A Study ofTPhases Recorded at the Kiruna Seismograph Station

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Abstract
Five cases of clear T phases from earthquakes in the Norwegian Sea recorded at Kiruna since 1951 are studied. To the author's knowledge these observations are the first of this kind in Europe and also the first so far to the north — on the borders of the Arctic Ocean. It is verified that T propagates as a sound wave through the water. Different phases, constituting T, have been identified, travelling along the land path as Pg, Sg, and a third wave with a land velocity of 2.7 km/sec, probably an S wave in more superficial layers than granite. The conditions for sound-channel transmission in the ocean are studied. The efficient use which can be made of the T phase in epicentre locations is illustrated with a particular case. The period of T is remarkably constant and equal to 0.5 sec. By amplitude calculations it is shown among other things that different submarine earthquakes are not equally efficient in producing a T phase; reasons for this behaviour are discussed. A theoretical explanation is given for the fact that at the same time as the amplitude of T may be larger than that of P at Kiruna, there is no T, but a clear P recorded at Uppsala. DOI: 10.1111/j.2153-3490.1954.tb01093.x

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