Tatsuhiko Hara

Determination of the isotropic component of the 1994 Bolivia Deep Earthquake

We determine the isotropic component of the moment tensor of the 1994 Bolivia deep earthquake using various seismic waves, including body waves, surface waves, and normal mode data, in the period band between 20 s and 1000 s. We carefully investigate whether the isotropic component can be obtained independently from the other components by checking the correlation matrices. We show that it is possible to obtain a precise estimate of the isotropic component by using normal mode data in the period band between 550 and 1000 s. We find that the Bolivia earthquake did not have a significant isotropic component in this period band.

The geological origin of long wavelength lateral heterogeneity at depths of 300–400km

On the basis of two three-dimensional (3-D) models of S-wave velocity, PUMO [Hara et at., 1993] and SH425.2 [Su and Dziewonski, 1991], we show that the deep roots of cratons and mid-ocean ridges provide a satisfactory explanation of the pattern and amplitude of the Earths long wavelength lateral heterogeneity in the depth range from 300 to 400km.