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Marine Geophysics

Marine Geophysics probes how the earth works deep below its oceans and interacts with them. This theme is concerned with the application of gravity, magnetic, heat flow, and general seismic methods and imaging techniques to study the structure of the earth beneath the oceans across a broad range of scales and resolution wavelengths. It is intimately associated with the concepts and problems of seafloor spreading, continental drift, and plate tectonics, which are in turn are tied to sedimentary basin-scale problems and resource exploration. A specific research aim is to understand the processes that forged the development of the North Atlantic lithosphere west of and including Ireland. In a more global context, relationships to the continental margins and sedimentary basins of North America are also investigated. This aspect is crucial in understanding the generation and accumulation of hydrocarbon reserves on both the Irish and Canadian continental margins. The research also relates to the history of ocean circulation patterns and climate change, which is preserved in sediments across the North Atlantic, interactions between the Earths hydrosphere and lithosphere and between geological and biological systems. It contributes to enabling the sustainable use of seafloor resources into the future.

Ongoing research in marine geophysics comprise the following:

Insitu Marine Laboratory for Geosystems Research (iMARL)

iMARL the “Insitu Marine Laboratory for Geosystems Research” is a network of various types of ocean floor located sensors, hosted by the Dublin Institute for Advanced Studies (DIAS). It comprises broadband Ocean Bottom Seismographs (OBS), broadband acoustic sensors, and sensors for measuring absolute water pressure & temperature at the ocean floor. A system capable of detecting tsunamis also forms part of the infrastructure. The sensor pool is largely mobile and can, in principle, be deployed around the world. However the current focus is on the NE Atlantic, offshore Ireland. One instrument will be fixed and will ultimately become a real-time sensing offshore element of the Irish National Seismic Network (www.insn.ie)

Strapped to sea-bed landers and deployed on the sea floor iMARL will allow for the detection of offshore earthquakes and offshore storms, as well as noise in the ocean and biologically generated acoustic signals (e.g. from cetaceans). Impacts from this equipment will include: natural resources quantification, natural hazard estimation, environmental and baseline climate related insitu ocean monitoring and the monitoring of marine noise pollution.

Through an award to the Dublin Institute for Advanced Studies (DIAS) the iMARL infrastructure is funded by Science Foundation Ireland (SFI) with support from the Geological Survey, Ireland.

Microseism generation in the North-East Atlantic

In January 2016, 10 Broad Band Ocean Bottom Seismographs (OBSs) units were deployed across the shelf offshore Donegal and out into the Rockall Trough. The main goal of the survey is to investigate the generation mechanism as well as spatial and temporal distributions of dominant microseism source regions in NE Atlantic. Compared to earthquakes, microseisms represent background seismic noise generated by ocean wave pressure fluctuations on the sea floor which produce low frequency seismic waves. For more details on this project click here (insert link).

obs_survey_map

Location map of the OBS stations and seafloor bathymetry.

Integrated geophysical and geological study of the Porcupine Basin

DIAS Geophysics continues its research on the Porcupine Basin by integrating wide-angle seismic data, ocean bottom seismometer data along with terrestrial based seismic stations to quantify variations in crustal geometry and seismic properties (for inferring petrological affinity of the rocks) along the basin axis and towards mainland Ireland with the aim of better understanding its geological evolution. For more information on this research click here (insert link)

porcupine

Bathymetry map of the Porcupine Basin depicting the location of WAS lines of the project (red lines), as well as the location of ocean bottom seismometers (yellow circles) and land stations (red triangles) used to record the data.

Ocean and Tidal Modelling

Oceans play an important role in the Earth system. At DIAS Geophysics, ongoing research focuses on wind and buoyancy driven circulations as well as tidally driven circulations within our oceans. Collaboration with the European Space Agency (ESA) Swarm satellite mission is investigating the magnetic signatures of the ocean circulation systems. The motivation is that the ocean-induced magnetic field may provide a greater understanding of ocean circulations. For more information about these research areas click here. (insert link)

tides2_small_crop

A snapshot of the ocean surface elevations (in metres) generated by the tidal force.

WAVEOBS

Ocean waves generate continuous low amplitude seismic signals, known as microseisms, that are recorded on seismometers globally. The WAVEOBS project was established with three primary goals; to get a better fundamental understanding of microseism sources; to investigate the use of ocean generated microseisms (OGM) as real time ocean wave height data; and to investigate their use as a climate proxy. Seismic arrays established in Ireland under the WAVEOBS project allow the monitoring and mapping of local microseism generation areas near Ireland. For more information on this project click here. (insert link)

waveobs_udaxuca_04-2012_0dot275Hz_HHZ-1

Source locations of microseisms off the west coast of Ireland