Attenuation measurements of split normal modes for the 1960 Chilean and 1964 Alaskan earthquakes

Measurements of attenuation for the Earth's longest period modes can be significantly biased by the effects of frequency splitting. Using our previously developed methods of time domain synthesis of split normal modes, we measure Q without such a bias. We also conduct numerical experiments to confirm the errors in Q measurements which result from neglecting the effects of splitting. In contrast to frequency domain this time domain technique allows us to reject data below the ambient noise level for each mode. The Q's of the longest period spheroidal (0S2–0S5) and torsional (0T3–0T4) modes are determined using long (500 hr) records from the Chilean and Alaskan earthquakes.