Seismic Constraints on Deep Slabs: Stress State, Structure,and Rupture Characteristics of Deep Earthquake

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9304553 Houston This research is a continuation of the search for a mechanism for deep earthquakes, one of the most important unresolved problems in geophysics. The work proposed here includes the assembly and analysis of broadband displacement waveforms of about 150 large deep earthquakes that occurred during 1987-1992. Events from 1982- 1986 showed a decrease in rise times of the P wave with earthquake origin depth. This is one of the few characteristics that shows a correlation with depth. The results will be used to test proposed mechanisms for deep earthquakes including phase transformations in the subducting slab. The results will also be compared with finite-difference modeling of the slab structure on waveforms and stress orientations from the Harvard CMT catalog. Integration of seismological and mineral physics results will further the evaluation of hypotheses of slab structure and deep earthquake generation. ***