Simultaneous Infrasound and Seismic Events

Technical Support
1

Simultaneous events occur. What has been folks experience in these cases? Do we have an idea what causes them?

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2

I think there’s only 4 ways simultaneous events (detected on say EHZ and HDF channels simultaneously) can occur. Happy for anyone to add any others they know of. ;o)

  1. a Seismic event is big enough to cause a change in air pressure at the station;
  2. an atmospheric event is big enough to cause ground movement that registers on the EHZ channel;
  3. the event is so close that the difference in seismic and atmospheric transmission speed is not significant;
  4. the signal is neither seismic nor atmospheric but electrical interference affecting both EHZ and HDF channels.

Close or very strong earthquakes can cause No 1.

Helicopters are a great example of No 2.

The log trucks passing my front gate (<100m from the Shake) are probably a good example of No 3.

I got very interested in this when trying to detect meteors in the HDF channel. Any signals that show simultaneously on the seismic channel were discounted (i.e. not likely meteors). Obspy has a cross correlation function which you can use to work out which channel is driving which. I wrote some code to do just that for the Shake and Boom which is available on my Github repository:

Look for RSanBCorr.py

Al.

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4

Hello again,

These are all the things I was thinking of, and I am happy to learn that you have generated a code to deal with them. I will look into it.

Steve

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5

I recently had such and event when the large New Jersey Earthquake, which I detected as a Seismic event, also caused enough shaking in the local environment to be registered as an Infrasound event. It confused me at first to see them both register a distant EQ, but Stormchaser helpfully told me what I was seeing.

The local shaking, by the way, was imperceptible here in Northern Virginia.

Regards.

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