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February 3, 2017
3:00pm in PLS 1140
Tom Pratt from USGS-Reston
The influence of eastern U.S. Atlantic Coastal Plain strata on earthquake ground motions, and damage in Washington, DC, during the 2011 Mineral, Virginia, Earthquake

Abstract: During the 2011 Mw5.8 Mineral, VA earthquake, many buildings in Washington, DC, including national landmarks like the Washington National Cathedral, the Smithsonian “Castle,” and the Washington Monument, sustained damage despite being 130 km from the epicenter. The surprisingly large amount of damage from weak ground motions raises questions of how much the southeast-thickening sedimentary strata of the Atlantic Coastal Plain (ACP) strata beneath the city amplify and trap seismic energy. Partially consolidated ACP marine sedimentary strata overlie crystalline or indurated sedimentary rocks throughout coastal regions of the eastern U.S., extending more than 200 km inland from the coast. The strata taper landward from as much as 1 km near the coast to pinching out in the Washington, DC area. Shallow sedimentary strata are known to amplify earthquake ground motions due to low seismic impedance and strong reverberations. Between November 2014 and August 2015, we used 27 seismometers to measure ground motions across Washington, DC, using four sites on crystalline rocks as reference sites. We also used data from continental-scale seismic experiments that span the ACP to examine the influence of the broader ACP strata on earthquake ground motions. Recordings of teleseisms and regional earthquakes provided data with sufficiently high signal-to-noise for computing amplitude ratios relative to the bedrock sites. Amplifications of 10 or greater are found in the Washington, DC area due to the ACP strata, with the peak amplifications occurring near the estimated resonant frequencies of buildings throughout the city. Amplitudes decrease as the strata thicken, but even coastal sites on 600 m of ACP strata show amplification factors as great as 5. We use the frequency of the resonance peaks to invert for an average velocity function within the ACP strata. This work indicates that amplification of short-period ground motions by thin ACP strata contributed to the damage in Washington, DC, during the 2011 earthquake, and documents longer-period amplifications that could affect larger structures beneath coastal regions of the eastern U.S. during earthquakes.

February 10, 2017
3:00pm in PLS 1140
Yingwei Fei from Geophysical Laboratory
Recovery of an oxidized majorite inclusion from Earth's deep mantle

Abstract: Minerals recovered from the deep mantle provide a rare glimpse into deep Earth processes. In this study I describe the first discovery of ferric iron-rich majoritic garnet found as inclusions in a garnet host within an eclogite xenolith from the Trans-North China Orogen formed at the end of oceanic subduction during the Paleoproterozoic (~1.85 Ga). The ferric iron-rich majoritic garnet inclusions show a deep origin, formed at least at a depth of 380 km. The host garnet and majorite inclusion record two distinctive depths in the asthenosphere that has important implications for the ancient supercontinent assembly and breakup. The preservation of the ferric iron-rich majorite, particularly in a garnet host, provides a rare opportunity to understand the mantle chemistry and dynamic process.

February 17, 2017
3:00pm in PLS 1140
Brent Grocholski from AAAS / Science Magazine
Scientific Publishing from the Inside Out

Abstract: Effective scientific communication requires both good writing and understanding the publication process. We will discuss a wide range of topics from the perspective of a Science editor that touch on all aspects of the writing, peer review, and publication process. This includes insights into what make for a successful submission to high profile journals like Science.

Additional Information: Facebook Live video of this presentation is available here.

February 24, 2017
3:00pm in PLS 1140
Kevin Lewis from Johns Hopkins University
Exploration of Gale Crater Mars with the Curiosity Mars Rover

Abstract: The Curiosity Mars rover has been exploring its landing site at Gale crater since 2012. Over this time it has begun to climb the lower slopes of Mount Sharp, a 5 kilometer high mound of sedimentary rock located within the crater. In this talk, we will combine orbital and rover-based geological and geophysical tools to understand the formation of Mount Sharp, with potential implications for other crater-hosted mounds found commonly in the Martian equatorial region. The ultimate goal of this work, and one of the key objectives of the Curiosity mission, is to understand the climate information recorded in the strata of Mount sharp exposed along the rover traverse.

Additional Information: Facebook Live video of this presentation is available here.

March 17, 2017
3:00pm in PLS 1140
Luciana Astiz from NSF
USArray Data quality: A look at seismicity across the lower 48 and preliminary results on Earth Tide observations
March 31, 2017
3:00pm in PLS 1140
Daniel Viete from Johns Hopkins University
April 7, 2017
3:00pm in PLS 1140
Johnny Zhang from Scripps Institution of Oceanography
Fe-Ni-S-C Liquid in the Earth's Mantle

Abstract: Fe-Ni-S-C phases are accessory phases in the Earth’s mantle, but carry important geochemical and geophysical implications due to the contrasting physical and chemical properties between metallic and silicate phases. In the shallow mantle (<200 km), the metallic phase occurs as monosulfide solid solution (mss) or melt with near-monosulfide stoichiometries. To constrain the sulfide melt stability field and its Fe-Ni exchange with mantle silicate minerals, we performed experiments at comparable conditions (P, T, fO2) to Earth’s shallow mantle. In the deeper part of the upper mantle (200-410 km), the mantle become reduced, corresponding to an increase of metal activities in sulfide melt. To contain the composition of Fe-Ni-S melt and its storage of deep carbon, we performed experiments and thermodynamic calculations to show the evolution of Fe-Ni-S-C compositions and mantle silicates at deep upper mantle conditions. Based on the experimental and modeling exercise, further discussion will be made on the recent Fe-Ni-S-C liquid from deep diamonds (Smith et al. 2016). In the deepest part of Earth’ mantle (<2900 km), we propose that small quantities of Fe-Ni-S-C liquid is the cause for the two large low shear velocity provinces (LLSVPs). These Fe-Ni-S-C liquid is likely trapped during the crystallization of a dense basal magma ocean and therefore a potential carrier of primordial geochemical signature.

April 14, 2017
3:00pm in PLS 1140
Sabine Stanley from Johns Hopkins University
April 21, 2017
3:00pm in PLS 1140
Stephen Macko from University of Virginia
April 28, 2017
3:00pm in PLS 1140
Lindy Elkins-Tanton from Arizona State University

The coordinator for the Colloquium Series is Dr. Nicholas Schmerr. You can contact him at