What's the physical quantity of waveforms


    I used the Python tools of Library Obspy (obspy.clients.Client) to download seismic waveforms from IRIS but encountered that the SAC header variable "IDEP" is "-12345".

So I want to know what's the physical quantity of the waveforms, displacement, velocity or acceleration? Can you help me? Thanks!

Kind regards

Hi Xuping,

If you used the FDSN client, without applying any corrections, I think the units would be in counts (see https://ds.iris.edu/ds/support/faq/6/what-is-a-count-in-timeseries-data/). To convert to another unit, you would need the channel response information from the “client.get_stations” method of your client.