ESS Seminars & Lectures - Autumn Quarter 2007



ALL ESS SEMINARS ARE HELD IN JHN 102, 3:30-4:50, UNLESS OTHERWISE NOTED


Thursday, October 4
ESS SEMINAR SERIES
Peter Kelemen, LDEO, Columbia University
Title:  "Feedback Mechanisms in Solid Earth Geodynamics: Field Examples and Simple Models"

Summary:  I will review work on feedback between reaction rates, rheology and physical mechanisms 
in solid earth geodynamics. One aim of this review is to stimulate scientists, younger and smarter 
than I am, to undertake research on the fundamental energetic constraints governing the morphology 
of natural fluid transport networks. A second is to present a viscous shear heating model for intermediate 
depth earthquakes, that is both functionally simple and a realistic alternative to the "dehydration 
embrittlement" mechanism currently favored by many. Another is to encourage solid earth scientists to 
consider how we may contribute to geologically rapid sequestration of atmospheric CO2 to counter 
anthropogenic CO2 output.



Thursday, October 11
ESS SEMINAR SERIES
Wendy Mao, Stanford University
Title:  "Viewing the core-mantle boundary through a diamond window"

Summary:  The Earth’s D” layer, the lowermost 130 to 300 km of the silicate mantle, is a region with a 
complex seismic signature. One particularly enigmatic feature are areas of ultra-low seismic velocities 
that have been observed at the base of D” where this boundary layer comes in contact with the liquid, 
iron-rich outer core. These regions may be associated with hot spots and the origin of mantle plumes. 
In a series of laser-heated diamond anvil cell experiments simulating the ultrahigh pressure-temperature
conditions of the core-mantle boundary, we observed that a large amount of iron can be incorporated into 
the recently discovered post-perovskite (ppv) silicate phase, and that this significantly changes its properties
relative to the pure MgSiO3 endmember. We determined the aggregate compressional and shear wave 
velocities of this iron-rich silicate at high pressure and found that ppv with up to 40 mol% FeSiO3 may 
be able to explain the properties seismically observed in ultra-low velocity zones.


Thursday, October 18
ESS SEMINAR SERIES
Ken Creager, University of Washington, Department of Earth and Space Sciences
Title:  "Episodic Tremor and Slip "
 
Summary: Every 14 months the Pacific Northwest experiences slow slip apparently on the down dip extension 
of the megathrust fault that is equivalent to a moment magnitude 6.5 earthquake.  While an earthquake of 
this size typically happens in only 10 s, the duration of these episodic tremor and slip (ETS) events is two or 
more weeks.  The ETS and related events scale with seismic moment proportional to duration, while typical
earthquakes scale with seismic moment proportional to the cube of the duration.  These events produce tremor 
that can be observed seismically.  Tremor amplitude is strongly modulated by tidal stresses, while tremor 
occurring at other times is sometimes triggered by stresses from surface waves of distant earthquakes.  
Both of these observations suggest the slip is very sensitive to small stresses (five orders of magnitude 
less than the normal stresses acting on the fault). 


INVERSE PROBLEMS SEMINAR SERIES
3:50 PM, THO 215
Ken Creager, University of Washington, Department of  Earth & Space Sciences
Title: "Seismological Applications of Inverse Theory: 3-D imaging, earthquake rupture history and tremor". 

Summary: This talk provides a few examples of the application of geophysical inverse theory to noisy data.  
We will discuss applications to determining the lateral variations in shear wave speeds near the base of 
Earth's mantle, three-dimensional structure of the crust and upper most mantle in Western Washington, 
the rupture history of the 2001 Nisqually Earthquake, and the detection and location of deep tremor, which 
is quite active in western Washington as I write this abstract. 



