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A system for automated moment tensor determination by inverting on-line broadband seismic waveforms operated by the FREESIA project has been developed. When an Email notice of earthquake occurrence arrives from the Japan Meteorological Agency (JMA), this system automatically retrieves the dataset for waveform inversion, examines the quality of data, and determines filtering coefficients as well as data windows. This inversion uses long period waves (from 20 seconds to 50 seconds) so that this procedure is insensitive to the onset of wave arrivals. This inversion uses at most 3 stations whose hypocentral distances are between 50km and 400km. The result of each inversion is automatically displayed on the World Wide Web within 5 minutes after the Email arrival. The obtained mechanisms are examined by comparing them with first motion solutions obtained by a microseismic network. If the variance reduction is greater than 50% and magnitude is greater than 4.0, the automatic solutions are found to be reliable.
Fukuyama et al. (Thu,) studied this question.