Earthquake

[cap n chris]

 

[Slug]

Does this explain why I, in Bedford, felt and heard, quite a large effect, and a friend, in Lincoln, (closer too the epicentre ) claims not to have felt that much at all. Was She, in effect " Between" the waves ?.

 

[Slug]

Where do You dig 'em up Chris.

 

[Peter Burgess]

Does this explain why I, in Bedford, felt and heard, quite a large effect, and a friend, in Lincoln, (closer too the epicentre ) claims not to have felt that much at all. Was She, in effect " Between" the waves ?.

What rocks are beneath your respective feet? I understand that some rocks 'transmit' the shock better than others. I think clay is worse, for example. We need a seismologist on the forum!

 

[graham]

I think clay is worse, for example. We need a seismologist on the forum!

Depends. I think in some circumstances clay will effectively liquefy and run.

Narsty if you've built on it.

 

[Slug]

Does this explain why I, in Bedford, felt and heard, quite a large effect, and a friend, in Lincoln, (closer too the epicentre ) claims not to have felt that much at all. Was She, in effect " Between" the waves ?.

What rocks are beneath your respective feet? I understand that some rocks 'transmit' the shock better than others. I think clay is worse, for example. We need a seismologist on the forum!

Bedfordshire is quite well represented in the Gravel and Clay departments, in fact most of Bedford itself sits on huge deposits of Clay , hence the main local industry, Brick making. Luton, sadly, also sits on a strong foundation, and not a major fault line
see link, http://www.bedsrigs.org.uk/map.html

 

[Peter Burgess]

You might also expect to notice it more in a high building than at ground level.

 

[ChrisB]

We need a seismologist on the forum!

I can't claim to be a seismologist but I am a seismic engineer, ie, I design buildings to resist earthquakes, so I study the effects of the earthquakes rather than their causes.

Amplification by soft soil is the most likely reason for higher than expected shaking at a distance from the epicentre. Soft soils like clay can resonate with the earthquake frequencies, which amplifies the motion. Mexico City is built on a dry lake bed, which is just like a bowl of jelly, and suffered a big earthquake in 1985. Buildings between about 6 and 14 storeys had the same natural frequency as the soil, so nearly all collapsed. Taller buildings were OK. Seismic waves are also amplified by the shape of the terrain, so you can get bigger shocks at the top of hills. Saturated soils can suffer from liquefaction, where the seismic waves increase the pressure of the water and the soil particles are forced apart, losing their normal interlock.

Chris

 

[Skyrmy]

You frequently see fallen stal, especially broken columns, and have some expert tell you that they fell during an earthquake. While there can be little doubt that some did, I suspect that the vast majority of breaks are down to much smaller and more localised effects, such as the sediment on which they are rooted being undermined by washout.

This pretty from up in Inlet 5 in Notts 2 has a distinct fracture at the point where it chamges section.
http://www.imageno.com/hzbxqaczfk5apic.html
Closer inspection shows that the base of the formation has shifted by approx 5mm.


By the way - I know the pic is c**p so no comments please  :spank: :spank: :spank:

 

[Slug]

Saturated soils can suffer from liquefaction, where the seismic waves increase the pressure of the water and the soil particles are forced apart, losing their normal interlock.

Chris




[/quote]

That, I have almost experienced. In 1983 I was on a NATO exercise in northern Turkey,  at a place called Pasinla not far from Mount Arrarratt . 9 days after We left for home the area was almost at the epicentre of a strong quake. I saw the very field we were operating from on the T.V. news, there was a row of telegraph poles that had sunk from around 14' high down to about 3', oddly, most of the phone cables were unbroken, though what had been a green field was now covered in a layer of fine silty mud. The expert wheeled in by the BBC put this down to the fact that the bedrock was only about 20' below the surface, and that the frequency of the vibrations was enough to ( His words ) "Fluidise" the ground above, leading to everything just sort of sinking.

Most of the locals that we had got to know and trade with were killed. I felt quite lucky to have left when we did.

 

[Wolfart]

all that luvrly art gone boo hoo 

 

[whitelackington]

Over many years earthquakes have a big influence  on cave development

"Faults"  often give a cave a linear aspect.