A Self‐Noise Model for the German DEPAS OBS Pool

Abstract

Ocean-bottom seismometers (OBSs) allow us to extend seismological research to the oceans to constrain offshore seismicity but also image the marine subsurface. A challenge is the high noise level on OBS records, which is created not only by bottom currents but also by the specific seismometer models used. We present a quantitative noise model for the LOBSTER OBS, which is the main instrument of the DEutscher Geräte-Pool für Amphibische Seismologie (DEPAS), currently the largest European OBS pool, stationed at AWI Bremerhaven. Studying sensor noise in vault conditions and current sensitivity at an oceanographic measurement mast, we can show that the previously reported high noise level of the instrument is caused by the original sensor (Güralp CMG-40T-OBS). We also show that a strong signal that has been reported between 1 and 5 Hz can be attributed to head-buoy cable strumming. We provide a currentdependent quantitative noise model that can be used for experiment design in future deployments and show that the performance of the pool OBS can be improved at moderate cost by replacing the CMG-40T-OBS with a sensor of a proven noise floor below 10 −8 nm=s 2 , for example, a Trillium compact.

A Comodulation Analysis of Atmospheric Energy Injection Into the Ground Motion at InSight, Mars

“…These prominent modes are artificial and associated with the lander body, solar panels, instrument deployment arm, load shunt assembly, and tether, coexciting with surges in atmospheric activity. Such features are also observed on Earth, for example, resonant modes in ocean‐bottom seismometers attributed to head‐buoy cables strumming from fluid motion, even at moderate current velocities (Stähler et al., 2018). Here, a further characteristic of the wind speed threshold is apparent: the abrupt attenuation of modes below 10 Hz at the 2.8 m s −1 wind‐speed threshold.…”

Segment‐Scale Seismicity of the Ultraslow Spreading Knipovich Ridge

“…We automatically picked P and S phases using the kurtosis-based PSPicker by Baillard et al (2014), but the picking results were not satisfactory and needed refinement by manual picking in SEISAN (Havskov & Ottemöller, 1999;Ottemöller et al, 2017). The main reason for the poor performance of the automatic picker are ocean bottom currents that acted on the OBS and produced harmonic tremor signals in the frequency range between 1 and about 10 Hz (Stähler et al, 2018). Filtering records between 7 and 17 Hz achieved the best results.…”

Passive seismic experiment “AniMaLS” in the Polish Sudetes (NE Variscides)

“…This is most likely due to high self-noise of this device type and, partially (for T noise > 30 s), to a lower corner period of the instrument (30 s vs. 120 s for other units). It is worth noting that the CMG-6T high long-period noise is at a very similar level to that for the ocean-bottom seismometer (OBS) version of the Güralp CMG-40T (30 s) sensor (Stähler et al, 2018), while the land version of CMG-40T shows substantially lower (by about 20 dB) self-noise in this period range (Custódio et al, 2014;Tasič and Runovc, 2012).…”