[Skywise]

Anyone else noticed the swarm going on in north west Nevada?

There's been 126 quakes in the area in the last seven days.

A link to the USGS map of the area,

http://tinyurl.com/q3eanr3

Brian

[Skywise]

The swarm in NW Nevada continues. As of this writing, there have been 415 quakes since the sequence started on June 11, 2014. The largest so far has only been a 3.6 but I think this bears watching. Nevada has had quite large quakes in the past.

Haven't been able to find anything on it, except for a couple news articles (minus all the 'weird' websites).

Brian

[PennyB]

(08-22-2014, 09:56 PM)Skywise Wrote: Anyone else noticed the swarm going on in north west Nevada?

There's been 126 quakes in the area in the last seven days.

A link to the USGS map of the area,

http://tinyurl.com/q3eanr3

Brian

A 4.1 quake there today---can't seem to find much info on this area. Anybody doing any work up there?

Penny

[Skywise]

(11-04-2014, 05:49 PM)PennyB Wrote:

(08-22-2014, 09:56 PM)Skywise Wrote: Anyone else noticed the swarm going on in north west Nevada?

There's been 126 quakes in the area in the last seven days.

A link to the USGS map of the area,

http://tinyurl.com/q3eanr3

Brian

A 4.1 quake there today---can't seem to find much info on this area. Anybody doing any work up there?

Penny

I've not found anyone talking about this area. It's interesting as it just keeps going and going.... Just when it seem to be dying off, off it goes again. And shallow. Many quakes are 0.0km.

And, there's NOTHING out there that I can see on the maps. It's an antelope preserve so not much human activity is going to be allowed. I'm not sure there's even any ranching.

Might have to see what geologic agencies in Nevada might be worth trying to query.

Brian

[Island Chris]

Hi all,

OK, I'm now very curious about what is going on. So, I actually made a figure comparing Nov 6 2014 earthquakes to Google Earth at same scale. I could not find easily much geology, but did find:
"The western edge is formed by a spectacular fault scarp with huge rims above vegetated talus slopes."
at:

http://www.blm.gov/style/medialib/blm/nv...%20WSA.pdf

I put a red oval on area of main quake swarm, which may have spread, and is now ~20 km across (=big).

Arrows are to possible fault scarps. This looks to be the Basin and Range of extension, where the ranges are footwalls of normal faults and the basins are the hanging-walls. It is common for the ranges to be back-tilted into the faults, above each fault. This could be the case here. While a very large scale geologic map of Nevada online showed faults in this area, I made no attempt to get a detailed map and match it to Google Earth. So, my interpretation is educated/speculative.

More on this in next post: I want to see if graphics work first:
OK, there is a symbol but cannot see graphics
Chris

[Island Chris]

OK, the graphic posted OK. The red arrows point to what I think are fault scarps.

If the EQ locations are any good, 20 km is a big area for a swarm, although the main activity looks like across a 5 km area. There has been a big debate about whether low-angle normal faults slip during large quakes: "low-angle" means dip less that 30 deg. Normal slip earthquakes are "supposed" to be on faults dipping 60 deg, but the big global ones dip 40-50 deg mainly. There is even a debate in the USA Basin and Range whether some of the observed giant flat faults are faults or bases if mega-landslides. I checked focal mechanisms of 3 of the larger quakes and they were normal slip with some oblique motion.

This area is remote and I wonder how much is known?

I'll email UCSB professor Phil Gans this figure and see if he has anything to say.

Chris

[Skywise]

Here's a Google Earth map, with all the quakes since the start of the swarm on April 12, 2014.

Also shown are faults from the USGS fault and fold database.

The only faults shown (in blue, hard to see, I know) are quaternary.

Brian

[Island Chris]

Thanks Brian,
Your figure is WAY easier understand than the two parallel maps I posted, plus you are using a fault data base and I was just interpreting the Google Earth image. At least I was basically correct on where I put arrows for faults.

It would be interesting to see some cross sections through the seismicity, perpendicular to fault strike. Is a lot of this on one large fault, and is it gently-dipping or steeper? Or, is it on a whole bunch of faults? The area of earthquakes seems to be expanding. Is there something deep that is creeping and loading shallower faults?

Chris

[Skywise]

(11-07-2014, 10:28 PM)Island Chris Wrote: It would be interesting to see some cross sections through the seismicity, perpendicular to fault strike. Is a lot of this on one large fault, and is it gently-dipping or steeper? Or, is it on a whole bunch of faults? The area of earthquakes seems to be expanding. Is there something deep that is creeping and loading shallower faults?

I've been curious about that as well. But I've not bothered to try to make a cross section because this data is all preliminary and/or automatic solutions. It would be better to use "relocated" quakes, and I wonder if anyone is going to do that.

I think the 'fuzziness' of the distribution is due to the preliminary solutions. I suspect that once relocated the quakes may line up quite well along the fault.

Brian

[Island Chris]

Brian
You certainly could be correct: is very remote and there could be few or no local stations, so locations could be off (but it probably states precision on each quake, at least those with focal mechanisms; I have not checked that). But, if these quakes are either on a "detachment fault" or some other non-steep fault, they could be spread out in map view. The fault pattern there that you sent looks complicated, so would not be surprised if quakes are on multiple faults.

Chris