Earthquakes and caves

[botkin02]

Today's earthquake in Japan got me thinking about earthquakes in general... today's was the 4th largest earthquake in recorded history!

Anyway, I remember the earthquake that 'hit' NW Georgia back in 2003. I remember is was in the morning and that I thought my roommates were shaking my bed to wake me up, but when I opened my eyes I was the only one in the room! (A new experience for this Florida boy!) Apparently it was only a 4.9.

Now that I've gotten into caving, I wonder, was anyone in a cave in NW GA or know of anyone who was underground when the earthquake hit? Or did anyone notice any new breakdown in caves afterwards? It'd be pretty freaky to be in a cave and all of sudden everything starts shaking...

Thoughts?

[norman1]

I know that this is an old post. And I guess that no one had any thoughts about this either. But I was just browsing for the same thoughts, as I live not far from a major fault line and was thinking about that as we are long overdue for a big one. My thoughts would be that the cavity inside would disrupt most of the damage but would lead me to thinking that there certainly must be falling rocks at some point even if the cavity did not collapse.

Norm

[caver.adam]

I think you will find this depends on a lot of factors. My understanding is that there is significantly less force in the cave than above. But your damage will depend on the type of rock you are surrounded by. Speaking statistically, worrying about dying in a cave because of an earthquake is a lot like worrying about dying while backpacking because of a storm. It's possible to get hit by lightning, but even if there is a thunderstorm the odds of getting killed aren't very high.

[norman1]

Thanks for the answer. I wasn't really worrying about it. I just got to thinking about it and was wondering if there might be some study or something about it on here since the limestone around here doesn't seem to be all that really sound.

[stx2006]

I know that Sequoyah Caverns has a fault line that runs through it. I asked the guide about it and she said they've never seen any damage after a earthquake. She said she was in the cave doing a tour one day and one happened and you could hear it but didn't really feel anything.

[Chads93GT]

Joe Walsh wrote about an earthquake experience in the 1960's when the LESG was surveying the Rimstone River Cave in Perry County, MO. While inside the cave some of the cavers noticed a ripple of water along the walls when no one was standing in the water. After exiting they learned that there was a mild earthquake. After I read about it in one of his publications with the MSS I asked him about if. He said that shockwaves move across the land like ocean waves on the water. If you are under the wave in the water you wont even notice the wave going over you, the same thing underground. That being said, they never noticed anything changed inside the cave.


For what its worth.

[norman1]

I know that Sequoyah Caverns has a fault line that runs through it. I asked the guide about it and she said they've never seen any damage after a earthquake. She said she was in the cave doing a tour one day and one happened and you could hear it but didn't really feel anything.

That's what I was wondering about. It reasons to me that the cave would disrupt the vibrations of an earthquake and not do the damage as above the ground but, I wasn't sure to what degree or if it was enough to dislodge loose stone. I have never been to Sequoiyah Caverns so what kind of stone do the have there? Is it flaky limestone like here in my area? At least from the couple of caves that I have seen here are like that. I have only been in the entrances a short distance because of not wanting to break my promise to the wife about going solo anymore. (I don't personally count brief preliminary trecks into caves as solo. )

Norm

[norman1]

That makes perfect sense to me. I believe that might just answer my question. Thanks

Norm

[BrianFrank]

For sure I'm not trying to start an argument here, but something caused ceilings to collapse in caves like Pettijohns (Entrance Room, Volcano Room), Tumbling Rock (many of the large rooms), Howards (Disaster Room), Blue Springs,TN (multiple areas) and others. I assume the reason was a strong earthquake that hit before good records were kept? I admit I'm not an expert, but it stands to reason

I might be in the minority, but the word earthquake does cross my mind for a brief second when I'm in a super tight squeeze realizing that if there is a shift of just a few inches, I will be in big trouble

[Larry E. Matthews]

Actually, my understanding is that a lot of the breakdown occurs as water is draining out of the cave and no longer "floats" the ceiling.

