GEMINI

Calculation of synthetic seismograms for global, spherically symmetric media based in direct evaluation of Green's functions

Project Description

Aim:

Computation of exact Green's Functions for the elastodynamic equation of a spherically symmetric Earth model, offering an alternative to the Normal Mode and Reflectivity approaches.

Method:

The Green's Function for the elastodynamic equation of a spherically symmetric Earth model is constructed directly in the frequency domain by expanding the displacement field into vector spherical harmonics and solving an inhomogeneous system of ordinary first-order differential equations.
Accuracy is comparable with Normal Mode computations, but some computation time can be saved for higher frequency, deeply turning body waves and if short time series are desired.
GEMINI is superior in accuracy (and ease of use) to the Reflectivity method because application of earth-flattening approximations, not accounting for the polar phase shift and missing of waves traveling along the major great circle arc can make reflectivity seismograms unreliable.
GEMINI is not recommended if very long, low frequency seismograms are desired. Then the Normal Mode method is appropriate. In case of high frequency, short distance seismograms the Reflectivity method is superior. For any application in between GEMINI is the method of choice.

Author:

Jörg Dalkolmo, Wolfgang Friederich

References:

• Dalkolmo, J., (1993): Synthetische Seismogramme für eine sphärisch symmetrische, nichtrotierende Erde durch direkte Berechnung der Greenschen Funktion. Diplomarbeit, Institut für Geophysik, Universität Stuttgart.
• Friederich, W. & Dalkolmo, J., (1995): Complete synthetic seismograms for a spherically symmetric earth by a numerical computation of the green's function in the frequency domain, Geophys. J. Int., 122, 537-550.