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Upper Mantle Structure

Upper Mantle Structure. We know… Gulf of California has low mantle seismic velocities above 200 km, in a global sense Nearby regions exhibit small-scale convection Crust thins to south, LVZ thickens to south

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Upper Mantle Structure

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  1. Upper Mantle Structure We know… Gulf of California has low mantle seismic velocities above 200 km, in a global sense Nearby regions exhibit small-scale convection Crust thins to south, LVZ thickens to south Anisotropy ~east-west fast direction in Baja, NE-SW on parts of mainland, perhaps NNW-SSE in between

  2. Owens Valley Peninsular Ranges N S Small-scale Mantle Convection Yang and Forsyth, in the works

  3. We need to know… • Characteristics of the upper mantle: Fluids? Depletion? Strain (anisotropy)? Temperature? • Small scale convection here? • Initial conditions in mantle? • Strain partitioning in mantle? • Structure of the lithosphere? • Petrology of the upper mantle? • Presence of remnant slab? • Depth dependence of anisotropy? • Crust well enough to strip off? (e.g., extension direction in Mexican B&R, e.g., mantle buoyancy) • Asymmetry of extensional process in different segments?

  4. We should study… • Existing data by… • Combined body wave/surface wave/attenuation/splitting inversion • Isolating crust from mantle (e.g., Ps conversion anisotropy, refraction) • Locating surface wave sources better • New experiments… • Using denser deployments in either northern or southern Gulf • Measuring magnetotullurics (MT) • With more seismometers to east • Complementary data such as… • Xenolith and volcanic petrology and geochemistry • Geomorphology and paleoelevations • Heat flow

  5. Seismometer Deployments • NARS • ~5 yr, 18 broadband • Collins et al. OBS • ~15 mo, 18 broadband • Proposed Array • 60 PASSCAL • 22 OBS • All broadband • 15-18 months

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