Thread: IRIS WEBINAR: Anisotropic Seismic Tomography and the Gutenberg Discontinuity - 2/26, 2 PM Eastern

"New Constraints on the Nature of the Gutenberg Discontinuity from
Anisotropic Seismic Tomography" will be presented at 2 pm EST (7 pm UTC)
on Wednesday, 2/26.

Register *only* if you intend to watch the live webinar:
https://www2.gotomeeting.com/register/368171466

You will be emailed a confirmation containing a link for watching the
live broadcast. A recording will be subsequently posted here:
http://www.youtube.com/user/IRISEnO. Access to older webinars, along
with related materials and more information on the series is found here:
http://www.iris.edu/hq/webinar/

Presenter: Dr. Caroline Beghein, Assistant Professor, University of
California-Los Angeles

Abstract: The origin of the lithosphere-asthenosphere boundary (LAB)
remains enigmatic. Tomographic studies argue in favor of a thermal LAB,
but detections of the Gutenberg (G) seismic discontinuity, often
associated with the LAB, cannot be explained by thermal effects alone.
In this study, we modeled 3-D seismic anisotropy and velocity in the
Pacific upper mantle and compared our models with the location of SS
precursor detections of the G. Our results are consistent with a purely
thermal LAB, but we found that the G is associated with vertical changes
in anisotropy within the lithosphere. This implies that the two are not
equivalent interfaces even though they may overlap in some locations. We
propose that the G results from dehydration under mid-ocean ridges,
generating a depleted, viscous layer that becomes overprinted by lowered
temperatures as the plate cools down. Partial melt may also be present
at the LAB where the two interfaces coincide and help explain enhanced
detections of the G near upwellings.

Please direct any related questions or the name of your favorite seismic
station to Andy Frassetto (andyf<at>iris.edu).

System Requirements
PC-based attendees: Windows® 8, 7, Vista, XP or 2003 Server
Mac®-based attendees: Mac OS® X 10.6 or newer
Mobile attendees: iPhone®, iPad®, Android™ phone or Android tablet