Prof. Dr. Barbara Romanowicz (UC Berkeley and Collège de France), "Imaging the earth's deep interior using seismic waves"
Professor of the Graduate School, University of California, Berkeley.
and Professeur Honoraire, Collège de France, Paris
In the mid 1960's, the plate tectonics revolution brought to light the dynamic nature of the earth's interior, with rising hot molten rock forming new crust at mid-ocean ridges and cold, thickened tectonic plates returning to the mantle at so-called subduction zones. We now understand that plate motions are driven by internal currents of matter that serve to evacuate heat accumulated deep in our planet. However, the precise mechanisms by which these motions interact with plates remains somewhat elusive.
Seismic waves generated by natural earthquakes penetrate deep into the earth's interior, accelerating or decelerating as they propagate, depending on the temperature and composition of the rock masses they encounter, thus illuminating the internal structure of our planet. Forty five ago, the first global seismic tomographic models revealed the presence of two large, antipodal, structures at the base of the Earth's mantle, that had no obvious relation to surface geology or plate tectonics. With the expansion of digital, very broadband seismic networks and related on-line databases, combined with improvements in theory and computer power, the resolution of mantle elastic structure has progressively improved. I will illustrate how state-of- the-art imaging techniques allow us to track the fate of tectonic plates that dive back into the mantle beneath the Pacific "ring of fire", follow the paths of deeply rooted hot mantle plumes, as they ascend towards the surface and are expressed there in the form of hotspot volcanism (of which Hawaii and Iceland are prominent examples). I will present some of the open science questions raised by the new imaging results, and discuss technical challenges and pathways for further progress in full waveform tomography, combining tools from seismology and other geophysical disciplines.