Effects of the number of events, their depth distributions, and the number of layers in a model on traveltime inversion

摘要

This study introduces the effects of the number of events, their source distributions, and the number of layers in the model on 1-D traveltime velocity inversion. The synthetic data generated from the known velocity model and hypocentral parameters allow us to test the accuracy of traveltime inversion. One dimensional traveltime inversion is performed using the hypocentral parameters determined by GA-MHYPO. The accuracy of traveltime velocity inversion with the synthetic data is tested by changing the number of events, the source positions, and the number of layers in a model. The estimated velocities in each layer are almost the same as the true velocity if the true depths of layer boundaries are known, accurate hypocentral parameters are used, and each layer has more than one event. The estimated weighted average velocity is close to the true one independent of the number of layers in the model and the number of events. The velocity errors in each layer decrease as the numbers of events in each layer increase in general. The estimated velocities using the noisy data are similar to those from the error-free data. However, the former has slightly larger velocity errors than the latter. Traveltime inversion may yield artificial low-velocity layers depending on used conditions. These results of synthetic studies are applied to the traveltime inversion of the Himalaya Nepal-Tibet Seismic Experiment earthquake data to estimate the detailed 1-D velocity structure beneath Nepal region.