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High-resolution Images of Mantle-wedge Structure along the Western Hellenic Subduction Zone Using Scattered Teleseismic Waves F. D. Pearce (MIT), S. Rondenay (MIT), Maria Sachpazi (National Observatory of Athens), M. Charalampakis (National Observatory of Athens), A. Hosa (University of Edinburgh), J. Suckale (MIT), L. H. Royden (MIT) The Hellenic subduction zone is located in the east-central Mediterranean region and exhibits large variations in convergence rate along its western edge [McClusky et al., 2000]. Differences in the lithosphere entering the subduction zone are believed to drive the different rates of convergence. While recent work has shown evidence for subducted oceanic crust beneath southern Greece [Suckale et al., 2009], no detailed images of the mantle-wedge structure beneath northern Greece have been available to test this hypothesis. Here, we use high-resolution seismic images across northern and southern Greece to investigate differences in the subducted crust along the strike of the western Hellenic subduction zone. We deployed 40 broadband seismometers from the IRIS Passcal pool across Greece in a northern line (NL) and southern line (SL), each roughly perpendicular to the trench axis as shown in Figure 1a. We recorded over 50 high-quality teleseismic events with good azimuthal coverage from each line and processed them using a 2D migration algorithm based on the generalized radon transform. High-resolution images of perturbations in S-wave velocity reveal NE dipping low-velocity layers beneath both NL and SL as shown in Figure 1b. We interpret the ~10 km thick low-velocity layer beneath SL as subducted oceanic crust and the ~20 km thick low-velocity layer beneath NL as subducted continental crust. The two imaged subducted crusts connect smoothly with images from marine seismic surveys [Finetti, 2005] and show a progressive deepening of the oceanic crust of SL relative to the continental crust of NL (Figure 1c). We conclude that along strike changes in slab buoyancy cause differential rollback between the two segments, which helps drive the large difference in convergence rates along the western Hellenic subduction zone. References Figure 1: a) Map of study area showing location of southern segment (SS) and northern segment of western Hellenic subduction zone separated by the Cephalonia transform fault (CTF). White circles denote station locations for NL and SL deployments. b) Images of perturbation in S-wave velocity for SL (top) and NL (bottom) at -5% to +%5 (red to blue). Solid lines delineate top and bottom of low-velocity layer, and the Moho of overriding plate. X-axis is horizontal distance perpendicular to strike measured from the intersection of SL with the trench of southern segment (solid yellow line in a)). c) Comparison of subducted crusts imaged from marine seismics (dashed) and this study (solid) for NL (black) and SL (blue), with dots showing smooth interpolation. Finetti, I. R. (2005), Depth contour map of the Moho discontinuity in the central Mediterranean region from new CROP seismic data, in CROP PROJECT: Deep seismic exploration of the central Mediterranean and Italy, edited by I. R. Finetti, pp. 597-606, Elsevier B.V., Amsterdam, The Netherlands. McClusky, S. et al. (2000), Global Positioning System constraints on plate kinematics and dynamics in the eastern Mediterranean and Caucasus, J. Geophys. Res., 105(B3), 5695-5719. Suckale J., S. Rondenay, M. Sachpazi, M. Charalampakis, A. Hosa, L. H. Royden (2009) High-resolution seismic imaging of the western Hellenic subduction zone using teleseismic scattered waves, Geophys. J. Int., 178(2), 775-791. Acknowledgements: This project was carried out as part of project MEDUSA, funded by the NSF Continental Dynamics Program, grant EAR-0409373. II-174 | 2010 IRIS Core Programs Proposal | Volume II | Upper Mantle Structure and Dynamics
