Long-term underwater geophysical observatory

In October 2019 iMARL deployed this seismic, hydroacoustic and absolute pressure instrument set, 400km off the coast of Galway at a depth of 3067km. It was recovered in April 2020. The OBS is an Aquarius+ designed by Guralp Systems Ltd.
The aim was to:

  1. Monitor seismic signals from a wide range of sources especially from microseisms and local and distant earthquakes
  2. Help detect and measure tsunamis

The system comprised:

  • A broadband Ocean Bottom Seismometer (OBS) with Absolute Pressure Gauge (APG)
  • Communicates through an acoustic link to a buoy moored in the vicinity of the underwater module
  • The buoy was equipped with a satellite communication system to allow near real-time communication between the seafloor station and the onshore national data centre at DIAS

Summary of specifications & technical data

  • Guralp Aquarius + is a compact OBS equipped with an acoustic modem
  • Digital feedback tri-axial broadband seismometer, operational at any angle, with a flat response between 120s and 100Hz
  • A three-axis magnetometer and a MEMS accelerometer record the seismometer’s 3D position on the seabed
  • Transmission of sensor data and State of Health parameters from the seabed following installation
  • Up to 9000 bps transmission of data between seabed and surface using acoustic communication
  • Tilt tolerance 180°
  • Dual redundant 128 GB Micro-SD card
  • Depths of up to 4000m for up to 18 months duration
  • Acoustic Burn-Wire release mechanism with satellite tracking system
  • LED strobe light to guide recoveries with location alerts sent via email, SMS and/or webpage
  • Battery pack (rechargeable lithium-ion) designed for deployments lasting up to 18 months. (1 hour to re-charge per 1 month deployment).


Absolute Pressure Gauge (APG) (to help with tsunami detection):

  • Resolution 1mm variation in 1000m of water
  • Accuracy 0.25% of full-scale