Mantle Reflectivity Structure around Convergent Plate Boundaries

The depth at which mantle constituents go through a phase change provides a very important constraint about the Pressure/Temperature structure of the mantle. Amongst many different metrics, amplitudes of surface reflected shear waves and their precursory arrivals (Figure 1) offer the most complete global coverage due to their insensitivity to the first order source-station distribution.

Figure 1. Schematic ray-paths of surface reflected shear waves (SS) and their associated precursory arrivals, S410S and S660S, recorded at 100°, 135°, and 170° epicentral distance. Black star and triangles represent the source and station locations, respectively.

In collaboration with Yu Jeffrey Gu, Sean Contenti, and Ryan Schultz from the University of Alberta, we use the amplitudes of SS waves and underside reflections from mantle interfaces, which arrive up to ~250-300 s before SS, to investigate subduction related mantle deformations at upper-/mid- mantle depths (see Figure 2).

We basically align the seismograms on SS phase, correct for topography (using ETOPO 2) and crustal thickness (using CRUST 5.0), and apply pre-stack depth migration using PREM-predicted travel-time curves. For more information please check Gu et al., (2012) and Contenti et al., (2012). Below are mantle reflectivity cross-sections that traverse northern Japan and Central America.

Figure 2. Mantle reflectivity structure beneath northern Japan (left) and central America (right) are shown by wiggles and hot colors, respectively (the figures are taken from Gu et al., (2012) and Contenti et al., (2012)). Differences in mantle reflectivity structure might be translated to the differences in slab-mantle interaction beneath various convergent margins.

The project is still ongoing for Mediterranean Subduction Zones.

Department of Earth and Planetary Sciences / Harvard University / 20 Oxford Street / Cambridge / MA 02138 / U.S.A. / Telephone: +1 617 495 2350 / Fax: +1 617 496 1907 / Email: