CONTRIBUTION OF SEISMIC TOMOGRAPHY IN MOMENT-TENSOR INVERSIONS USING TELESEISMIC SURFACE-WAVE SPECTRA

The knowledge of lateral heterogeneities is crucial for path correctio ns in moment tensor inversions using surface waves. After some attempt s to use regionalized Earth models for very long-period surface-wave m oment-tenser inversions, recent tomographic Earth models offer the pos sibility to make short-period path corrections and therefore retrieve more reliable moment tensors for teleseismic earthquakes. First we try to evaluate the precision required for path corrections in comparison with source effects. Some selected Earth models are tested to evaluat e how their results compare to those using multiple-frequency filterin g techniques. Some real cases illustrate the sensitivity of moment-ten sor solutions to the different path corrections, and it appears clearl y that regionalized Earth models and tomographic models deduced from l ong-period data alone (greater than 150 sec) cannot lead to trustworth y broadband moment-tenser inversions. Recent tomographic models using phase velocities at much shorter periods (40 to 200 sec) offer a preci sion comparable to that of the multiple-frequency filtering technique. Both methods lead to acceptable source mechanisms, using a small numb er of stations, in more than two cases out of three. The use of recent global tomographic models based upon shorter-period surface waves mig ht thus be a useful alternative to heavy multiple-frequency filtering techniques to automate source studies, especially for rapid determinat ions using a small number of stations.