Tuesday, October 23
Astrobiology Seminar
2:30 PM, PAA-118 (UW Physics/Astronomy Auditorium)
Robert M. Winglee, Professor and Chair, University of Washington, Dept. of Earth and Space Sciences and
Darci Snowden, UW ESS Graduate Student
Title: "Plasma/Upper Amtospheric Interactions Within the Saturn/Titan System"

Summary: Titan is the only moon in the solar system that is able to maintain a thick atmosphere, with 
possible oceans of methane and ethane on its surface. This environment is probably the closest facsimile 
to the early atmosphere on the Earth, albeit at very much lower temperatures. The upper atmosphere is 
subject to ionization and erosion from incident plasma that is rotating within Saturn's magnetosphere. 
This interaction can lead to modifications of the optical emissions that is different from the planetary 
emissions and thereby allow remote sensing of its upper atmospheric conditions. 3-D simulations are 
used to quantify how the interaction between Titan and Saturn changes under variable solar wind conditions. 
It is shown that this interaction leads to the generation of a comet-like tail which can extend several Saturn 
radii in length. This tail can be subject to disruption during storm-like conditions within the planetary 
magnetosphere. Potential applications to other systems are discussed, including the Jovian system and 
extrasolar planets. 


Thursday, October 25
ESS SEMINAR SERIES
Edward J. Garnero, Arizona State University
Title:  "Deciphering Earth's Dynamic Interior Using Seismology"

Summary:  Earth's surface shows evidence for complex dynamical and chemical processes at a 
number of scales, with attendant strong variability.  At the largest scales, plate tectonics plays 
a key role in the distribution of continents, as well as the creation and destruction of oceanic 
crust and lithosphere. However, important questions persist regarding the cycling and evolution 
of material in Earth's interior, and how these processes may govern large scale surface processes.  
How deep does subducted oceanic lithosphere penetrate into the mantle?  From what depths do hot
 spot volcano magmas come from? Are there unique geochemical reservoirs in the deep mantle?  
Does mantle rock store oceans worth of H2O, and if yes, why and how?  To address these questions, 
the tool of seismology is useful as it enables the most detailed depiction of Earth's present day 
interior structure. One must appeal to other disciplines, e.g., geochemistry, mineral physics, 
and geodynamics, to place current day seismological information into an evolutionary context.  
In this seminar, I will review several recent geophysical findings and discuss their impact on our 
understanding of the large scale material cycling in Earth's mantle, with particular emphasis on 
plumes and slabs.



Thursday, November 1
ESS SEMINAR SERIES
Bradley Hacker,  UC Santa Barbara
Title:  "Continental Relamination"

Summary:  A long-standing paradigm for the genesis and evolution of Earth’s continental crust holds 
that the crust is andesitic and reached this composition in the ‘subduction factory’ by delamination 
or foundering of the bottom of the arc into the mantle. However, the range of suggested compositions 
for the lower crust and our incomplete understanding of subduction-zone processes render this 
paradigm non-unique. Recent discoveries from (ultra)high-pressure xenoliths and terranes, combined 
with re-evaluation of methods for inferring lower crustal compositions from seismic velocity data, 
show that “relamination” of buoyant, subducting continental crust may be an efficient means of 
altering the composition of the lower crust.
	Ultrahigh-pressure terranes show that large areas (>60,000 km2) of continental crust are 
subducted to depths >100 km where they undergo heating to temperatures of 600–1000°C for periods 
of up to 20 Myr. Xenoliths from the Pamir show that subduction erosion can drag continental rocks to 
depths >90 km and temperatures of ~1200°C. In both settings, devolatilization and melting transform 
cold, hydrous, low-density crust into hot, less-hydrous residues. Felsic and intermediate rocks attain 
densities similar to the middle–lower continental crust; buoyancy may drive such rocks to rise through
 the mantle to pond at the Moho or higher crust levels. The calculated seismic wavespeeds of such 
material are indistinguishable from the bulk lower crust. Both ultrahigh-pressure continental subduction 
and subduction erosion operate at rates of 1–1.5 km3/yr, such that over the lifetime of Earth either could 
have led to large-scale ‘continental relamination’, refining the composition and physical properties of the 
continental lower crust.



