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Download Upper Mantle Structure - RCL
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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, NESW on parts of mainland, perhaps NNW-SSE in between Small-scale Mantle Convection N Owens Valley Peninsular Ranges S Yang and Forsyth, in the works 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? 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 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
