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Project LOKI: DEPAS ocean-bottom seismometer operations at Loki's Castle vent field in 2019-2020

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.

SEAMSTRESS: DEPAS ocean-bottom seismometer operations on Vestnesa Ridge in 2020-2021

“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.

Seismic neTwoRk/Array in norThwEstern arGentina (STRATEGy)

The STRATEGy network was a temporary seismic network in the NW Argentinean Andean Foreland. It run for about 15 months between June 2016 and August 2017 and consisted of 13 stations for the most parts. Each station contains a Lennartz LE3D/5s seismometer, an Omnirecs DataCube³ext digitizer (100 Hz sampling rate) with external GPS antenna and internal flash memory. Station 14A consisted of a Mark L-4C-3D short-period sensor. The power was supplied through an external batteries that were recharged during the day via a solar panel. The sensors were oriented to magnetic north. The header of the waveform files (NSLC-IDs) still remained in its prior form (network code ST) and haven’t been adapted to the FDSN given code. Station codes (double digits) were assigned from North to South. The last digit of the station code is either A (for their initial position of a station site) or B (the station has been moved during the networks operation time due to low quality recordings at the respective initial site). Each site was chosen on 3 criteria: (1) minimizing the depth to bedrock, (2) maximizing remoteness, and (3) maximizing security, preferentially located within sight of nearby settlements. However, one station (02A) was lost due to theft and many others experienced recording gaps due to animals chewing on cables, malfunctions of electrical parts and mainly flooding of the stations during the austral summer monsoon. The overall network geometry evolved partially due to accessibility of remote locations, maintaining similar interstation distances and focusing around the epicenter of the Mw 5.7 El Galpón earthquake 9 months prior to the network’s starttime. The smallest depths to bedrock were achieved by concentrating the sites around two major bedrock ranges and their piedmont, Cerro Colorado and Sierra de la Candelaria. Waveform data are available from the GEOFON data centre, under network code 2S.

PatachE Stress Observation (PESO)

The PESO array provides two weeks of local seismological observation in the vicinity of the IPOC (Plate Boundary Observatory Network Northern Chile) station Patache (CX.PATCX) to investigate the subsurface structure and the ambient seismic field. Waveform data is available from the GEOFON data centre, under network code 7F, and is fully open.

Illgraben

The Illgraben is a 10 km² steep side valley located in Switzerland. This active debris flow catchment supplies 5-15% of the total sediment load of the Rhône River upstream of Lake Geneva. The 30-80° steep catchment slopes host frequent rock falls and slides. From 2012 to 2014, a network of up to ten Nanometrics Trillium Compact 120s broadband seismometers, sampled by Digos DataCube³ext loggers at 200 Hz (and later by centaur), was deployed in and around the catchment to monitor distributed geomorphic activity. Waveform data is available from the GEOFON data centre, under network code 9J, and is fully open.

META-WT

The META-WT project was designed to perform a 4-weeks seismic experiment in Germany with a dense seismic array of ~400 three-component geophones that covered (1) a 2.5km x 2.5km wind farm area in Brandenburg, Germany, with almost 200 wind turbines (WTs) and a well-studied subsurface structure and (2) a 20-km long radial line from the center of the wind farm with one geophone every half-kilometer. The objective was to capture the spatio-temporal seismic wave-field signature of the wind farm from continuous recordings of ambient noise. Due to the dense interstation distance and proposed geometry the experiment allowed for analyzing both small-scale wave field characteristics at an unprecedented spatial resolution and the longer distance radiation pattern of the wind farm. Waveform data is available from the GEOFON data centre, under network code XF.

Temporary DAS Deployment associated with the DEEPEN project in the Hengill region, Iceland (DEEPEN)

From June to August 2021 the DEEPEN project deployed a dense seismic nodal network across the Hengill geothermal area in southwest Iceland to image and characterize faults and high-temperature zones at high resolution. The nodal network comprised 498 geophone nodes spread across the northern Nesjavellir and southern Hverahlíð geothermal fields and was complemented by an existing permanent and temporary backbone seismic network of a total of 44 short-period and broadband stations. In addition, two fiber optic telecommunication cables near the Nesjavellir geothermal power plant were interrogated with commercial DAS-interrogators. During the time of deployment, a vibroseis survey took place around the Nesjavellir power plant. The here published dataset contains a subset of the downsampled DAS-recordings from the eastern fiber optic array. To save storage space, only every fourth trace was made available. The original data were downsampled from 1000Hz to 250 Hz using the das-convert tool (https://doi.org/10.5880/GFZ.2.1.2021.005). Further traces or the original data can be obtained upon request. Waveform data are available from the GEOFON data centre, under network code ZH.

University of Potsdam Experimental 3D-3C Array

The network consists of a vertical borehole array equipped with 3C sensors (geophones) for the analysis of swarm earthquakes in the Western Bohemia / Vogtland area located in the German/Czech border region. A surface array is completing the 3D observation of the wave field with 3C sensors (geophones). Waveform data is available from the GEOFON data centre, under network code 6A.

SISLACQ2021

Deployment of 10 seismometers for monitoring the induced seismicity of the Lacq gas field, France. This project focus on the analysis of the seismicity induced by anthropogenic activities (gas extraction and wastewater injection) related to the gas field, located in Lacq, France. We aim to answer the following questions: which part of the Lacq induced seismicity is generated by wastewater injection? by the mechanical evolution of the reservoir depletion? Is the seismicity confined to the (minor) faults of the reservoir or can regional tectonic faults be activated, generating large earthquakes? What scenarios of ground shaking and damages could be expected in case of a major event in the area? What is the associated seismic hazard and risk?

Myanmar subduction to collision imaging array (MySCOLAR)

The temporary seismic array of MySCOLAR in northern Myanmar consists of 30 broadband stations. The overall scientific goals are to understand the transition from continental collision to oceanic subduction, to quantify the partitioning of deformation in the accretionary prism, in the Burma Plate and along the strike-slip Sagaing fault system and to image the subducting Indian Plate beneath Myanmar and southwest China. The seismological analysis methods applied to this dataset will include location of local earthquakes and determining their focal mechanisms, surface wave tomography from ambient noise and earthquake data, body wave tomography from local and teleseismic earthquakes, full waveform inversion for Earth structure, receiver functions, and shear wave splitting. A subset of the stations was transmitting data in real time, and these stations contributed to real-time earthquake analysis by the Department of Meteorology and Hydrology (DMH) in Myanmar and the GEOFON earthquake monitoring service. Waveform data are available from the GEOFON data centre, under network code 6C.

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