Infrasound Signals from Close Earthquakes

[sheeny]

Last night a small M2.6 earthquake occurred 54kms away from my shake (R21C0).

Here’s my normal seismic reports and section plots FYI:

As an aside, I reckon, based on the section plots that the quake time should be more like 08:59:58 UTC not 09:00:00 UTC as officially estimated at the time of processing.

As the quake was nice and close (just 54kms away) I thought I’d see if an infrasound signal could be detected from it. If you look closely at my seismic report, I calculate the arrival time window for an infrasound signal. This is based on how the speed of sound changes with temperature and altitude in the atmosphere, so signals inside the window could be a related infrasound signal, but outside that window they cannot be (without extenuating circumstances like significant prevailing winds etc).

So an infrasound signal from the quake should arrive between 9:02:33 UTC and 9:02:57 UTC.

So running a Boom Report in that window gave:

Which is a pretty tenuous detection, but I estimated the infrasound arrival to be 9:02:43 UTC.

Playing around with the lower filter frequency however, made the arrival clearer:

Al.

[Stormchaser]

Another very interesting analysis sheeny! I think this quake was a prime example due to its closeness/magnitude regarding what you were looking for.

And the plots are always great to see.

[sheeny]

Thanks Stormchaser.

I put the infrasound calcs into my report for explosive events in particular, but curiosity being what it is, thought I’d give it a whirl.

I need another event or access to Tim’s station with my python code to verify, though. I can’t pick it with DataView on his shake with a rough manual estimate of when the HDF signal should arrive… which itself is not a good sign for verification, but it may just be my estimated arrival time isn’t good enough.

I guess it is more likely to work on quakes where there is vertical movement of the ground.

Al.