Walker Lane geologic trough - E. California, W. Nevada

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Astronuc

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I read an interesting article about a relatively new fault zone, relatively new in the sense that it was realized after GPS stations were distributed by DOE in SW Nevada with the intent of demonstrating stability of the region near Yucca Mountain.


The article on Wired - https://www.wired.com/story/walker-lane-move-over-san-andreas-fault/

In the late 1980s, Stanford geologist Amos Nur coauthored a paper speculating that the San Andreas Fault might be looking for a new outlet in the Mojave Desert. Several years later, a strong 7.3-magnitude earthquake near the town of Landers, California, supplied compelling evidence that Nur might be right: Following that quake, a string of mysterious aftershocks rumbled up the Eastern Sierra, illuminating a network of faults that geologists had not previously thought were connected. This was the Walker Lane.

U.S. route 395 runs north from Hesperia and Victorville, California, northeast of Los Angeles, running up to Reno, Nevada along the eastern flank of the Sierra Nevada. The highway passes black cinder cones of Coso Volcanic Field and eroded scars of a mighty 19th-century earthquake near Lone Pine, and Hot Creek (near Mammoth Lakes), where one might see steam from water that boils up from an active supervolcano deep underground. Just east of Yosemite National Park near the Nevada border lies Mono Lake, with its surreal mineral formations known as tufa towers. James Faulds, Nevada’s state geologist, sees them as evidence for potential seismic and tectonic activity.

Another feature in Nevada is Pyramid Lake.

Most of the attention in California is focused on the San Andreas Fault and related faults between LA and San Francisco - probably because of the population density and expensive real estate.

Nevertheless, folks along eastern California and western Nevada should be aware of potentially strong seismic activity.
 
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davenn

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I read an interesting article about a relatively new fault zone, relatively new in the sense that it was realized after GPS stations were distributed by DOE in SW Nevada with the intent of demonstrating stability of the region near Yucca Mountain.

or maybe the lack thereof of stability 😉

In the late 1980s, Stanford geologist Amos Nur coauthored a paper speculating that the San Andreas Fault might be looking for a new outlet in the Mojave Desert. Several years later, a strong 7.3-magnitude earthquake near the town of Landers, California, supplied compelling evidence that Nur might be right: Following that quake, a string of mysterious aftershocks rumbled up the Eastern Sierra, illuminating a network of faults that geologists had not previously thought were connected. This was the Walker Lane.

The idea of migration of plate boundary migration of strain release to newer (relatively speaking) faults is interesting
and I see similar possibilities/pattern in the NE corner of the South Island of New Zealand.
The Alpine Fault that runs the length of the South Island, splays into several large faults in the NE of the region.
1) the Wairau Fault - the continuing main trace of the Alpine Fault -no major event in recorded history - 500 years
2) further SE, the Awatere Fault - no major event in recorded history - 500 years
3) further SE, the Clarence Fault - no major event in recorded history - 500 years
4) further SE, the Hope Fault - Major ruptures in 1888 and 2016

Further to the SE is a large number of smaller parallel and at this time disjointed faults including the faults that ruptured
in the 2010 ands 2011 Christchurch damaging events and I do wonder if we are seeing a continuation of the trend of
significant new splay faults being formed in the region that are now the ones that accommodate the majority of the plate
motion.

A basic fault map, I have drawn up, of the region showing the major faults and the lesser ones including the faults that
ruptured in the Christchurch 2010 and 2011 quakes

NE Sth Is basic fault map.JPG




Dave
 
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Steelwolf

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I live in the Puget Sound area WA State, USA, about 25 mi NW of Mt Rainier, and we have a number of faults running though the area since we have the San Juan plate breaking up under us and coming back up as St Helens (this last time around). So I always pay particular attention to this type of info. Seismology being a major field of study here, where we have a major field TO study, with several active to dormant volcanoes in our backyard. Being within 80 miles of St Helens, when she lifted off, was an experience. You could hear the boom, sort of, but there was a constant 'white noise' to the air and ground. The fish stopped biting entirely (I was on a lake at the time) and the water-skiers were starting to leave tracks in the pumice/ash on the surface of the lake.

Since then it has been a matter of course to track these and use the EQMashup site to get a reckoning of the EQ activity at any time. That mashup, live, is at: http://www.oe-files.de/gmaps/eqmashup.html
 

davenn

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since we have the San Juan plate
I will assume you really mean the Juan de Fuca Plate ? :smile:

Seismology being a major field of study here,
for you personally ?

Since then it has been a matter of course to track these and use the EQMashup site to get a reckoning of the EQ activity at any time. That mashup, live, is at: http://www.oe-files.de/gmaps/eqmashup.html

wasn't aware of that site
I have always used the USGS site, it's also real time for everything around the world


It has done me well for many years for figuring out where that quake I recorded was :smile:


Dave
 

BillTre

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The idea of migration of plate boundary migration of strain release to newer (relatively speaking) faults is interesting
This made me wonder about the origin of the faults. They have to originate at some time.
  • Has a fault even been observed in its initial formation? (Probably not easy to tell since its difficult to tell they are there until you get an earthquake from them).
  • Is there some unique seismic signature for such events? Are they extra large? (Thinking probably unknown for the reason above).
  • I suppose that there are models about how the crust deforms and eventually breaks under different conditions of strain or tension, but I never hear of them. Do such things actually exist?
 

Steelwolf

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@davenn, Yes, The Juan de Fuca plate, Islands, Strait and all, frequently referred to locally as the San Juans, connects to major series of faults and strongly impacts others. The USGS site is always nice.


