High-Resolution Seismic Study of Subducted Slabs

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We propose to investigate the waveforms, amplitudes, and traveltimes of body waves from earthquakes and explosions to examine the detailed velocity structure of subducting slabs in the depth range 0 to 1500. Creager and Jordon (1986) propose that penetration of subducting slabs under the Kurile Islands and other subduction zones to depths of at least 1000 km is necessary to explain travel time anomalies of deep earthquakes. Such penetration would also affect the amplitudes and waveforms of the body waves from earthquakes. Methods we have recently developed allow the calculation of the waveform and amplitude effects of high-velocity, subducting slabs. A preliminary review of available data show that we can test and refine seismic models of slabs with these new methods. We propose, as well, to refine models of slabs in the upper mantle, which empirically cause even greater waveform, amplitude and timing anomalies than the deep slabs. Our method may also help to locate where the earthquakes occur relative to the high-velocity slab (e.g., toward the top or in the middle). Reconciliation of the amplitude, waveform distortion, and timing of body waves from deep events is necessary to understand the geometry of slabs near and below the 650 km discontinuity.