Thursday, November 8
ESS SEMINAR SERIES
Richard Peltier,  University of Toronto
Title:  "Dynamics of the Ice-Age Earth"

Summary:  The Late Quaternary ice-age cycle, with characteristic timescale near 100 kyr, has been an 
enduring characteristic of climate system variability since mid-Pleistocene time. The phenomenon owes 
its existence to the action of gravitational n-body effects in the solar system and may be employed as a 
probe of both the Earth's visco-elastic interior and of climate system sensitivity. Both lines of analysis 
will be explored.


Thursday, November 15
ESS SEMINAR SERIES
William McDonough, University of Maryland
Title:   "Neutrino Geophysics and the Earth's budget of radioactive elements" 

Summary:  A significant portion of the Earth’s thermal energy comes from radioactive decay, with K, Th and 
U being the chief contributors of radioactive heat generation.  This nuclear fuel, in part, drives convection in 
the Earth’s interior and plate tectonics. 
    Geochemists describe the Earth as having half (or more) of the heat producing elements in the continents 
and the remainder in the mantle (with negligible or no core contribution), with the total radiogenic contribution
being 19 TW, relative to the total planetary heat loss of 46 ± 3 TW, the planetary Urey ratio. 
    The mantle Urey ratio describes proportion of radiogenic heat production relative to the total heat loss from the
mantle.  Geodynamic models typically assume mantle Urey ratios of 0.4 to 0.7 to model the balance of thermal 
forces in convection models.  In contrast, geochemical models predict a mantle Urey ratio of 0.3 or less.
    Thus, these geophysical and geochemical models are at odds.  Neutrino geophysics involves the detection of
anti-neutrino emissions from the decay U, Th and K inside the Earth.  The U and Th anti-neutrino flux (2 x 107
cm-2 s-1) from the Earth are consistent with their estimated 16 TW radiogenic power geochemical models.  Recent
developments in Neutrino Geophysics and future prospects will be discussed.


Thursday, November 29
ESS SEMINAR SERIES
Richard Carlson,  Carnegie Institute of Washington DC
Department of Terrestrial Magnetism
Title:  "Composition of Earth's Interior: The Importance of Early Events"

Summary:  The detection of excess 142Nd caused by the decay of 103 Ma half-life 146Sm in all terrestrial 
rocks compared to chondrites suggests that the silicate earth experienced an early differentiation event.  
New Sm and Nd isotopic data for meteorites provide a strong argument that this difference in 142Nd/144Nd 
is not caused by nucleogenic heterogeneity or a non-chondritic Earth, but that the difference likely reflects 
the decay of 146Sm in differentiated terrestrial reservoirs with different Sm/Nd ratios.  This early 
differentiation event, which occurred prior to ~4.51 Ga, left the outer portion of the Earth slightly depleted 
in refractory incompatible lithophile elements compared to chondritic estimates. Both the continental 
crust and the mantle source of mid-ocean ridge basalts (MORB) originate from this early-formed depleted 
reservoir. Continent – depleted mantle mass balance calculations show that the early-formed depleted 
mantle occupies between 75 – 95% of the mantle depending on the composition assumed for average 
continental crust.  If the bulk-silicate earth has chondritic relative abundances of the refractory lithophile
elements, then there must exist within Earth’s interior an incompatible element enriched reservoir that 
contains roughly 40% of Earth’s 40Ar and heat producing radioactive elements.  The existence of this 
enriched reservoir is demonstrated by time-varying 142Nd/144Nd in Archean crustal rocks.  Calculations 
of the mass of the enriched reservoir along with seismically determined properties of the D” layer at the 
base of the mantle allow the speculation that this enriched reservoir formed by the sinking of dense melts 
deep in a terrestrial magma ocean.  The enriched reservoir may now be confined to the base of the mantle 
because of a combination of compositionally induced high density and low viscosity, both of which allow only 
minimal entrainment into the overlying convecting mantle.


Thursday, December 6
No ESS Seminar Today

ESS Holiday Party
3:30 PM, JHN 170



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