@BillTre From what I have seen just in growing up with we have models for a few different mechanisms that could be culprit. There is the Late Major Impact Hypothesis with heavy cracking and initial underthrust, Plume and Spread Hypothesis (with tectonic plates, subduction and all) and have seen also the idea that life on the early, rather even crust, once life formed and started to form skeletons such as plankton starting to lay down diatoms and what would later become limestone. If it was in one location predominantly then maybe it was enough to do some form of initial depression, likely pulling in the edges as well, leading to primary faulting...and it is all downhill from there.

(All these possibilities were in my World Book and Britannica Encyclopedias editions as a kid, which having my neck broke at 6 made those books my best friends. Talk about having it easy with Google, lol. I had heavy books and few cross references unless I had the actual books. I do not think these ideas will have fallen far from the view of today's science)

However, I suspect it is a broad combination of all three mechanisms and now with the jumble of assorted plates it is either hold fast and strong, break up or sink with some zones doing automatic backfilling where the continents leave room.

And to finish with a bad joke:
Do you know what Mt Rainier told Mount Baker after Mt St Helens let go?

Sorry, not my fault.
 

davenn

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Has a fault even been observed in its initial formation? (Probably not easy to tell since its difficult to tell they are there until you get an earthquake from them).
Yeah, that's the problem, for a new fault,there is no fault break visible there till it does its first rupture.

Dr Alan Lind of the USGS HQ in Menlo Park, near San Francisco, did a wonderful experiment
demonstrating the lack of precursors to a new fault break, when I visited him back in 1999.

He took a wooden, yard long ( for the Americans ;), ruler in both hands and started to bend it in half.
Nothing happened to the ruler till it finally snapped with the build-up of stress/strain.


Is there some unique seismic signature for such events? Are they extra large? (Thinking probably unknown for the reason above).
Not that I am aware of ( not saying there isn't) I have never heard a seismologist say ....
"It was a new fault break because we recognised that from the seismic signature."
Rather they say ....
"It was a new fault break because we had not mapped a fault at that location before"

And that last one is one of 3 possibilities
a) they had mapped the region and noted all the faults
b) they had only roughly mapped the region and only had a basic idea of faults in that area
c) There had been no mapping done in that area and no idea there were faults there


I suppose that there are models about how the crust deforms and eventually breaks under different conditions of strain or tension, but I never hear of them. Do such things actually exist?
Yes there are. much study has been done on rock failure. That sort of stuff was covered when
I did geology at university. I would have to go googling for recent info


Dave
 

BillTre

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And that last one is one of 3 possibilities
a) they had mapped the region and noted all the faults
b) they had only roughly mapped the region and only had a basic idea of faults in that area
c) There had been no mapping done in that area and no idea there were faults there
Is there a way to map faults other than by mapping the occurrence of earthquakes?
 

Steelwolf

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I would think that with our preset mapping capabilities now, with Lidar mapping of changes daily that show slip incidences and the like would be able to show 'silent' faults, places where the land moves but there are not 'large' quakes associates with them. We get similar slipping here in the Pacific Northwest that actually reverses for a short time each year, but there is little actual vibration for it and has been tracked more with radio based sensors emplaced in hillsides and the like previously.

Other than that, historically it has been from noting the places where there was visible physical change such as lifting, rifting and displacement along the fault. (Where the roads or pipelines ruptured) That and historical records or being able to find geographic dicontinuities in the rock. It is possible to find old faults that have 'healed' by transforming the minerals to be stronger than the rock to either side once the pressures causing the fault in the first place ease some, or changing of direction of faulting.

Here in the Pacific Northwest we have several micro-plates that have converged on the West Side of the continental plate, largely from accretting the top of whatever is on the Pacific and Juan de Fuca plates as they are subducted. We have an interesting mix of geology here because of that, but are also right atop a subduction zone. We can see areas with cliff faces of folded metamorphic rock bedded in next to sandstone and basalt flats. Throw in the Puget Sound and periodic huge tsunami and our Western Shores have a lot of sand and clay from self-dissolving volcanoes and vast plains of tuff, fossilised volcanic ash. So we get new faults, or Previously Unknown Faults, as they prefer to call them as well as being able to see old faults and discontinuities in the landscape.
 

davenn

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Is there a way to map faults other than by mapping the occurrence of earthquakes?

Yes, by seismic surveying. On land they use small explosives or thumper trucks to be able to penetrate
several km into the ground to see underground structure .... layering, faults. The reflected signals that
are picked up by multiple geophones, like the ones I use at home to record local quakes, show depth
to and thickness of the layers.

seismic.jpg


vibrosesis-truck.jpg


long strings of geophones like these are laid out.....

fig5.jpg



At sea they use boomer units towed behind boats. These units produce bursts of sound ( hence the
name boomer) that goes down through the sea through the sea floor and again like the land system
the reflected sound waves are picked up on the unit being towed by the boat.
I spent a day or 2 on a boat off the local coast back home in NZ as part of my 3rd year uni studies.

I cant find a decent photo of a boomer unit behind a boat so you will have to settle for a drawing

Clipboard01.jpg



Some surveying results...

a couple of nice anticlines....

Clipboard01.jpg


layers offset by faulting....
Clipboard01.jpg



Dave
 

davenn

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I would think that with our preset mapping capabilities now, with Lidar mapping of changes daily that show slip incidences and the like would be able to show 'silent' faults, places where the land moves but there are not 'large' quakes associates with them.

GPS is used to show surface deformation

seismic surveying as in my last post is used to show what is happening underground


Dave
 

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