For broadband ocean bottom seismometer (OBS) data, external noise is typically more pronounced than on seismometers installed onshore. However, the sources of this external noise are only partly understood. In particular, the impact the instrument design (form-factor of the floatation, pressure vessel, hight-to-width ratio) has on the amplitude of external noise is not fully understood. As a developer of OBS systems, K.U.M. Kiel GmbH has deployed two different types of OBS systems side-by-side for a period of 77 days. Both instruments included the same seismic sensor, a Nanometrics Trillium Compact 120 OBS. Station LOBS was a K.U.M. LOBSTER-type instrument carrier (https://jlsrf.org/index.php/lsf/article/view/165) which is the main instrument type in the DEPAS pool “German instrument pool for amphibian seismology”(https://www.awi.de/en/science/geosciences/geophysics/methods-and-tools/ocean-bottom-seismometer/depas.html). Station NEUA was a more recently developed system of the K.U.M. NAMMU-Type instrument, that has a completely different design (https://www.kum-kiel.de/products/nammu.html), with a single flotation, a single pressure tube containing the seismometer, datalogger and batteries. The side-by-side deployment of the different instruments allows a direct comparison and the availability of the oceanographic and meteorological data from the nearby metocean station DARSS-SILL (https://www.io-warnemuende.de/marnet-darss-sill.html) allows a detailed investigations of the instrument-design-related noise sources at OBS stations. Waveform data is available from the GEOFON data centre, under network code 1Q.
This is the first deployment of a teleseismic broadband array consisting of 12 three-component stations with an aperture of about 50 km in the deep ocean in about 5000 m water depth. The data can be compared with two other deployments on Madeira and in western Portugal mainland which had similar array layouts and recording time spans (network Y7). The broadband data enable furthermore analysis of the crust and upper mantle beneath the array near to the Gloria fault, a major transform fault in the North Atlantic. Recordings of numerous local and regional earthquakes make a precise location of active structures possible. Waveform data is available from the GEOFON data centre, under network code 3J.
“This ocean-bottom seismometer deployment is part of the SEAMSTRESS project examining tectonic stress effects on Arctic methane seepage. The project is led by PI Andreia Plaza-Faverola at the Centre for Arctic Gas Hydrates, University of Tromsö, Norway. A total of 10 ocean bottom seismometers (OBS) were deployed on Vestnesa Ridge, a sediment drift body just north Knipovich Ridge at its intersection with the Molloy Transform fault (cruise CAGE-20-5). The aim of the experiment was to look for stress release along faults that control seepage sites on Vestnesa Ridge. The network consisted of 8 Lobster type broadband OBS from the German Instrument Pool for Amphibian Seismology (DEPAS) and 2 3C geophones provided by the University of Tromsö. Instruments were free-fall deployed and spaced by about 10 km. They recorded continuously at 100 Hz for 11 months between August 2020 and July 2021.Short, intersecting refraction profiles were shot across all OBS stations, such that OBS positions at the seafloor could be determined within 10 m (cruise CAGE-21-3). Clock drift in this experiment was nonlinear and skew values were only obtained for 6 of the stations. Skew-corrected station VSN01 served as reference station to obtain the clock drift of all other stations using noise cross-correlation and subsequently correct also for the thus determined nonlinearity of time drift. Waveform data are available from the GEOFON data centre, under network code Y9.
BEAR ISLAND (The Dynamic Continental Margin Between the Mid-Atlantic-Ridge System (Mohns Ridge, Knipovich Ridge) and the Bear Island Region) is an interdisciplinary project exploring the stress conditions and sources, and the dynamics and deformation characteristics of the continental margin between the Mid-Atlantic Ridge and Bear Island from its top sedimentary cover to its imprint in the upper mantle. In this region the margin includes an extremely thick sedimentary wedge and steep slopes, with at least one major paleo-fracture zone cutting through the wedge. Recent studies in this area indicate very low seismic velocities in the lithosphere and the stress field undergoes an extensional-compressional transition. It is therefore of particular interest to understand the structural architecture, the stress and the dynamics of the whole region because of its natural hazard exposure and the processes involved in the formation of the margin and the opening of the North Atlantic. To achieve this, deep seismic sounding data, as well as records from temporary broadband installations, supplementary to data from existing seismic stations in the region were collected. A key element of the project was the operation of a long-term network of broadband ocean-bottom seismometers (OBS). Additionally, two new broadband seismometers and a small temporary seismic array with 13 sensors were operated. Active seismic refraction/reflection experiments were conducted along two profiles crossing the region and recorded with additional short period OBSs and land stations. Twelve broadband ocean-bottom seismometers (OBS) from the German Instrument Pool of Amphibian Seismology (DEPAS) were deployed as part of this network with RV Horyzont II in September 2007. They were distributed on the Barents shelf, the slope and the deep sea near the Mid-Atlantic Ridge. Nine instruments could be recovered in August 2008 with RV Horyzont II. One instrument was fished before, one was destroyed during recovery and one got lost. Seven stations recorded data for the full deployment period; two stations have no skew value. The time correction for these stations was estimated by noise cross-correlations. Based on previous experiments, the accuracy of the positions is estimated to 500 m. Waveform data is available from the GEOFON data centre, under network code 9C.
The WAVEOBS project was established with three primary goals; to get a better fundamental understanding of microseism sources in the north-east Atlantic near Ireland; to investigate the use of ocean generated microseisms as real time ocean wave height data; and to investigate their use as a climate proxy. Waveform data is available from the GEOFON data centre, under network code 4V, and is fully open.
