EPSS Colloquium - winter-2012

Jan. 19, 2012
4 p.m. - 5 p.m.
3656 Geology

Presented By:

• German Prieto - Universidad de los Andes, Bogotá, Colombia

The physical mechanism of intermediate-depth earthquakes is still under debate. In contrast to conditions in the crust and shallow lithosphere, at temperatures and pressures corresponding to depths >50 km one would expect rocks to yield by creep or flow and not by brittle failure, so there has to be a physical mechanism that allows for brittle or brittle-like failure for intermediate-depth earthquakes. Two such mechanisms have been proposed: dehydration embrittlement and thermal shear runaway. Earthquake nests represent a region with high earthquake concentration that is isolated from nearby activity. I will discuss general observations on the three famous intermediate-depth earthquake nests - Vrancea, Hindu-Kush and Bucaramanga. The emphasis will be on the Bucaramanga nest (Colombia) and how high-resolution seismological observations (tectonic setting, precise earthquake locations, focal mechanisms, stress drops, etc.) may provide key constraints on the mechanism responsible. Given the nature and characteristics of this nest, it can be thought as natural laboratory for understanding the physics of intermediate-depth earthquakes.

Jan. 26, 2012
4 p.m. - 5 p.m.
3656 Geology

Presented By:

• Michael Jura - UCLA

Knowing that extrasolar planetary systems are common, we would like to learn whether the Earth is normal or distinctive. Bulk Earth is 94% composed of O, Mg, Si and Fe and very deficient compared to the Sun in volatiles such as C and N. With our recent observations of white dwarf stars that have recently accreted tidally-disrupted minor planets that are about 300 km in diameter, we find a similar compositional pattern in extrasolar asteroids. While there must be individual exceptions, in aggregate, the studied extrasolar asteroids also are as "dry"; they probably formed interior to a snow line. Although the current sample is tiny, it appears that bulk Earth is compositionally normal for a rocky body. In the future, we may learn whether extrasolar planetesimals have undergone differentiation, a fundamentally important process in the history of our own planet.

Feb. 2, 2012
4 p.m. - 5 p.m.
3656 Geology

Presented By:

• P.U.P.A. Gilbert - University of Wisconsin

Mapping the Amorphous-to-crystalline transitions in CaCO3 biominerals with 20-nm resolution One of the most fascinating aspects of calcite biominerals is their intricate and curved morphology, quite different from the rhombohedral crystal habit of geologic calcite. These morphologies, as well as space-filling and greater resistance to fracture, are achieved via amorphous precursor mineral phases (1). In this talk we will show that in sea urchin larval spicules two distinct phase transitions occur, 1?2 and 2?3 (2). Both transitions are regulated by inhibiting proteins, which introduce activation barriers between states otherwise spontaneously transforming because they are energetically downhill (3). 1. Y Politi, RA Metzler, M Abrecht, B Gilbert, FH Wilt, I Sagi, L Addadi, S Weiner, and PUPA Gilbert. Mechanism of transformation of amorphous calcium carbonate into calcite in the sea urchin larval spicule. Procs. Natl. Acad. Sci. USA 105, 17362-17366, 2008. 2. AV Radha, TZ Forbes, CE Killian, PUPA Gilbert, and A Navrotsky. Transformation and crystallization energetics of synthetic and biogenic amorphous calcium carbonate. Procs. Natl. Acad. Sci. USA 107, 16438–16443, 2010. 3. YUT Gong, CE Killian, IC Olson, NP Appathurai, RA Metzler, AL Amasino, FH Wilt, PUPA Gilbert. Phase Transitions in Sea Urchin Larval Spicules. Under review.

Feb. 9, 2012
4 p.m. - 5 p.m.
3656 Geology

Presented By:

• Troy Carter - UCLA

I will give an overview of the challenges associated with harnessing nuclear fusion as a terrestrial power source and the progress that has been made in research in this area. In particular, I will discuss turbulence in magnetically-confined plasmas and how transport associated with this turbulence limits the confinement achievable in current and planned experiments. I will present recent UCLA research that has helped advance our understanding of the basic physics of turbulence and turbulent transport in magnetized plasmas.

Feb. 16, 2012
4 p.m. - 5 p.m.
3656 Geology

Presented By:

• Max Werner - ETH Zurich

Seminar Description coming soon.

