Observations of Lg and Rg waves and remarks about the nature of Lg

Abstract

The result of the seismic sounding in the Black Sea (l) showed that to the South of the Crimean peninsula the granitic layer is interrupted in the deep part of the sea. The preliminary data about the weakening of the Lg and Rg waves when they piopagate through the central part of the Black Sea was exposed in our previous work (**) and by M. Bath (2). The further investigation consists in finding the clear waves Lg on the continental paths. We succeeded in this comparing the records of waves at stations Tiksi from the earthquakes of two groups. The lirst group of earthquakes: Mongolia, Pamir, Southern China. The second group: Aleutian Islands, Kamchatka, Kuril Islands, Japan. Por the Mongolian earthquakes very sharp beginnings of waves, especially Lg1( having great amplitudes with the period of 2 to 1 sec are observed. On the records of the station Tiksi clear waves Lg and Rg are noticed (fig. 1). For the earthquakes of Southern China these waves are clear, however the amplitudes are smaller and the periods of the waves are greater than previous. On the whole the first group of the paths corresponds to the continental structure of the earth's crust. The mean values of the velocities of these waves are: Lgx — 3.53 km/sec; Lg2 - 3.31 km/sec; Rg - 3.05 km/sec. For the epicentres of the Aleutian Islands no clear beginnings of the waves Lg and Rg are distinguished. The period of 18 to 21 sec with the superposition of rather weak waves of short period is predominant on the records of surface waves (fig. 2). The direction of the paths in