At 2:30pm today, there was probably the largest reported UK earthquake event in ten years, measuring between 4.4 to 4.9 on the Richter scale. It?s epicentre is described as Cwmllynfell south of Penwyllt. From my personal observation in Morriston, northern Swansea, it sounded like an explosion deep in the ground, causing my book case to visibly shake, although the cat slept through the event!

People need to be aware of this big shake up when visiting places, especially mines which tend to suffer more. The last big tremor we had this way back in the 80s caused a large section of bedding to collapse at the portal of St. David?s Sump in Daren Cilau. Take care!

I also felt the shock today while at home near Crickhowell.  Strongest earthquake in Wales since 1906 apparently.

My house didn't exactly shake about, but there was a deep rumbling that sounded like the central heating might possibly have blown up, and it went on for several seconds.

Cavers will have been underground at the time - so hope all is OK and reports awaited with interest as the epicentre was near Pontardawe in the Swansea Valley...

Has Dranen been sealed for good then ?

Has Dranen been sealed for good then ?

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I can confirm Draenen is open for business and I was in Gilwern Passage at about that time and did not feel a thing out of the ordinary.

Stuart France said:

Cavers will have been underground at the time - so hope all is OK and reports awaited with interest as the epicentre was near Pontardawe in the Swansea Valley...

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There is currently a Daren Cilau camp on this weekend, I hope all are okay.   

Best guess is that around the time of the earthquake they would probably be digging in a couple of sites off Half Mile Passage.
Either or both of:-
Kilburn High Road a nice stable dig along a flat out passage.
Flyby dig, Hmm! up into a boulder choke.     

Maj.

Yeah, nothing noticed in Draenen.

I think a couple of people on the Daren camp were heading towards the back end.

Stuart France said:

I also felt the shock today while at home near Crickhowell.  Strongest earthquake in Wales since 1906 apparently.

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That's definitely not true: there was a strong earthquake - magnitude 5.4 on the Lleyn Peninsula in 1984 (~30 times stronger than today's one), with two aftershocks that were magnitude 4. Strongest in south Wales perhaps?

Tom Elliot and I were in Daren but felt nothing. At 2:30 we were approaching BCNNTE. Alex Henderson

Interesting to read that those of us underground at the time of this Earthquake never even realised it had happened. I was always under the impression that we would of felt something.

ptpeaty said:

... The last big tremor we had this way back in the 80s caused a large section of bedding to collapse at the portal of St. David?s Sump in Daren Cilau. Take care!

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It was early 2000's IIRC - the roof came down at the junction of the King's Road and World's End.

Was underground in Wookey at the time of the quake today.  Nothing noticed though others on surface in the locality - Cheddar, Wookey village etc. felt it.

I believe it's quite common that people underground don't feel earthquakes. I guess it's something to do with the actual shockwaves only being able to manifest themselves on the surface, where they aren't constrained by the surrounding bedrock.*

*(I am only surmising this, there is no scientific basis.)**
**(Well, there might be, but I haven't bothered to see if there is or not...). 

When visiting the Frasassi caves in Umbria, we were told that when the last major earthquake hit (1997?), people in the cave felt nothing even though towns only 20km away or less were devastated.

There used to be a man who run the butty van at Hellifield called Stan Strange. He found himself in August 1945 working in a coal mine at Nagasaki. He never noticed the explosion that saved his life.

via USGS

Can you feel an earthquake if you're in a cave? Is it safer to be in a cave during an earthquake?

There is nothing different about a cave that would make it immune to the shaking from an earthquake.  Just as there are safer and less safer places to be on the surface of the earth during an earthquake, there are also various characteristics inside caves that make some cave locations safer or less safe than others.  First of all, whether or not you feel an earthquake in a cave depends chiefly upon the magnitude or size of the earthquake and the distance from the earthquake source to the cave in question. The closer and larger the earthquake, the more shaking you?ll feel.  The rest of the information about cave stability and shaking effects is based on limited observations and is a major area of active research.

The complexity of the cave seems to be a very important factor with regard to issues of cave passage "stability".  A small tube-like passage appears to be a relatively safe location that doesn?t tend to collapse or sustain much, if any, damage from earthquake shaking.  However, large cave passages or ?rooms? are notably less stable places.  It is in these areas where fallen chunks of limestone or marble are commonly observed, and where broken or toppled cave formations tend to be found.

Shaking effects inside caves include damage to delicate formations like soda straw stalactites that effectively ?die? and top growing.  Sometimes stalagmites or columns can be toppled. Toppled or not, renewed growth on them can occur.  These effects are far short of a total passage collapse, but collapse of portions of cave ceilings has been observed in caves, notably from caves in Missouri and Indiana near the New Madrid and Wabash seismic zones.

So are caves safe in earthquakes? Generally yes, but it depends on the cave characteristics and where you are in it.

An interesting note: Cavers who witnessed earthquakes while underground have described sounds as if a distant aircraft was passing by, as in becoming perceptibly louder, then fading away.

Les W said:

**(Well, there might be, but I haven't bothered to see if there is or not...). 

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Try https://books.google.co.uk/books?id=cQYtDQAAQBAJ&pg=PA173&lpg=PA173&dq=earthquake+transmission+rock+soil&source=bl&ots=Bt1yirBQ7b&sig=9dcmY0u_FTThPYBSEvWrP35ld9E&hl=en&sa=X&ved=0ahUKEwiP55akiLDZAhWiD8AKHbgPDXoQ6AEIOjAC#v=onepage&q=earthquake%20transmission%20rock%20soil&f=false.  I recall discussing the topic of movement in a siesmic event with a colleague whose job it was to double check seismic safety cases of nuclear power stations and he stated one could be standing on the soil outdoors and feel very little but stand on a floor in a multi-storey office block and be thrown around.  That was after our office block was subject to a noticeable earthquake on the 7th floor but those on the ground floor felt nothing.

Maj said:

There is currently a Daren Cilau camp on this weekend, I hope all are okay.   

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All out okay.
They knew nothing about the earthquake, although a pan fell over at 4:00am Sat morning that surprised them all. 

Maj.

Looks like someone shat themselves underground. linky 

Four Aftershocks so far ,getting bigger !

Bridge Cave looked normal today. The first piece of wood you come to on your right as you enter the choke appears to have dropped but I doubt it was doing anything anyway and probably dropped out ages ago anyway.

AWW said:

Looks like someone shat themselves underground. linky  [emoji38]

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[emoji23][emoji23]

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