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August 23 @ 4:00 pm - 5:00 pm CDT

Current Research in EEPS Seminar: Hejun Zhu

Department of Geosciences, The University of Texas at Dallas

Abstract Title: Mapping mantle flows underneath – North America and Caribbean

Abstract:

In this talk, I will present a new 3-D azimuthally anisotropic model, namely US32, for the
North American and Caribbean Plates. This model is constrained by using seismic data
from USArray and full waveform inversion technology. The inversion uses data from 180
regional earthquakes recorded by 4,516 seismographic stations, resulting in 586,185
frequency-dependent phase measurements. Three-component short-period body waves
and long-period surface waves are combined to simultaneously constrain deep and
shallow structures. The current azimuthally anisotropic model US32 is the result of 32
pre-conditioned conjugate-gradient iterations. In this model, I observe a complex depth-dependent
pattern for fast axis directions across the North American and Caribbean
Plates. At shallow depths, these fast axis directions follow local geological provinces,
such as the Snake River Plain, Cascadia subduction zone, Rio Grand Rift, etc. At greater
depths, the anisotropic fabrics follow the absolute plate motion at most places. At depths
around 700 km, the fast orientations are perpendicular to the strikes of the mapped
Farallon slab, suggesting the presence of 2-D corner flows, induced by this ancient
subduction below the mantle transition zone. In addition, underneath the Cascadia and
Cocos subduction zones at depths from 250 to 500 km, the fast directions suggest the
presence of toroid-mode mantle flows, running around the edges of fast downwelling
materials.

 

 

Details

Date:
August 23
Time:
4:00 pm - 5:00 pm
Event Category:

Details

Date:
August 23
Time:
4:00 pm - 5:00 pm
Event Category:

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