Infrasound analysis of I18DK, northwest Greenland

Abstract

Within the scope of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), four methods are used to verify the treaty. One of these methods is based on the detection of infrasound waves generated by a nuclear explosion. Seismological, hydroacoustical and radionuclide measurements are also applied. The International Monitoring System (IMS) will consist of 60 infrasound stations of which 35 stations are currently operational. The goal of this MSc Research is to process and subsequently interpret the data obtained from an infrasound station situated on the northwestern shoreline of Greenland. This station is operated by Denmark and labeled as I18DK. I18DK is situated in an area which receives an ever increasing attention from a geophysical perspective. I18DK has continuously been operational from April 2003 and onwards. I18DK is an infrasound array with an aperture of about 1200 meters, where air-pressure fluctuations are recorded by eight microbarometers at a sample-rate of 20 Hz. The data are filltered in two bandwidths, which are both processed based on Fisher-statistics afterwards. The first bandwidth ranges from 0.1 up to 1.0 Hz, while a second analysis is performed on data between 1.0 and 6.0 Hz. Both bandwidths yields interesting results. Several different source types are known to generate infrasound, for example, calving of icebergs and glaciers, explosions, earthquakes, oceanic wave-wave interaction, volcanic eruptions and aurora. The challenge is to distinguish between these different source types and use the outcome of the array analysis to better understand these phenomena. Microbaroms are by far the most frequent signals in the 0.1-1.0 Hz band. Their direction of origin can be related directly to oceanic wave-wave interaction intensity of Kedar et al. (2008). Furthermore, can their detectability be related to the wind direction at upper stratospheric levels. The rate of occurrence of icequakes and the calving of glaciers is of interest in relation to global warming. The glaciers south of I18DK produce significant infrasound during summer time. A direct link can be found between the number of warm days in a year and the number of infrasound detections from a north-northeast direction. These signals seem to be generated by run-off of water from the local ice cap north of I18DK.