Vulcano Eyjafjallajokull a rischio eruzione!

[Aragorth]

The thing that I could not understand is why are not recorded earthquakes from that station (too few great peaks), probably the station filters only low-frequency and excludes real earthquakes

exactly. I believe they have filters to avoid the big "shaking" just to see how to the mass is vibrating, so they can see possible trends, etc. however they can still see the big earthquakes, but thats hard to avoid anyway.

[Michele Boncristiano]

exactly. I believe they have filters to avoid the big "shaking" just to see how to the mass is vibrating, so they can see possible trends, etc. however they can still see the big earthquakes, but thats hard to avoid anyway.

yes consider that 1 nm (nanometer) = 1 millionth of millimeter (0,000000001 mm) so ar very very small movements

[Aragorth]

yes consider that 1 nm = 1 millionth of millimeter (0,000000001 mm) so ar very very small movements

Umm no, 1 nanometer per second is 1 x 10^-9 m/s so 0,000000001 m/s

It goes up ...

http://hraun.vedur.is/ja/oroi/god.gif

[Michele Boncristiano]

Umm no, 1 nanometer per second is 1 x 10^-9 m/s so 0,000000001 m/s

Yeeeeees I've wrote right in letters 1 millionth of millimeter and than to many zeros in number ..is

1 nm (nanometer) = 1 millionth of millimeter (0,000001 mm)

[Aragorth]

Yes I've wrote right in letters 1 millionth of millimeter and than to many zeros in number ..is

1 nm (nanometer) = 1 millionth of millimeter (0,000001 mm)

true

I am searching for some good pages about such measurements, like this one in nm/s... do you have any maybe?

[Michele Boncristiano]

true

I am searching for some good pages about such measurements, like this one in nm/s... do you have any maybe?

pages of what?

[Aragorth]

pages of what?

Some website with good explanation of such tremor measurements..

Also, if you noticed on the graphics... its a 10min median average... so it cuts the peaks.

[Cliff]

I've asked to me the same thing about time n the answer I gave me is that the tremor shown in that graph is a continuous series of very small accelerations...so u have constant acceleretion but very very small. Moreover in that graph r shown only positive acceleration's peaks (above time axis), for example the red line is probably a line connecting all maximum aceleration's peaks of red frequency, so it isn't the real accelerogram 'cos if it were the red line should go continuously above n below time axis in a very short time space (as an earthquake has both positive and negative accelerations) so you'd see red all the area above the red line ...maybe ...that's my reading, I know well accelerograms but that's the first time I see tremor graphs.
A clarification: these above are not acelerations but velocities (nm/s) but it's the same!!

Immagine

Nell'asse y è riportata l'ampiezza delle oscillazioni a una data frequenza (per questo è sempre positivo)....

[Davide1987]

Katla, aumento continuo

[Michele Boncristiano]

Nell'asse y è riportata l'ampiezza delle oscillazioni a una data frequenza (per questo è sempre positivo)....

quelle (http://forum.meteonetwork.it/imgcache/64879.gif) sono velocità (nm per secondo) non ampiezze ma poco conta; se integri la velocità ottieni l'ampiezza ovvero lo spostamento, se invece la derivi ottieni l'accelerazione. E' indifferente graficare lo spostamento (ampiezza) piuttosto che la velocità o l'accelerazione proprio perchè dall'una ottieni le altre due (derivando o integrando), in ogni caso sia lo spostamento (ampiezza) sia la velocità che l'accelerazione sono sia negative che positive esattamente come in un onda; il terreno daltronte và sia "in avanti" che "indietro". Ad es. da questo accelerogramma, integrando ottieni le velocità ovvero il velocigramma che sarà fai conto di vedere la stessissima onda ma più smussata/morbida, se integri ancora ottieni gli spostamenti ovvero il sismogramma che sarà ancora la setssissima onda ma immaginala ancora più smussata/morbida.



...queste nozioni me le ricordo bene perchè furono argomenti che trovai abbastanza difficili (..soprattutto la trasformata di Fourier che scompone l'accelerogramma in infinite onde sinusoidali...) quando dovevo fare l'esame di sismologia e così mi rimasero impressi

Some website with good explanation of such tremor measurements..

Also, if you noticed on the graphics... its a 10min median average... so it cuts the peaks.

I don't know Aragorth, I have my book of sismology but I'm scared of opening it back!!!