OT: Earthquakes

[Sirhornsalot]

We just had our 7th trembler today moments ago. Biggest one hit around 6:30 p.m. centered near old Texas Stadium in Irving and registered a 3.5.

This, after we had about 16 during the month of November.

Any geologists on the board who can explain whether this means less likely chance of a big one or are we warming up to a big one?

This has been going on for months.

 

[Sirhornsalot]

Make that 9 now

 

[Randolph Duke]

We just had our 7th trembler today moments ago. Biggest one hit around 6:30 p.m. centered near old Texas Stadium in Irving and registered a 3.5.

This, after we had about 16 during the month of November.

Any geologists on the board who can explain whether this means less likely chance of a big one or are we warming up to a big one?

This has been going on for months.

There just aren't enough igneous fault zones close to Dallas to create the forces necessary to produce a major earthquake in the area. The largest earthquake in the eastern U.S. was 200 years ago up in Missouri. The geology in that area is much different than in the Dallas area. Dallas has mostly sedimentary formations which produce a totally different type of fault than do igneous formations. Sedimentary rocks are softer than igneous rocks and therefore break under lesser strains. The resistance to breaking is what stores energy in igneous faults, so when the faults finally slip and the formations move, the energy released is enormous. The tendency of sedimentary formations to fault easily accounts for the incredible number of oil and gas bearing formations. It is the faults that trap the fluids that migrate through porous sedimentary rocks.

In short, there isn't going to be a big quake in Dallas any more than there is going to a tsunami or volcanic explosion. There aren't the tectonic forces at play in Texas and the geologic formations aren't right.

 

[HornEsch]

What he said

 

[Randolph Duke]

If I was going to play Earthquake Jeopardy and the subject was "Shifting ground in highly localized spots in sedimentary soil" I would respond "What is the lack of groundwater due to the area drought."

It is taking one hell of a lot of force to move the ground in that area. The biggest natural event in the Dallas area has been the change in groundwater and soil moisture.

 

[Chitownhorn]

The biggest natural event in the Dallas area has been the change in groundwater and soil moisture.

I thought it was Jerry Jones and Chris Christie's man hug. 

http://deadspin.com/jerry-jones-and-chris-christie-enjoy-passionate-slow-m-1677468896

 

[Sirhornsalot]

There just aren't enough igneous fault zones close to Dallas to create the forces necessary to produce a major earthquake in the area. The largest earthquake in the eastern U.S. was 200 years ago up in Missouri. The geology in that area is much different than in the Dallas area. Dallas has mostly sedimentary formations which produce a totally different type of fault than do igneous formations. Sedimentary rocks are softer than igneous rocks and therefore break under lesser strains. The resistance to breaking is what stores energy in igneous faults, so when the faults finally slip and the formations move, the energy released is enormous. The tendency of sedimentary formations to fault easily accounts for the incredible number of oil and gas bearing formations. It is the faults that trap the fluids that migrate through porous sedimentary rocks.

In short, there isn't going to be a big quake in Dallas any more than there is going to a tsunami or volcanic explosion. There aren't the tectonic forces at play in Texas and the geologic formations aren't right.

Thanks for the detailed, thoughtful response. That explains it well. We do have a fault line in the area (balcones) but I understand it hasn't been active in a long time.

Heads-Up North and Central Texas folks - special weather statement just issued. Thursday snow and ice south of I-20. Saturday night snow and ice north of I-20. Reinforcing cold air coming from the north. 

 

[Worster1]

Thanks for the detailed, thoughtful response. That explains it well. We do have a fault line in the area (balcones) but I understand it hasn't been active in a long time.

Heads-Up North and Central Texas folks - special weather statement just issued. Thursday snow and ice south of I-20. Saturday night snow and ice north of I-20. Reinforcing cold air coming from the north. 

I was going to post the same geological explanation that Randolph Duke gave, but he beat me to it

I work in Richardson and live in McKinney so I am probably too far east of Irving to feel those tremblers, but it has to be a little unnerving to keep having the shakes!

