Elucidation of the lithosphere/asthenosphere system via Broadband Ocean Bottom Seismology – Normal Mantle Project

Although plate tectonics started as a theory of the “ocean” nearly 50 years ago, the detail of the mechanism how it works is still poorly known. It has been hampered partly by our inability to determined in-situ the structure of the lithosphere/asthenosphere system in the ocean. Recent advances in ocean bottom broadband seismometry, together with advances in the seismic analysis methodology, have now enabled us to resolve the regional 1-D structure of the entire lithosphere/asthenosphere system, from the surface to a depth of ~150km, including seismic anisotropy (both radial and azimuthal), with deployments of ~10-15 broadband ocean bottom seismometers (BBOBSs). We have thus succeeded to model the entire oceanic lithosphere/asthenosphere system without a priori assumption for the shallow-most structure, the assumption often made for the global surface wave tomography. In the seminar, I will cover the background of the research, our new multi-band approach for the “broadband ocean bottom seismology” and findings, preliminary results from our “Normal mantle project” in which we conducted a broadband seismic and EM array survey in the northwest Pacific and found abnormal, as well as normal, mantles, and hopefully convince the audience that we are now at an exciting stage that a large scale array experiment in the ocean (e.g., Pacific Array) is becoming approachable to elucidate how plate tectonics worked beneath ocean.