Shake 3D waveform offsets


I want to perform some geophysical studies with three 3D units that I purchased a few months ago. This is the first time I turned one unit on (due to the quarantine), and all the recordings have a constant offset in each component.
I am importing and processing the miniseed recordings in Geopsy, and this is what every original recording looks like:

It looks like the N-S and vertical components have a strong positive offset, while the E-W component is negatively offset.

Geopsy has a detrending function that can remove this offset, making it look like a normal recording:

I was wondering if this was normal, has anyone ever seen anything like this? I will test the other two units over the next few days, and report if they also have the same offset.


Hi Stefano,

Yes, this is fairly normal. It is usually a good idea to run a de-mean operation before working with the data as you’ve done here. The data quality is not affected by this phenomenon.



Thank you Ian for the quick response, I’m glad these offsets are normal.