## Time-domain approach for the transient responses in stratified
viscoelastic Earth

**Ladislav Hanyk** ** , **
**J. Moser , **
**David A. Yuen** ** & **
**Ctirad Matyska**
### Summary

We have developed the numerical algorithm for the computation of
transient viscoelastic responses in the time domain for a radially
stratified Earth model. Stratifications in both the elastic parameters and
the viscosity profile have been considered. The particular viscosity
profile employed has a viscosity maximum with a contrast of
O(10^{2})
in the mid lower mantle. The
distribution of relaxation times reveals the presence of a continuous spectrum
situated between O(10^{2}) and
O(10^{4}) years. The principal mode is
embedded within this continuous spectrum. From this initial-value approach
we have found
that for the low degree harmonics the non-modal
contributions are comparable to the modal contributions.
For this viscosity model the differences between the time-domain and
normal-mode results are found to decrease strongly with increasing
angular order.
These calculations also show
that a time-dependent effective
relaxation time can be defined, which can be bounded by the relaxation times
of the principal modes.

Geophys. Res. Lett., **22** (1995), 1285-1288.