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Earthquake In Cm?


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The USGS has a site : Recent earthquakes

but it hasn't been updated for this afternoon yet, I think, only lists two in AK

On September 16th, there was an eartquake in Tokyo that lasted for 7 minutes.

Trapped in a high rise building, balancing to stay upright we watched other skyscrapers swaying.

One minute through the quake, some people went to a website that already had the epicenter location and strenght.

Thais should update their technology and procedures.

It's not a Thai site.

Even worse - do they have one?

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This is a simple exercise to estimate roughly the distance from the earthquake's epicenter and your position. It might be difficult for people with no previous experience with earthquakes.

Could you estimate the time (in seconds or minutes) elapsed between the initial bang or horizontal movement and the start of the vertical movement of the earth?

The shorter it is the closer you are to the epicenter, and vice versa.

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There are two waves generated from an earthquake:

(1) Faster longitudinal compression P-waves, associated with the horizontal movement of the earth surface.

(2) Slower transversal S-waves associated with vertical movement of the earth surface (and most destructive).

Because of the difference in velocity between the two waves, by measuring the time span between the arrival of the p-wave, at the initial bang associated with compression, and the start of the vertical movement, associated with the arrival of the S-wave, the distance from the earthquake can be estimated. The closer you are to the epicenter the smaller this time is, and vice versa.

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~

My guess was an explosion or some kind of surface impact. We are between Airport Plaza and Hang Dong, very close to the southern end of the runway and it jarred our house. Not a sonic boom because it didn't have that double ba-boom and it seemed way too short for an earthquake.

Let us know if any of you find out, eh?

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This is a simple exercise to estimate roughly the distance from the earthquake's epicenter and your position. It might be difficult for people with no previous experience with earthquakes.

Could you estimate the time (in seconds or minutes) elapsed between the initial bang or horizontal movement and the start of the vertical movement of the earth?

The shorter it is the closer you are to the epicenter, and vice versa.

----------------------------------

There are two waves generated from an earthquake:

(1) Faster longitudinal compression P-waves, associated with the horizontal movement of the earth surface.

(2) Slower transversal S-waves associated with vertical movement of the earth surface (and most destructive).

Because of the difference in velocity between the two waves, by measuring the time span between the arrival of the p-wave, at the initial bang associated with compression, and the start of the vertical movement, associated with the arrival of the S-wave, the distance from the earthquake can be estimated. The closer you are to the epicenter the smaller this time is, and vice versa.

------------------------------

For me it was a violent shaking that was over very quick. I would say it lasted about 1/2 second. Nothing more. Does that mean it was directly below me?? :o

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~

My guess was an explosion or some kind of surface impact.  We are between Airport Plaza and Hang Dong, very close to the southern end of the runway and it jarred our house.  Not a sonic boom because it didn't have that double ba-boom and it seemed way too short for an earthquake.

Let us know if any of you find out, eh?

It was an earthquake.See Lops post above.I live about 10 KM north of the city and felt and heard it.It was a rumble not an explosian.

Edited by chuchok
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For me it was a violent shaking that was over very quick.  I would say it lasted about 1/2 second.  Nothing more.  Does that mean it was directly below me?? :o

If you could not distinguish clearly any time difference between the two movements, i.e. the horizontal first and then the vertical, yes, you were very close to the epicenter.

G

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This graph represents an earhtquake signal detected at three different locations. Note the time difference between the arrival of the P and S waves depending on the distance from the epicenter.

post-24316-1133701756_thumb.jpg

From this one the distance from the epicenter can be calculated, if the time difference between the arrivals of the two waves is known.

post-24316-1133701815_thumb.jpg

P

Edited by Gulliver_in_LOS
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