2002]

That is insanely crazy!! 800 feet you say.... woah!

I wonder if my grandparents knew about the fault when they built this house back in 1970... just for reference, they didn't know it was that close when I asked them recently.

Suppose it beats being literally right on top of the fault scarp, but regardless of whether or not this house gets pancaked I can say that anchor bolts can only do so much...