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A Glassy Lowermost Outer Core Vernon F. Cormier (University of Connecticut) New theories for the viscosity of metallic melts at core pressures and temperatures, together with observations of translational modes of oscillation of Earth's solid inner core, suggest a rapid increase in the dynamic viscosity near the bottom of the liquid outer core. If the viscosity of the lowermost outer core (F region) is sufficiently high, it may be in a glassy state, characterized by a frequency dependent shear modulus and increased viscoselastic attenuation. In testing this hypothesis, the amplitudes of high frequency PKiKP waves are found to be consistent with an upper bound to shear velocity in the lowermost outer core of 0.5 km/sec at 1Hz. The fit of a Maxwell rheology to the frequency dependent shear modulus constrained by seismic observations at both low and high frequency favors a model of the F region as a 400 km thick chemical boundary layer. This layer has both a higher density and higher viscosity than the bulk of the outer core, with a peak viscosity on the order of 10^9 Pa-sec or higher near the inner core boundary. If lateral variations in the F region are confirmed to correlate with lateral variations observed in the structure of the uppermost inner core, they may be used to map differences in the solidification process of the inner core and flow in the lowermost outer core. References Cormier, V.F., (2009) A glassy lowermost outer core, Geophys. J. Int., 179, 374-380. Acknowledgements: This research was supported by grant EAR 07-38492 from the National Science Foundation. The author appreciates discussions with David Gubbins and the ICB group of the 2008 CIDER workshop, as well as reprints from and discussions with Douglas Smylie. 1.00 0.75 = 10 11 Pa-s = 10 9 Pa-s V S (km/s) 0.50 0.25 0.00 1e-03 1e-02 1e-01 1e+00 Frequency (Hz) Shear velocity as a function of frequency for two different models of viscosity and in the lowermost outer core. II-250 | 2010 IRIS Core Programs Proposal | Volume II | Outer and Inner Core Structure
Localized Temporal Change of the Earth’s Inner Core Surface Lianxing Wen (State University of New York at Stony Brook) The accumulation of seismic data recorded in the Global Seismographic Network (GSN) makes it possible for many discoveries to be made related to the Earth’s inner core. One of these discoveries in recent years is the localized temporal change of the Earth’s inner core surface. The discovery is made by comparing the seismic signals of an earthquake doublet, defined as earthquakes that occurred at different times but in almost exactly same location, recorded by the GSN stations. Seismic phases used are the compressional waves reflected off the inner core surface (PKiKP) and propagating through the inner core (PKIKP) for an earthquake doublet occurring in South Sandwich on 12/01/1993 and 09/06/2003. Temporal changes of PKiKP travel time and waveform are observed at three GSN stations, ARU, AAK and OBN (Fig. 1), while no discernable temporal change at other seismic stations. The PKiKP and PKIKP phases recorded at station ARU arrives 0.11 s earlier and the PKIKP phase about 0.04 s earlier in event 2003 than in event 1993 (Fig. 1b). Moreover, the PKiKP-PKIKP differential travel time is about 0.07 s smaller in event 2003 than in event 1993 (Fig. 1c). The later portion of the AAK waveforms, with the energy primarily associated with the PKiKP phases, arrives about 0.07 s earlier in event 2003 than in event 1993, while the earlier portion of energy appears arriving at about the same time (Fig. 1d). The PKiKP waveforms observed at station OBN exhibit two characteristics: 1) the PKiKP main phase in event 2003 arrives about 0.07 s earlier than in event 1993; and 2) the PKiKP coda waves show waveform dissimilarities between the two events (Fig. 1e). These observations indicate a localized enlarged inner core radius by 0.98 to 1.75 km beneath middle Africa between the occurring times of the doublet. The discovered localized temporal change of the inner core surface will have many implications to our understanding of the growth of the inner core, thermodynamic processes near the inner core boundary, convection in the outer core and driving forces for geodynamo. The GSN contributes uniquely to the discovery with its anchoring stations providing continuous openaccess data, making it possible 1) to discover and locate many earthquake doublets, and 2) to confidently identify the subtle signals related to the temporal change of Earth’s inner core surface between the doublets. References Wen, L., Localized temporal change of the Earth's inner core boundary, Science, 314. no. 5801, pp. 967 - 970, DOI: 10.1126/science.1131692, 2006. Acknowledgements: I acknowledge the Global Seismographic Network for providing seismic data. This work is supported by the National Science Foundation, under grant #EAR 0609717. Fig. 1. a) Ray paths of PKIKP (black) and PKiKP (light blue) waves. b-e) Superimposed PKiKP-PKIKP waveforms of the doublet recorded at stations ARU (b,c) and AAK (d), and PKiKP waveforms at OBN (e). Waveforms in b), d) and e) are superimposed with time shifts that account for the differences in relative origin time and hypocenter position of the doublet. Panel c) is the same as panel b) except that the waveform for event 2003 is shifted 0.04 s more backward in time. Waveforms are filtered with the WWSSN short-period instrument response. [From Wen (2006)]. 2010 IRIS Core Programs Proposal | Volume II | Outer and Inner Core Structure | II-251
