This thread is for general earthquake discussion.

Not that I think it is significant but what prompted me was the magnitude 4.8 quake off the west coast of Norway http://earthquake.usgs.gov/earthquakes/eventpage/us20007cxs#executive

The reason it made me stop and ink is becaus it is in a very similar location to that of the massive historical underwater land slip known as the Storegga Slide (and not I don't expect a repeat). https://en.m.wikipedia.org/wiki/Storegga_Slide 

Anyway as mentioned,  this thread is for any general earthquake-related discussion and will be kept "sticky".

The BGS downgraded it to 3.8 magnitude.

This area is seismically quite an active area; there was a 4.8 M event in January 2007, and the strongest quake in the last 100 years was a 5.7 M event in 1927. Oil and gas installations have to be designed to cope with potentially damaging earthquakes in this area.

This area has been unusually quiet in the last few years compared to more active periods in 1980's and 1990's.

Yes, thanks for mentioning it. I find earthquakes in North Sea & Norwegian Sea interesting, prompting me to reply.

I am surprised by BGS downgrade (and perhaps little disappointed, although I don't wish any damage to installations-and glad there hasn't been any).

We haven't been convincing enough with the rest of the world regarding 'climate change', so you know the liberals will blame this on the US as usual. why do earthquakes happen

On September 3, 2016, a magnitude 5.6 earthquake that occurred in Pawnee, Oklahoma, was recorded by Weston Observatory (see seismogram below). This earthquake is tied with another magnitude 5.6 earthquake in Prague, OK (November 6, 2011) as the two largest known earthquakes in Oklahoma.  

http://www.dw.com/en/strong-earthquake-strikes-central-italy-shaking-historic-buildings-in-rome/a-36165190

Some reports say two separate earthquakes

https://www.rt.com/news/364216-italy-quake-hits-perugia/

Yes, there were two quakes - one at 17:10UTC (M5.5) and a stronger one at 19:18UTC (M6.1). 

Is there precedent for a string of near-major earthquakes in this or any other region? (I concede that a 6.6 feels major if you're in the middle of it, but with the logarithmic scale used, it's a long. long way off a 7.5, say). And if so, what happened thereafter? With Italy being a volcanic region, often a fact overlooked since it's been quiet for a generation (Vesuvius in 1944), should we expect some magma movement and eruptions which are now overdue?

I did wonder about the potential link to volcanic activity but have a hunch it would be a tenuous one. However I would be very surprised if the experts are not checking...just in case.

In the immediate future I would expect to see the aftershocks continue for a few days but whether there are more quakes in this area of magnitude - I've no idea. It's what makes the situation so fascinating but equally so potentially deadly.

Good post over on Volcano Cafe about this:

http://www.volcanocafe.org/the-apennine-fault/

Looks as though there is a history of faults 'unzipping' in that area and it looks to be purely tectonic, though it may not be fully over which must be concerning for people living in the region.

I'm no expert, but from what I've read the connections between tectonic events and volcanic activity tend to be tenuous at best, and difficult to prove. A famous example of a potential connection between the two would be the 62 AD Pompeii earthquake, which was of course followed 17 years later by the 79 AD eruption of Vesuvius. 

Report of a 7.4 quake in New Zealand.

Just heard about that - heard it was near Christchurch.

More on that New Zealand earthquake.

http://www.independent.co.uk/news/world/australasia/earthquake-new-zealand-christchurch-latest-magnitude-74-quake-hits-strikes-a7414661.html

USGS has revised the magnitude of the quake to 7.8 and EMSC have it at 7.9. Either way it looks like a rather large quake in a populated area.

Tsunami followed 1 wave at least 8ft high. BBC NEWS has images of cracks in roads and othe r damage.

Looking at the new Paper on how the Moon has kept mantle temps high ( and our dynamo up and running to keep us safe from the universe) due to the gravitational peturbations it causes ( not just the tides eh?) could this 'closest since 1948' Supermoon be wiggling faults allowing movement?

From my daughter staying in Tokyo. Not the first email one wants to read in the morning = apart from the last bit!

"We were woken up by the earthquake this morning. All ok in Tokyo"

From the Telegraph

Japan earthquake; small tsunami at Fukushima after 7.4 magnitude quake

http://www.telegraph.co.uk/news/2016/11/21/japan-earthquake-73-magnitude-earthquake-strikes-fukushima/

24 die in Aceh Province, Sumatra, from an undersea earthquake measuring 6.4. The death toll is likely to rise.

http://www.bbc.co.uk/news/world-asia-38232611