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dgavin
2013-May-24, 09:19 PM
About 30 miles (50km) SE of Lassen near Greenville, there is a major earthquake swarm under way, so far, of 180 events, the two largest being a 5.7 and a 4.9 Magnitude. These are all shallow about 12km - 0km deep, and are along the known Mohawk fault zone. This appears to be all strike/slip related earthquake swarms and not volcanic.

Swift
2013-May-24, 09:33 PM
The 5.7 made the news (LA Times (http://www.latimes.com/local/lanow/la-me-ln-57m-quake-largest-to-hit-california-since-2008-20130524,0,5898728.story), though I heard about it on CNN this morning).

beskeptical
2013-May-24, 10:04 PM
Don't get too excited just yet. (http://www.nps.gov/lavo/naturescience/volcanoes.htm)


new! recent volcanic activitya series of earthquakes occured approximately 40 miles southeast of lassen volcanic national park on may 24, 2013. Volcanic activity is not expected as a result of the earthquakes, although changes may occur in hydrothermal areas for a few days following the nearby earthquakes.
the volcanoes of lassen the volcanoes in lassen volcanic national park are monitored by the united states geological survey (usgs). Seismic stations located throughout the park allow scientists to measure earthquakes in real-time. A new exhibit in the loomis museum includes an interactive map displaying sesimic stations and recent earthquakes within the park. This same map is visible online as part of thecalifornia volcano observatory (http://volcanoes.usgs.gov/volcanoes/lassen_volcanic_center/).

That's a long way away. Volcano seismograph monitoring shows quiet. (http://volcanoes.usgs.gov/volcanoes/lassen_volcanic_center/lassen_volcanic_center_monitoring_17.html)

ABR.
2013-May-25, 04:29 AM
I'm about 40 miles from the epicenter of all this activity. The initial 5.7 was a really good shaker. It shook the house much more noticeably than the 6.9 quake near Eureka a few years back, but then, that epicenter was much farther away. The 4.9 woke me up with a start. I think several other aftershocks disturbed my sleep as well. Other than those, we haven't felt any of the smaller aftershocks today. Several friends living in the Central Valley reported feeling very queasy during the initial quake.

dgavin
2013-May-25, 11:24 PM
While non Volcanic, it is quite the earthquake swarm. It's up to 242 events now. It appears be slowing down, with only 3 events in the last hour.

Interestingly enough, most of the Activity is between Wolf Creek, and Sheepcamp Creek areas. And it was the start of a full moon yesterday! Maybe we should be checking the woods for werewolves or Lycan's. :rimshot:

beskeptical
2013-May-26, 02:19 AM
This looks to be a very informative blog about the quakes. (http://www.wired.com/wiredscience/2013/05/earthquake-swarm-near-greenville-in-california/)

There's a link to this report on the fault systems in the area: Geodetic Constraints on the Slip Rate of the Mohawk Valley Fault Zone, California (http://earthquake.usgs.gov/research/external/reports/08HQGR0027.pdf)

The Mohawk Valley Fault Zone (MVFZ) is a seismically active, predominantly strike-slip, fault zone in the northern Walker Lane, California.
We established 18 new GPS monuments across the MVFZ. These monuments are similar to all other monuments established by the Nevada Geodetic Laboratory in the area, some of which were already established in the study area. These sites have been occupied for at least three campaigns over >2 year time-span. Most campaigns were 1-2 months long. We analyzed all data for these sites as well as for the regional continuous GPS sites from EarthScope’s Plate Boundary Observatory, and created position time-series from which we derived horizontal velocities. We rotated these velocities into a frame relative to the northern Sierra Nevada –Great Valley microplate by minimizing the velocities of 8 continuous stations. Velocities in this frame are predominantly oriented parallel to the trace MVFZ. We used the gradient of the along-strike velocities to infer a strike slip rate of 2.70.2 mm/yr (with a locking depth of 16.43.1 km). The normal rate is zero to within uncertainties. We will occupy all stations again in 2010, after which uncertainties in the velocities will be small enough to consider 1) any along-strike variation of slip, 2) a superimposed effect of other regional faults, 3) the possibility of unrecognized fault-normal component, and 4) the possible effect of asymmetry in crustal rigidity between the Sierra Nevada crust to the west and Sierra Valley to the east.

dgavin
2013-May-26, 03:05 PM
Up to 258 events now. The 5.7 event after looking at things was only 3 km from Lake Almanor's dam. The 4.9 was 2km Away. Thankfully as it turns out this is a Army Corps earthen dam used for irrigation and flood control and not a concrete dam used for power generation.