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volume ii - accomplishments Facilit
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volume ii - accomplishments Facilit
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CONTENTS Introduction..............
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Non-Volcanic Tremor along the Oaxac
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Detecting the Limit of Slab Break-o
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Lower Mantle, Core-Mantle Boundary
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• Non-Earthquake Seismic Sources
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acoustics community by permitting a
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Near-Surface Environments - Hazards
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Why Do Faults Slip? Emily Brodsky (
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Another probe of fault evolution is
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to provide a best match with the Gl
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tectonic disruption and mass accumu
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W3 ∆ 5 . A number of intriguing r
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thermal and compositional effects r
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Towards a Global School Seismic Net
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On-Line Seismology Curriculum for U
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Teachers on the Leading Edge: Earth
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USArray Education and Outreach in S
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From an IRIS Lecture Tour to a Gene
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Explorer Series Robert Bartolotta (
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Workshop “Earth System Science fo
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The IRIS Internship Cycle: From Int
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Community-Outreach Efforts in Data
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Site Reconnaissance for Earthscope
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jAmaseis: Seismology Software Meeti
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Near Real-Time Simulations of Globa
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FuncLab: A MATLAB Interactive Toolb
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Five Years of Distributing the Seis
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IRIS DMS Data Products, Beyond Raw
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Local Earthquakes in the Dallas-Ft.
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Epicentral Location Based on Raylei
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Analysis of Spatial and Temporal Se
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Exceptional Ground Motions from the
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The 2010 Mw7.2 El Mayor-Cucapah Ear
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Effects of Kinematic Constraints on
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Imaging of the Source Properties of
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Teleseismic Inversion for Rupture P
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The Global Aftershocks of the 2004
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The 17 July 2006 Java Tsunami Earth
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Seismic Cycles on Oceanic Transform
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Migration of Early Aftershocks Foll
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Apparent Stress Variations at the O
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Automated Identification of Telesei
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Evaluating Ground Motion Prediction
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Tremor Monitoring Aaron Wech (Unive
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Slow Slip and Tremor in the Norther
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0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2
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Intimate Details of Tremor Observed
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Global Search of Triggered Tremor a
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Slab Morphology in the Cascadia For
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Source Analysis of the Memorial Day
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Iceberg Tremor and Ocean Signals Ob
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Elucidating the Stick-Slip Nature o
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Probing the Atmosphere and Atmosphe
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Volcanic Plume Height Measured by S
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Eruption Dynamics at Mount St. Hele
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A Search for the Lunar Core Using A
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Seismic Imaging of the Mt. Rose Fau
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Structure of the California Coast R
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Temporal Variations in Crustal Scat
