Wandering filtered seismogram



I’ve been playing around with Obspy recently and finally managed to get around to filtering my own data and plotting something up. The picture is supposed to show the Tauranga earthquake from a couple weeks ago, on my device.
However, I’ve reached an issue where the filtered response is wandering and is not set to 0. I know this is an issue that can happen but I can’t remember what it’s called and I’m struggling to find a solution. Could someone please give me some guidance to fix this problem.

Thank you in advance,


I suggest you band pass filtering. Assuming that it’s geophone signal, I normally apply high pass filter at 0.05~0.1Hz.



Hi Seokho,

Thank you for the advice and giving me some filter applications.
While looking for the correct way to write out a bandpass filter, I found the detrend function, which was the thing I was trying to remember. Having said that, they both produce very similar results and it appears, initially at least, that the bandpass is more useful. This will be an interesting thing to look into.

Again, thank you very much for your advice,

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Oops. I didn’t mean that you should apply a bandpass with the passband of 0.05 to 0.1. That’s the usual range of frequencies I use as the lowcut frequency.

Ah okay, I understand what you meant now.

Having said that, applying the bandpass did appear to solve my problem, so that’s a bonus.

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