Imaging the Mantle Wedge in the Central America Subduction Zone: The TUCAN Broadband Seismic Experiment Geoffrey Abers (Lamont-Doherty Earth Observatory of Columbia University), Karen Fischer (Brown University), Ellen Syracuse (University of Wisconsin), Catherine Rychert (University of Bristol), Laura MacKenzie (Schlumberger Data and Consulting Services) Central America was selected as a MARGINS Focus Site for the Subduction Factory initiative. In order to understand how the Subduction Factory processes trench inputs into volcanic arc outputs, we make direct observations of mantle structure. The TUCAN (Tomography and other observations Under Costa Rica And Nicaragua) experiment deployed 48 broadband seismographs in the Central America Focus Site in 2004-6. This One-Pager shows results from three kinds of imaging in Nicaragua, where arc output features globally significant geochemical signatures of subduction. The migrated receiver function image (A) shows a strong P-S conversion from what appears to be the top of the subducting plate to 200 km depth, the first time a steep slab has been imaged with these kinds of signals. The velocity contrast at the top of the plate is sharp and below the seismicity shallower than 80 km depth, probably Moho of the subducting crust. Deeper, the mode conversion is broad, consistent with the 15-30 km gradient expected for the thermal boundary layer. Seismic attenuation (B), a proxy for temperature, indicates a typically hot wedge beneath arc and backarc, quantitatively consistent with temperatures and water contents inferred from primitive lavas and melt inclusions [Plank et al., 2007]. The updip limit of hot mantle is inferred to be where the slab reaches 80 km depth. These two images show that the subducting crust passes from beneath cold to hot mantle and rapidly metamorphoses to eclogite. The ratio of P to S velocities, Vp/Vs (C), shows a somewhat different pattern, near-normal values for much of the wedge but a narrow, high-Vp/Vs column ascending nearly vertically from the slab to the volcanic arc. Since this pattern differs from that of 1/Qs or 1/Vp alone, this anomaly cannot be purely due to temperature. The presence of partial melt could produce such an effect, and given the relationship between 1/Qs, Vp/Vs and the location of the arc. Thus, we are imaging separately but in one place the wedge geometry, temperature structure and melt distribution across the subduction factory, one of the major goals of MARGINS. 0 50 100 150 200 0 km 40 80 120 160 200 SW B. A. SW 0 km 40 80 120 160 200 5 0 km 50 100 150 5 15 10 5 1000/Qs 0 2 4 6 8 10 NE Fast dVs/ Vs Slow −100 0 100 200 trench volcano seismograph earthquakes C. Δ Vp/Vs −.08 −.04 .00 .04 .08 100 km 200 300 400 Three seismic images of the Nicaragua Subduction Factory. (A) 2D receiver function migration (MacKenzie et al., 2008, 2010). Image shows S-wave velocity variations needed to generate scattered wavetrain, such as Moho and top of subducting plate. (B) S-wave attenuation as 1000/Qs, from tomographic inversion (Rychert et al., 2008), at 1 Hz. 1/Qs responds to temperature and indicates hightemperature region beneath and behind arc. (C) Vp/Vs anomalies from regional travel-time tomography (Syracuse et al., 2008). In regions of high temperature, high Vp/Vs may indicate presence of melt, perhaps showing a vertical melt column beneath volcanic arc. NE scattered P coda References MacKenzie, L.M., G.A. Abers, S. Rondenay and K.M. Fischer, Imaging a steeply dipping subducting slab in southern Central America, Earth Planet. Sci. Lett., in press, 2010. MacKenzie, L.S., G.A. Abers, K.M. Fischer, E.M. Syracuse, J.M. Protti, V. Gonzalez, and W. Strauch, Crustal structure along the southern Central American volcanic front, Geochem. Geophys. Geosyst., 9, Q08S09, 2008. doi:10.1029/2008GC001991 Rychert, C.A., K.M. Fischer, G.A. Abers, T. Plank, E.M. Syracuse, J.M. Protti, V. Gonzalez, and W. Strauch, Strong along-arc variations in attenuation in the mantle wedge beneath Costa Rica and Nicaragua, Geochem. Geophys. Geosyst., 9, Q10S10, 2008. DOI: 10.1029/2008GC002040 Syracuse, E.M., Abers, G.A., K.M. Fischer, McKenzie, L., C. Rychert, J. M. Protti, V. Gonzalez, and W. Strauch, Seismic tomography and earthquake locations in the Nicaraguan and Costa Rican upper mantle, Geochem. Geophys. Geosyst., 9, Q07S08, 2008. doi:10.1029/2008GC001963 Acknowledgements: The TUCAN project was carried out in close collaboration with M. Protti and V. Gonzalez of OVSICORI/UNA in Costa Rica, and W. Strauch and colleagues of INETER in Nicaragua. This work funded by the National Science Foundations’s MARGINS program, under awards OCE-0203650 (Boston Univ.) and OCE-0203607 (Brown). 2010 IRIS Core Programs Proposal | Volume II | Upper Mantle Structure and Dynamics | II-175