 

[North Texas Golfer]

Are we sure that Sirhornsalot wasn't working on some huge landscaping job with a bunch of big excavators and earth movers?

 

[joeywa]

We used to have those things out here on the left coast, but we sent them to y'all.  Enjoy our gift. 

 

[Sirhornsalot]

Are we sure that Sirhornsalot wasn't working on some huge landscaping job with a bunch of big excavators and earth movers?

The tundra is frozen right now. he he

Speaking of which, high of 18 in Green Bay on game day. Low of 5. No snow in the forecast though.

 

[North Texas Golfer]

The tundra is frozen right now. he he

Speaking of which, high of 18 in Green Bay on game day. Low of 5. No snow in the forecast though.

So it was a combination of big excavators, giant earth movers, and frozen tundra that caused them

 

[Randolph Duke]

Thanks for the detailed, thoughtful response. That explains it well. We do have a fault line in the area (balcones) but I understand it hasn't been active in a long time.

Heads-Up North and Central Texas folks - special weather statement just issued. Thursday snow and ice south of I-20. Saturday night snow and ice north of I-20. Reinforcing cold air coming from the north. 

People hear "Balcones Fault" and think of the San Andreas Fault. Big difference. The San Andreas Fault is the meeting of two continental plates, where the colliding surfaces are both granite. The Balcones Fault is actually a fault zone which is the boundary between rock formations of two different eras having markedly different hardnesses. The rocks on the west side of the Balcones are Precambrian and Paleozoic with hardnesses much greater than the sedimentary Cretaceous rocks on the east side. The Balcones was active until the different formations found an equilibrium after the Gulf of Mexico receded. That all sorted itself out about 10 million years ago and even when those forces were working themselves out, it would have happened without large earthquakes found in places like California.

Because the rocks are of two different hardnesses, the forces of movement along the boundary of the Balcones fault are easily dissipated because the harder surface will ablate the softer surface. Think of it like a glacier wearing away the surface of the earth (the glacier will move a thousand times faster than the Cretaceous formations of the Balcones fault, but the example is still valid). There is movement, but because the harder ice scours the softer sedimentary soils, there is no large build-up of energy and no sharp releases of the energy. In the San Andreas, because each fault surface is hard granite, there is no ablative process. A sharp movement of the plates occurs when the granite fractures and releases the pent up energy. That is what we know as an earthquake. 

The geologists will start closely monitoring the depth of the movements that people are noticing and get a better idea what is going on geologically. If what is going on is actually movement of the Cretaceous formations, it will be interesting, but nothing earth shattering. (see what I did there?) Most likely it is some localized shifting of the ground for some reason. If the Balcones has been inactive for ten million years, it is unlikely it has suddenly become highly active and only in a small area. If it was the Balcones becoming more active, it would probably be happening over a larger area. 

 

[Sirhornsalot]

Nice explanation, RD. And yes, I see what you did there.

 

[North Texas Golfer]

The tundra is frozen right now. he he

Speaking of which, high of 18 in Green Bay on game day. Low of 5. No snow in the forecast though.

Not to derail the thread but, speaking of frozen tundra and Green Bay, did you see that Jethro Pugh passed away today?

 

[Juan]

I thought it was Jerry Jones and Chris Christie's man hug. 

http://deadspin.com/jerry-jones-and-chris-christie-enjoy-passionate-slow-m-1677468896

— Twitter API (@twitterapi) November 7, 2011

 

[Sirhornsalot]

Wow, he was one of the great ones. Sorry to hear that.

 

[Randolph Duke]

Nice explanation, RD. And yes, I see what you did there.

My guess is it is related to localized changes in groundwater. In other words, probably settlement and not large scale geologic activity. If the Balconies had stored up enough energy to cause a quake swarm in one area, the release of energy would be released over a much larger area and would be far more widespread. My educated opinion is Godzilla is coming to unleash his wrath upon the jetpack man and once he eats Steve Patterson, all will be well.

 

[castlebravo1]

And, I'm sure, all of this is due to fracking.