Author Topic: Earthquakes and boulder chokes  (Read 6536 times)

Offline The Old Ruminator

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Re: Earthquakes and boulder chokes
« Reply #25 on: March 12, 2011, 10:01:21 am »
From the above link.

21 December 1248 SW England

 

This earthquake evidently affected chiefly the south-west of England. Much discussion has taken place about the reported damage to Wells cathedral, described to Matthew Paris by the Bishop of Bath (William of Bytton). This was the fall of the tholus, apparently some large stone decoration in the course of erection above the nave, or possibly the lantern of the central tower. This report is somewhat undermined by the facts that (a) the chapter records make no mention of the earthquake; (b) Bishop Bytton was in Rome at the time and (c) modern examinations of the fabric have shown no trace of the damage to the stonework.

 

Apart from what happened at Wells cathedral, it is said that the tops of chimneys, parapets and pillars were thrown down, and that large cracks appeared in walls (at unspecified places) suggesting a maximum intensity in the range 7-8 MSK. The earthquake was probably also felt at Exeter (Polwhele 1793).

 That was the one I was thinking about.  To be honest it seems quakes are far more prevalent than we might think and where we have a structural weakness like the Withybrook Fault effects might be more widely felt.

Offline Les W

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Re: Earthquakes and boulder chokes
« Reply #26 on: March 12, 2011, 10:51:25 am »
I seem to recall a plaque at the top of Glastonbury Tor that claims the church that was built there was destroyed in an earthquake. Only the tower survived.
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Offline Bob Mehew

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Re: Earthquakes and boulder chokes
« Reply #27 on: March 12, 2011, 07:54:42 pm »
The UK experiences trivial earthquakes quite frequently.  In my old job, one of the entertaining tasks for some of our specialists was to come up with the size of an earthquake likely to affect a nuclear installation on a frequency of in 10,000 years.  I recall one piece of work being done was to go and get information on the number, size etc of grave stones which had toppled over in an earth quake.  I wonder if one might be able to do some fancy calculation on whether a straw of a certain length might break into bits due to being vibrated by an earthquake?  Or we could install our own earth quake detectors such as http://en.wikipedia.org/wiki/File:EastHanSeismograph.JPG  :)

Offline potholer

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Re: Earthquakes and boulder chokes
« Reply #28 on: March 18, 2011, 12:11:21 pm »
The point being, that just 'cos you feel it on the surface, you may not underground - apparently.

I seem to remember reading somewhere that some miners working underground during the 1906 San Francisco earthquake returned to the surface unaware that it had happened.
When we were in Slovenia, shortly after there'd been a decent-sized earthquake nearby, there were a few small aftershocks that people didn't seem to notice while underground (~-400m) even though they were noticed on the surface.

Though to be fair, I guess that things noticed on the surface in small shocks (furniture rattling, etc) don't exist underground.
The couple of small quakes I've felt in Stafford in recent years while sitting or lying down indoors, I'm not sure I'd have noticed if walking outdoors, hanging on a rope, etc.

Offline gus horsley

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Re: Earthquakes and boulder chokes
« Reply #29 on: March 18, 2011, 12:24:10 pm »
It's down to the mechanical strength of the rock.  Hard compact rocks like granite and massive limestones don't convey the shock waves the same way as weaker rocks and unconsolidated sediments.  The Mexico City quake created the most amount of damage in buildings built on the site of an old dried up lake, forming an oval zone of devastation.

Offline Pitlamp

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Re: Earthquakes and boulder chokes
« Reply #30 on: March 19, 2011, 08:38:09 am »
We had three of us in the water at Malham yesterday and nothing fell down. That section of roof is now safely scaffolded (phew!).

Offline gus horsley

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Re: Earthquakes and boulder chokes
« Reply #31 on: March 19, 2011, 01:11:21 pm »
We had three of us in the water at Malham yesterday and nothing fell down. That section of roof is now safely scaffolded (phew!).

That's good news.  maybe it was the earthquake that did a bit of "gardening".

Offline Pitlamp

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Re: Earthquakes and boulder chokes
« Reply #32 on: March 04, 2020, 12:34:29 pm »
Just noticed there was a magnitude 4.0 quake in the North Sea, just over a week ago (Saturday 22-2-20). Although some distance away, anyone planning a visit to anywhere loose in Dales caves should bear it in mind. 4.0 is quite big for the UK. If I was one of those actively digging in the North York Moors caving area, I'd be especially careful.

Online mikem

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Re: Earthquakes and boulder chokes
« Reply #33 on: March 04, 2020, 01:17:42 pm »
183 quakes were recorded worldwide that day - noone seems to have reported feeling our one:
https://www.volcanodiscovery.com/earthquake/news/98691/Earthquake-report-world-wide-for-Saturday-22-February-2020.html

There was also one on Teesside on 23rd Jan (which was noticed) & Taunton 5th December:
https://earthquakes.bgs.ac.uk/earthquakes/recent_uk_events.html

Although a lot of broken formations, that were previously assumed to be earthquake damage, have now been shown to be caused by ice expansion under the surface.

Offline Cavematt

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Re: Earthquakes and boulder chokes
« Reply #34 on: March 04, 2020, 01:24:12 pm »
Hi Pitlamp – If our current dig in the North York Moors was large or deep enough to be troubled by an earthquake, I would be a very happy man  ;D
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