In the framework of investigating the ventilation of deep-sea basins in the Indonesian archipelago, 222Rn was determined in near bottom water samples. In one of these basins, the Halmahera Basin, excess 222Rn concentration and the related standing crop was unexpectedly high. At this station excess Radon has an almost uniform concentration of about 2 dpm·kg-1 up to 120 meters above the bottom. In this paper the possibility is discussed that the high standing crop in this basin is connected with three submarine earthquakes with a magnitude of resp. 4.4, 5.4 and 5.9 mb that took place four days after we took the samples, possibly in combination with submarine faults, which are typical for the Indonesian archipelago. The epicentres were within 100 km from the station. All over the world variations in 222Rn concentrations have been observed prior to earthquakes (up to 500 km from the epicentre). This can be regarded as an important non-seismic precursor to earthquakes, but it has to our knowledge never been observed in deep-sea basins.
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