I have not been able to find anything specific, but I think rubble pile earthen dam's are a bit more resilient to earthquakes then concrete dams. I haven't been able to find if there has been any shifting of the material at the dam yet or not. I suspect that will have to wait for a inspection report of some kind.

Gillianren
2013-May-26, 03:36 PM
Based on my California history class (so something I heard about twenty years ago, and take it for what it's worth!), it depends a great deal on the dam. One of the greatest disasters in LA history was caused by the collapse of an earthen dam, but there were several ways it was badly built, and they've been studied at length--and presumably aren't the case in this one.

ABR.
2013-May-26, 05:39 PM
From our local paper's account of the quake (http://www.chicoer.com/news/ci_23322527/state-emergency-plumas-county-deals-fallout-greenville-earthquake?source=rss_viewed).


PG&E supervisor Hans Simonsen, who lives in the area, said inspection reports from last night indicated "everything's OK" with the Almanor dam.

Simonsen said the dam was checked about an hour after the quake, and is being checked this morning too.

"We'll check and recheck," he said about 8:45 a.m.

PG&E spokesman Paul Moreno said that crews checked all of PG&E dams in the area, including Canyon Dam, Bucks Lake, Butt Valley, Big Meadow, and along Pitt River.

"We were looking for any change in turbidity in the water and the structure at the dams. Nothing was found at any dam. All are in good condition," Moreno said about 9:15 a.m. today.

beskeptical
2013-May-26, 05:54 PM
Up to 258 events now. The 5.7 event after looking at things was only 3 km from Lake Almanor's dam. The 4.9 was 2km Away. Thankfully as it turns out this is a Army Corps earthen dam used for irrigation and flood control and not a concrete dam used for power generation.

I have not been able to find anything specific, but I think rubble pile earthen dam's are a bit more resilient to earthquakes then concrete dams. I haven't been able to find if there has been any shifting of the material at the dam yet or not. I suspect that will have to wait for a inspection report of some kind.Do you always worry so much? ;)

dgavin
2013-May-27, 07:40 AM
Do you always worry so much? ;)

Someone say I was worried? News to me:D

dgavin
2013-May-28, 06:54 PM
Total up to 289 Events for the earthquake swarm. Looking at a few historical swarms in the area, this one is has a slightly above average number of events, but so was the initial quake so that stands to reason.

dgavin
2013-May-28, 07:19 PM
Looks like the 5.7 and then 4.9 quakes, may have some remote relation to Episodic Tremor and Slip (ETS) activty in the region that started just after the 4.9 aftershock, moving from Lake Almanor towards the normal ETS region around Redding, and then back. I have no idea what this might mean, but even if it's pure coincidence, it's still an intresting bit of information.

18464

dgavin
2013-May-30, 11:10 PM
Up to 313 Events to this swarm as of today. The ETS that appears sligtly related is also still on going, with the bulk of the deep slip tremors directly underneath the swarm location.

I wouldn't of though a moderate 5.7 quake and it's aftershocks could of affected the plates enough to cause ETS slipage around the 80-100km debth area, bit it is starting to appear that the two (Swarm and ETS) in this area are somehwat related. As to the mechinism of the relation I honestly don't have any idea. If this continues for a few more days I'll gather some data and talk to a local geologist.

dgavin
2013-May-31, 06:35 PM
Up to 332 events on this swarm. The ETS that appears sligtly related has ceased for now.

dgavin
2013-Jun-03, 07:12 PM
Upto 370 events over the weekend so swarm activity increased just a little, and the ETS Tremors/slip in the area also returned.

It's looking like the ETS in the lake Almanor region, is related to the eathquake swarm.

*edit to add*

As promised, as there appears to be more then a cursory coincidence with a related ETS and a Swarm, I just sent off an email with my observations, and a few questions to the PNSN.

BigDon
2013-Jun-04, 05:30 AM
So would these quakes be putting more strain on the San Andreas fault system or relieving it?

As I can see the cut of the San Andreas from my front porch I like to keep up on how it's feeling. :)

dgavin
2013-Jun-04, 07:31 PM
ETS(Episodic Tremor and Slip) is related to Plate Subduction. These events (The Swarm and the ETS) are inland at the south edge of the Cascadia subduction zone, and are seperate from San Andreas, which curves out to sea as it approaches the Subduction region.

