Wednesday, April 30, 2008

Is Water Lubricating a Mogul, NV Fault?


This is what I'm wondering. Yesterday, a geologist living in Mogul suggested to me that the recent earthquakes there remind him of the 1970's earthquakes in Denver, which turned out to have been caused by water injection in the area - with the water lubricating the faults and causing the earthquakes. Read up on the Denver earthquakes here with additional references here and here [the latter two are abstracts only]. The amounts of injected water they are talking about for Denver sounds rather large, and the injection (and earthquakes) took place over a considerable period of time.

As Andrew has noted, the Mogul-Somersett earthquake swarm is unusual: it didn't start with a large earthquake and dwindle into aftershocks, and it hasn't reached any kind of climactic peak. Also, the earthquakes have all been shallow. At least one geologist living in Mogul has expressed concern that, with the large Somersett development or subdivision located relatively high on a ridge above the valley Mogul lies in (Mogul is adjacent to and somewhat elevated from the nearby Truckee River and its floodplain), water from landscape watering and from the golf course might be lubricating a possible northwest-trending fault - the Nevada Seismological Laboratory (NSL) has more information about the quakes and a couple maps.

It may be that there isn't enough water seeping into the ground from the hillsides above Mogul to cause these earthquakes, and Ken Smith and Glenn Biasi at the NSL have been busy trying to diminish local rumors about the quakes, including the definitely false one that the local mountain, Peavine, is a volcano (it's not, never has been). From the Reno Gazette-Journal [I suspect some quotation marks are missing, or the paragraphs are parsed strangely].

What about golf courses?

Another question is whether golf courses in th area changed the way the water table impacts the geologic structure.

Earthquakes can follow when the water table is changed, Biasi said. A well-known example is Hoover Dam.

As the rocks have less pressure, they will slip, causing earthquakes.

"Did the golf course perhaps raise the water table and contribute to this?" Biasi said. "We don't think so because you have a river at the bottom [of the valley]."

"It set the water table very high already, so the golf course could not have raised it very far."

Landscape watering would contribute to the problem, he noted. They can't rule it out because they don't know how high the water table was before the [Somersett] development occurred, Biasi said.

"It's a real long shot, but one we don't have any date to comment on," Biasi said.

In other words, it sounds like a possibility, one that has not at all been confirmed. In the meantime, my former colleague (and a couple other geologists?) are trying to contact Mike Alger, the geologist and meteorologist for KTVN Channel 2 and the Reno Gazette-Journal in order to have this issue looked into.

7 comments:

Lost Geologist said...

What you write sounds not at all implausible. On the contrary I think it may well be the case. We have a similiar case in southern Germany in the region of Berchtesgarden and Bad Reichenhall if my memory not fails me. Locals and geologists had been wondering for long about the odd correlation between rainy times and earth activity. Turns out that one of the local mountains is cross-cut by deep faults. If rain continues for more than a week there is enough liquid to lubricate these normally dry faults and the mountain itselfs starts rumbling. The result is usually very shallow earthquakes that can be strong enough to wake up light sleepers and can definitly felt by anyone awake. Glady so far they never caused any mentionable damage.

Lost Geologist said...

a quick search on google let me find these two articles:

Evidence for rainfall-triggered earthquake activity“, S. Hainzl, T. Kraft, J. Wassermann, H. Igel, and E. Schmedes, Geophysical Research Letters, Vol. 33, Oktober 2006

„Meteorological triggering of earthquake swarms at Mt. Hochstaufen, SE-Germany”, T. Kraft, J. Wassermann, E. Schmedes, H. Igel, Tectonophysics, Juni 2006

I didn't read them but it sounds what you are talking about.

Silver Fox said...

It does, indeed. Thanks for finding those references, maybe I can pass them on to those who are concerned in the Mogul/Reno area.

steve said...

Wow! Thanks for this great discussion! I live in south west Reno with my wife and children and this has us quite concerned. we felt the 4.7 a couple of the 3s and even 2 of the 1.5s. I guess that all depends on the shake.
The thing that concerns me is the relation to the Wells event and continuing seismic activity around the state and swarm off of Oregon. At times I have felt silly starting the earthquake preparation but you just don't know. What we do know is that there has been sizable activity in the past.

Thanks again, Steve

Silver Fox said...

steve, most geologists would not think that the Mogul/Reno, the Wells, and the Oregon earthquakes are directly related. The whole state of Nevada including Reno, however, is in a tectonically active area. So it's definitely wise to know the basics of earthquake preparedness - and the Nevada Bureua of Mines and Geology has some information here along with several free downloads.

Remember, don't panic, just be prepared and informed.

steve said...

Sooo, I spoke with a resident of "Somersett" today. I guess they recently had a town hall meeting with a Geologist(s) from UNR that lives there in Somersett/Mogul.Long story short the swarm in Mogul immediately preceded the activity in Wells.
This appears to be a Great Basin seismic event if you ask me or them...

BTW do you live in Manhattan, one of your pics and caption led me to believe that. I lived in Round Mountain and Tonopah for 18 longs years, worked at Cyrpus Tonopah, Western State Northumberland and build leach pads at RMGC ugh.

Silver Fox said...

The Wells earthquake occurred on February 22; the Mogul swarm began on February 28. There is a very good plot of time v. cumulative number of quakes at Mogul here showing a number of "jumps" in seismicity - the first small increase being 10 days after swarm onset, another big "jump" about 48 days after Feb. 28th, a third increase about 57 days after onset, and a fourth small increase in quakes about 63 days after onset of the swarm. (Unfortunately, they don't plot the actual dates, and I'm not going to add those up!)

I wasn't at the meeting, so I'm not sure what was said, what was implied or not implied, and what was interpreted by listeners. Wells is a long way from Mogul. When I have time, I'll check in with the NBMG and see what they think.

BTW, I have been through Manhattan and Round Mountain quite a number of times. I worked near Northumberland in the late 70's - early 80's when they were just drilling out the gold deposit on Northumberland Pass. Sounds like you've worked in some interesting places!

Stay prepared!