Lateral variation of Q from singlet modal Q measurements of 0 S 2

Attenuation parameter Q of five singlets for the spheroidal mode 0 S 2 (m=−2, −1, 0, 1, 2) are measured from a strain recording for the 1960 Chilean earthquake and three gravimeter recordings for the 1977 Indonesian (Sumbawa) earthquake. From the variation of modal Q as a function of m, three spherical harmonic components of radially averaged Q, angular degree and order (0,0), (2,0) and (4,0), can be determined. The solution indicates lower Q values in the polar regions than in the equatorial regions of the lower mantle, although error bars for (2,0) and (4,0) are large. Assuming a thermally activated process with the activation energy of about 100 kcal/mol, this variation of Q is consistent with a few tens of degrees of lateral temperature variations. With better 0 S 2 data, large scale temperature variation in the lower mantle can be constrained in principle.