Toroidal splitting observations from the Great 1994 Bolivia and Kuril Islands Earthquakes



The June 9, 1994, Bolivia earthquake and the October 4, 1994, Kuril Islands earthquake provide a unique opportunity for a splitting analysis of the Earth's long-period toroidal free oscillations. We present toroidal splitting observations for the 6 fundamental modes 0T4, 0T5, 0T6, 0T7, 0T8, and 0T9, and for the 5 first overtones 1T1, 1T2, 1T3, 1T4 and 1T6. The first identification of mode 1T1 is made possible by simultaneously fitting the multiplets 1T1 and 0T7. The observed splitting is reasonably well explained by current shear velocity models of the mantle. Our analysis yields new estimates of the center frequencies and quality factors of these 11 toroidal modes.