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Originally posted by PuterMan
Quite a lot of subduction zone activity around Crete in the past 48 hours
I know from talking to..a certain person...that volcanic tremor will easily register out to 120 km's or more, so if it was tremor, all those instruments on and around Santorini would probably be pegged out.
Recently, exactly from the 28th May, we have in Crete - particularly Agios Nikolaos - on-going tremblings and earthquakes. We had around 10 within 24hours (that day/night) and it's going on up to yesterday. Today (1st June) it's quiet so far.
First 2 days the earthquakes were very shallow - we're checking all the time the website:
We are living here since few years and nth like this happened before, If there was an earthquake it mainly occurred somewhere on the sea and maybe once or twice per year. What is happening here since the 28th May (Thursday) is pretty frightening and definitely alerting.
Sometimes we can clearly feel just vibrations - the feeling is exactly the same like You can read in some posts or websites where the scientists explain the foreshocks - like the magma is moving.
The last earthquake we had, the one we could feel, was yesterday night at 23.37 local time (GMT +3). Earthquakes and tremors, I'm writing here about, happen every time in approximately the same area around and in the city of Agios Nikolaos (not farther than 10km from the centre of the town).........
....What is very interesting in this point, especially when looking at the whole situation of recent growing seismic activity from "our" (Agios Nikolaos) point of view is - we have a lake here called "Voulismeni" - it has a volcanic rocky formations around. It's said that the lake is somehow connected with the Santorini volcano - when there was an eruption, here in the lake, the water with it's power was "throwing" dead fish out. Generally, when You observe the water level in the lake there are moments when the water is rising and than after a while is dropping again - with "perfect timing" like in a clock. There is sth going on here for sure.
You don't have to be a scientist to see what is happening.
It might also have to do with the Polar Shift, so widely discussed all over different blogs and websites. For example today (1st June) there was a 5.6 earthquake in Antarctica.
The lake connects to the harbour of the town by a channel dug in 1870.
Originally posted by PuterMan
The THR ones were all pegged out, and still are, which was why I was looking at this in the first place.
I have never seen such a badly placed set of seismo and, as I have been saying, these would be completely useless if there was VT as you would not see it.
In addition to be showing so much noise they must be on really sensitive settings. Pointless IMHO.
Hmm, while I see periods of high noise at THR3 and at the others, for the moment those stations are anything but completely clipped (what I meant by pegged out). So I am not sure why you would make such a statement, especially with your knowledge. But it's not true, at least at the moment. You can see this by looking at other peaky signatures and seeing where the clipping point is set on their webicorder plotter settings.
It appears the broadbands are low pass filtered at 3k, and they are still showing a fair amount of noise and man made activity, like at SAP2:
Originally posted by PuterMan
That says HHZ, the channel, and the 3000 refers to the counts.
One of the problems with seismology is that what they call Hertz for the instruments is not hertz it is samples per second and that ain't the same thing. I would be extremely surprised if there was any signal above around 30 Hz that was worth looking at except perhaps for harmonics but even they would not be much higher than that, and I also seriously doubt that they are sampling at 3000 samples per second considering that most instruments sample at 100 sps, There are a few very much faster instruments but are these they? Extremely unlikely.
What happened to mv then and how does mv translate to counts?
E1 Consider a voltmeter built around a 10 bit A/D converter. We will assume the following.
The range of the voltmeter is from 0-3v, and it does DC voltage measurements. It does not measure negative voltages.
Then, with 10 bits we can draw these inferences.
Ten bits will produce 210 intervals. That's 1024 intervals.
If there are 1024 intervals over a range of 3v, each interval will be 3/1024 = .00293v.
It is easier to compute the displayed voltage if the interval is adjusted to .003v.
That would make the range 0-3.072v. (That's .003 x 1024.)
If you are measuring a voltage that varies around 3v, that would allow you to keep the range the same, but still change the range (if the instrument also has a 0-30v range, for instance) when the voltage got large enough. Manufacturers like to build in a little "hysteresis" to prevent constant range changes in situations like that and it might be especially hard on auto-ranging meters.
If you wanted to measure negative voltages and have the range be from -3v to +3v, you would have intervals of .006v, and the meter would measure from -3.072v to +3.072v.
If you wanted to measure voltages on a 0-30v scale, you would probably use a voltage divider or some other way to reduce the voltage by a factor of (exactly) 10 (i.e., multiply it by exactly 0.1) and then use the same converter as on the 0-3v scale.
If we could use a 12 bit A/D, then some conclusions would change.
Twelve bits will produce 212 intervals. That's 4096 intervals.
If there are 4096 intervals over a range of 3v, each interval will be 3/4096 = .000732v.
It is easier to compute the displayed voltage if the interval is adjusted to .0075v.
That would make the range 0-3.072v - just as it was in the case of the 10 bit converter,
That produces the same advantages as you had with the 10 bit converter.
If you wanted to measure negative voltages and have the range be from -3v to +3v, you would have intervals of .0015v, and the meter would measure from -3.072v to +3.072v.
Quanterra model Q330: 419,430 counts/volt, or 2.384 uV/count at a Gain of 1
RefTek model RT130: 629,327 counts/volt, or 1.58997 uV/count at a Gain of 1
Another thing I am curious about is if the designation "HHZ" for example is derived from the instrument itself, or from the settings used in the software to display the instrument's output.
Puterman can i just say a couple of things here but please please please dont take this the wrong way.
I am sure that there are many like me on here who havent got as much knowledge as you regarding the technical terms you post.
Is there any chance you can simplify your replies please. Some of the terms you use go way over my head, i am not taking the piss but i feel that more would find your posts and replies of greater benefit if they understood your terms.
Your posts are informative and educational but hey i aint no scientist but simplify please.
I happen to think thats also the reason why we are struggling globally in general because we are making everything more complicated that it needs to be.
I sincerely hope you are not offended as i think you are an asset to ATS i am just sharing my opinion. Please take this as its meant.
Do you have a blog? If not i would consider doing one. I would happily allow my kids to use it as a tool for their education.
If I get away from this stuff for a while, as I have been, different compartmentalized elements of the technical knowledge fade away, leaving gaps in brain logic assembly- and thus cause errors in assimilation as I made above.
I still maintain that Santorini remains seismically quiet, and is not an imminent threat unless things change.