I am reading and trying to understand the output of my Shake and Boom. Did my device actually pick up the Vanuatu quake? Or are the P and S indicators calculated values that don’t necessarily indicate my device picked up the quake?
Thanks.
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Hello chansky, good question!
Let’s start by clarifying (also for everyone who reads this thread) that your second point is the correct one. The P/S markers are calculated based on the iasp91 reference model, which is
a parameterized velocity model that has been constructed to be a summary of the travel time characteristics of the main seismic phases.
(NSF SAGE: Data Services Products: EMC-iasp91 )
This model takes into account the location of your Shake relative to the earthquake data it has and automatically computes the P and S pickers that are displayed on the screen. These are displayed in any case, with or without clear seismic wave arrival.
Now, onto the quake you highlighted; an M4.9 at that distance is unlikely to be received as its signal 10000 km away will be very faint. However, the main M7.3 shock is easily visible on your Shake, even without filtering:
As you can observe, due to the long distance between your location and the quake epicenter, the earthquake signal appears only in the very low frequencies of the spectrum. You’ll always see this with distant earthquakes compared to closer ones, where the signal is spread more towards the higher frequencies.
I hope this clarified the event for you, but if you have other doubts/questions, feel free to ask!