The aim of the project is to deploy 10 Broad Band Ocean Bottom Seismographs (OBSs) units across the shelf offshore Donegal and out into the Rockall Trough in order to study microseims. Compared to earthquakes, microseisms represent background seismic noise generated by ocean wave pressure fluctuations on the sea floor which generate low frequency seismic waves. This project is a collaboration between the Dublin Institute for Advanced Studies (DIAS) and the Helmholtz Center GFZ Potsdam (Germany) with instruments provided by the Alfred Wegener Institute (AWI in Germany). Waveform data is available from the GEOFON data centre, under network code 2V.
BRAVOSEIS (Bransfield Volcano Seismology) is an interdisciplinary project exploring volcanism in the Bransfield back-arc basin, Antarctica. Partners from Spain (amongst others UGR, project leader), Germany (AWI, GFZ) and the US (CUNY, UW, WHOI) performed various geophysical onshore and offshore measurements in the Antarctis seasons 2017-2018, 2018-2019 and 2019-2020. A key element of the project was the operation of a large long-term amphibious network of broadband seismometer in the Bransfield Strait, on the adjoining South Shetland Islands, and on the Antarctic Peninsula. Nine broadband ocean-bottom seismometer (OBS) from the German Instrument Pool of Amphibian Seismology (DEPAS) were deployed as part of this network with RV Sarmiento de Gamboa in January 2019 (cruise SDG076). They were distributed along the entire basin, one station supplemented a dense array of short-period OBS around the Orca seamount. Eight instruments could be recovered in February 2020 with RV Hespérides (cruise HE0188), one OBS is still missing. All stations recorded data for the full deployment period. Unfortunately, the clock drift of all stations turned out to be non-linear, a skew measurement was possible for four stations only. The clock drift was corrected by means of noise cross-correlations. Based on previous experiments, the accuracy of the positions is estimated to 500 m. Waveform data is available from the GEOFON data centre, under network code ZX.
This ocean-bottom seismometer deployment is part of the LoCHnESs (Loki Castle Hydrothermal iN-situ Experiments and Surveys) project examining hydrothermal fluid circulation at Loki's Castle vent field. The project is led by PI Thibaut Barreyre at the Centre for Deep Sea Research, Department of Earth Science, University of Bergen, Norway. A total of 8 ocean bottom seismometers (OBS) were deployed near Loki's Castle vent field at the Mohns-Knipovich Ridge bend, Norwegian-Greenland Sea. The aim of the experiment was to monitor seismicity related to changes in the hydrothermal circulation system and to reveal interaction between an active detachment fault and the axial volcanic ridge hosting the vent site. The network consisted of 8 DEPAS Lobster type broadband OBS from the German Instrument Pool for Amphibian Seismology (DEPAS). Instruments were free-fall deployed and spaced by about 5-8 km. They recorded continuously at 100 Hz for 12 months between July 2019 and July 2020. Two instruments (LOK01 and LOK06) could only be deployed one month later and recorded at 250 Hz. OBS positions at the seafloor were determined by interpolation at 2/3 of the distance between the deployment and recovery position at the seafloor. Position accuracy is estimated to be about 100 m. Skew values were obtained for all stations and reached values of up to 24 s. Clock drift in this experiment was nonlinear. Skew-corrected station LOK02 served as reference station to obtain the clock drift of all other stations using noise cross-correlation and subsequently correct also for the thus determined nonlinearity of time drift. Waveform data are available from the GEOFON data centre, under network code 8M.
This dataset includes five stations of an Ocean Bottom Seismometer (OBS) experiment conducted at the southern end of the Fonualei Rift and Spreading Center in the Lau Basin, southwestern Pacific. The OBS recorded continuously for 32-days on 4 components, including a hydrophone and a 3-component 4.5 Hz geophone. The experiment was conducted during RV Sonne cruise SO267, project ARCHIMEDES I.
“Gakkel Deep is a pilot project that installed a network of four broadband ocean bottom seismometers (OBS) near Gakkel Deep, the deepest depression in the Arctic Ocean, at the eastern end of the ultraslow spreading Gakkel Ridge. The area is covered year-round by sea ice. In order to enable a safe recovery of the OBS in a sea ice covered ocean, the OBS were modified to include a positioning system that allows to track the instruments at meter accuracy during descent and ascent and when stuck beneath ice floes. This pilot studied aimed at testing the recovery procedure of the OBS, checking the performance of the modified instrument design, getting an overview of ambient seismic noise at the bottom of the Arctic Ocean and at contributing to a better understanding of the origin of the Gakkel Deep depression with more than 3000 m of topography. The network is shaped as a rectangle with 8 km and 10 km side length and is centered at about 82°N 119.5°E at water depths between 3600 m and 4100 m. It is positioned slightly to the east of the present plate boundary in an area with volcanic structures. Instruments from the German Instrument Pool of Amphibian Seismology (DEPAS) were deployed during RV Polarstern cruise PS115/2 on September 15, 2018. Instrument recovery was completed during RV Polarstern cruise PS122/1 on September 27, 2019. The data set contains about 377 days of continuous records at 250 Hz sample rate. The station locations were determined with Ultra Short Baseline (USBL) ranging, the accuracy is approx. 10 m. The non-linear clock drift was determined by means of noise cross-correlations and applied to the data set. Waveform data are available from the GEOFON data centre.
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