ESTOC

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Project title and acronym

SEISMIC AND ACOUSTIC noise analysis at ESTOC site (SEACOUT)

Host facility

ESTOC

Modality of Access

MoA2 – Partially remote (the presence of the user is required at some stage, e.g. for installing and uninstalling an instrument)

Description

Seismometers measure earth motion in the Earth’s crust. About 90 percent of all natural earthquakes occur underwater, where great pressure (depth} and cold temperatures make measurements challenging. An ocean-bottom seismometer (085} is a seismometer that can be deployed on the seafloor for weeks or months, their sensors can record earthquakes, volcanic eruptions, tremors or any acoustic event regardless of their origin but depending on the sensor characteristics, essentially the frequency range. Physically, seismic noise consists mostly of surface waves. Low frequency waves (below 1 Hz) are generally called microseisms; high frequency waves (above 1 Hz} ore called microtremors. The objective is to analyze the environmental noise in the area of ESTOC site, with the primarily aim to identify and / or differentiate regional seismic and biological sources of acoustic generation and wave propagation of the ocean noise, and to improve the performance of the 0BS. Blue and fin whales produce very loud calls at frequencies as low as 20Hz (Wilcock, 2012). Passive acoustic monitoring using 0BS is usually used to study seismicity for long periods of time (typically months} but it is also an important tool for studying the distribution and abundance of large whales in the oceans, characterizing their behavior and habitat usage (seasonally), and assessing how they are impacted by anthropogenic sounds (Zimmer, 2011). In this study we will focus on two different sources in the 1 to 50 Hz range records: : low-frequency calls of whale species, blue and fin whales, and the spectra of volcanic tremors dominated by frequencies around 10Hz.

To achieve this we envisaged to deploy a small array of 4/6 short period four standard components 085 (i.e. 3 components geophone OYO GS-11D, 4,5 Hz and a HighTech HTI-01-PCA( hydrophone) to monitor ambient noise around the E5TOC site for a period of 6-9 months.

Using an array of several OBS’s recording simultaneously the ambient noise allows to improve our understanding of the acoustic record wave field and its origin, and to derive physical properties of the oceanic crustal structure when required. Noise sources will be investigated through probability density functions (PDF) of the power spectral density (P50), which provides information on the generation and propagation of seismic noise in the study area (Core/a et al., 2014). The locations and tracking of sounds generated by marine mammals will be performed using a seismological hypo central location code (Gaspà et al., 2006).

References

Corela, C., G. Silveira, L. Matias, M. Schimmel and W. Geissler (2014}. AGU Fall meeting, Abstract ID: 21865.

Gaspà Rebull 0., Diaz Cusi J., Ruiz Fern6ndez M., Gallart Muset 1.,(2006),, J Acoust Soc Am. 120{4}:2077-85.

Wilcock, W.S.d:, . Tracl. Acoust. Sac. Am. 132, 2408-2419 (2012).

Zimmer, W. X. Z. (2011). Passive Acoustic Monitoring of Cetaceans. Cambridge Uni. Press, New York.