EAPS

Hejun Zhu, Jackson School Distinguished Postodctoral Fellow at the Univeristy of Texas at Austin
Monday, April 6th | 3:45 - 5:00 pm | 54-915

"Seismic Structure of the European Continent: Wavespeads, Attenuation, and Anisotropy"

We use adjoint tomography to iteratively determine seismic models of the crust and upper mantle beneath the European continent and the North Atlantic Ocean. This study consists of three stages. In stage one, frequency-dependent phase differences between observed and simulated seismograms are used to constrain radially anisotropic wavespeed variations. In stage two, frequency-dependent phase and amplitude measurements are combined to simultaneously constrain elastic wavespeeds and anelastic attenuation. In these two stages, long-period surface waves and short-period body waves are combined to simultaneously constrain shallow and deep structures. In stage three, frequency-dependent phase and amplitude anomalies of threecomponent surface waves are used to simultaneously constrain radial and azimuthal anisotropy. After this three-stage inversion, we obtain a new seismic model of the European curst and upper mantle, named EU60. Long-wavelength elastic wavespeed variations in model EU60 compare favorably with previous body-and surface-wave tomographic models. Some hitherto unidentified features, such as the Adria microplate, naturally emerge from the smooth starting model. Subducting slabs, slab detachments, ancient suture zones, continental rifts and back-arc basins are well-resolved in model EU60. We find an anti-correlation between shear wavespeed and anelastic attenuation at depths < 100 km. At greater depths, this anti-correlation becomes relatively weak, in agreement with previous global attenuation studies. Furthermore, enhanced attenuation is observed within the mantle transition zone beneath the North Atlantic Ocean. We find that the direction of the fast anisotropic axis is closely tied to the tectonic evolution of the region. Averaged radial peak-to-peak anisotropic strength profiles identify distinct brittle-ductile deformation in lithospheric strength beneath oceans and continents.

4:00PM in 54-915, reception preceding seminar at 3:45
All are welcome to attend.
Questions? Contact Allison Provaire at 617.253.3382 or provaire@mit.edu