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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
Page 135 and 136: Optimized Velocities and Prestack D
Page 137 and 138: 40 Crustal Structure beneath the Hi
Page 139 and 140: Controlled-Source Seismic Investiga
Page 141 and 142: Northward Thinning of Tibetan Crust
Page 143 and 144: An Integrated Analysis of an Ancien
Page 145 and 146: Crustal Velocity Structure of Turke
Page 147 and 148: Ambient Noise Tomography of the Pam
Page 149 and 150: Ambient Noise Monitoring of Seismic
Page 151 and 152: Mushy Magma beneath Yellowstone Ris
Page 153 and 154: Imaging the Seattle Basin to Improv
Page 155 and 156: Developing a Database of ENA Ground
Page 157 and 158: Lithospheric Layering in the North
Page 159 and 160: eflective zones on depthmigrated se
Page 161 and 162: FischerFig05.pdf 1 2/8/10 12:31 PM
Page 163 and 164: S-Velocity Structure of Cratons, fr
Page 165 and 166: Seismic Structure of the Crust and
Page 167 and 168: Subducted Oceanic Asthenosphere and
Page 169 and 170: Detecting the Limit of Slab Break-o
Page 171 and 172: Pn Tomography of the Western United
Page 173 and 174: 3-D Isotropic Shear Velocity Model
Page 175 and 176: Seismic Anisotropy Associated with
Page 177 and 178: Anisotropy in the Great Basin from
Page 179 and 180: Source-Side Shear Wave Splitting an
Page 181 and 182: S-Velocity Structure of the Upper M
Page 183 and 184: Velocity Structure of the Western U
Page 185: Segmented African Lithosphere benea
Page 189 and 190: A Slab Remnant beneath the Gulf of
Page 191 and 192: Imaging the Southern Alaska Subduct
Page 193 and 194: Opposing Slabs under Northern South
Page 195 and 196: Effect of Prior Petrological Constr
Page 197 and 198: Global Azimuthal Seismic Anisotropy
Page 199 and 200: The Stratification of Seismic Azimu
Page 201 and 202: Upper Mantle Anisotropy beneath the
Page 203 and 204: The Teleseismic Signature of Fossil
Page 205 and 206: Seismic Anisotropy under Central Al
Page 207 and 208: Stress-Induced Upper Crustal Anisot
Page 209 and 210: 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
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Upper Mantle Discontinuity Topograp
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Edge-Driven Convection beneath the
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Imaging Attenuation in the Upper Ma
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Three-Dimensional Electrical Conduc
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Core-Mantle Boundary Heat Flow Thor
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Constraints on Lowermost Mantle Ani
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Localized Double-Array Stacking Ana
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Waveform Modeling of D" Discontinui
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Absence of Ultra-Low Velocity Zones
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Moving Seismic Tomography Beyond Fa
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A Three-Dimensional Radially Anisot
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The Importance of Crustal Correctio
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Slabs Do Not Go Gentle Karin Sigloc
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Localized Temporal Change of the Ea
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Core Structure Reexamined Using New
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Large Variations in Travel Times of
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Observations of Antipodal PKIIKP Wa
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Regional Variation of Inner Core An
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Wide-Scale Detection of Earthquake
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