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High-Resolution Locations of Trigge
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Adjoint Tomography of the Southern
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Crustal Structure of the High Lava
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Controlled Source Seismic Experimen
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Structural Interpretations Based on
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Optimized Velocities and Prestack D
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40 Crustal Structure beneath the Hi
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Controlled-Source Seismic Investiga
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Northward Thinning of Tibetan Crust
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An Integrated Analysis of an Ancien
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Crustal Velocity Structure of Turke
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Ambient Noise Tomography of the Pam
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Ambient Noise Monitoring of Seismic
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Mushy Magma beneath Yellowstone Ris
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Imaging the Seattle Basin to Improv
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Developing a Database of ENA Ground
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Lithospheric Layering in the North
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eflective zones on depthmigrated se
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FischerFig05.pdf 1 2/8/10 12:31 PM
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S-Velocity Structure of Cratons, fr
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Seismic Structure of the Crust and
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Subducted Oceanic Asthenosphere and
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Detecting the Limit of Slab Break-o
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Pn Tomography of the Western United
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3-D Isotropic Shear Velocity Model
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Seismic Anisotropy Associated with
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Anisotropy in the Great Basin from
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Source-Side Shear Wave Splitting an
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S-Velocity Structure of the Upper M
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Velocity Structure of the Western U
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Segmented African Lithosphere benea
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Imaging the Mantle Wedge in the Cen
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A Slab Remnant beneath the Gulf of
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Imaging the Southern Alaska Subduct
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Opposing Slabs under Northern South
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Effect of Prior Petrological Constr
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Global Azimuthal Seismic Anisotropy
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The Stratification of Seismic Azimu
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Upper Mantle Anisotropy beneath the
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The Teleseismic Signature of Fossil
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Seismic Anisotropy under Central Al
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Stress-Induced Upper Crustal Anisot
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Tau-p Depropagation of Five Regiona
Page 211 and 212: Mapping the Upper Mantle with the S
Page 213 and 214: Upper Mantle Structure of Southern
Page 215 and 216: The Africa-Europe Plate Boundary in
Page 217 and 218: The Isabella Anomaly Imaged by Eart
Page 219 and 220: Tomographic Image of the Crust and
Page 221 and 222: Small-Scale Mantle Heterogeneity an
Page 223 and 224: Mantle Heterogeneity West and East
Page 225 and 226: New Geophysical Insight into the Or
Page 227 and 228: The Plume-slab Interaction beneath
Page 229 and 230: Imaging the Shear Wave Velocity "Pl
Page 231 and 232: Slab Fragmentation and Edge Flow: I
Page 233 and 234: Mantle Shear-Wave Velocity Structur
Page 235 and 236: Discordant Contrasts of P- and S-Wa
Page 237 and 238: Upper Mantle Discontinuity Topograp
Page 239 and 240: Edge-Driven Convection beneath the
Page 241 and 242: Imaging Attenuation in the Upper Ma
Page 243 and 244: Three-Dimensional Electrical Conduc
Page 245 and 246: Core-Mantle Boundary Heat Flow Thor
Page 247 and 248: Constraints on Lowermost Mantle Ani
Page 249 and 250: Localized Double-Array Stacking Ana
Page 251 and 252: Waveform Modeling of D" Discontinui
Page 253 and 254: Absence of Ultra-Low Velocity Zones
Page 255 and 256: Moving Seismic Tomography Beyond Fa
Page 257 and 258: A Three-Dimensional Radially Anisot
Page 259 and 260: The Importance of Crustal Correctio
Page 261: Slabs Do Not Go Gentle Karin Sigloc
Page 265 and 266: Core Structure Reexamined Using New
Page 267 and 268: Large Variations in Travel Times of
Page 269 and 270: Observations of Antipodal PKIIKP Wa
Page 271 and 272: Regional Variation of Inner Core An
Page 273: Wide-Scale Detection of Earthquake
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