Properties of Noise Registered by Pop-Up Ocean-Bottom Seismographs

Ковачев, С. А.; Demidova, T. A.; Son’kin, A. V.

doi:10.1175/1520-0426(1997)014<0883:ponrbp>2.0.co;2

Cited by 8 publications

(8 citation statements)

References 3 publications

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“…Similar results were reported by Kovachev et al, (1997), showing oscillation modes specific to the body of an OBS excited by near-bottom currents. These motions affected the seismic sensor, even when the sensor compartment lies several meters away from the noise source.…”

Section: Introductionsupporting

confidence: 89%

“…The presence of oscillating frequencies also affects the shape of recorded earthquakes signals as they can also cause oscillations of the mechanical components of the station. Kovachev et al (1997) concluded that the oscillations were caused by the interaction of the OBS components with the near-bottom current flow. However, unlike the von Kármán vortex mechanism, the observed resonant frequency was independent of the current flow speed.…”

Section: Introductionmentioning

confidence: 99%

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The OBS noise due to deep ocean currents

Corela

Loureiro

Duarte

et al. 2022

Preprint

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Abstract. Ocean bottom seismometers (OBS) are usually deployed for seismological investigations but these objectives are impaired by noise resulting from ocean environment. We split the OBS recorded seismic noise into three domains, short-period, microseisms and long-period, also known as tilt-noise. We show that the first and third domains are controlled by bottom currents but these are not always a function of the tidal forcing. Instead we suggest that the ocean bottom has a flow regime resulting from two possible contributions, the permanent low frequency bottom current and the tidal current. The recorded noise displays the balance between these two currents along the full tidal cycle, between neap and spring tides. In the short-period noise band the ocean current generates harmonic tremors that corrupt the dataset records. We show that, in the analyzed cases, the harmonic tremors result from the interaction between the ocean current and mechanical elements of the OBS that are not essential for sea bottom recording and thus have no geological origin. The data from a new Broadband OBS type, designed and built at Instituto Dom Luiz (University of Lisbon)/CEIIA, hiding no essential components from current flow, shows how utmost of the harmonic noise can be eliminated.

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Section: Introductionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

The OBS noise due to deep ocean currents

Corela

Loureiro

Duarte

et al. 2022

Preprint

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“…Throughout the entire 41 month period of monitoring, there is only one other instance (station 8, April–July 2004) where two distinct tremor bands are sustained within the 4–8 Hz frequency range for a significant period of time. Kovachev et al [1997] has suggested that in low current environments (<4 cm/s) noise arises primarily due to the resonance of the OBS frame and components, predicting stable frequencies that do not depend on the velocity of the currents. Consequently, the observed changes in frequency content through time further argue against a current driven noise source.…”

Section: Data Analysis and Observationsmentioning

confidence: 99%

Seismic tremor at the 9°50′N East Pacific Rise eruption site

Monigle

Bohnenstiehl

Tolstoy

et al. 2009

Geochem Geophys Geosyst

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[1] Ocean bottom seismic observations within the 9°50 0 N region of the East Pacific Rise indicate persistent, low-amplitude tremor activity throughout the October 2003 through February 2007 period of monitoring. These signals exhibit either monochromatic or polychromatic spectral characteristics, with a $6 Hz fundamental frequency and up to two harmonics. Individual events cannot be correlated between nearby (<1 km) stations, implying the presence of multiple, small-amplitude sources positioned within the shallow crust. Tremor exhibits a semidiurnal periodicity, with some stations recording activity during times of increasing tidal extension and others detecting tremor signals during times of increasing compression. The amplitude, duration, and rate of activity also correlate positively with fortnightly changes in the amplitude of the tides. These spatiotemporal patterns are consistent with tremor generation in response to tidally modulated fluid flow within a network of shallow cracks. Tremor energy flux is spatially and temporally heterogeneous; however, there are extended periods of greater and lesser activity that can be tracked across portions of the array. Despite their shallow crustal origin, changes in tremor amplitude and spectral character occur in the months prior to a major microearthquake swarm and inferred seafloor spreading event on 22 January 2006, with an increase in the degree of correlation between tremor activity and tidal strain in the weeks leading up to this event. After the spreading event, two eruption-surviving stations near the axis continue to show high rates of tremor activity, whereas these signals are suppressed at the single station recovered from the near-axis flanks. This off-axis quiescence may result from the dikeinduced closing of cracks or perhaps from the emplacement of impermeable flows near the station.

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“…Trehu (1985) and Kovachev et al. (1997) attributed the noise to turbulences and vortices on the vibrating components of OBS instead of the Karman vortex shedding alone because the dominant frequency is greater than the vortex‐shedding frequency of any elements of OBS and independent of the current velocity.…”

Section: Introductionmentioning

confidence: 99%

“…The noise was characterized as being high-frequency (about 1-7 Hz), narrowband and large amplitude. Trehu (1985) and Kovachev et al (1997) attributed the noise to turbulences and vortices on the vibrating components of OBS instead of the Karman vortex shedding alone because the dominant frequency is greater than the vortex-shedding frequency of any elements of OBS and independent of the current velocity.Recent studies have asserted that bottom currents could generate low-frequency noise (e.g., <0.1 Hz) through turbulent interactions between the currents and the sensor package (…”

mentioning

confidence: 99%

Current‐Induced Noise in Ocean Bottom Seismic Data: Insights From a Laboratory Water Flume Experiment

Yang

Liu

et al. 2023

Earth and Space Science

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The ocean‐bottom currents are believed to be largely responsible for the high noise level in ocean bottom seismograph (OBS) data, in particular on the horizontal components. Due to the lack of in‐situ experiments and measurements, the generation mechanism and characteristics of the current‐induced noise are still poorly understood. In this paper, we designed an experiment to explore the features of current‐induced noise. A sensor module from a typical passive‐source OBS was installed in a water flume that can produce controllable steady water flows. We measured and analyzed the recorded noise with changing current velocities, with and without shielding. With other noise sources, such as infragravity waves precluded, this experiment demonstrates that the currents can generate low‐frequency noise, particularly <0.1 Hz. The noise level depends on the current velocity as well as the frequency. While the current‐induced noise affects the horizontal components significantly, its impacts on the vertical component appear negligible. The experiment shows that current‐induced noise has a dominant direction approximately perpendicular to the currents, a pattern consistent with an actual OBS on the flank of Mariana Trench, where the current direction is supposed to be along the trench. Shielding the sensor module with a plastic casing can substantially suppress the noise, indicating that shielding is a practical, low‐cost scheme to reduce the current‐induced noise.

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Properties of Noise Registered by Pop-Up Ocean-Bottom Seismographs

Cited by 8 publications

References 3 publications

The OBS noise due to deep ocean currents

The OBS noise due to deep ocean currents

Seismic tremor at the 9°50′N East Pacific Rise eruption site

Current‐Induced Noise in Ocean Bottom Seismic Data: Insights From a Laboratory Water Flume Experiment

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