The Application of Broadband Arrays and Networks to Seismic Monitoring of Uncalibrated Regions
Final rept. 1 Dec 93-31 Aug 97
SOUTH CAROLINA UNIV COLUMBIA DEPT OF GEOLOGY
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Temporary broadband networks are clearly an advantage to efforts to calibrate relatively unknown regions. Our results demonstrate the type of information that can be determined with this type of data. The combination of broadband, digital three-component array data and state-of-the-art multidimensional digital signal processing algorithms have provided considerable insight into both the composition of the regional wavefield and the nature of lithospheric heterogeneities. Our Lg results have clarified a long-standing debate about the cause of Lg blockage by the Tibetan Plateau. Understanding the nature of this blockage is critical to understanding the effect it has on common discriminants that utilize Lg. Continuing regional waveform modeling has led to a better understanding of north-south variations in mantle structure and the effects these variations have on regional waveforms. We have also been able to better quantify the effect of event mislocation on derived layered velocity models in the Tibetan Plateau. Studies of teleseismic shear-coupled P-waves have revealed a zone of partial melting in the northern Tibetan Plateau that is closely related to the anomalous upper mantle structure in the region. We have completed the determination of a local magnitude scale for events recorded by the 1991-92 Tibetan Plateau seismic experiment. This analysis suggests that there is a distance bias that underestimates magnitudes for station-event separations of more than 600km. This may be related to the increased attenuation of Lg at similar distances that we observed in our Lg analysis. Much of this work has been published in journals, meeting abstracts, and symposium volumes.