Juan de Fuca Plate Activity

[dgavin]

I've been researching things to find any alternative explaination about why suddenly there are so many medium sized events here in the last few months, as opposed to what i said three posts ago.

It seems that in January/Febura, NOAA released a series of under water siesmographs onto Jaun De Fuca plate. While that might account for an increase in reporting of smaller events, I don't think that would account for an increase in reporting the 4-5 magnitude events.

So were still looking at an unusual amout of medium sized quakes, without much indication as to what it might lead too yet.

[dgavin]

Another 4.5 on the South Gordo portion of Jaun de Fuca plate today.

[dgavin]

And another 4.2 quake today at the northern most interface of North America (Canada), Pacific and Jaun de Fuca plates.

[dgavin]

3 more quakes this week after a long peorid of quiet, 3.3, 3.6 and 4.4 magnitudes.

*edit to add*

Another quake today, 3.7 Mag.

[dgavin]

4 more Quakes, two today. 4.5 followed by a 4.8 on the norther edge of plate today, a 3.3 and 2.1 on the mid and south parts of plate ealier this week.

I finnaly found out that the seemingly sudden appearence of these quakes and continuing frequency of them, is due to the recent installation of ocean based Siesmographs. On average Jaun De Fuca has around 600 quakes a year, typically 3 of which are over 5.0 magnitude. Before this year they were only detected through Hydrophones left in operation after the last war (WW2) so the data was only availabe through US Navy channels.

So now we have real time ocean based Siesmographs in operation now, and seeing the results of that.

[dgavin]

Nothign to worry over, but just an FYI.

Toady at 8pm Pacific Time, many siemographs from nothern Calif, to southern Canada picked up a slow/slip tremor signature of the Jaun-de-fuca Subduction zone. The strogest readings were from the Mid. Oregon stations.

These do happen occasioanly, but this is the first time I've seen this happen since I started watching webicorders. The wave forms had a frequency span measuring in the 30's of seconds. Nice to finaly catch one of these types of background events.

[grapes]

Still reading.

[Ara Pacis]

Is this the location from which the infamous 1700 Cascadia subduction zone megathrust earthquake and tsunami originated?

[dgavin]

Ara,

My method of location is a bit rough and based more on signal stregths and arrival times, then on the proper methods (As i'm not trained well enough in those fomulas yet). The strongest signals were alost directly below 3 Sisters and Newberry calder areas, while the arrival timing puts it bit more towards the coastal region of Oregon.

So if i'm not to far off, it is south of the 1700 event which occured mostly along the washington coast.

[dgavin]

Besides the Mt. Axial activity along the Jaun De Fuca ridge, there was a 3.6 quake off the coast of Eureka, Calif., and a 4.3 just off shore of the calif/oregon border.

I'd almost have to say these are follow up events to the slow slip event from Mar 24th.

It's been quiet on the plate for a number of months, and then activity picks up again just after the slow/slip event. The quakes are all located at the spreading/transform boundries between pacific plate, and Jaun De Fuca plate. This also makes some sense if the slow/slip process reduces enough stress, then the spreading of the Jaun De Fuca ridge will be less impeeded.

[dgavin]

June 18th a 4.8 and a 4.2 about 1 - 5km's from the rift zone.

Today a 3.8 along the mid plate transfrom zone.

[dgavin]

Today (Sat Feb 4th) there was a 2.6. Quake off the Oregon Coast at 11 am, followed by a 4.3 near by that at 11:30am and then a 5.7 Quake at 12 noon, off the coast of Washington/Canada.

The 5.7 seems to be a standard Strike/Slip fault, the others have no movement tensors posted yet.

[Tensor]

... have no movement tensors posted yet.

Not surprising, I've been ill and spend most of the day in bed, so yeah, no movement here.

[dgavin]

Not surprising, I've been ill and spend most of the day in bed, so yeah, no movement here.

[dgavin]

A small 2.2 micro earthquake today, off oregon southern coast. Thats 4 quakes this week so far on the Jaun De Fuca plate. Nothing untoward about this activity though.

This was a nice one to look at in that it showed up on a number of broad band and volcano's seismographs, in spite of it's small magnitude. Noticed it first on Newberry/Pine Mountain stations, and can even follow and the see the signal arriving earlier the closer to SW coast stations are.


As far as Tensor movement goes, hopfully our Tensor is up and moving around again

[dgavin]

Late updates: On Sat Feb 4th there was an additional 4.8 Mag. quake near the 5.7 area. and a 3.0 quake near the 4.3 one on the pacific plate side of the Jaun De Fuca ridge. 6 Quakes total.

[dgavin]

Another quake reported late, on feb 7th, magnitude 3.4 directly on a part of the rift area, this one half way between the 4.3 and 3.0 from saturdays quakes.

And yesterday another 3.0 at the southmost part of the Jaun de Fuca rift off california coast, this one only at a depth of 600m (has not been reviewed yet though). Considering it's depth, this might be related to a hydrate release. It had a very -short- duration, 22 seconds, and there was no precursor P wave identifiabale (the webicorders may not be sensitive enough to see that though)

8 quakes total now.

[dgavin]

Another 3.0 just posted from jan 9th, near the other one and close to the same time. This one appears to be a normal strike/slip along the rift. 9 total now, still counting.

[dgavin]

Last night, 7:30 PST Valentines quake coming in at a 6.0 mag along the Jaun de Fuca Ridge.

[dgavin]

USGS posted five more older events from Jaun de Fuca, a 4.5 and 4.2 up by Canada, two 3.0’s at the southern edge, and a 2.5 just off shore from Lincoln City, OR.

Count for this week now at 6 quakes, with one strong.
Last two weeks total now upto 15 quakes.

At this point this is just slightly higher then the average amount of activty on Jaun de Fuca, but it's not anything significant to worry about.

[Sticks]

Name of thread changed to Jaun de Fuca Plate Activity

[dgavin]

Thanks Sticks!

Another 2.1 today about 80km from Depot Bay near the subduction region itself.

[Gillianren]

So we've introduced a misspelling into the thread title? It's Juan. Not "Jaun." It's the Spanish for "John."

[Swift]

So we've introduced a misspelling into the thread title? It's Juan. Not "Jaun." It's the Spanish for "John."

Everyone clap hard and think of their happy spelling thoughts....

[Trebuchet]

So we've introduced a misspelling into the thread title? It's Juan. Not "Jaun." It's the Spanish for "John."

As long as it didn't become "San Juan de Fuca", which is all too common, I'm happy.

[Gillianren]

Right. Two different guys. (Actually, there are a lot of San Juans. But you know what I mean.) Though the Wikipedia page on Juan de Fuca is more interesting than I would have expected.

[dgavin]

Two Aftershocks from the 6.0 added to USGS from prior days activity, a 2.1 and a 2.7. Weekly Count up to 9 again.

The reason these are sometimes delayed, is the Juan de Fuca plate seismographs are not on the list of stations that automatically post events. I asked a local Geologist that works for our Trasportation Dept. here about the delay on these.

So the smaller the event, the more delay there is before a Seismologist gets to it.

[dgavin]

Updates to last weeks activity: Another 4.7 near canada coast, and a 3.1 southern mid-plate.
Two week total: 18 with 1 mag 6.0

This week so far:
3.0 magnitude along subduction area off N. California, 3.4 aftershoock in the region of the prior weeks 6.0.

[dgavin]

A small quake yesterday, 2.7 off the southern oregon coast.

Total events at 21 so far, with an appearent slowing trend last week.

[dgavin]

Two small quakes today, 2.7 and a 2.8 west of Newport in the subduction region.