Earthquakes in the Aegean around Santorini and Ios

AntarcticPilot said:
I was wondering about that, too.
Click to expand...
Yesterday GH was saying that there does seem to be evidence of magmatic intrusion, based on ground level rises of up to 6cm/year, but apparently this is well below the level likely to be associated with a risk of eruption. Something to do with a deep chamber filling an upper chamber, I think I understood it as.
 
johnalison said:
Yesterday GH was saying that there does seem to be evidence of magmatic intrusion, based on ground level rises of up to 6cm/year, but apparently this is well below the level likely to be associated with a risk of eruption. Something to do with a deep chamber filling an upper chamber, I think I understood it as.
Click to expand...
Ooh-er, sounds like an egg-timer being run in reverse...
 
mjcoon said:
Surely boats will not notice earthquakes unless there is both a tsunami and they are in shallowing water...
Click to expand...
A boat at sea will scarcely notice them - perhaps a shudder as the seismic waves pass them. Also, water can only transmit P (compressive) waves, not S (Shear) Waves. Tsunamis only develop into steep, high waves when they encounter shallow water - in deep water they are no more than another small wave. So, a boat AT SEA is generally not in danger unless passing over a shoal. A boat in a harbour or at anchor would be a different matter, though - a likely outcome is being swept inland!
 
T
AntarcticPilot said:
A boat at sea will scarcely notice them - perhaps a shudder as the seismic waves pass them. Also, water can only transmit P (compressive) waves, not S (Shear) Waves. Tsunamis only develop into steep, high waves when they encounter shallow water - in deep water they are no more than another small wave. So, a boat AT SEA is generally not in danger unless passing over a shoal. A boat in a harbour or at anchor would be a different matter, though - a likely outcome is being swept inland
Click to expand...
 
Wansworth said:
Tuesunami is Japaneses for harbour wave
Click to expand...
That makes sense, because that is where the waves would have been both high enough to be noticed and within sight of many people. Out at sea I believe that even large tsunamis can be no more than some inches high, so even Japanese fisherman would not generally have appreciated them as they passed. For want of another term, we may as well call these waves tsunamis from their point of origin. Since they can be caused by various factors, from earthquakes and land slips to icebergs, there is no obvious name for them and we may as well abandon the old term 'tidal wave'. Incidentally, I saw the other day that the longest tsunami ever recorded was seen recently. It lasted an astonishing 9 days and was caused by a land slip in a fjord, I think in Greenland, with the wave sloshing back and forth, detected seismographically.
 
The north and east of Britain (and elsewhere) was badly affected by a tsunami about 8,000 years ago, penetrating up to 18 miles inland, and causing (directly and indirectly) a radical - perhaps 25% - reduction in population and a long term shift away from coastal settlement there. (And that was with waves 3 to 6m high, whereas Shetland would have had them at 15 - 20m high.)

While the immediate cause of the tsunami was a massive collapse (actually a series of collapses) of the part of the edge of the continental shelf off Norway - the Storrega Slide(s) - that collapse in turn was likely triggered - i.e. the timing of it, not the ultimate cause - by earthquake activity.

Hold on to your hats!
 
Last edited:
AntarcticPilot said:
. . .

The issue is very simple - strain energy builds up along a moving fault line; we can measure that using a variety of techniques, both satellite (Interferometric SAR) and ground-based instrumentation.. We can also spot areas where the fault is not moving, and so strain energy is building up. So for terrestrial faults, we can see where and how big a quake is likely to occur. Of course, none of this works for submarine faults such as those involved in this case!

But we CAN'T (yet) detect the onset of the trigger that initiates an earthquake; it is probably down in the noise and an essentially random event. There have been attempts to detect the "stuck" points on faults, I think the story you relate was one such if my memory serves, but there has been no general success, and even if we can detect the "sticking" points, we still can't predict them becoming unstuck!
. . .
Click to expand...

It's a pity that it involves such violence. Can't the plates learn to respect their differences, and learn to rub along nicely with each other? ;)
 
AntarcticPilot said:
Water shallow enough to anchor will cause the wave to develop; it's deep sea that makes the difference.
Click to expand...
I think there is a difference between theory and practice, next you will be saying in confused seas, well of course it's to be expected that conditions can disguise the effect.
 
I have experienced lots of earthquakes when i lived in the Ionian, some would send the tourists running screaming from a bar whilst the locals simply steadied their drinks! you could be sat in your car and feel it moving but when in a small boat in sheltered waters you could see the disturbance on the water, only slight and hard to describe, but if you hold a cup of water and flick the side of the cup it sort of quickly shimmers/ripples, that is what the sea does when close inshore, its over in a second, blink and you will miss it!
 
You must log in or register to reply here.

Share this page

Top