PGS: Carnegie’s Janiszewski on imaging volcanic arcs

Please join us for our annual Joint Meeting of the Potomac Geophysical Society & DMV Chapter of the Association of Environmental and Engineering Geologists at 7:00 pm Thursday, May 16, 2019 at the DoubleTree by Hilton McLean Tysons, 1960 Chain Bridge Road, 22102.  As always, guests are welcomed and we encourage you to spread the word about our meetings to your colleagues and students (a flyer is attached).  Due to the special nature of this meeting, we are requesting earlier RSVP’s (noon this Friday, May 10), and the cost for the optional dinner is slightly higher ($40 members, $45 non-members).  If you plan on attending, please RSVP to dcgeophys@gmail.com.  We hope to see you there!

This month’s program:

Volcano Variety: Understanding Arcs with Multi-Scale Seismic Imaging
by Helen Janiszewski, Carnegie Science DTM

While evidence for variety in volcano structure and eruptive styles abounds at the earth’s surface, magmatic architectures at volcanoes tens of kilometers beneath the earth’s surface and the ultimate causes of such variety remain enigmatic. At individual volcanoes, magmatic structures in the mid- to lower-crust have typically been difficult to geophysically or petrologically constrain. New results at two volcanoes in the Aleutian island arc – Akutan and Cleveland, which despite being only ~ 300 km from each other have different recent eruptive histories – reveal seismically low-velocity regions in the mid- to lower-crust, likely caused by a region of partial melt. However, the spatial and vertical extents of these low velocity zones beneath the two volcanoes vary substantially implying differing magmatic architectures. The causes are still unknown, although the depth to the top of the subducting crust varies by nearly 20 km perhaps implying different structures in the downgoing lithosphere beneath these volcanoes. The seismic structure of the downgoing Pacific plate in this region of the Aleutians is relatively poorly constrained at the scale of arc-volcano spacing. Instead we investigate the Cascadia subduction zone, where the recent onshore-offshore Cascadia Initiative seismic experiment has allowed seismic imaging at these scales. Prior to subduction, the oceanic plate deviates from simple thermal cooling models with along-strike variation observed at scales similar to variation in arc properties, suggesting that there may be more heterogeneity in oceanic lithosphere than previously thought. This represents an important consideration for understanding many tectonic phenomenon, including the input to volcanic arc systems, and demonstrates the need for future experiments both focused on understanding the role of structures in the subducting plate in conjunction with detailed imaging of individual volcanoes.

Originally from New Jersey, Helen Janiszewski completed her undergraduate education at Rutgers University with majors in Geological Sciences and Physics and minors in Mathematics and Russian Language.  She graduated in 2012 and moved to New York City to complete her PhD in seismology at the Lamont-Doherty Earth Observatory at Columbia University which she completed in 2017.   Helen is now a Postdoctoral Fellow at the Department of Terrestrial Magnetism at Carnegie Science in Washington, DC.  Her research is focused on using seismic data to image the structure of the Earth’s crust and mantle, particularly in subduction zones, to better understand our planet’s underlying tectonic processes such as those related to earthquakes and volcanoes.

The PGS meeting location is within one-half mile of the Tysons Corner Metro station, near I-495, and has free parking available.  Our private meeting room is located on the second floor of the hotel.  The optional dinner cost will be discounted to $40 for members in good standing (have paid dues), and $45 for non-members, and is inclusive of coffee, tax and gratuity.  Drinks may also be purchased in the private meeting room on a cash basis.  Members and guests may attend the presentation after dinner for no charge; we estimate that the presentation will begin at 8:15 p.m.  For attendees who arrive early, social time will be held in the Tysons Social Tavern on the first floor of the DoubleTree by Hilton hotel.

In summary:
Social Time: 6:00-7:00 p.m., Tysons Social Pub (formerly O’Malley’s Pub), first floor DoubleTree by Hilton
Dinner: 7:00-8:15 p.m., Peachtree Room, Harvest Cafe, second floor DoubleTree by Hilton

Meeting & Presentation: 8:15-9:30 p.m., Peachtree Room, Harvest Cafe, second floor DoubleTree by Hilton

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