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OBIC Receives Funding To Develop Broadband Ocean-Bottom Seismographs

Project Title: Reduction of noise on broadband ocean-bottom seismographs through sensor design optimization using numerical and laboratory studies

Investigator: Nick Harmon
Co-Investigators:

Stephen Turnock – University of Southampton, Ship Science
Christine Pierce – University of Durham
Funded by NERC
Total Award: (NERC Contribution) £124,429.40 (Split between Durham and Southampton) 

Duration: 2 years

Seismology is the main tool for understanding the structure and dynamics of the Earth’s interior. Yet, due to the extreme environment and remoteness of the deep ocean basins there is a dearth of seismic coverage on the ocean bottom.

Within the past decade broadband ocean-bottom seismographs (OBS) have been developed that can be deployed from any oceanographic vessel, record data autonomously for periods of over a year, and be recovered from the seafloor. While the data quality for these instruments for the vertical component of ground motion approaches that of similar temporary deployments on land, the horizontal components, which record shear waves, are plagued by high noise levels caused by tilting due to ocean-bottom currents.

The poor data quality of the horizontal components is a serious limitation of broadband ocean-bottom seismology and hinders our ability to study both the dynamics of the Earth’s interior and important tectonic processes that occur on the ocean floor, which produce earthquakes, volcanism and tsunamis.

This project investigates whether a smaller profile hydrodynamically stable sensor package or instrument “pseudo-burial” can yield significant improvement in horizontal component noise levels. In the first stage of development we will use theoretical understanding coupled with numerical simulations of fluid flow to propose a sensor package shape that helps controls descent attitude, landing, and minimises the flow induced noise when the sensor is in place.

In the second phase we will construct prototype sensors and compare and contrast the fidelity of a broadband seismic sensor using analogue fluid experiments. In the analogue experiments, we will also experiment with “pseudo-burial” of sensor packs by simulating a deployment of the sensors in sediment-filled bags to reduce coupling between the pack and the water column. If successful, this research will solve a long-standing issue in ocean-bottom seismology, and will be a huge leap forward in our ability to understand the shear velocity structure of the Earth’s interior. These experiments are first steps towards expanding the NERC Ocean-Bottom Instrumentation Facility (OBIF) capabilities into broadband ocean bottom seismology.

Workshop for Developing a Broadband Ocean Bottom Seismometer Pool in the UK

To be held: Sept 15 at NOC, Southampton

The UK seismological community does not yet have the capacity to perform large-scale broadband ocean bottom seismic experiments. This workshop is designed to raise awareness in the geophysical community of the UK of this type of instrumentation and develop a plan to expand the NERC Geophysical Equipment Facility to include broadband ocean bottom instrumentation through science driven NERC consortium grants and European Union 7^th Framework Programme grants.