Model Validation RegSEM waveform fit: model 3 + Baffin Bay 6.0 event

Model Validation RegSEM waveform fit: model 3 + Oklahoma 5.6 event

Isotropic Vs Craton and WUS separated by the Rocky Mountain Front (RMF) Transition zone depth: slow craton; fast WUS; subducted JdF slab

Radial Anisotropy (ξ) Sutures: VSv>VSh

Shear Wave Splitting Shear wave splits to the fast and slow symmetry axis in the anisotropic medium http://garnero.asu.edu/research_images/images_all.html

Integrated effect of the medium (δt and ψ) Spread sensitivity along ray path ψ http://garnero.asu.edu/research_images/images_all.html

Region Long and Becker, EPSL, 2010

Shear Wave Splitting

Shear Wave Splitting

Laminated Mantle Don L. Anderson’s nomenclature (2011) Region B: Seismic Lid & Low Velocity Layer G-discontinuity L-discontinuity “the most heterogeneous & anisotropic region of the mantel” Anderson, J. of Petrology 2011

Laminated Mantle Local Tomography Regional Tomography Crust + Shallow upper Mantle A+B Regional Tomography Upper mantle B+C Global Tomography Full mantle B+C+D and core Anderson, J. of Petrology 2011

Laminated Mantle Mantle discontinuities Regional Tomography Region B: Moho; G-discon. (ocean); Hales discon.(continents); L- discon. (220 km); Lithosphere-asthenosphere-boundary Region C: 410-km discon.; 520-km discon.; 660-km discon. Region D: D’’-discon. Classic mantle subdivision Regional Tomography Anderson, J. of Petrology 2011

“2-Layer” SKS Model Lithosphere or asthenosphere origin of the SKS Silver and Chan 1996; Vinnik et al 1989 Apparent SKS fitting from 3D model 2-layer model prediction: lithosphere layer and asthenosphere layer Second application

“2-Layer” Model at HRV Surface wave and local SKS modeling results (Levin et al. 1999) agree well: Top: east-west direction (N100E) Bottom: plate motion direction (N50E) N100E N50E

Western US upper mantle (2010 Model) Sharp transition from craton to WUS along the RMF Subducted JdF in the transition zone Depth dependent anisotropy field explains the “swirl” SKS splitting pattern Deep anisotropy associated with the stagnant slab?

Depth Dependent Anisotropy in WUS Excellent ray azimuthal coverage from the TA

Isotropic Vs Fast Craton and its Boundary wrt. the western US Fast Vs 100-200 km under Great Plains Slow Ridges (<100 km) “Neutral” CP in Vs “Neutral” CA Coast Ranges Slow B&R (~250 km) N This 3D Vs plot summarizes some of the key features. The plot shows the isosurfaces for 3% positive and 1.5% negative variation, down to 400 km. We are viewing from south west. CA is here. Wyoming is here. Unsolved features like beneath Texas, downgoing instability

Isotropic Vs Fast Vs (250-400 km) under Oregon: Correlating with the subducted JdF slab: van der Lee and Nolet 1997; Burdick et al. 2009; Obrebski et al. 2010; Schmandt and Humphreys 2010 N One specific feature I want you to keep in mind is the high velocity feature under Oregon. Now we are viewing the model from north west, washington, texas.

Need Berkeley Logo to show different “wavelength” of the study so that the story here might not be sold

Shallow depth azimuthal anisotropy Rapid anisotropy pattern change across the RMF Large amplitude, shallow depth (<150 km), NA/JdF Absolute Plate Motion (APM) parallel

Intermediate Depth Azimuthal Anisotropy Intermediate depth (~150), E-W under B&R, N-S along the RMF, E-W under SRP dichotamy

Deep Azimuthal Anisotropy Large amplitude, Pacific APM parallel Deep (>250 km) E-W direction under Washington and Oregon dichotamy

Anisotropy and SKS in WUS Circular pattern of the SKS splitting (Savage and Sheehan, 2000) This 3D depth dependent anisotropy model can explain some of the hot topics in SKS measurements in the western US. More than one-layer of the anisotropic domain needed.

Circular pattern of the SKS splitting Schutt and Humphreys, Pure and Applied Geophysics, 1998 Savage and Sheehan, JGR, 2000

Circular pattern of the SKS splitting NA-SWS-1.1, Liu, G-Cubed 2009 Eakin et al., EPSL, 2010

Proposed Interpretations from others Savage and Sheehan (2000): Active upwelling Zandt and Humphreys (2008): Passive edge/toroidal flow West et al (2009): Lithospheric drip + associated mantle flow

Savage and Sheehan Models Plume model Model 3 Mantle Upwelling Savage and Sheehan 2000

Zandt and Humphreys model Slab Rollback + Slab window Passive edge/toroidal Flow Zandt and Humphreys, Geology, 2008

West et al. model Center of the circular pattern Low Volcanism Low Heat flow Large Vp variation Small Splitting Time They first observed a high velocity body from ~100 down to below the transition zone. Downward Drip + mantle flow  West et al., Nature Geo., 2009

Berkeley Model Circular Pattern Predicted by 3D model Not good along the Wasatch front/western border of the CP where extremely large change of Velocity and fast axis directions over 50km distance have been reported from the LA Ristra array studies, which is beyond our current resolution.

Anisotropy and SKS in WUS More than “one-layer” of anisotropic domain is needed. Deep east-west direction beneath Oregon More than one-layer of the anisotropic domain needed.

