What's the physical quantity of waveforms

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1

Hello,

    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
Xuping

2

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.

Best,
Jon