So I don't think you have to worry about these affecting San Andreas fault at all.

Ara Pacis
2013-Jun-04, 07:36 PM
I don't think you have to worry about these affecting San Andreas fault at all.

I have the foreboding feeling that these sound like famous last words.

dgavin
2013-Jun-04, 08:00 PM
I have the foreboding feeling that these sound like famous last words.

*Exessive Hyperbole and Humor warning*

I suppose there is always some remote change that this swarm will trigger a serious ETS Event, that travels back up the Subduction region, causing a mega-thrust quake around 8 to 10 magnitude, which then in turn triggers a complete slip event along the entire San Andreas fault, which in turn then triggers rift zone seperation between baha and mexico, that then pushes Baha Californina and points west of San Andreas out to sea about a half mile.

Big Don, depending on which side of the falut zone he is on, would still be in California with beach front property, or the newly fromed, San Andreas Island, with beach front property.

San Andreas Island would then apply for state hood, be summarily denied because no one want's 51 states, and a new civil war breaks out over that issue. :doh-default:

Ara Pacis
2013-Jun-04, 09:45 PM
*Exessive Hyperbole and Humor warning*

I suppose there is always some remote change that this swarm will trigger a serious ETS Event, that travels back up the Subduction region, causing a mega-thrust quake around 8 to 10 magnitude, which then in turn triggers a complete slip event along the entire San Andreas fault, which in turn then triggers rift zone seperation between baha and mexico, that then pushes Baha Californina and points west of San Andreas out to sea about a half mile.

Big Don, depending on which side of the falut zone he is on, would still be in California with beach front property, or the newly fromed, San Andreas Island, with beach front property.

San Andreas Island would then apply for state hood, be summarily denied because no one want's 51 states, and a new civil war breaks out over that issue. :doh-default:

Just add a bit about the separation resulting in a weird monster, like a half-octopus/half-bear, and you'd have yourself a Syfy creature feature movie. :)

Ara Pacis
2013-Jun-04, 09:49 PM
Just add a bit about the separation resulting in a weird monster, like a half-octopus/half-bear, and you'd have yourself a Syfy creature feature movie. :)

FYI, in case anyone is interested, my most recent time-tingle tells me that a big quake might happen in Alaska. This is because I saw a documentary two nights ago, I think, about tsunamis and I blipped when they mentioned Hawaii getting one from the Anchorage earthquake a few decades ago. I could make a joke, but we have rules about politics and religion.

BigDon
2013-Jun-05, 03:04 AM
Well, I've lived here since 1960 and have ridden out some interesting earthquakes, besides Loma Prieta.

My favorite Loma Prieta story: One insurance company office had an old fashioned, 1200 pound Wells Fargo floor safe. According to the pattern in the hardwood floor, the building performed a ten foot long figure eight maneuver underneath the safe, but the illusion is the safe took a hike across the room and then ended up back in the same position. The owners of the office were so impressed they had the repair people conserve the floor pattern by sanding it even and filling it in with clear resin.

dgavin
2013-Jun-11, 07:42 PM
Nothing back from PNSN on my observation report on potentialy related ETS and surface quake swarms. But it's only been a week, so they may be verifying what I reported. The seeming relation of swarm and ETS, are still going on at Lake Almanor, but at a much reduced rate for both types of activity.

dgavin
2013-Jun-14, 07:13 PM
Looks like the possibly related ETS portion of the swarm may be over. The Last ETS events in the swarm area were on the 3rd, and nothing since.

BigDon
2013-Jun-17, 10:21 PM
Sorry for the side track Mr. Gavin.

What's an ETS if I may ask?

profloater
2013-Jun-17, 10:25 PM
Sorry for the side track Mr. Gavin.

What's an ETS if I may ask?

guess that's an Episodic Tremor and Slip (ETS) looking at the previous posts

dgavin
2013-Jun-18, 12:25 AM
What Profloater said. ETS events are deep quakes, related to the actual movement of the oceanic crust underneath the continental crust. Basically quakes from that slow slip process, that occur at the junction of a subducting plate and the overlaying plate. Which is why I found it a little odd when a moderate surface quake and aftershocks, apparently seems to be related/maybe caused a small episode of ETS events much much deeper down.

And still waiting to hear back from PNSN on that, as it's something I can't explain. It may be something new never seen before, as ETS has only been measurable for about 15 years. May explain why I haven't heard back from them yet.