PGS: USArray and mantle structure

The November meeting of the Potomac Geophysical Society will be held November 17th at the Fort Myer Officers’ Club in Arlington, VA (http://www.fmmcmwr.com/maps.htm) in the Glassed-in room in the Fife and Drum (main dining room).

This month’s talk will be: “Use USArray to map mantle structure: from top to bottom”

Speaker: Daoyuan Sun

Affiliation: DTM/Carnegie Inst. Washington

Bio:  University of Science & Technology of China, BS, 1995 – 2000
Caltech, PhD, 2003 – 2009. Carnegie Institute of Washington,  Postdoc  Fellow, 2010 – present.
My current research interest in: theory of seismic wave propagation; aveform modeling of the deep earth structure (D” layer and western US upper mantle); and integrated study of seismology, geodynamics and mineral physics.

Title: Use USArray to map mantle structure: from top to bottom
Abstract: With the advent of USArray, there is an unprecedented opportunity for investigating the seismic structures of the crust and mantle. This data has been processed with multiple methods, which include body wave and surface wave tomography, receiver functions and shear wave splitting. These images reveal a highly heterogeneous mantle beneath US and related small-scale convection. However, the details of these features are not well constrained. Among these structures, those sharp ones causing
waveform complexity are most interesting, which provide the base for the dynamic modeling of the mantle evolution. The records from USArray display waveform complexity at all ranges, and localizing the structural edges causing these features involve considerable study. A newly developed
Multi-Path Detector (MPD) technique has been applied to USArray data to directly map out the sharpness of structures. Both upper mantle and lower mantle are studied by MPD and detailed waveform modeling. Here, we will concentrate on two objects. (1) Down-going slabs and low velocity
features in the upper mantle beneath western US, which can provide direct information about the interaction between downwelling and upwelling process beneath western US. (2) Detailed 3D image of low velocity structures (-8% in Vs and -5% in Vp) that sitting on  the normal Core-Mantle Boundary beneath western US and Canada. These structures represent a new class of topography in the deepest parts of the mantle. We suggest that these results can be explained by dynamically-stabilized structures containing small amounts of iron-rich (Mg,Fe)O that may have fractionally crystallized from a primordial magma ocean.

New Meeting Room and Dining Arrangements: We now meet in the glassed-in room at the back of the main dining room—The Fife and Drum. We order individually from the Club menu, which has a nice variety of dinner offerings. We pay a single bill (I pay it with my Officers Club credit card), so we collect at least $25 from each diner with the agreement, that if one orders more than $20 in food and drink, he adds the amount over $20 to his contribution. The $5 overcharge goes to the Room Fee, Tax, Gratuity, and the Speaker’s Dinner. We collect on the Honor System. We did this for the first time in September, and it worked well. This room change and use of the menu have greatly reduced the loss that we have incurred in the past for having fewer than 20 people dining, and the change has preserved the viability of using the Officers Club for our meetings.

Reception at 6:00. Order Dinner at 7:00. Talk at 8:30 PM. Please note that the meal orders will be taken at 7:00. Allow 15 minutes for security entering Ft. Myer as all civilian vehicles are searched. To ensure access to and from Fort Myer use the Hatfield Gate, open 24 hours a day (http://www.fmmcmwr.com/directionsmyer.htm). Reservations are not necessary, however, we need a head count, so, if you wish to attend dinner ($25), please inform Bob Fraser at 540-888-3001 or via E-mail at fraser.robert@comcast.net. If you wish, please feel free to attend the talk without dinner. Non-members and guests are welcome. Visit the PGS web site at http://www.potomacgeophysical.com for new meeting announcements, etc. Please send changes of address or email to fraser.robert@comcast.net.

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