Deep anisotropy & Subducted slab Fast Vs (250-400 km) under Oregon:

Origin of the deep anisotropy Isotropic Vs So what causes the deep anisotropy?

Origin of the deep anisotropy Anisotropy direction Isotropic Vs Fast velocity correlates with the east-west fast axis direction, indicating there is contribution from the slab! There are a lot of slab segments in the WUS transition zone.

Origin of the deep anisotropy Anisotropy direction Isotropic Vs Slab Fast velocity correlates with the east-west fast axis direction, indicating there is contribution from the slab! There are a lot of slab segments in the WUS transition zone.

Stagnant Slab Frozen-in/structural anisotropy in the stagnant/flattened slab Slab rollback caused stagnant segments above the 660-km and slab flattening above the transition zone. Also the rollback may cause east-west flow around 150-km depth Schmid et al., EPSL, 2002; Fukao, Annu. Rev. Earth Planet. Sci. 2009

Depth dependent anisotropy in the WUS Shallower than 150 km NE-SW plate shear At 150 km circular flow due to slab rollback At > 350 km east-west frozen-in/structural anisotropy in the stagnant/flattened slab Slab Rollback Plate shear Pacific Plate NA Plate Plate shear Slab rollback caused stagnant segments above the 660-km and slab flattening above the transition zone. Also the rollback may cause east-west flow around 150-km depth Stagnant slab Frozen-in fabric 660 km Modified from Fukao, Annu. Rev. Earth Planet. Sci. 2009

Global Stagnant Slab in Transition Zone SEMum2.2 Vs model (French et al 2011 AGU) Expect to see

Future Directions Higher frequencies: better vertical resolution in the lithosphere Numerical approach: Spectral Element Method and Adjoint methods Other regions: East Asia and Middle East Global detection of the LAB and MLD Plunging symmetry axis: geodynamic implications Anisotropy detecting with SKS and receiver functions

Laminated Mantle Mantle discontinuities Region B: Moho; G-discon.; Hales discon.; L- discon. (or 220-km); Lithosphere-asthenosphere-boundary (LAB) Region C: 410-km discon.; 520-km discon.; 660-km discon. Region D: D’’-discon. Classic mantle subdivision Anderson, J. of Petrology 2011

Region B in the continents Xenolith data suggest depleted (i.e. high velocity) layer goes down to 150-175 km range: Lee et al. 2011; Fischer et al. 2010; Eaton et al. 2008 Sheared peridotites or refertilized by the melts from asthenosphere near the base of the lithosphere Fischer et al., Annu. Rev. Earth Planet. Sci. 2010; Lee et al., Annu. Rev. Earth Planet. Sci. 2011 Romanowicz, Science 2009

North American Regional Inversion Rich tectonic history of the continent USArray Transportable Array (TA) of EarthScope Better inversion technique inherited from global inversion

NA Continent Formation Hoffman, P. F. (1988) United Plates of America, The Birth of a Craton: Early Proterozoic Assembly and Growth of Laurentia, Annu. Rev. Earth Planet. Sci., 16(1), 543-603 Karlstrom 1988 Condie et al. 1992 Thomas 2006 … Whitmeyer & Karlstrom 2007 Big picture http://csmres.jmu.edu/Geollab/Whitmeyer/web/documents/WK2007A2.ppt

NA Assembly Processes Whitmeyer & Karlstrom 2007 Collision of Archean blocks Accretion of juvenile terranes Rifting along margins http://csmres.jmu.edu/Geollab/Whitmeyer/web/documents/WK2007A2.ppt

NA Continent Assembly & Evolution Whitmeyer & Karlstrom 2007 Collision of Archean blocks Accretion of juvenile terranes Rifting along margins http://csmres.jmu.edu/Geollab/Whitmeyer/web/documents/WK2007A2.ppt

NA Continent Assembly & Evolution Whitmeyer & Karlstrom 2007 Collision of Archean blocks Accretion of juvenile terranes Rifting along margins Rich history makes it ideal for studying continental tectonics through various means e.g. seismology http://csmres.jmu.edu/Geollab/Whitmeyer/web/documents/WK2007A2.ppt

USArray of EarthScope: Ubiquitous Coverage of the Continent A network of seismometers deployed across the U.S. to record earthquakes and provide high-resolution images of the continent's structure and the Earth's deep interior. “A network of seismometers deployed across the U.S. to record earthquakes and provide high-resolution images of the continent's structure and the Earth's deep interior.” http://www.earthscope.org/observatories/usarray

NA Station Coverage IRIS DMC Canadian Geological Survey; GEOSCOPE >20years >2000 Stations Most dense broadband coverage

Anisotropy layering: craton wide feature All over the craton Continuous lines: % Fo (Mg) from Griffin et al. 2004 Grey: Fo%93 black: Fo%92

Surface wave and receiver function MLD LAB MLD LAB in the WUS MLD in the craton Nearly same depth (gray bar)! People feel confused when

LAB or MLD Kumar et al SRL in press http://www.solid-earth-discuss.net/4/1/2012/sed-4-1-2012-print.pdf

Velocity matters In WUS: LAB on top of asthenosphere MLD In WUS: LAB on top of asthenosphere In Craton: MLD in the middle of high Vs lid Need to consider velocity! People feel confused when Surface wave model Yuan et al 2011