Space Geodesy Programme

During April 2014, HartRAO installed a seismometer station on Marion Island, as part of the SANAP Space Geodesy project (principal investigator Prof. Ludwig Combrinck) and as a node of a new academic seismic network. This installation is in collaboration with Tshwane University of Technology (TUT), with Dr. Stoffel Fourie as project leader of the academic seismic network. Marion Island is located between South Africa and Antarctica at 46.9 degrees South and 37.75 degrees South, which on the edge of the African continental plate, close to the contact zone with the Antarctic plate. Two known volcanic activities have been recorded. The first observed eruption was during November 1980  and the second on the 24th of June 2004.

Although the island is very noisy for a seismic installation due to the ocean wave noise and vibrations imparted by the strong winds, it is expected that the placement of the sesimic station will provide valuable information concerning seismic activity on Marion Island.

In addition to the existing Global Navigation Satellite Systems (GNSS) receiver, tide gauge and the French DORIS system, which are all utilised to monitor positional displacements of the Earth, the installation of a seismometer and accelerometer was successfully completed during the April 2014 Marion Island takeover. This new installation will benefit crustal motion and seismic hazard research and monitoring as well as support tsunami monitoring. The equipment will operate within the Global Seismographic Network (GSN) and all data will be freely available to the global scientific community.

The GSN is the principal global source of data and information for earthquake locations, earthquake hazard mitigation, and earthquake emergency response. In collaboration with National Oceanic and Atmospheric Administration (NOAA) Tsunami Warning Centers, the Japanese Meteorological Agency (JMA), and the Australian Tsunami Warning System, the GSN provides essential data for tsunami warning response globally. The Marion Island GNSS and tide gauge are part of global tsunami monitoring networks (it resorts under the Indian Ocean Tsunami Warning System). The GSN operates with close ties to the International Monitoring System (IMS) for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), where nearly 30 GSN stations are now linked directly to the CTBTO International Data Centre. The GSN is an official observing system within the Global Earth Observing System of Systems (GEOSS).

A strong earthquake, registered as M 6.1 (USGS), occurred 244 km WNW of Marion Island, on July 22, 2013 at 07:01 UTC. USGS registered M 6.1 at depth of 10 km, EMSC registered initially M 6.1 but later changed to M 6.3 at depth of 33 km, GEOFON (GFZ, Potsdam who has provided SA with the tide gauge and GNSS equipment) registered M 6.3 at depth of 10 km. The epicentre was located at coordinates 46.042°S 34.825°E. This addition of a seismometer on Marion Island will improve locational abilities in three dimensions and will provide valuable data from an area that has no seismic instruments (see Figure 1).
 

Figure 1. A seismic station located on Marion Island will provide valuable data from an area that is very sparsely equipped.


The seismic installation consists of a stainless steel box, containing the seismometer, accelerometer (see Figure 2), logger unit and power conditioning unit. The box is bolted onto an existing concrete pillar close to the DORIS hut.
 

Figure 2. The  seismometer  installation  on Marion Island. The DORIS hut is in the background. Power and an ethernet cable is fed from the hut to the seismometer.

The installation of a seismic monitoring station at Marion Island is of benefit to the global community and will provide valuable data concerning seismic activity at the Prince Edward Islands. In particular it will play a valuable role in the Indian Ocean Tsunami Warning System. The scientific instrumentation consumes low power, is unobtrusive and will have small, if any, impact on the environment.

Repair work was done to the DORIS system, fortunately the system became fully functional after the DORIS antenna was replaced. The location of the DORIS antenna was surveyed in and tied via GPS to the permament Marion Island GNSS receiver installation, which is located close to the tide gauge (Figures 3 and 4). I had a lot of support from Carson McAfee, Philip Mey and Mpho Mphego of the South African Space Agency (SANSA). Mpho has taken over from Carson as resident SANSA engineer for the year as part of the overwintering team so is invaluable in terms of future support during the year.



 
Prof. Ludwig Combrinck
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Hartebeesthoek Radio Astronomy Observatory
SANAP Space Geodesy Project, SNA2011120100006.