Feb. 23, 2012
4 p.m. - 5 p.m.
3656 Geology

Presented By:

• Yoshihiro Kaneko - UCSD

Study of the earthquake source brings about a set of fascinating interdisciplinary problems characterized by nonlinearity, a broad range of spatial and temporal scales, rare but catastrophic events, competing physical mechanisms, remote observations, inverse problems, non-uniqueness, and substantial societal significance. The ultimate challenge is to understand and quantify factors controlling the spatio-temporal behavior of active faults, including earthquake nucleation, seismic patterns, and the interaction of seismic and aseismic fault slip. My research aims to address this challenge by developing realistic physical models of earthquake source over several seismic cycles that rely on recent dramatic advances in observations, computational resources, and laboratory experiments. The goal is to use the models in conjunction with seismic, geodetic, and geological observations to constrain earthquake-source properties in terms of experimentally-derived constitutive laws, and then to study the potential set of future behaviors. Here, I will present two examples that illustrate this approach. In the first one, numerical modeling is used to establish the relation between variations in fault friction properties, the pattern of interseismic coupling (which characterizes the degree of fault locking between seismic events), the properties of earthquake sequences, and the observable characteristics of individual seismic events. The second example presents an innovative method for inferring fault friction properties based on comparison of numerical simulations and geodetic observations, which is applied to the central section of the North Anatolian fault (Turkey).

March 1, 2012
4 p.m. - 5 p.m.
3656 Geology

Presented By:

• Britney Schmidt - University of Texas

With an icy exterior covering a global ocean, Europa has long been a target of interest in the search for life beyond Earth. Europa exists in a dynamic environment, subject to intense irradiation and impact as well as immense tides from Jupiter. These processes deliver important thermal and chemical energy that could be critical to supporting a putative biosphere. In the past few decades the debate about habitability of Europa has been focused strongly on the thickness of the ice shell. However, an arguably more critical question is: how does the ice shell recycle? New analysis of Europa's enigmatic "chaos terrains," indicates that chaos features form in the presence of a great deal of liquid water, and that large liquid water bodies exist within 3km of Europa's surface comparable in volume to the Great Lakes. The detection of shallow subsurface "lakes" implies that the ice shell is recycling rapidly and that Europa may be currently active. In this presentation, we will explore environments on Europa and their analogs on Earth, from collapsing Antarctic ice shelves to to subglacial volcanoes in Iceland. I will present these new analyses, and describe how this new perspective informs the debate about Europa's habitability and future exploration.

March 8, 2012
4 p.m. - 5 p.m.
3656 Geology

Presented By:

• Raj Dasgupta - Rice University

The Earth is unique among the terrestrial planets in our solar system in having a fluid envelope that fosters life. The key behind Earth’s habitable climate is well-tuned cycles of carbon (C) and other volatiles. While on ten to thousands of year time-scales the chemistry of fluids in the atmosphere, hydrosphere, and biosphere is dictated by fluxes of carbon between the near surface reservoirs, over million to billion years this is maintained by chemical interactions of carbon between the Earth’s interior, more specifically the Earth’s mantle, and the exosphere. This is because of the fact that the estimated total mass of C in the mantle is greater than that observed in the exosphere and the average residence time of carbon in the mantle is on the ?1 Ga. But how did the Earth’s mantle attain and maintain the inventory of mantle carbon over geologic time and is the residence time of carbon in the mantle as constrained by the present-day fluxes a true reflection of the carbon ingassing and outgassing rates throughout the history? Also, when in the history of the planet carbon inventory of the mantle got established and how did it change through geologic time? The answers to these questions are important because understanding the origin and chemistry of carbon and how they regulate feedbacks between the planet’s interior and the atmosphere is of fundamental importance owing to far-reaching implications for a number of fields of natural sciences, such as the thermal history of the Earth, internal differentiation, long-term evolution of climate, and origin and evolution of life. Because the abundance and mode of storage of mantle carbon are central to carbon’s role in global geodynamics, it is critical to constrain the processes that modulated the carbon inventory of the Earth’s mantle through time. In this talk, I will try to review ingassing, outgassing, and storage mechanisms of terrestrial carbon, from the time period of early planetary differentiation and magma ocean in the Hadean to the plate tectonic cycles of the modern Earth through Phanerozoic.

March 15, 2012
4 p.m. - 5 p.m.
Geology 3656

Presented By:

• An Yin - UCLA

Seminar Description coming soon.