Probably the best historical record is to read about Mammoth Cave during the massive earthquakes of 1811. It scared the crap out of the miners, but doesn't sound like much breakdown occurred.

At any rate, you're a lot more likely to get killed in a car wreck going to or from a cave than in the cave for any reason.

Larry E. Matthews
NSS #6792-F

[VRcaver]

As an undergrad I worked in the geophysics department at my college. My roommate was a geophysics major. When posed the question about earthquakes in caves, the answer is as previously discussed here. The damage comes from when the P waves (compression waves) and S waves (longitudinal waves) reflect off the surface. This creates two other wave types, the Love wave and the Rayleigh wave. These are the damage creating waves. Since caves are sub-surface they don't get the same reflections. That is, unless the passage or room is particularly large compared to the wavelength. Now, entrances are another story. That is where you should be worried about earthquakes while caving!

More reading here: http://www.exploratorium.edu/faultline/ ... waves.html

[norman1]

As an undergrad I worked in the geophysics department at my college. My roommate was a geophysics major. When posed the question about earthquakes in caves, the answer is as previously discussed here. The damage comes from when the P waves (compression waves) and S waves (longitudinal waves) reflect off the surface. This creates two other wave types, the Love wave and the Rayleigh wave. These are the damage creating waves. Since caves are sub-surface they don't get the same reflections. That is, unless the passage or room is particularly large compared to the wavelength. Now, entrances are another story. That is where you should be worried about earthquakes while caving!

More reading here: http://www.exploratorium.edu/faultline/ ... waves.html

Now that is more on the lines of my question however, I thought all of the answers had merit in their own right. Now, for the second question...As chad had said on the surface the ground acts as a wave does on water which I believe to be true. So, my thoughts are not only would the entrance be affected but what about the cave passages that are a relatively close to the surface, say thirty to fifty feet of the surface, after all I'm not taking about real deep caves in my area. My belief is that those "shallow" cave passages would most certain loosen some of it's ceiling stones if not the entire cave collapse.

Let's also keep in mind here that I'm also thinking about those tight squeezes that I'm sure most of us have been in where if we had even an inch of ceiling shift on top of us then we're stuck in a bad way.
I forgot the name of the poster that had earlier stated that he didn't want to start a brawl. Neither do I. I think everyone is entitled to their own opinion whether or not I agree with it. I'm just looking for the compilation of opinions that makes the most rational sense to me for the sake of my own curiousity (oh hell, spell checker) on this subject. After all I am a self proclaimed explorer so, why not ask.

Norm

[Larry E. Matthews]

You need to think in geologic time on this question. Earthquakes in most parts of this country are fairly rare events and even in earthquake hot spots, the BIG ones are fairly rare events............that is if you measure time in human life spans.

But caves take millions of year to form and exist for millions of years. They experience a lot of earthquakes over time. If a big earthquake would flatten your crawlways, then hardly any cave would have crawlways, or big rooms, left.

Think millions of years, not 50 years.

Larry

[Chads93GT]

That has always been my thought. The cave wants to be there. It is stable. Sure some areas may be unstable due to ceiling fractures (breakdown rooms) but for the most part, caves are stable. Mines on the other hand do not want to be there, hence all of the bracing that goes into the mines when they were dug. They dont want to be there. The rock doesnt want them to be there and gravity sure as hell doesnt want them to be there. Ill take an earthquake in a cave over an earthquake in a mine any day.

Entrance collapses happen without earthquakes. Recently we had a 4-600 pound slab peel off of the ceiling in the entrance of one of our long survey projects. I cant count the times we have sat under the slab that peeled off. Kind of scary.

[steven.millett]

http://www.hongmeigui.net/news.php?page=6

Earthquake damages Furong Dong showcave

February 5, 2003 Late-breaking news from Tian Xing: We've been told that the Furong Jiang dam has successfully filled to 260m ASL, but the filling triggered a magnitude 3.5 earthquake which broke a large number of speleothems in Furong Dong (one of China's premier show caves). It is now closed for tourists.