The data comprise continuous records of seismic raw data acquired with ocean bottom seismometers (OBS). The data were collected at Poseidon mud volcano chain during expedition POS515 with the research vessel POSEIDON (Riedel et al., 2017) in the Mediterranean Sea, Calabrian Arc offshore southern Italy (map under further details). The entire data set consists of 12 OBS stations. Each OBS consist of 4 channels (channel 1: hydrophone; channel 2: horizontal component 1; channel 3: horizontal component 2; channel 4: vertical component). Data are not corrected for clock-drift. Data format is Passcal-SEGY. Data are accessible using the seismological software tools provided by EarthScope: https://www.passcal.nmt.edu/content/software-resources. The data were recorded using: HTI-04_PCA_ULF hydrophones from High Tech Inc., Short-period 4.5 Hz geophones and Three-component seismometers (K/MT-210 manufactured by KUM GmbH). The recording device is an MBS recorder of SEND GmbH

Data are stored for each OBS location separately. Data comprise the entire recording period. We are using the Julian Day numbering convention. There are 12 OBS stations in total (P01 - P12). Julian days are from day 183 (= July 2, 2017) until day 186 (= July 5, 2017).Physical location of OBS drop position can be found in the associated cruise report (Riedel et al., 2017).A data-file for any given OBS has a name following this format:e.g. P.01.17.183.16.22.17.0504.1P........ Poseidon mud volcano chain: P.01......**. OBS station number: 01..17. ..... Year: 2017...183..... Julian Day of the start of the record: 183....16... Hour of the start of the record: 16.....22... Minute of the start of the record: 22......17.*. Second of the start of the record: 17.......0504. Serial number of the MBS-Recorder: 0504...*.....1 This value is the recorded channel (1= hydrophone, 2= horizontal 1, 3 = horizontal 2, 4 = vertical)Sampling rate of the recordings was at 1000 Hz.Clock time drift (skew) with respect to GMT +0OBS P01: Clock start recording Julian Day 183, 16:20:00, End recording Julian Day 187, 12:10:00, drift +9 msOBS P02: Clock start recording Julian Day 183, 16:41:00, End recording Julian Day 187, 12:46:00, drift -28 msOBS P03: Clock start recording Julian Day 183, 15:50:00, End recording Julian Day 187, 12:29:00, drift -24 msOBS P04: Clock start recording Julian Day 183, 17:00:00, End recording Julian Day 187, 16:25:00, drift -26 msOBS P05: Clock start recording Julian Day 183, 17:21:00, End recording Julian Day 187, 14:36:00, drift +35 msOBS P06: Clock start recording Julian Day 183, 17:27:00, End recording Julian Day 187, 13:34:00, drift -153 msOBS P07: Clock start recording Julian Day 183, 17:34:00, End recording Julian Day 187, 13:43:00, drift -2 msOBS P08: Clock start recording Julian Day 183, 17:43:00, End recording Julian Day 187, 17:02:00, drift -131 msOBS P09: Clock start recording Julian Day 183, 17:52:00, End recording Julian Day 187, 16:46:00, drift +22 msOBS P10: Clock start recording Julian Day 183, 18:10:00, End recording Julian Day 187, 15:31:00, drift +24 msOBS P11: Clock start recording Julian Day 183, 18:21:00, End recording Julian Day 187, 15:04:00, drift +1 msOBS P12: Clock start recording Julian Day 183, 18:28:00, End recording Julian Day 187, 14:02:00, drift -252 msJulian Day 183 = July 2, 2017