Site survey for a T-phase station (HA-09) at Tristan Da Cuhna, United Kingdom

Baptie, B.J.; Petrie, D.L.; Browitt, C.W.A.. 2002 Site survey for a T-phase station (HA-09) at Tristan Da Cuhna, United Kingdom. Nottingham, UK, British Geological Survey, 101pp. (CR/02/322N) (Unpublished)

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Abstract/Summary

The purpose of the site survey was to determine a suitable location and prepare for the establishment of a hydroacoustic T-phase station at Tristan Da Cuhna. Seismic measurements were made at 9 temporary sites at different geographical locations around the island for periods of continuous recording of at least 24 hours, with at least two stations operating simultaneously. Stations were found to be very noisy due to a combination of local geological conditions and proximity to natural noise sources. We used power spectra to compare noise levels at different sites and identify noise sources. Noise levels in the 2-7 Hz range are high and dominated by the surf noise due to waves crashing against the shore. Amplitudes of these signals are higher on the horizontal components than on the vertical. Almost all sites show very high noise levels in this band and we find that noise exceeds the commonly used high noise model. Thirteen seismo-acoustic events from earthquake sources in oceanic areas at a range of distances and azimuths deemed likely to generate T-phase arrivals occurred during the survey. However, no T-phase arrivals from any of these events could be positively identified. In addition, RMS amplitudes at coastal stations exhibit a strong correlation with tidal variations. Measurements from sites to the southwest of the settlement of Edinburgh were found to exhibit the lowest noise in the 1-10 Hz range. Therefore, in the absence of measured signal-to-noise ratio for T-phase arrivals at different stations, we suggest that this may be the most suitable area for the establishment of a permanent station. Such a station will require a radio telemetry link with a base station at the settlement, with at least one repeater station. A second sensor should be deployed in the area of the Settlement of Edinburgh, close to the central facility, with a direct cable link to provide power and data transmission. This station, though perhaps noisier, based on the measurements made over the survey period, will present less logistical complexity, which is an important consideration owing to the remoteness of the site. This additional station will also provide both an element of redundancy and slight improvement in azimuthal coverage of ocean areas to the north.

Item Type:	Publication - Report
Programmes:	BGS Programmes > Seismology and Geomagnetism
Funders/Sponsors:	British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.:	This item has been internally reviewed, but not externally peer-reviewed.
Date made live:	25 Nov 2024 11:13 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/538434

Item Type:

Publication - Report

Programmes:

BGS Programmes > Seismology and Geomagnetism

Funders/Sponsors:

British Geological Survey

Additional Information. Not used in RCUK Gateway to Research.:

This item has been internally reviewed, but not externally peer-reviewed.

Date made live:

25 Nov 2024 11:13 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/538434